The 8th International Conference on Physics and Astrophysics of Quark Gluon Plasma (ICPAQGP-2023) will take place during 7-10 February 2023 in Puri, Odisha, India. The previous editions of this conference were held successfully in 1988 at Mumbai, 1993 in Kolkata, 1997 at Jaipur, 2001 at Jaipur, 2005 at Kolkata, 2010 at Goa, 2015 at Kolkata. The last edition was postponed due to covid-19 pandemic.
Exciting results are available from relativistic heavy ion collision experiments. The conference will focus on recent theoretical and experimental developments in the field of Quark-Gluon Plasma (QGP) and its astrophysical connection to the early Universe. It will also focus on the physics issues related to upcoming experiments.
Duration of talks:
Plenary : 30 minutes (25+5)
Mini-review : 25 minutes (20+5)
Contributory : 15 minutes (12+3)
Poster session:
Session I (February 08, 2023, 10:30-12:00) : Abstract Ids between 7 and 101
Session II (February 08, 2023, 15:00-16:30) : Abstract Ids between 103 and 226
Poster Size : A0
CBM is a fixed target heavy-ion experiment at the FAIR facility of GSI Darmstadt, Germany, for
studying the QCD matter at high net-baryon densities and moderate temperature with heavy-ion collisions in the energy range of 2-11~AGeV (for Au nuclei). A Muon Chamber (MuCh) chamber system will perform the task of dimuon detection at CBM. It consists of alternating detector stations and absorber layers. Large area triple GEM detectors will be employed in the first two stations of MuCh, where the particle rates reach up to about 400 kHz/sq. cm. in the inner zones. The detailed detector layout will be discussed. As part of FAIR phase-0 program two full-size prototypes with 2000 readout pads have been commissioned in the mCBM experiment at GSI for tests in nucleus-nucleus collisions of 1-2 A GeV. Data have been acquired in self-triggered mode, using a dedicated STS/MuCh-XYTER self triggered readout chip. The detectors have been tested with nucleus-nucleus collisions for varying beam intensities. First detailed response of the GEM detectors will be reported. The challenging aspects of time based event building and results highlighting the observation of spatial correlations between MuCh modules and other detector systems revealing a time-synchronous response from a free-streaming data will be discussed.
The study of the strongly-interacting matter will benefit from larger data samples that will be collected in Run 3, thanks to major upgrades of the ALICE detectors. The main focus will be on rare probes and the study of observables that were not accessible with previous data. The LHC Run 3 has started and pp collisions at the unprecedented centre-of-mass energy of $\sqrt{s} = 13.6$ TeV have been recorded. The ALICE Collaboration has collected approximately 20 pb$^{-1}$ of minimum-bias pp collision events, which correspond to about 30 times more data than that collected in Run 2. In November 2022, a sample of about 1 million Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.36 TeV has also been collected. These high-quality data will be used in a preliminary phase for the characterization of the new detectors and calibrations.
In this talk, the performance regarding particle identification with the ALICE Time Projection Chamber and Time-Of-Flight detectors using a newly developed analysis framework will be presented. The results of this work will be compared with that of Run 2 to assess the quality of the new data and of the detector calibrations. In addition, perspectives on the near-future studies will be discussed based on the large amount of data that ALICE will be able to record in Run 3.
The model of pinning and unpinning of superfluid vortices is considered the most popular explanation behind pulsar glitches. However, the reason behind the almost instantaneous unpinning of a large number of vortices still needs a proper mechanism. We proposed that the neutron-vortex scattering in the inner crust of a pulsar may be responsible for such vortex unpinning. The strain energy released by the crustquake is assumed to be absorbed in some part of the inner crust. It causes pair-breaking quasi-neutron excitations from the existing free neutron superfluid in the bulk of the inner crust. The scattering of these quasi-neutrons
with the vortex core neutrons should unpin a large number of vortices from the thermally affected regions and result in pulsar glitches. We consider a few geometries of the affected pinning region to study the implications of the vortex unpinning in the context of pulsar glitches. We find that a Vela-like pulsars
can release about $\sim 10^{11} - 10^{13}$ vortices by this mechanism and results in glitches of size $\sim 10^{-11} - 10^{-9}$. We also explored the possibility of a vortex avalanche triggered by the movement of the unpinned vortices. An estimate of the glitch size caused by an avalanche shows a favorable result. The time scales associated with various events are compatible with glitch observations.
Proving the hypothesis on the possible existence of various baryon-rich exotic QCD phases in the core of a pulsar remains a challenge. We suggested a technique of probing the phases by studying the effects of phase transition induced density fluctuations on pulse profile modulation. Such density fluctuations cause the initial moment of inertia tensor of an oblate shape pulsar (with the pulsar deformation parameter $\eta$) to get random additional contributions for each component. These contributions are assumed to be Gaussian distributed with certain width characterized by the strength of density fluctuations $\epsilon$. Using sample values of $\epsilon$ and $\eta$, we solve Euler's equations for the rotational dynamics of the pulsar to observe the effects of wobbling through the modifications of pulse profiles. Our results show a specific pattern in the perturbed pulses, which are observable in modulations of pulses over a large period. Once the density fluctuations fade away, leading to a uniform phase in the interior of the pulsar, the off-diagonal components of the MI tensor also
vanish, eventually causing the wobbling of the pulsar to die away. This feature allows one to distinguish these transient pulse modulations from the effects of any initial wobbling. Since the decay of these modulations in time is directly related to the relaxation of density fluctuations in the pulsar, it gives valuable information about the nature of phase transition occurring inside the pulsar.
We investigate the equation of state derived from a dynamical quark model. In particular, we explore how the effect of momentum dependent dispersion relations of the
quasi particle will affect the speed of sound in dense matter.
Effect of diquark gap and connections to other parameterised quark EoS will be explored.
The dynamics of the hot and dense quark-gluon plasma(QGP) formed in high energy heavy ion collisions is well described by the Relativistic viscous hydrodynamics formalism. In the initial stages of heavy-ion collisions, a strong transient magnetic field (10^14- 10^15 T) is also produced primarily due to the spectator protons. The dynamics of electrically conducting QGP under the intense electromagnetic field are expected to be described by the Relativistic magnetohydrodynamics formalism (RMHD). Also, any relativistic theory should preserve causality, i.e., superluminal signal propagations in fluids are strictly prohibited. In this talk, we will discuss the evolution of dissipative stresses in the presence of an external magnetic field where signal propagations are causal. The causal relativistic magnetohydrodynamics theory was derived using the kinetic theory in RTA (relaxation time) approximation. Also, we will briefly discuss various modes of wave propagation and the allowed parameter space for causality to hold in curved space-time.
We study the effect of surface tension of the phase boundary in the dynamics of an expanding fluid. A fluid at local thermal equilibrium, but has a slowly varying temperature profile, like the plasma formed in heavy ion collisions, will have rapidly varying order parameter field at the edge of the plasma where the temperature falls below the transition temperature. In the case where the
free energy admits a first order transition, the gradient energy of this field will act as surface tension. We couple hydrodynamics and order parameter field evolutions to study the effect of this surface in the expansion of the plasma. We see that the surface slows down the expansion which reflects in the development of radial flow and momentum anisotropy.
Bulk matter produced in heavy ion collisions can have multiple conserved quantum numbers like baryon number, strangeness and electric charge. The diffusion process of these charges can be described by a diffusion matrix describing the interdependence of diffusion of different charges. The is estimated here from the Boltzmann kinetic theory for the hadronic phase within relaxation time approximation. Here, we impose the Landau-Lifshitz conditions of fit. This leads to, e.g., the diagonal diffusion coefficients to be manifestly positive definite. The explicit calculations are performed within the ambit of hadron resonance gas model with and without excluded volume corrections. It is seen that the off-diagonal components can be significant to affect the charge diffusion in a fluid with multiple conserved charges. The excluded volume correction effects is seen to be not significant in the estimation of the elements of the diffusion matrix.
Using the semi-classical formulation of kinetic theory, we obtain the evolution equations of the scalar and axial-vector components of the Wigner function of massive spin-half particles in the relaxation time approximation and construct the dissipative hydrodynamics to describe a spin-polarizable relativistic fluid. The relativistic Boltzmann equation is solved for the non-equilibrium corrections to the extended phase-space distribution function, which is then used for the non-equilibrium parts of the conserved currents of the system. We find the evolution of the spin tensor may depend on gradients of multiple hydrodynamic variables and thus conclude that an appropriate characterization of the spin-polarization phenomena, observed in relativistic heavy-ion collisions, may require a detailed description of multiple spin-transport coefficients [1,2].
