A crucial open question is why many models of expanding systems exhibit an apparent simplification in their description while gradients in the system are still large and hydrodynamics is not expected to apply. We discuss a new conceptual approach to understand the pre-equilibrium bulk evolution of a system in terms of a reduced set of slow modes. We propose that the emergent dominance of these...
Spin alignment of vector mesons produced in non-central heavy-ion collisions could occur due to the large angular momentum and intense magnetic field expected in the initial stages of these collisions. Experimentally, vector meson polarization is observed from the angular distribution of the decay daughters with respect to a quantization axis. The study of the angular distribution of the decay...
Measurements of anisotropic flow in relativistic heavy-ions have been shown to be highly sensitive to nuclear structure. With a proposed $^{16}$O$^{16}$O run at the Large Hadron Collider and RHIC we study the potential for finding $\alpha$-clustering in $^{16}$O. Here we couple the iEBE-VISHNU event-by-event hydrodynamic package with $^{16}$O nucleonic configurations from ab initio nuclear...
In the present investigation we use $^3P_0$ model to calculate the partial decay width of Y(4008) state decaying to $D\bar{D}$ pairs in hot and dense nuclear medium. The impact of nuclear density and temperature is inculcated through the mass modification of pseudoscalar $D$ meson, calculated using chiral hadronic SU(3) plus QCD sum rule approach. The results of the present work will prove as...
We study the modification of $\eta$ meson mass in a medium comprise of nucleons and hyperons. The interaction terms for the $\eta$ mesons are derived using chiral hadronic mean field SU(3) model. Within chiral SU(3) model, in-medium properties of nucleons and hyperons are modified through their interactions with the scalar ($\sigma$, $\zeta$ and $\delta$) and vectors fields ($\omega$, $\rho$...
In 1974, J. L. Anderson and H. R. Witting proposed the Relaxation Time Approximation (RTA) to the relativistic Boltzmann equation [1], following all the development already made in the non-relativistic case by Bhatnagar, Gross and Krook [2]. This approximation is used in several fields of physics and has been recently employed to study the hydrodynamization of the matter produced in...
Direct photons are a powerful tool to study the properties of QCD matter in nuclear collisions. We investigate the contribution of pre-equilibrium photons before hydrodynamization in addition to those of conventional prompt and thermal photons to obtain a comprehensive picture of direct photon emission in the hybrid model based on relativistic hydrodynamics [1]. Numerical simulations at an LHC...
Quarkonia are considered a distinguished tool to study the strongly-interacting medium formed in ultra-relativistic heavy-ion collisions. However, their production is also sensitive to initial state effects such as the modifications of the parton distribution functions (PDF) in the nucleus or the gluon saturation at low Bjorken-x. These phenomena are typically studied using proton-nucleus...
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). A new technique, the sliding dumbbell method (SDM), is designed to study the CME-like charge separation. In the SDM, the whole azimuthal plane is scanned for each event by sliding the...
We present our calculation of electromagnetic effects, induced by the spectator charge on Feynman-xF distributions of charged pions in peripheral Pb+Pb collisions at CERN SPS energies, including realistic initial space-time-momentum conditions for pion emission. The calculation is performed in the framework of our simplified implementation of the fire-streak model, adapted to the production of...
The properties of QCD matter produced in ultrarelativistic heavy ion collisions can be determined in a global analysis of LHC and RHIC observables. Bayesian analysis [1] has provided meaningful credibility ranges for the ratio of shear viscosity to entropy density $\eta/s$, as well as for key parameters describing the initial state, essentially confirming earlier results like those obtained...
Measurements of elliptic flow in relativistic nuclear collisions are known to be sensitive to the quadrupole deformation of the colliding nuclear species. We explore the possibilities offered by high-precision data collected in Ru+Ru and Zr+Zr collisions at RHIC for studies of nuclear deformation at high energy. By exploiting the fact that isobaric systems share the same hydrodynamic...
Relativistic heavy-ion beams are accompanied by a large flux of equivalent photons, giving rise to a set of photon-induced processes. These ultra-peripheral collisions (UPCs) can lead to photon-photon interactions. This poster presents a new measurement of exclusive dimuon production, which provides detailed constraints on the nuclear photon flux and its dependence on impact parameter and...
By describing the initial stage of heavy ion collisions in terms of freely-evolving classical fields, we perform a first-principles calculation of the energy density one- and two-point correlation functions at finite proper time. Our approach allows us to systematically resum the contributions of high momentum modes that would make a power series expansion in proper time divergent. In order to...
We study the thermal equilibration and properties of the matter produced at the Beam Energy Scan (BES) program by employing the Parton-Hadron-String Dynamics (PHSD) transport approach which consistently describes the whole non-equilibrium dynamics of heavy-ion collisions, from the early nucleon hard scatterings, to the partonic phase based on the effective propagators and couplings from the...
We exploit the concept of hydrodynamic attractors to establish a macroscopic description of the early time out-of-equilibrium dynamics of high energy heavy-ion collisions. One direct consequence is a general relation between the initial state energy and the produced particle multiplicities measured in experiments. When combined with an ab initio model of energy deposition, the entropy...
