In an earlier paper we developed a QCD inspired theoretical parton bubble model (PBM) for RHIC/LHC. The PBM quantitatively agreed with the strong charged particle pair correlations observed by the STAR collaboration at RHIC in the highest energy Au + Au central collisions, and also agreed with the Hanbury Brown and Twiss (HBT) observed small final state source size approximately 2f radii in the transverse momentum range above 0.8 GeV/c. The model assumed a substructure of a ring of localized adjoining 2f radius bubbles(gluonic hot spots) perpendicular to the collider beam direction, centered on the beam, at mid-rapidity and located on the expanding fireball surface of the Au + Au collisions. In this paper we extend the model (PBME) to include the changing development of bubbles with centrality from the most central region where bubbles are very important to the most peripheral where the bubbles are gone. Energy density is found to be related to bubble formation and as centrality decreases the maximum energy density and bubbles shift from symmetry around the beam axis to the reaction plane region causing a strong correlation of bubble formation with elliptic flow. We obtained reasonably quantitative agreement (within a few percent of the total correlations) with a new precision RHIC experiment which extended the centrality region investigated to the range 0-80% (most central to most peripheral). The characteristics and behavior of the bubbles imply they represent a significant substructure formed on the surface of the fireball at kinetic freezeout
We calculate elliptic and triangular flow parameters of thermal photons using an event-by-event hydrodynamic model with fluctuating initial conditions at 200A GeV Au+Au collisions at RHIC and at 2.76A TeV Pb+Pb collisions at the LHC for three different centrality bins. The photon elliptic flow shows strong centrality dependence where $v_2(p_T)$ increases towards peripheral collisions both at RHIC and at the LHC energies. However, the triangular flow parameter does not show significant dependence to the collision centrality. The elliptic as well as the triangular flow parameters found to undere…
We attempt to describe the rapidity and transverse momentum spectra of strange as well as non-strange hadrons e.g. cascade,cascadebar, lambda , lambdabar, proton, protonbar,(omega+omegabar, Kaon, anti-Kaon and their ratios in the ultra-relativistic collisions of gold nuclei at (Root sNN)=200 GeV. This is done by using a statistical thermal freeze-out model which incorporates the rapidity (collision) axis as well as transverse direction boosts developed within an expanding hot and dense hadronic fluid (fireball) till the final freeze-out. We determine the thermo-chemical freeze-out conditions p…
Recently we have shown that the centrality dependence of the multiplicity of different hadron species observed in RHIC and SPS experiments can be well understood in a simple model, dubbed core-corona model. There it is assumed that those incoming nucleons which scatter only once produce hadrons as in pp collisions whereas those which scatter more often form an equilibrated source which decays according to phase space. In this article we show that also kinematical variables like $v_2/ε_{part} (N_{part})$ as well as $v_2^i/ε_{part} (N_{part})$ and $<p_T^i (N_{part})>$ of identified particles are…
We investigate proton rapidity correlations for a fireball that fragments due to non-equilibrium effects at the phase transition from deconfined to hadronic phase. Such effects include spinodal fragmentation in case of first order phase transition at lower collision energies, and cavitation due to sudden rise of the bulk viscosity at the crossover probed at RHIC and the LHC. Our study is performed on samples of Monte Carlo events. Correlation function in relative rapidity appears to be a sensitive probe of fragmentation. We show that resonance decays make the strength of the correlation even s…
We calculate azimuthal correlations in dAu collisions at different rapidities and centralities and argue that experimentally observed depletion of the back-to-back pick can be quantitatively explained by gluon saturation in the Color Glass Condensate of the Gold nucleus.
We have estimated centrality variation of chemical freeze-out parameters from yield data at mid-rapidity of $π^\pm$, $K^\pm$ and $p$, $\bar{p}$ for collision energies of RHIC (Relativistic Heavy Ion Collider), Beam Energy Scan (RHIC-BES) program, and LHC (Large Hadron Collider). We have considered a simple hadron resonance gas model and employed a formalism involving conserved charges ($B, Q, S$) of QCD for parameterization. Along with temperature and three chemical potentials ($T,μ_B,μ_Q,μ_S$), a strangeness under-saturation factor ($γ_S$) has been used to incorporate the partial equilibratio…
The pseudorapidity distributions of charged particles measured in p+p($\rm \overline{p}$) collisions for energies ranging from $\sqrt{s_{NN}}=23.6$ GeV to 13 TeV, d+Au collisions at $\sqrt{s_{NN}}=200$ GeV, p+Pb collisions at $\sqrt{s_{NN}}= 5.02$ TeV and A+A collisions at RHIC and LHC are investigated in the fireball model with Tsallis thermodynamics. We assume that the rapidity axis is populated with fireballs following q-Gaussian distribution and the charged particles follow the Tsallis distribution in the fireball. The theoretical results are in good agreement with the experimental data fo…
Squeeze out happen when the expanding central fireball flows around a large surface flux tube in a central Au-Au collision at RHIC. We model such an effect in a flux tube model. Two particle correlations with respect to the $v_2$ axis formed by the soft fireball particles flowing around this large flux tube is a way of measuring the effect.