[1] Bhadury, S. et. al. Phys.Lett.B 814 (2021) 136096.
[2] Bhadury, S. et. al. Phys.Rev.D 103 (2021) 1, 014030
We establish the theoretical formalism to study how the color fields in the glasma state dynamically generate spin polarization of quarks and the spin correlation of a quark and an antiquark in high-energy nuclear collisions. By utilizing the perturbative solution of the quantum kinetic theory for spin transport of massive quarks under classical color fields with dynamics following linearized Yang-Mills equations, we derive the spectra of spin polarization and correlation of quarks at small momentum and central rapidity in the integral form of gluon-field correlators. Applying the Golec-Biernat Wusthoff dipole distribution, it is found that the effect on spin polarization vanishes. In contrast, we find the non- vanishing out-of-plane spin correlation and make a qualitative estimation based on the dimensional analysis. This glasma-induced spin correlation pertinent to spin alignment of vector mesons could be prominently enhanced at weak coupling and large collision energy.
Strong magnetic field and large global angular momentum are expected to be generated in relativistic heavy-ion collision experiments. Hydrodynamic simulations for the evolution of hot and dense QCD matter formed in heavy ion collisions would have to rely on either magnetohydrodynamics or spin-hydrodynamics formulations for calculation of observables pertaining to magnetic field or global angular momentum, respectively. However, these two effects are not entirely separable due to the possible spin alignment of medium constituents in the presence of magnetic fields and magnetization of the medium due to rotation, similar to the Einstein-de Haas effect and Barnett effect. Therefore a unified framework of “spin-magnetohydrodynamics” needs to be developed for precise calculation of experimental observables. Here we present the first formulation of this unified framework in a relativistic context.
Based on: Phys.Rev.Lett. 129 (2022) 19, 192301.
The hydrodynamic evolution of a quark-gluon gas with non-zero quark masses and net baryon number is explored. For far-off-equilibrium initial conditions the expansion trajectories appear to violate simple rules based on the second law of thermodynamics. For Bjorken flow we present a detailed analysis within kinetic theory that provides a full microscopic understanding of these macroscopic phenomena and establish their thermodynamic consistency. We also demonstrate that, for certain far-off-equilibrium initial conditions, the well-known phenomenon of “viscous heating” turns into “viscous cooling” where, driven by dissipative effects, the temperature decreases faster than in adiabatic expansion.
In proton--proton collisions, the measurements of beauty-hadron production cross sections are an effective tool to test the perturbative QCD (pQCD) calculations. In addition, they provide the required reference for measurements performed in Pb--Pb and p--Pb collision systems, in order to study the in-medium mass dependent energy loss and the possible effects of cold nuclear matter, respectively.
In this contribution, the production of electrons from beauty-hadron decays in pp collisions at midrapidity with ALICE will be presented. The Time Projection Chamber (TPC), Time Of Flight (TOF) and ElectroMagnetic Calorimeter (EMCal) are used for particle identification. The presence of EMCal along with the TPC is exploited to measure the beauty-hadron decay electron production cross section in the high transverse momentum region. The $p_{\rm T }$-differential production cross section of electrons from beauty-hadron decays measured with ALICE in pp collisions at different centre of mass energies $\sqrt{s}$, ranging from 2.76 TeV to 13 TeV will be presented. In addition, the comparison of these measurements with different models will be shown.
Open heavy-flavour hadrons are one of the the key diagnostic tools available to study the dense, hot strongly interacting matter formed in relativistic heavy-ion collisions. The charm and beauty quarks are produced at the early stages of the collision via hard scattering due to their large bare masses, which exceed the QCD scale parameter ($\lambda_{\text{QCD}}$) significantly. In pp collisions, where a hot and strongly interacting medium is not expected to be formed, the measurement of heavy-flavour production serves as a reference for heavy-ion collision studies, and provides a crucial testing ground for pQCD models, and for understanding hadronization mechanisms in vacuum. Multiplicity dependent measurements in pp collisions, are also valuable tools to investigate the hadronization mechanisms and characterize multiparton interactions. They also help to search for possible connections between small and extended interacting systems.
In this presentation, an overview of the latest ALICE results on the production measurements of heavy-flavour hadrons in pp and Pb–Pb will be presented. The hadronization mechanisms of heavy quarks will be investigated by the measurements of the yield ratios of charm and beauty hadrons, and their modification from pp to Pb-Pb collisions will be discussed. A discussion of nuclear modification factor and elliptic flow in Pb–Pb collisions will also be shown.
Measurements of heavy-flavours tagged jets and heavy-flavour particle azimuthal correlation with charged particles allow for comparisons of the heavy quarks (charm and beauty) production, propagation, and hadronization across different collision systems. The measurement of heavy-flavour jets and correlation gives direct access to the initial parton kinematics and can provide further constraints for heavy-quark energy loss models.
This contribution presents the production of heavy-flavour decay electrons in pp, p--Pb, and Pb--Pb collisions to study the possible effects of cold nuclear matter and the in-medium mass-dependent energy loss.
In order to investigate the cold and hot nuclear effect on the fragmentation of heavy-flavours, the azimuthal correlations between heavy-flavour decay electrons and charged particles in pp, p--Pb, and Pb--Pb collisions, and beauty-jet production and jets measurement from heavy-flavour decay electrons are presented in pp and p--Pb collisions. Finally, an evaluation of the performance for $\rm{D^{0}-\bar{ D^{0}}}$ correlation studies based on a simulated analysis for ALICE~3 will be shown.
The study of prompt direct photons, from Compton scattering and annihilation hard processes in hadronic collisions, can test perturbative quantum chromodynamics theory predictions. In pp collisions, they can be used to constrain parton distribution functions as they come directly from the parton-parton hard scatterings. The measurement of direct photon production is complicated due to the presence of large photon background from hadron decays, especially from neutral mesons.
In this contribution, we will present the measurement of isolated photon production in pp collisions at $\sqrt{s}$ = 8 TeV using the data collected by the ALICE detector. The isolation technique is used to select prompt direct photons and reduce contamination from decay and fragmentation photons. The results have been compared to a theoretical prediction.
The exclusive photoproduction of $\Upsilon$ and $\rho$ meson is studied in ultraperipheral pPb collisions at $\sqrt{s_{NN}} = 5.02$ TeV. The differential cross-section of $\Upsilon$ and $\rho$ meson has been measured as a function of transverse momentum squared $p_{T}^{2}$, and rapidity $y$. The slope of the squared transverse momentum ($p_{T}^{2}$) dependent differential cross section is extracted to determine the size of the production region. Also, we measured the $\Upsilon$ and $\rho$ photoproduction cross-section as a function of the photon-proton centre-of-mass energies $W_{\gamma p}$, which provides valuable information of the gluon distribution at small values of parton fractional momenta $x$. The results are compared to various theoretical predictions and to previous measurements.
Jet angularities are a novel class of jet substructure observables that allow one to change the sensitivity to the relative contributions of collinear and soft emissions in a jet, through a continuous parameter a (a < 2 for Infrared Safety). For a ≤ 0.5, jet angularities weigh collinear radiations in the jet more strongly than the soft emissions while for a close to 1, the observable becomes sensitive to the spread of the jet. Studying the medium modifications to the substructure of a jet via a smooth jet observable like angularities, thus becomes an interesting prospect to get an insight of conditions in the quark-gluon plasma medium.
In view of this, we first compute the results for pp collisions using a field-theoretic framework of Soft Collinear Effective Theory (SCET). We find our results agree well with the recent ALICE distributions within the theoretical error bands. We then study the medium modifications by including an additional off-shell Glauber mode in the theory. The thermal modifications to the jet in this set-up are effectively incorporated through medium-modified splitting functions. Finally, we provide a comparison of these results to the vacuum case.