By measuring the momentum correlations of pions created in heavy-ion collisions we can gain information about the space-time geometry of the particle emitting source. Recent experimental results from multiple different collaborations demonstrated that to properly describe the shape of the measured correlation functions, one needs to go beyond the Gaussian approximation. Some studies suggest...
Studies of longitudinal decorrelation of anisotropic flow provide unique constraints on the initial conditions and dynamical evolution of the quark- gluon-plasma in heavy-ion collisions. With data collected by the STAR experiment at RHIC, the factorization ratio for flow harmonics, rn(ฮท, ฮทref )(n = 2,3), are obtained over a wide ฮท range for 27, 54.4 and 200 GeV Au+Au collisions as a function...
Quantum-statistical correlation measurements in high-energy physics represent an important tool to obtain information about the space-time structure of the particle-emitting source and hence, the spatio-temporal evolution of the fireball. Out of the several final state effects which may modify the measured femtoscopic correlation functions; one may be the interaction of the investigated...
When two heavy ions collide at ultrarelativistic energies a very rich and non-trivial sequence of stages emerges in the evolution of the produced fireball. An important ongoing program in the field is the development of new observables and analysis techniques for anisotropic flow measurements, which would be sensitive only to one particular stage at a time in the heavy-ion evolution (e.g. only...
The McLerran-Venugopalan (MV) model is a Gaussian effective theory
of color charge fluctuations at small-$x$ in the limit of large valence
charge density, i.e. a large nucleus made of uncorrelated
color charges. In this work, we explore the effects of the first non-trivial
(even C-parity) non-Gaussian correction on the color charge density to
the MV model in SU(2) and SU(3) color groups...
In heavy-ion collisions a strong magnetic field is created ($\sim$ 10$^{15}$ T), which together with the presence of a non-zero electric and axial charge density, leads to vector and axial currents called the Chiral Magnetic Effect (CME) and Chiral Separation Effect (CSE), respectively. Their coupling gives rise to a collective excitation in the quark-gluon plasma (QGP) called the Chiral...
We study exclusive quarkonium production in the dipole picture at next-to-leading order (NLO) accuracy, using the non-relativistic expansion for the quarkonium wavefunction. This process offers one of the best ways to obtain information about gluon distributions at small x, in ultraperipheral heavy ion collisions and in deep inelastic scattering. The quarkonium light cone wave functions needed...
Studying the QCD matter produced under extreme condition of temperature and density called Quark Gluon Plasma (QGP) is among the important goals of ongoing as well as upcoming particle physics experiments. QGP state is so far believed to be formed only in heavy ion collision and not in the pp collision. Unlike heavy ion collision, $pp$ collision does not create QGP and hence the data from $pp$...
We have compared four models of initial conditions of a fluid dynamic description of high energy heavy ion collisions, focusing on the expectation values and event-by-event fluctuations in the initial transverse energy density profiles from Pb-Pb collisions. Specifically, introducing a Fourier-Bessel mode expansion for fluctuations, we determine expectation values and two-mode correlation...
Fluctuations of event-wise average transverse momentum ($[p_\mathrm{T}]$)
and the harmonic flow ($v_n$) carry important information
about initial-state geometry.
Collisions of nuclei with large quadrapole deformation are predicted
to produce an initial state with enhanced shape and size fluctuations,
and result in non-trivial correlation between $v_n$ and $[p_\mathrm{T}]$
...
Strongly intensive observables can be used to measure forward-backward (FB) correlations between charged particles produced in hadronic collisions in two separate pseudorapidity intervals. Within the model of independent statistically identical particle sources, these observables do not depend on the mean value and fluctuations in the number of the sources, therefore the deviation from the...
ATLAS measurements of dimuons produced via $\gamma\gamma$ scattering processes in inelastic, non-ultra-peripheral Pb+Pb collisions at 5.02 TeV are presented using an integrated luminosity of 1.9 nb$^{โ1}$. The $\gamma\gamma \rightarrow \mu^{+}\mu^{-}$ pairs are identified via selections on pair momentum asymmetry and acoplanarity, and the contribution from the heavy flavor decay background is...
Abstract: J/ฯ-meson is a bound state of charm and anti-charm (c ฬc) quark pair, whereas the heavy (anti)charm quarks are produced in the initial stages of ultrarelativistic heavy-ion collisions. The J/ฯ production is sensitive to the presence of the deconfined state of quarks and gluons, quark-gluon plasma, which is expected to form in the nuclear collisions. Prompt J/ฯ-mesons are produced at...
Neutron structure and skin thickness in nuclei have been traditionally measured by low-energy scatterings where the nuclei are only gently disturbed. Their precisions have been limited by theoretical uncertainties in modeling the nuclear force. Here, we propose an unconventional approach to probe the neutron skin by smashing isobar nuclei completely apart at relativistic energies to compare...