With the adiabatic assumption in the cooling process, we discussed a new mechanism on Upsilon(1S) suppression that is due to the fast heating process at the early stage of the fireball instead of its finite decay width in finite temperature medium produced in the heavy ion collisions. We calculated the transition probability after the fast heating dissociation as a function of the temperature of the medium and the nuclear modification factor in central collisions, and found that the suppression is not negligible at RHIC, even if the width of Upsilon(1S) vanishes.
Statistical fluctuations in the transverse distribution of sources in relativistic heavy ion collisions and an asymmetric emission profile associated with the wounded nucleons lead to rapidity dependence of the reaction plane. The size of this effect is estimated for the gold-gold collisions at the highest RHIC energy ($\sqrt{s_{NN}}=200 \mathrm{GeV}$) in the Glauber model using GLISSANDO. The hydrodynamical evolution of the resulting torqued fireball is carried out in 3+1 dimensions considering a perfect fluid. Hadronization is simulated using THERMINATOR including non-flow contribution comin…
In this paper, STAR's measurement of clan multiplicity is presented for AuAu collisions at $\sqrt{s_\mathrm{NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV, for a variety of centrality classes. The mean number of particles per clan is found to decrease with decreasing centrality. Within the same centrality class, the mean number of particles per clan exhibits a reduction between 19.6 GeV and 62 GeV, with the minimum around 27 GeV. The structure is visible for most centralities, and most prominent for central collisions.
We take the experimental data for transverse momentum spectra of identified charged hadrons in different centrality classes for nucleus-nucleus (A+A) collisions at various Relativistic Heavy-Ion Collider (RHIC) energies measured by the STAR collaboration. We analyse these data in the framework of color string percolation model (CSPM) in order to extract various percolation parameters at different centralities at RHIC energies to study the effect of collision geometry and collision energy. We use these parameters to study the centrality dependent behaviour of initial temperature of the percolat…
The hydrodynamic model for the expansion of the fireball in relativistic heavy-ion collisions is presented. Calculations using relativistic hydrodynamics of a fluid with small viscosity yield a satisfactory description of the experimental data on the particle spectra, the elliptic flow or the interferometry radii.
With the help of AMPT default model, we study the influence of initial size (centrality of collisions) on higher cumulant ratios of net-proton distributions. If the centrality is presented by impact parameter, there is a strong centrality dependent, in particular, in those peripheral collisions. This dependence is slightly reduced if the centrality is presented by number of participant, or charged multiplicity. However, the dynamical ratios are almost centrality independent. So the centrality dependence of dynamical ratios at RHIC beam energy scan are presented.