In this exploratory study, we investigate the novel scaling features in the jet quenching parameter ($\hat{q}$) among the static and Bjorken expanding medium profiles for radiative and transverse momentum broadened parton cascades. With these scalings, firstly, we study the impact of the sensitivity of the time for the onset of the quenching Bjorken profile as well as the partonic chemistry of the jet fragments on the inclusive jet $R_{AA}$ for a purely radiative turbulent cascade. In addition, we have also studied the effect of the nPDF as well as vacuum like emissions on the jet $R_{AA}$. Next, we study the impact of the expansion of the medium on the rapidity dependence of the jet $R_{AA}$ as well as jet $v_2$ and comparing with ATLAS data. Secondly, we account for the transverse momentum broadening in the cascade to probe the angular structure for hard and soft momentum jets in expanding media. We find that subsequent splittings primarily govern the broadening in comparison to collisional energy loss, which could impact the phenomenological description of out-of-cone radiation and jet quenching in media.
The hard scattered (high $p_{\rm T}$) partons produced in high energy hadronic and nuclear collisions fragment into a collimated spray of final state particles, known as jets. Jet properties are sensitive to details of parton showering processes and are expected to be modified in the presence of a dense partonic medium. Measurement of intra-jet properties in p-Pb collisions will help to investigate cold nuclear matter effects and enrich our current understanding of particle production in such collision systems. In this work, we will present the measurement of charged-particle jet properties, the mean charged-constituent multiplicity and fragmentation functions for leading jets in the range of jet $p_{\rm T}$ from 10 - 100 GeV/$c$ at midrapidity in p-Pb collisions at 5.02 TeV with ALICE. Results will be compared with Monte Carlo predictions.
Hadronic resonances are effective tools for studying the hadronic phase in ultrarelativistic heavy-ion collisions. In fact, their lifetime is comparable to that of the hadronic phase, and resonances are sensitive to effects such as rescattering and regeneration processes, which might affect the resonance yields and shape of the transverse momentum spectra. These processes can be studied considering the yield ratio of resonance to the corresponding long-lived particle as a function of the charged-particle multiplicity. Similar characteristics to those in heavy-ion collisions have been observed in the multiplicity-dependent studies of particle production in pp and p--Pb collisions. Resonance measurements may provide insight into the potential emergence of collective-like phenomena and a non-zero lifetime of the hadronic phase in small collision systems.
In this contribution, we present new ALICE results on the measurement of mesonic and baryonic resonances in small collision systems at LHC energies, including the measurements of K$^{*\pm}(892)$, $\Lambda(1520)$, $\Sigma^{\pm}(1385)$, $\Xi^{0}(1530)$, $\phi(1020)$ as a function of the charged-particle multiplicity.
Hadronic resonances are short-lived particles that decay via strong interaction. Resonances having a lifetime comparable to that of the hadronic phase (phase between chemical and kinetic freeze-out) are subject to regeneration and rescattering occuring in this phase, which lead to the modification of their yields and spectral shapes. Both these competing effects decide the final yield of the resonances at kinetic freeze-out surface. The measured resonance yields depend on their lifetime, the hadronic interaction cross section of their decay products, and the hadronic phase lifetime. \
Rescattering and regeneration can be studied via the yield ratio of resonance to the
corresponding long-lived particle with the same quark content as a function of system size, which is compared with model predictions with and without hadronic interactions. Recent results on resonance production in Xe--Xe and Pb--Pb collisions at various centre-of-mass energies, highlighting new results on K$^{\pm}$(891), $\Sigma$$^{\pm}$(1385), $\Xi$*$^{0}$(1820) and $\Lambda$(1520) are presented. The measurements are used to study the system-size and collision-energy evolution of transverse momentum spectra, yields, mean transverse momentum, yield ratios to long-lived hadrons and nuclear modification factors. These results are compared to lower energy measurements and model calculations wherever available.
We have studied the momentum transport coefficients, viz. shear and bulk viscosity, in a weakly magnetized ($eB\ll T^2$) deconfined thermal QCD medium at finite quark chemical potential ($\mu$). The magnetic field generates anisotropy in the medium, causing the previously isotropic scalar transport coefficients to become anisotropic and separate into several components. Depending upon the direction of the magnetic field and current, we can have three possible components, namely, longitudinal, transverse, and Hall.
We have obtained five shear ($\eta_0,\eta_1,\eta_2,\eta_3$ and $\eta_4$) and two bulk viscous components ($\zeta_0$ and $\zeta_1$) using relativistic Boltzmann transport equation under relaxation time approximation. Interaction among partons is incorporated through the quasiparticle mass of quarks and gluons ($T$, $\mu$, $B$ dependent), calculated using one-loop perturbative thermal QCD.
It is observed that the magnetic field acts differently on left (L) and right (R)-handed chiral modes of quark. This leads to the lifting of degeneracy in mass of those modes, in contrast to the strong magnetic field case ($eB>>T^2$), where the modes are degenerate. The magnetic field dependence of L and R modes of $\eta_0, \eta_1$ and $\eta_3$ is opposite in nature, viz. the L mode magnitude decreases whereas the R mode magnitude increases, with the magnetic field. This is in contrast to $\eta_2$ and $\eta_4$, for which, both the L and R mode magnitudes increase with the magnetic field. The L modes of both $\zeta_0$ and $\zeta_1$ show an increment with magnetic field for the entire temperature range. For the R mode, up to $T \sim 0.35 \mathrm{GeV}$, the magnitude at $e B=0.2 m_\pi^2$ is greater than at $e B=0.1 m_\pi^2$; beyond $T \sim 0.35 \mathrm{GeV}$, the magnitude at $e B=0.1 m_\pi^2$ becomes greater than that at $e B=0.2 m_\pi^2$. Also, these shear and bulk viscosities get amplified with quark chemical potential for both modes. Additionally, we have also examined the effects of
the magnetic field on specific shear and bulk viscosities, Prandtl number, and Reynolds number for L and R modes over a given temperature range.
The chiral imbalance along with the magnetic field produced during heavy-ion collisions may cause a charge separation in the magnetic field direction, a phenomenon known as the chiral magnetic effect (CME). Experiments conducted in the last decade to search for the CME in heavy-ion collisions have been inconclusive. The RHIC's isobar program was implemented in an effort to resolve this issue. In addition, a new technique for investigating the CME called the Sliding Dumbbell Method (SDM) [1] has been developed. This approach looks at each individual event to determine the back-to-back charge separation. The SDM facilitates the selection of events corresponding to various charge separations ($f_{DbCS}$) across the dumbbell. A partitioning of the charge separation distributions for each collision centrality into ten percentile bins is done in order to find potential CME-like events corresponding to the highest charge separation across the dumbbell.
In this contribution, the results based on CME sensitive $\gamma$-correlator ($\gamma = \langle \cos(\phi_a+\phi_b - 2\Psi_{RP}) \rangle$) will be discussed for each bin of $f_{DbCS}$ in each collision centrality for isobaric collisions (Ru+Ru and Zr+Zr) at $\sqrt{s_{\mathrm{NN}}} = 200$ GeV measured with the STAR detector. The background contribution due to statistical fluctuations is obtained by randomly shuffling the charges of the particles in a particular collision centrality. The correlated background is calculated for each $f_{DbCS}$ bin of charged shuffled events using their corresponding original events.
References
[1] J. Singh, A. Attri, and M. M. Aggarwal, Proceedings of the DAE Symp. on Nucl. Phys. 64, 830 (2019) "http://www.sympnp.org/proceedings/64/E66.pdf"
The interplay between quantum anomalies and electromagnetic fields leads to a series of non-dissipative transport effects in QCD, such as the Chiral Magnetic Effect and the Chiral Separation Effect, among others. In this work we study anomalous transport phenomena with lattice QCD simulations using improved staggered quarks in the presence of a background magnetic field. In particular, we calculate the conductivities both in the case of free fermions and in full QCD, analyzing the dependence of these coefficients with several parameters, such as the temperature and the quark mass
We study the effect of Higgs in the fundamental representation, on Z_3 symmetry in SU(3)-Higgs theory. In the presence of the Higgs, the Euclidean action breaks the Z_3 symmetry explicitly. The determination of the strength of explicit breaking requires integration of the matter fields. We carry out this using lattice Monte Carlo simulations, near the confinement-deconfinement transition. The partition function averages of observables that are sensitive to the Z_3 symmetry, i.e the Polyakov loop, gauge Higgs interaction terms etc. show that the strength of Z_3 explicit breaking decreases steadily with the lattice cut-off, and is possibly vanishingly small in the continuum limit. Simultaneously the strength of the confinement-deconfinement transition grows stronger. These results suggest that similar studies in QCD are necessary to determine the explicit breaking of Z_3 symmetry in the QGP-hadron transition. For small explicit breaking Z_3 meta-stable states are expected near the transition and may be relevant for heavy-ion collisions.