The deconfined state of matter created in hot and dense medium at ultra relativistic heavy-ion collision causes back-to-back charge separation along the direction of magnetic field produced due to energetic spectator protons, a
phenomena known as the chiral magnetic effect (CME). A new technique, the Sliding Dumbbell Method (SDM), is developed to search for back-to-back charge separation on...
The system created in relativistic nucleus-nucleus collisions may possess large orbital angular momentum leading to the particle global polarization perpendicular to the reaction plane. The local asymmetries in the velocity fields due to anisotropic flow can generate vorticity and particle polarization along the beam direction. In parity violating weak decays of hyperons, the momentum...
Preliminary STAR-BNL data shows Pearson coefficient ($\rho\left(v_{n}\{2\}^{2},\left[p_{\mathrm{T}}\right]\right)$) could be an intriguing observable to probe the shape deformation in atomic nuclei. Using a well-built and popular multi-phase transport calculation (AMPT), millions of collision events are produced from initial stages to final hadrons comparing with limited statistics from...
The seeds of jets are highly energetic partons, which are produced from hard scatterings in heavy ion collisions. As such, they might be affected by the precursor state of the quark-gluon plasma, the so-called glasma, via strong classical color fields. Starting from the glasma initial conditions, the Yang-Mills equations are solved analytically to leading order within the...
The last decade of hadron spectroscopy has unveiled a wealth of states that do not have the properties expected of particles composed of 2 or 3 valence quarks.
Among the most intriguing of these exotics is the X(3872), which various models attempt to describe as a hadronic molecule, a compact tetraquark, an unexpected charmonium state, or their mixtures. Production in heavy ion collisions,...
It is well established that high multiplicity pp and p-Pb collisions exhibit many of the signatures associated with the formation of a sQGP in heavy-ion collisions. If final-state interactions are responsible for this, one would also expect some amount of jet modification.
Here, we present the search for jet quenching effects by studying the yield of charged particles associated with high...
There exist simple and direct relations between the state of the system at early times, and final-state observables. For example, the final elliptic flow is approximately proportional to the initial eccentricity, which represents the leading term in a cumulant expansion of the initial density. This expansion is a systematic method written in terms of length scales that contains the global...
Going beyond the simplified gluonic cascades, we have introduced full flavor treatment by including both gluon and quark degrees of freedom for partonic cascades inside
the medium. We then solve the set of coupled evolution equations with splitting kernels calculated analytically for exponentially expanding and Bjorken media to arrive at
medium-modified parton spectra for quark and gluon...
It is well established that the spatial asymmetries of the overlap region in the initial state of a heavy ion collision, together with their fluctuations, are quite faithfully translated into final-state momentum anisotropies by a fluid-dynamical evolution. We investigate the relationship between initial-state eccentricities and final-state anisotropic flow harmonics for a simplified...
It is a long standing puzzle that hydrodynamic calculations give larger
elliptic flow for ultra-central Pb+Pb events than experiments. One explanation
is that sampling from a single particle distribution in Glauber model generates
too much shape fluctuation, which can be expected to be modified by NN
correlations. We study the fluctuation of shape-deformation as currently
implemented...
The out-of-equilibrium quark-gluon plasma and how it equilibrates in the pre-equilibrium stage of ultrarelativistic heavy-ion collision is of decent interest. Based on effective kinetic QCD theory including both gluon and all light quark/antiquark degrees of freedom, we investigate the pre-equilibrium dynamics of the quark-gluon plasma and how it connects to near-equilibrium viscous...
In the recent past the STAR collaboration reported the measurement of ฮ hyperon in non-central AuAu collisions. The origin of this polarization was successfully modeled as the vorticity present in the QGP fluid due to the non-zero angular momentum in non-central collisions. Other phenomena may generate vorticity in a fluid. A fast parton crossing the QGP transfers momentum and energy to it and...
We present a systematic study of the pre-equilibrium dynamics of relativistic heavy-ion collisions using the microscopic transport model SMASH. We focus on the time evolution of the distributions of energy-momentum currents and three types of conserved charges, produced by string excitation and fragmentation at intermediate and high energies. We address their dependence on the system size and...
The spinodal instability is the prime signal for the first-order phase transition in the Quantum-ChromoDynamics phase diagram relevant for the RHIC beam energy scan. We evolve planar unstable black branes dual to a plasma with a first order phase transition subject to the spinodal instability. By varying criticality we extract characteristics of the interface between the cold and hot stable...
Recently, jet substructure observables have been widely used in the study of jets. Some observables are sensitive to the wide angle soft particles within the jet, for example, the Lund plane distribution with different jet radii and soft drop parameters. As the jet loses energy and momentum during its evolution inside the quark-gluon plasma (QGP), the โlost" energy and momentum is deposited in...
Momentum anisotropy, quantified by the coefficients of anisotropic flow, $v_n$, is observed in the final states of both small and large nuclear collision systems. In large A-A systems, anisotropy is of geometric origin, and determined by a hydrodynamic response to the initial spatial anisotropy of the system. In smaller systems, such as p-A, d-A or peripheral A-A collisions, a range of...