Event-by-event fluctuating initial conditions (IC) in the ideal hydrodynamic calculation are known to enhance the production of thermal photons significantly compared to a smooth initial state averaged profile in the range $p_T >$ 1 GeV/$c$ for 200A GeV Au+Au collisions at RHIC and 2.76A TeV Pb+Pb collisions at LHC. The 'hotspots' or the over-dense regions in the fluctuating IC produce more high $p_T$ photons compared to the smooth IC due to the strong temperature dependent emission of the thermal radiation. This enhancement is expected to be more pronounced for peripheral collisions, for lowe…
In high energy collisions nuclei are practically transparent to each other but produce very hot, nearly baryon-free, matter in the central rapidity region. Where do the baryons go? We calculate the energy loss of the nuclei using the color glass condensate model. Using a space-time picture of the collision we calculate the baryon and energy densities of the receding baryonic fireballs. For central collisions of large nuclei at RHIC and LHC we find baryon densities more than ten times that of atomic nuclei over a large volume which appear at high rapidities. These results can and are being used…
Recent measurements of jet production rates at large transverse momentum ($p_T$) in the collisions of small projectiles with large nuclei at RHIC and the LHC indicate that they have an unexpected relationship with estimates of the collision centrality. One compelling interpretation of the data is that it captures an $x_p$-dependent decrease in the average interaction strength of the nucleon in the projectile undergoing a hard scattering. A weakly interacting or "shrinking" nucleon in the projectile strikes fewer nucleons in the nucleus, resulting in a particular pattern of centrality-dependent…
We study elliptic and triangular flow in the collisions of deuteron-gold nuclei at $\sqrt{s_{\rm NN}} = 200$ GeV at RHIC and of proton-lead nuclei at $\sqrt{s_{\rm NN}} = 5.02$ TeV at the LHC, utilizing (3+1)-dimensional ideal hydrodynamics for the dynamic evolution of the fireball and a Glauber-based Monte-Carlo energy deposition model for simulating the fluctuating initial conditions. Sizable values of elliptic and triangular flow are obtained for both colliding systems, and the results are consistent with PHENIX, ALICE, ATLAS and CMS measurements. For these studied centralities, we find tha…
A study using UrQMD is presented concerning the higher moments of net protons from Au+Au collisions at 7.7, 11.5, 14.6, 19.6, 27, 39, 62.4, and 200 GeV, concentrating on $C_{4}/C_{2} = κσ^{2}$. Higher moments of net protons are predicted to be a sensitive probe of the critical point of QCD. At the QCD critical point, particular ratios of the moments of net protons are predicted to differ from the Poisson baseline. Recently STAR has published the higher moments of net protons for Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4, and 200 GeV. UrQMD quantitatively reproduce…
Heavy ion collisions at RHIC/LHC energies are well described by the (nearly ideal) hydrodynamics. Last year this success has been extended to higher angular harmonics, $v_n,n=3..9$ induced by initial-state perturbations, in analogy to cosmic microwave background fluctuations. Here we use hydrodynamics to study sound propagation emitted by quenched jets. We use the so called "geometric acoustics" to follow the sound propagation, on top of the expanding fireball. The conical waves, known as "Mach cones", turn out to be strongly distorted. We show that large radial flow makes the observed particl…
The central goal of jet quenching studies in high-energy nuclear collisions is the characterization of those QCD medium properties that are accessible by these probes. Most of the discussion in the last years has been focused on the determination of the jet quenching parameter, $\hat q$. We present here an extraction of this parameter using data of inclusive particle suppression at RHIC and LHC energies for different centralities. Our approach consists of fitting a $K$ factor that quantifies the departure of this parameter from an ideal estimate, $K\equiv \hat q/(2ε^{3/4})$, where $\hat q$ is …
Event by event EPOS calculations in which the expansion of the system is described by {\it ideal} hydrodynamics reproduce well the measured centrality dependence of $v_2/ε_{part}$, although it has been claimed that only viscous hydrodynamics can reproduce these data. This is due to the core - corona effect which manifests itself in the initial condition of the hydrodynamical expansion. The centrality dependence of $v_2/ε_{part}$ can be understood in the recently advanced core-corona model, a simple parameter free EPOS inspired model to describe the centrality dependence of different observable…
Heavy quark observables are applied to probe the initial energy density distribution with violation of longitudinal boost invariance produced in relativistic heavy-ion collisions. Using an improved Langevin model coupled to a (3+1)-dimensional viscous hydrodynamic model, we study the nuclear modification factor ($R_\text{AA}$), directed flow ($v_1$) and elliptic flow ($v_2$) coefficients of heavy mesons and their decayed electrons at the RHIC energy. We find that the counter-clockwise tilt of the nuclear matter in the reaction plane results in a positive (negative) heavy flavor $v_1$ in the ba…
The centrality dependence of the charged-particle multiplicity densities ($dN_{ch}/dη$) and transverse energy densities ($dE_{T}/dη$) are investigated using the two-component Glauber approach for broad range of energies in heavy ion collisions at RHIC and LHC. A comprehensive study shows that the data is well described within the framework of two component model which includes the contribution of "soft processes" and "hard processes" for different centrality classes and energies. The data at two different energies are compared by means of the ratio of $dN_{ch}/dη$ (and $dE_{T}/dη$) to see the …
In this work, we study electrical conductivity and Hall conductivity in the presence of electromagnetic field using Relativistic Boltzmann Transport Equation with Relaxation Time Approximation. We evaluate these transport coefficients for a strongly interacting system consisting of nearly massless particles which is similar to Quark-Gluon Plasma and is likely to be formed in heavy-ion collision experiments. We explicitly include the effects of magnetic field in the calculation of relaxation time. The values of magnetic field are obtained for all the centrality classes of Au+Au collisions at $\…