The rate of dilepton production is calculated from a hot magnetized hadronic medium in the framework of real time formalism of finite temperature field theory. The principal component in dilepton production is the thermo-magnetic spectral function of $\rho^0$ obtained by solving the Dyson-Schwinger equation. This is followed by evaluating the one loop self-energy of $\rho^0$ containing thermo-magnetic propagators of charged pion in the loop. The study of analytic structure of thermo-magnetic spectral function shows that there is a non-trivial yield in dileption production in low invariant mass region due to the fact that charged pions occupy different Landau levels before and after scattering of $\rho^0$ in addition to the usual contribution coming from Unitary cut beyond two pions threshold. This is purely magnetic field effect.
Femtoscopic correlations of identified and unidentified hadrons are measured with data recorded by the CMS experiment at the LHC over a broad multiplicity range and pair transverse momentum. The first femtoscopy measurements carried in CMS for all pair combinations of $\mathrm{K}^{0}_{\mathrm{S}}$, $\Lambda$ and $\overline{\Lambda}$ are reported. These identified particles are employed to perform $\mathrm{K}^{0}_{\mathrm{S}}\mathrm{K}^{0}_{\mathrm{S}}$, $\Lambda\overline{\Lambda}$ and $\mathrm{K}^{0}_{\mathrm{S}}\Lambda\oplus\mathrm{K}^{0}_{\mathrm{S}}\overline{\Lambda}$ femtoscopic correlations in pPb collisions at $\sqrt{s_{_{\mathrm{NN}}}} =$ 8.16 TeV, and of $\Lambda\Lambda\oplus\overline{\Lambda}\overline{\Lambda}$ in PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV, for the first time. The shape of the correlation function is observed to vary largely for different particle pair species, revealing the effect of the strong final state interaction in each case. In addition, we present results for the source radii of charged hadrons considering the Levy type source distributions in PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV. The invariant radii results for $\mathrm{K}^{0}_{\mathrm{S}}\mathrm{K}^{0}_{\mathrm{S}}$ in pPb and PbPb collisions show similar behavior with multiplicity and pair transverse momentum as observed for charged hadrons. The strong interaction scattering parameters, scattering length and effective range, are extracted from $\Lambda\Lambda\oplus\overline{\Lambda}\overline{\Lambda}$ and $\Lambda\overline{\Lambda}$ correlations using the Lednicky-Lyuboshits model for both pPb and PbPb collisions and compared with other experimental and theoretical results.
Two-particle electric charge balance function has been measured in proton-lead and lead-lead events with the CMS detector at the LHC. Particle correlations can be used as a probe of the charge creation mechanism, and the balance function is constructed using the like- and unlike-charge particle pairs to quantify these correlations. Compared to previous measurements, the pseudorapidity range is extended up to $|\eta| $ < 2.4. This larger phase space region is essential for studying the system time evolution. The width of the balance function, both in relative $|\eta|$ and relative azimuthal angle, is found to decrease with multiplicity for low transverse momentum ($p_{T}$ < 2 GeV/c). The effect is observed for both collision systems, and it is consistent with a late hadronization scenario, where particles are produced at a later stage during the system evolution. The multiplicity dependence is weaker for the higher $p_{T}$, which signifies that the balancing charge partners are strongly correlated compared to the low-$p_{T}$ region. Model comparisons cannot reproduce the multiplicity dependence of the width in $\Delta\eta$, albeit a model which incorporates collective effects can reproduce the narrowing of the width.
We employ the repulsive mean-field interactions among the hadrons and investigate how the susceptibilities of conserved charges deviate from ideal Hadron Resonance Gas (HRG) description. The repulsive mean-field interactions are incorporated by modifying the single particle energies by a term proportional to the number density of hadrons. We assume different mean-field interactions for mesons and baryons. We find that the repulsive mean-field interaction influences the susceptibilities of conserved charges of hadron gas significantly. The effect of repulsive hadronic interactions on the ratios and differences of susceptibilities is also investigated at zero chemical potentials. We also show that the repulsive interaction modelled in this way, leads to good agreement with the results of lattice QCD for some of the ratios of baryon charge susceptibilities at non-zero baryon chemical potential.
Measurement of charge-independent and charge-dependent two-particle number correlations ($R_{2}$) and transverse momentum correlations ($P_{2}$) provide key information about particle production mechanism, diffusivity, conservation of charge and momentum in high-energy collisions. These observables are measured
in pp collisions at $\sqrt{\textit{s}}$ = 13 TeV within transverse
momentum range of 0.2 $\leq$ $\textit{p}_{\rm T}$ $\leq$ 2.0
$\rm{GeV}/\textit{c}$, to better understand the jet contribution and
nature of collectivity in small systems. The shapes of $R_2$ and
$P_2$ on the near- and away-side are qualitatively similar but
quantitatively different. Moreover, the narrower width of $P_2$
compared to $R_2$ is also observed in pp collisions, as in the recently published ALICE results in p--Pb and Pb--Pb collisions. These results served as a baseline for p--Pb and Pb--Pb results, as they are sensitive to the interplay between the underlying event and mini-jets in pp collisions.
The early production of heavy-flavour quarks, i.e. charm and beauty, in ultra-relativistic collisions makes them an excellent probe to study the evolution of the strongly interacting systems.
Jets tagged by the presence of heavy-flavour hadrons and correlation measurements involving heavy-flavour hadrons give a close access to the parton kinematics allowing comparisons of their production, propagation and fragmentation across different systems.
In this contribution, the measurements of the fragmentation function of jets containing fully reconstructed D$^{0}$ mesons and $\rm{\Lambda^{+}_{c}}$ baryons in pp collisions will be presented. The first observation of dead-cone effect impacting heavy-flavour parton showers will be discussed with the measurement of D$^{0}$-tagged jets in pp collisions. The partons are expected to lose energy while traversing through the QGP medium at a different rate to their inclusive counterparts. To address the effects of in-medium energy loss, measurements of the nuclear modification factor of D$^{0}$ meson-tagged jets will be presented in the $0-10\%$ most central Pb$-$Pb collisions.
In order to have a deeper insight of charm-quark fragmentation, the measurements of azimuthal correlations between D mesons and charged particles will be presented in both pp and p$-$Pb collisions. The measurements in p$-$Pb collisions are important to probe the impact of cold nuclear matter effects while pp collisions serve as a validating tool for Monte-Carlo models along with providing a baseline for future Pb$-$Pb measurements. The discussion will be carried forward by presenting an evaluation of the performance of D$^{0}$$-$$\bar{\mathrm{D}}^{0}$ correlation studies based on simulations for ALICE 3.
Using the high statistics datasets of the HotQCD Collaboration,
generated with the HISQ (2+1)-flavor action for light and strange quarks,
and treating the charm sector in the quenched approximation, we analyze
the second and fourth order cumulants of charm fluctuations and
the correlations of charm with lighter conserved flavor quantum numbers.
We can make use of a factor 100 larger statistics on $N_\tau =8$ lattices
and datasets on lattices with temporal extent $N_\tau=12$ and $16$, which
never have been used in studies of charm fluctuations. This allows us to
perform the continuum limit for charm fluctuations in the quenched
approximation.
Analyzing correlations of charm fluctuations with baryon number and
electric charge fluctuations we can project onto charmed baryon and
meson correlations and compare results with quark model extended hadron
resonance gas model calculations. We aim at a precise determination of
the dissociation temperature of charmed hadrons and will probe the
sensitivity of the fluctuations observables to the presence of
multiple-charmed baryons.
The QCD vacuum is known to have a rich structure with non-trivial topologies. These can be classified with the topological charge, whose second moment can be shown to be related to the mass of the axion. It is also of interest the introduction of non-perpendicular electric and magnetic fields in QCD, which enhances the weight of non-zero topological sectors. For weak electromagnetic fields the topological charge becomes proportional to $\vec{E}\cdot\vec{B}$ and the proportionality factor is the QCD contribution to the axion-photon coupling. We use Lattice QCD simulations with improved staggered quarks and background electromagnetic fields to compute at finite lattice spacing the QCD contribution to the axion-photon coupling, as well as the dependance of the axion mass with temperature and the magnetic field.
The transition from hadron to the quark-gluon plasma phase is a smooth crossover in QCD with physical quark masses, nevertheless, the (almost) chiral nature of the light quarks is believed to drive such a transition. This phenomenon can be studied using lattice QCD techniques and the most popularly used fermion discretization, the staggered fermions only have a remnant of the full chiral symmetry of QCD, which is (perturbatively) believed to be recovered in the continuum limit. We for the first time study the eigenvalue distribution of the QCD Dirac operator with highly improved staggered quark discretization as a function of three different lattice spacings across the crossover transition temperature $T_c$, and perform the continuum extrapolation. From the features of the eigenvalue spectrum, we can conclude that though the flavor non-singlet part of the chiral symmetry is restored above $T_c$ the flavor singlet $U_A(1)$ part of it remains broken. Moreover, we observe a level repulsion between the infrared eigenvalues is quadratic to the spacing similar to the Gaussian unitary ensemble(GuE) of chiral random matrix theory, unlike the near-zero modes. The consequences of these findings will be discussed.
For $SU(N_c)$ gauge theories there is a first-order phase transition for $N_c \ge 3$, which signals the deconfinement of the color degrees of freedom at temperature $T_d$. However, its mechanism is not yet understood but is believed to be of topological origin. In this work we measure the topological constituents of $SU(3)$ gauge theory configurations generated using lattice techniques for different volumes and lattice spacings, using the overlap Dirac operator zero modes since it has exact chiral symmetry and an index theorem on the lattice. We focus on a temperature range from 0.9 to 1.5 $T_d$, where the Polyakov loop has non-trivial holonomy to understand the specific nature of these constituents, particularly instanton-dyons. We measure the average distance between the instanton-dyons and their correlations with the Polyakov loop. Furthermore, we measure the topological susceptibility and its higher moments using the Wilson flow technique which may allow us to isolate the contribution of the instanton-dyons towards driving (de)confinement.
Strong magnetic fields occur across the universe in several physical
systems. This is the case for magnetars, heavy-ion collisions and the
primordial universe. These fields are strong enough to have an impact
on the interactions at the QCD scale. In this work, we applied lattice
QCD simulations to gain new insights into how QCD thermodynamics
is affected by the presence of a background magnetic field. We
simulated 2 + 1 flavors of staggered quarks with physical masses and considered
both uniform and non-uniform magnetic fields to study the effect of
such backgrounds on a series of QCD observables. In particular, we focus
on the phase diagram, steady currents and the magnetic susceptibility.
Bare perturbative results at finite temperatures have some serious problems, infrared sensitivity of the massless gauge theories, gauge-dependent damping rates, etc. Additionally, QCD thermodynamics are poorly convergent if truncated order-by-order in the coupling constant. To overcome these problems, Braaten and Pisarski proposed a gauge invariant reorganization of the usual perturbation theory at the finite temperature where higher order diagrams contribute to the lower order one. This is known as HTL perturbation theory.
HTL perturbation theory is a gauge-invariant reorganization of the usual perturbation theory at the finite temperature and chemical potential where higher-order diagrams contribute to the lower order. HTL is formulated considering one-loop quark and gluon self-energy, and one replaces all the bare N-point functions with the HTL resummed one to study any observables. HTL perturbation theory successfully studies the various properties of quarks and gluon in a thermal medium. One such study is the QCD thermodynamics, and it was calculated to the highest possible loop order. People have put very less effort into formulating the HTL in NLO order. Recently, we have studied the quark propagator up to the next-to-leading order. In this talk, I will discuss the computation of the quarks and gluons self-energies and propagators to NLO in perturbation theory.
Particle production at the Large Hadron Collider (LHC) energies results from the interplay of hard and soft QCD processes and is sensitive to non-linear QCD evolution in the initial state. Global observables such as multiplicity and rapidity dependence of particle production provide important constraints for initial state models and help in understanding the underlying description of particle production. Moreover, investigating the system-size dependence of the particle production at the same collision energy is particularly important for directly studying medium effects in different collision systems.
In this contribution, we will present measurements of inclusive photons using the Photon Multiplicity Detector (PMD) at forward rapidities in pp and p$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. We will also present charged-particle production using the Forward Multiplicity Detector (FMD) at forward rapidities in pp, p$-$Pb and Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. Finally, the results will be compared with the predictions from QCD-inspired Monte Carlo event generators.
Machine learning techniques are well-known in the high-energy physics community and have helped solve numerous problems in this field. This work studies various applications of machine learning tools in the physics of heavy-ion collisions. One of the crucial initial state observables, the impact parameter, plays a vital role in establishing the initial state effects, which subsequently affects the final state observables in heavy-ion collisions. However, measurement of this quantity is almost impossible in experiments. Thus, we propose to use ML-based regression models such as the gradient boosting decision trees (GBDT) to obtain a prediction of impact parameter in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV using a multiphase transport model (AMPT). We also estimate an event shape observable, transverse spherocity from experimentally available final state observables using the same GBDT model. The regression model trained with the minimum bias data is shown to predict the centrality-wise transverse spherocity distributions. Another direction is the possible use of deep learning techniques for the event-by-event elliptic flow estimation in RHIC and LHC energies. The ability of deep learning models to learn unique patterns and correlations from data to map highly complex non-linear functions is a matter of interest. A novel method is proposed to feed the track-level kinematic information as input to the deep neural network (DNN). The model is trained with Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV minimum bias simulated events. All charged hadrons are considered for the training. The trained model is successfully applied to estimate the centrality dependence of $v_2$ for both RHIC and LHC energies. Also, the proposed model is quite successful in predicting the transverse momentum ($p_{\rm T}$) dependence of $v_2$ as well. This work is being extended to estimate the elliptic flow of pions, kaons, and protons and study the scaling properties of $v_2$. Results of the DNN estimator are compared to both simulation and experiment, which concludes the robustness and prediction accuracy of the model.
Recently different statistical-based Machine learning techniques are being used vastly in the field of computational heavy-ion physics to overcome the need for immense computational power. We have developed a general machine learning code using the Bayesian statistics that enables us to quantify the multi-parameters model by comparing multiple experimental observables simultaneously. Though this framework is universal and can be applied to any model or data set, in this study, we have implemented this frame-work in the Viscous Blast-Wave model, which has six parameters, including the η/s. We have calibrated the model to reproduce experimental data and extracted all the model parameters and their correlation simultaneously.
We demonstrate high prediction accuracy of three important properties that determine the initial geometry of the heavy-ion collision (HIC) experiments by using supervised machine learning (ML) methods. These properties are the impact parameter, the eccentricity, and the participant eccentricity. Although ML techniques have been used previously to determine the impact parameter of these collisions, we study multiple ML algorithms, their error spectrum, and sampling methods using exhaustive parameter scans and ablation studies to determine a combination of efficient algorithm and tuned training set. This gives multifold improvement in accuracy for all three different heavy-ion collision models. The three models chosen are a transport model, a hydrodynamic model, and a hybrid model. The motivation for using three different heavy-ion collision models was to show that even if the model is trained using a transport model, it gives accurate results for a hydrodynamic model as well as a hybrid model. We show that the accuracy of the impact-parameter prediction depends on the centrality of the collision. With the standard application of ML training methods, prediction accuracy is considerably low for central collisions. We have improved the accuracy by using different sampling techniques. We discuss how the errors can be minimized and the accuracy can be improved to a great extent in all the ranges of impact parameter and eccentricity predictions
Heavy quarks (charm and beauty) have masses much larger than the characteristic energy
scale of QCD interaction. Due to this they are typically produced in hard scattering processes
with large Q2 and thus offer a unique perspective to study the transition from quark to
hadrons in all collision systems. The latest measurements of charm meson and baryon
production in pp collisions allowed the first measurement of the total charm production cross
section including the contribution of all ground-state charm hadrons and the first
measurement of the fragmentation fractions of charm in hadrons in pp collisions. The
measurement of the charm baryon-to-meson yield ratios show a significant increase with
respect to the measurements performed in e+e− and ep collisions, which suggests that the
fragmentation of charm is not universal across different collision systems. Thus, precise
measurements of charm baryon and meson production are crucial to study the charm quark
hadronization in a partonic rich environment like the one produced in pp collisions at the
LHC energies. In this contribution, the recent measurements of charm meson and baryon
production in pp collisions will be shown. Also the comparison with the models to better
understand the charm quark hadronization will be presented.
Measurement of charm-hadron production in hadronic collision systems allow investigating the charm-quark hadronization mechanisms. In addition, measurements based on event shape observables allow isolating events according to their topologies, dominated by soft and hard processes. They provide information about the energy distribution in an event and provide tools to study the perturbative as well as non-perturbative aspects of the QCD. The event shape observables permit to isolate jetty-like (high-$p_T$ jets) and isotropic (partonic scattering with low $Q^2$ ) events.
In this contribution, recent results on open-charm meson production measured by the ALICE Collaboration in pp collisions at $\sqrt{s}$ = 13 TeV as a function of event activity from the Run 2 of the LHC will be presented. Measurements of the averaged self-normalized yield as a function of charged-particle multiplicity and transverse spherocity ($S_o$ ) at midrapidity for $D^{∗+}$ , $D^+$ and $D^0$ mesons will be shown. The self-normalized yield are shown for different multiplicity, transverse spherocity and $p_T$ intervals. In addition, comparison with measurements performed at $\sqrt{s}$ = 7 TeV will be shown and comparison with models will be discussed.
The investigation on hot-dense QCD medium in ultra-relativistic collisions is non-trivial. It is believed that asymptotically free quark-gluon plasma came into existence after a few microseconds of the "Big bang" when energy and matter densities were enormously high. The essential characteristic of the strongly interacting quarks-gluons plasma phase is collective behavior. Observations in various heavy-ion collisions at RHIC and LHC energies have exhibited such demeanor. The other observations, like strangeness enhancement, also support the existence of quark-gluon plasma in heavy-ion collisions. In comparison, the sight of QGP in $p+p$ collisions is ignored so far due to the lack of particle number density in $p+p$ collisions. Thus over the decades, the $p+p$ collision system served as a baseline for heavy-ion collisions and helped reveal the unconventional behavior of the heavy-ion collisions. In contrast to that, recently, collective behavior and strangeness enhancement have been observed in $p+p$ collisions at the LHC energies. These observations suggest that the existence of a QGP-like medium in small systems cannot be ruled out completely if collision energy is large enough. Inspired by these observations, we attempt to investigate the existence of a QGP-like medium in $p+p$ collisions through charmonia suppression at $\sqrt{s} = $ 5.02, 7, and 13 TeV collisions energies. We employ 1+1D second-order viscous hydrodynamics to obtain the temperature cooling law for the QGP medium evolution. Further, we use the Unified Model of Quarkonia Suppression (UMQS) to explain the experimental data available corresponding to normalized charmonium yield $\left(\frac{dN_{J/\psi}/d\eta}{< dN_{J/\psi}/d\eta>}\right)$ with respect to the normalized charged-particle multiplicity $\left(\frac{dN_{ch}/d\eta}{< dN_{ch}/d\eta>}\right)$. Our UMQS model contains possible QGP effects such as color screening, collisional damping, and gluonic dissociation; these effects reduce the quarkonia yield in ultrarelativistic collisions. The regeneration of charmonia is also considered in this model through detailed balanced to counter the suppression effects. Our model explains the charmonia normalized data with a reasonably good agreement, while PYTHIA and other models deviate at high net charged particle multiplicity ends. Our theoretical study supports the idea of the existence of a QGP-like medium in $p+p$ collisions.
Emphasizing the possibility of moderate suppression of heavy quarkonium states, we invite some attention towards the issue of real time evolution of quarkonia during the cooling phase of quark gluon plasma(QGP). In this context, we have used time dependent perturbation theory to show that $\Upsilon(1S)$, $\Upsilon(2S)$, $J/\Psi$ can further be dissociated in the medium at a temperature below their dissociation thresholds even though they survive the Debye screening. We have presented and compared the dissociation probabilities and dissociation rates of these states in real and complex valued potential in this article. In the first case we have dealt with wave functions of the Schroedinger equation corresponding to various quarkonia species where as for the later one, we have considered the stochastic average of the same . A precise comparison of these two aspects has been presented. We realise that our method is an approximate way to analyse the short time behaviour of quarkonium in real valued potential and for long time behaviour one must adopt a non perturbative technique for solving schr\"odinger equation of quarkonium bound states in evolving QGP. On the other hand the perturbation technique seems to be valid enough to deal with the same for a complex valued quark anti-quark potential when it is dealt with the stochastic average of wave functions only.
A deconfined medium of quarks and gluons called Quark-Gluon Plasma (QGP) is produced when heavy-nuclei are collided at relativistic energies. The formation of QGP is often characterized by a phenomenon called strangeness enhancement where the production of strange-to-non-strange particles are enhanced relative to peripheral or proton-proton interactions. Besides the enhancement in K/π ratios, a non-monotonic energy dependence was also reported for Λ̄ to p̄ ratios at CERN SPS, attributed to a signature for the strangeness enhancement . As anti-particles are produced directly from the reaction, the Λ̄/ p̄ ratios are considered as a cleaner probe for the strangeness enhancement. However, at this energy range hadronic interactions are dominant and, particularly for Λ̄ and p̄, processes like baryon-anti-baryon (BB̄) annihilation can significantly modify final yields and spectral shape which may lead to an apparent enhancement in the Λ̄/p̄ ratios. In this work, we use UrQMD hadronic transport model, to investigate the role of baryon-anti-baryon (BB̄) annihilation on Λ, Λ̄ hyperon production and its effect on Λ̄/p̄ ratios. The UrQMD calculations with BB̄ annihilation can produce the trend of average transverse mass spectra for Λ and Λ̄, as well as, the characteristic enhancement in Λ̄/p̄ ratios in data as a function of centrality and collision energy. Furthermore, Λ̄/p̄ ratios extracted from the feed-down corrected SPS data are in good agreement with UrQMD model calculations with BB̄ annihilation. This suggests that Λ̄/p̄ enhancement can not be interpreted as a direct signature for strangeness enhancement and BB̄ annihilation has a significant role to play.
The existence and location of the QCD critical point is an object of both experimental and theoretical studies. The comprehensive data collected by the NA61/SHINE during a two-dimensional scan in beam momentum (13A-150A GeV/c) and system size (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La, Pb+Pb) allows for a systematic search for the critical point – a search for a non-monotonic dependence of various correlation and fluctuation observables on collision energy and size of colliding nuclei. In particular, fluctuations of particle number in transverse momentum space are studied. They are quantified by measuring the scaled factorial moments of multiplicity distributions.
This contribution reviews ongoing NA61/SHINE studies to search for the critical point of the strongly interacting matter.
Short-lived hadronic resonances with widely varying lifetimes provide an excellent tool to study the hadronic phase produced in relativistic heavy-ion collisions. They undergo rescattering and regeneration within the hadronic phase, which modifies their yields. The dynamics of these particles, especially the $K^*(892)^0$ meson, and thus varying yields have been used extensively to study the hadronic phase lifetime. In this work, we explore the applicability of hydrodynamics in the hadronic phase using the Knudsen number ($Kn$). Further, we employ 1+1D second-order viscous hydrodynamics for the evolution of hadronic medium and to obtain the hadronic phase lifetime. The evolution is assumed to break down when the limit, $Kn > 1$, is attained. It is assumed that the particle yield gets preserved at this limit. The obtained lifetime is then used within a transport model for $K^*(892)^0$ mesons modelled by including rescattering and regeneration effects to predict their final state yield. The results obtained in our calculations are qualitatively in agreement with the experimentally obtained hadronic phase lifetime and $K^*(892)^0/K$ ratio.
We show that the transverse mass and rapidity spectra of protons and pions produced in Au-Au collisions at sNN=2.4 GeV can be well reproduced in a thermodynamic model assuming a single-freeze-out scenario of particles from a spheroidally symmetric hypersurface. This scenario corresponds to a physical picture used by Siemens and Rasmussen in the original formulation of the blast-wave model used commonly at RHIC and LHC energies. Our framework extends this approach by incorporating a Hubble-like expansion, flow asymmetry with respect to the beam direction, and resonance decays. With the model parameters determined by the hadronic abundances and spectra, we make further predictions of the pion HBT correlation radii that turn out to be in qualitative agreement with the measured ones. Altogether, our results bring evidence for substantial thermalization of the matter produced in heavy-ion collisions in the few-GeV energy regime and its spheroidal expansion.
Directed flow is understood to be sensitive to the initial conditions of heavy ion collisions and is used to constrain the initial matter profile. However, in the present study we have shown the importance of the $v_1$ of resonances and light nuclei which probes some additional physics of heavy ion collisions. We have proposed a model for the initial energy and net-baryon density which is able to describe the directed flow($v_1$) of light flavor hadrons and the observed $v_1$ splitting between baryons and anti-baryons. Inorder to probe the effect of hadronic stage on $v_1$, we have calculated the directed flow of resonances like $K^{*0}$ and observed a dominant effect due to the rescattering of $K^{*0}$ with the pion rich medium. More interestingly, we have observed that the directed flow of deuteron and triton which are sampled thermally from the freezeout hypersurface has different trend as compared to the deutron and triton obtained from coalscence model. With the model calculation of deuteron and triton $v_1$, we will demonstrate the relevance of quark coalescence model. Further, the effect of critical equation of state on the $v_1$ of identified particles and on the splitting between baryon and anti-baryon directed flow will be discussed.
One of the outstanding problems in thermal QCD is to understand how and whether the heavy quarks produced in the early stages thermalize in the medium formed in a heavy-ion collision (HIC). Recent sets of experimental data point to the fact that charm quarks show the same collectivity as light quarks. In this study, we perform classical-statistical lattice simulations for relativistic charm (representing a Dirac particle), to compute the momentum broadening and real-time spectral functions of heavy quarks in the presence of strongly populated gauge fields, as they exist in the early non-equilibrium stage of HICs.
Relativistic dissipative hydrodynamics is an efficient tool to explore the collective behavior of strongly interacting QGP (Quark Gluon Plasma) medium produced in heavy-ion collision experiments. This effective theory relies on some necessary microscopic inputs and relativistic kinetic theory often serves as the source. Within this statistical framework the dissipative quantities can be expressed in terms of the out of equilibrium phase space distribution functions, employing the Boltzmann equation. The Relaxation Time Approximation (RTA) simplifies the incorporation of the microscopic interaction to the Boltzmann equation via a single parameter known as relaxation time. However, as an artifact of this simplification, one needs additional matching conditions to satisfy the conservation laws of energy-momentum and number current. In this work, we have derived the relativistic dissipative hydrodynamics from a more general Bhatnagar-Gross-Krook (BGK) approximation which converges to the RTA description as a limiting case. The BGK kernel conserves the number current by construction and thus no specific matching condition for the same is necessary. This additional freedom leads to a class of physically consistent hydrodynamic descriptions constrained by a single matching condition ensuring energy-momentum conservation. This framework provides a platform to explore the effects of general matching conditions on transport coefficients and their deviation from the usual RTA prescription. We have also proposed a modified BGK collision kernel which can be particularly useful for systems with vanishing net baryon density and derived relativistic dissipative hydrodynamics from it.
The correlation of dynamical density fluctuation has been investigated within the scope of the Mueller-Israel-Stewart theory. The dynamic structure of the density fluctuation without the presence of the magnetic field shows three Lorentzian peaks. The central Rayleigh peak is surrounded by two Brillouin peaks symmetrically situated around the Rayleigh peak. But with the presence of an external constant magnetic field, the structure factor shows four peaks identified as one Rayleigh peak, two Brillouin peaks, and one peak due to the coupling of the magnetic field with the fluid velocity. The emergence of the extra peak due to the coupling can play an important role in measuring the relaxation of the system.
With the spectacular success of lattice techniques in establishing the phase diagram of strongly interacting matter described by Quantum Chromodynamics (QCD) at baryon densities $\mu_B/T<3$, it is now necessary to understand the nature and the interactions of the different phases. We revisit the problem of how well a model consisting of hadrons and resonances(HRG) up to 3 GeV with a repulsive mean-field interaction among them explains the thermodynamic properties of QCD. We show that by carefully including the dependence of hadron masses on the light quark mass, calculations within the HRG model without any repulsive interactions already give us a pseudo-critical temperature (at zero baryon density) $T_c=161.2 \pm 1.6$ MeV and the curvature of crossover curve $\kappa_2=0.0203(7)$ [PRC 106 (2022) 4, 4], which are in good agreement with the latest continuum extrapolated lattice results. The inclusion of repulsive interaction enables us to extend this study to very high baryon densities where the lattice results are not currently available. We report first results on the chiral and thermodynamic observables and some implications for the neutron star equation of state.
References: Phys.Rev.C 106 (2022) 4, 4, e-Print: 2206.04579 [hep-ph]
Heavy quarks placed within a hot deconfined medium undergo Brownian motion. At low momenta, the diffusion in momentum space is characterized by a transport coefficient $\kappa$, which needs to be calculated nonperturbatively for a strongly interacting plasma. We have calculated $\kappa$ for the charm and bottom quarks in a gluonic plasma, using lattice gauge theory and an expansion in the inverse of
the heavy quark mass. The results for $\kappa$ in the temperature range of interest for heavy ion collision experiments will be presented, and their phenomenological implication discussed.
The high-energy collisions can be viewed as collision of two colored glasses using the Color-Glass condensate (CGC) picture. It results in the production of the strong coherent gluon fields known as Glasma. The colored electric and magnetic fields evolve by the means of Classical Yang-Mills (CYM) equations. The lifetime of this pre-equilibrium stage is of the order of formation and thermalization time of Quark-Gluon Plasma (QGP), typically a short fraction of fm/c.
Heavy quarks (HQs) produced in the early phase of the ultra-relativistic heavy-ion collisions are efficient probes each for the pre-equilibrium Glasma phase and the equilibrated quark-gluon plasma. We study the diffusion of the HQs in the evolving Glasma (EvGlasma) using Wong’s equations. We compare the transverse momentum broadening, $\sigma_p$ of the HQs in the evolving Glasma fields with that of a standard, Markovian-Brownian motion in a thermalized medium with the same energy density of the Glasma fields. We observe that the $\sigma_p$ of HQs increases non-linearly during the very early time in the Glasma, suggesting heavy quarks super-diffuse in the gluon fields. We also find that for a smaller value of saturation scale, $Q_s$, the average transverse momentum broadening is approximately the same for the two cases, but for a larger value of $Q_s$, Langevin dynamics underestimates the $\sigma_p$. Adding to this, we are also studying the anisotropic angular momentum flow of HQs in the Glasma, and we present some preliminary interesting results.
During the early stages of the heavy-ion collision experiments, the heavy quarks (charm and bottom) are created via hard scattering. Due to their large mass, they do not thermalize with the constituents of the quark-gluon plasma (QGP) over the lifetime of the plasma. Hence, they witness the entire evolution of QGP and are effective probes to study the strongly interacting matter. We study the heavy quark transport coefficients (drag and momentum diffusion) for collision and radiative processes, using perturbative QCD and kinetic theory for viscous QCD medium. The thermal medium effects are incorporated through the effective fugacity quasiparticle model, based on the lattice QCD equation of state. The effective modelling of the QCD medium as quasiparticles with encoded in-medium interactions modifies the momentum distribution function of the QGP constituent particles, i.e. light quarks, anti-quarks, and gluons by the introduction of a temperature-dependent effective fugacity parameter. Viscous corrections to heavy quark transport coefficients due to shear and bulk viscosities of the medium are incorporated at first-order in the thermal distribution function by solving the effective Boltzmann equation within relaxation time approximation. We observe that the soft gluon radiation substantially affects the heavy quark transport coefficients in the viscous QGP. Preliminary results for the effect of second-order shear viscous correction on the heavy quark transport coefficients will also be presented.
Bound states of the heavy quark and its anti-quark are the hard probes that provide crucial information about the conditions formed in the thermal medium. It was shown that these bound states, particularly bottommonium, dissociate in the QGP medium due to the color screening of the real potential and scattering with the thermal constituents known as Landau damping, also responsible for developing the imaginary part of the potential. While efforts have been made to explore the quarkonium suppression in the static limit, i.e., $\omega\rightarrow 0$, effects arising from the finite frequency region of the gluon spectral function remains less explored.
In view of this, we investigate the finite frequency effects by using the full gluon spectral function on the quarkonium dissociation. To study the singlet octet transitions, we first implement lattice-motivated medium-modified potential for the singlet states and evaluate the bound state wavefunction and the corresponding binding energy at each temperature. For the octet states, we work in the two limiting cases of the Debye screening. First, we consider no screening and take repulsive Coulomb potential for the octet state. Second, we assume complete screening and take free wave functions. We further investigate contributions from the pole of the propagator as well as Landau damping in 1S and 2S states. In particular, we quantitatively compare the contributions arising from pole and Landau damping for the realistic values of temperature.
Several heavy-ion collision experiments at RHIC and LHC have been performed in identifying quark-gluon plasma (QGP) matter. In recent times, non-central heavy-ion collisions are of more interests where very strong magnetic field is produced in the direction perpendicular to the reaction plane. Many theoretical efforts have been made to study the modification of the strongly interacting matter in presence of an external magnetic field.
The heavy quarkonium is one of the important probes to investigate the properties of nuclear matter in presence of finite temperature and magnetic field. Also the time scale of quarkonia formation and the magnetic field generation are of similar order. So the study of heavy quarkonia in presence of magnetic field is of great interest.
In this work we have explored the imaginary part of the Heavy Quark (HQ) potential and subsequently the dissociation of heavy quarkonia at finite temperature and magnetic field. With respect to earlier investigations on this topic, present work contain three new ingredients. First one is considering all Landau level summation, for which present work can be applicable in entire magnetic field domain - from weak to strong. Second one is the general structure of the gauge boson propagator in a hot magnetized medium, which is used here in heavy quark potential problem first time. Third one is a rich anisotropic structure of the complex heavy quark potential, which explicitly depends on the longitudinal and transverse distance. By comparing with earlier references, we have attempted to display our new contributions by plotting heavy quark potential tomography and dissociation probability at finite temperature and magnetic field.
The decay rates of the $X Y Z$ exotics discovered in the heavy quarkonium sector are crucial observables for identifying the nature of these states. Based on the framework of nonrelativistic effective field theory, we calculate the rates of semi-inclusive decays of heavy quarkonium hybrids into standard heavy quarkonia. We compute the contributions to the decay rates at leading and subleading power in $1/m_Q$, where $m_Q$ is the heavy quark mass. In particular, we compute for the first time spin-flipping decays and explore heavy quark symmetry breaking in exotic decays. We compare our predictions with experimental data of inclusive decay rates for candidates of heavy hybrids.
There have been different proposals for signatures of the formation of a deconfined thermal medium(quark-gluon plasma) in heavy-ion collisions. The suppression of $J/\Psi$ in the deconfined medium is one of the cleanest signals among many other signatures like elliptic flow, jet quenching etc. for the formation of the deconfined medium. However, there are very few signals effective for the formation of QGP in small systems such as the systems produced in proton-proton, proton-deuteron and deuteron-deuteron collisions. Here the medium formed is shown to be very short-lived compared to that formed in heavy ion collision as the system undergoes 3-dimensional spherical expansion from the very beginning of the hydrodynamic phase. We model the dynamics of the small systems for different sizes of the formed systems after the Gubser flow model and we infer that the hydrodynamic expansion phase timescale is smaller by a factor of at least 2. We then calculate the dissociation probability of $J/\Psi$ through the non-adiabatic evolution of the state using the time-dependent perturbation theory for different values of thermalization time. We find rather small dissociation probability of $J/\Psi$ in small systems in contrast to that in the systems produced in Au-Au/Pb-Pb collisions, thereby establishing that quarkonia($J/\Psi$) suppression may not be a very useful signature for the formation of the thermal medium for proton-proton/proton-deuteron or deuteron-deuteron collisions.
Short-lived resonances, like $K^{*0}$, are useful tools to study particle production mechanisms and the properties of the hadronic phase at the late stage of heavy-ion collisions. Properties of the resonances are expected to be modified due to the interaction of their decay daughters with the hadronic medium via the rescattering and regeneration processes. The particle yield ratios ($K^{*0}/K, \phi/K^{*0}$) can provide information about the interplay between these in-medium effects. Recently, the STAR experiment at RHIC has accumulated high-statistics data samples of Au+Au collisions with enhanced detector capabilities and a wider pseudorapidity coverage during the BES-II program, which also help extend resonance measurements.
We will report on the measurement of the production of $K^{*0}$ resonances in Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6 and 14.6 GeV. Results include transverse momentum ($p_T$) spectra, mean transverse momenta and the integrated yield as a function of rapidity and charged particle multiplicity. The $\langle p_T \rangle$ of $K^{*0}$ will be compared with those of other hadrons. The resonance to non-resonance ratios ($K^{*0}/K$) will be shown as a function of centrality to study the rescattering/regeneration effects. An estimate of the lower limit of the hadronic phase lifetime will be shown as a function of centrality, and compared to previous RHIC and LHC results.
In ultra-peripheral collisions (UPCs) where two relativistic nuclei pass one another at a distance more than twice the nuclear radius, quasi-real photons from one nucleus may interact via a virtual quark-antiquark pair with gluons from the other nucleus and form short-lived vector mesons (e.g., $\rho^{0}$, $J/\psi$, $\phi$). Lorentz-boosted electromagnetic field of a relativistic nucleus can be quantized as linearly polarized photons. Due to the photon polarization in the vector meson production processes, a unique diffractive or spin interference pattern can be observed. In order to study the interference pattern, we will present the cos(2$\Delta\phi$) modulation, where $\Delta\phi$ is the angle between the $J/\psi$ and one of its daughters, in Au+Au UPCs at $\sqrt {s_{NN}} =$ 200 GeV recorded in 2014 and 2016 by STAR. This angular modulation is sensitive to the nuclear geometry and gluon distribution inside the colliding nuclei.
STAR collaboration has observed more strange hadrons in Cu+Cu collisions compared to Au+Au collisions at RHIC energy[1], $\sqrt{s_{NN}}$=200 GeV. We calculate the yield of $K, \Lambda, \Xi, \Omega$ using momentum integrated Boltzmann equation. Following a microscopic approach by considering possible hadronic interactions the strange hadron yields are calculated for different centralities of Cu+Cu collisions at midrapidity. Then the ratios of the yields of strange hadrons to pions are evaluated for a given number of participating nucleons and compared with the observed data. The calculation for Cu+Cu collisions is also compared with that of Au+Au collisions. The possibility of enhanced production in case of Cu+Cu collisions are analysed with different initial conditions.
[1]G. Agakishiev et al., for STAR Collaboration, PRL 108, 072301 (2012).
The Beam Energy Scan (BES) program at Relativistic Heavy-Ion Collider (RHIC) aims to map the QCD phase diagram. Finite-temperature lattice QCD calculations suggest a smooth crossover transition from normal nuclear matter to the Quark-Gluon Plasma (QGP) phase at high temperature and vanishing baryon chemical potential. Several QCD-based models suggest there is a first-order phase transition between hadronic matter and the QGP at low temperature and high baryon chemical potential, and the first-order phase transition line should end at a critical point (CP) towards the crossover region. The BES program aims to experimentally locate the CP in the QCD phase diagram. It is suggested that light nuclei are formed by the coalescence of nucleons close to each other in phase space. This makes them sensitive to the baryon density fluctuations that become larger in the vicinity of the CP. Therefore, yields and ratios of light nuclei could be an experimental probe to the first-order phase transition.
In this talk, we will present the energy and centrality dependence of transverse momentum spectra of light nuclei ($d$ and $t$) in Au+Au collisions from the BES-I data. We will also report the energy and centrality dependence of yields and ratios of light nuclei. STAR has also recorded high statistics data from Au+Au collisions at various energies in the BES-II program which comes with enhanced detector capability. The performance of light nuclei analysis in this dataset will be demonstrated.
Lattice QCD has provided accurate information at zero baryon density. Lattice QCD is also used at small baryon densities using Taylor expansion of pressure. The agreement between QMHRG and Lattice QCD for pressure and second order chiral susceptibility is good. However there are significant differences between QMHRG and Lattice prediction of higher order susceptibilities. Also at finite density the difference are significant. This suggests importance of non-resonant interactions in QCD thermodynamics. Also the most appropriate hadronic model that describes the confined phase of QCD should be ubiquitous, irrespective of the thermodynamic conditions.
We have chosen hadronic models which are well constrained from the neutron star merger data and nuclear matter properties. We have calculated susceptibilities upto fourth order subject to constraints $n_Q/n_B=0.4, n_S=0$ and $\mu_Q=\mu_S=0$. Comparision with Lattice Data at finite density shows repulsive interactions due to omega meson play important role in bridging the gap between QMHRG and Lattice QCD. This is an alternative approach to VDW-HRG models where repulsion is introduced using phenomenological parameters.
Using energy density of QCD crossover transition at zero baryon density, attempt has also been made to explore the phase diagram of QCD. Constraint is put on the location of QCD critical point for .8<T/T$_0$<.85 and the baryon density for transition at high density and low temperature relevant for neutron star.