Directed flow in Au+Au collisions from the RHIC Beam Energy Scan at the STAR experiment

We report results of $v_1(y)$ and $dv_1/dy$ near mid-rapidity for $\pi^{\pm}$, $K^{\pm}$, $K_s^0$, $p$, $\overline{p}$, $\Lambda$, $\overline{\Lambda}$ and $\phi$ from Beam Energy Scan Au+Au collisions at $\sqrt{s_{NN}} =$ 7.7 - 200 GeV using the STAR detector at RHIC. The $dv_{1}/dy$ of $\pi^{\pm}$, $K^{\pm}$ and $K_s^0$ mesons remains negative over all beam energies. The $dv_1/dy$ of $p$ and $\Lambda$ baryons shows a sign change around 10 - 15 GeV, while net baryons (net p and net $\Lambda$) indicate a double sign change. The $dv_1/dy$ of $\overline{p}$, $\overline{\Lambda}$ and $\phi$ show a similar trend for $\sqrt{s_{NN}}>$ 14.5 GeV. For the first time, $v_{1}$ measurements are used to test a quark coalescence hypothesis. Many measurements are found to be consistent with the particles being formed via coalescence of constituent quarks. The observed deviations from that consistency offer a new approach for probing the collision process at the quark level.Comment: 7 pages, 4 figures to appear in CPOD 2017 proceedings, PoS(CPOD2017)00

Scaling of elliptic flow in heavy-ion collisions with the number of constituent quarks in a transport model

We studied the number of constituent quark scaling (NCQ) behaviour of elliptic flow ($v_{2}$) under the framework of A Multi-Phase Transport model (AMPT) at both top-RHIC and LHC energies. The NCQ-scaling in $v_{2}$ holds at top-RHIC energy with AMPT string melting version, while it breaks in Pb+Pb collisions at LHC energy using the same framework. The breaking of NCQ-scaling at LHC energy has been studied by varying the magnitude of parton-parton scattering cross-section and lifetime of hadronic cascade as implemented in AMPT. We find that the breaking of NCQ scaling in Pb+Pb collisions at $\sqrt{s_{NN}}$ =2.76 TeV is independent of the magnitude of parton-parton cross-section and the later stage hadronic interactions. Further we observed that scaling holds in a small collision system like Si+Si at $\sqrt{s_{NN}}$ = 2.76 TeV. We discussed that the breaking of NCQ scaling is possibly due to high phase-space density of constituents quarks in Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV.Comment: published version, Phys. Rev. C 93, 034908 (2016

Hadronic Resonance Production with ALICE Experiment at LHC

The production of resonances in heavy-ion collisions is expected to be sensitive to the properties of strongly interacting matter created in such collisions. We report on the measurements of $\phi$ and $K^{*0}$ resonances in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. The masses, widths and yields in Pb-Pb collisions as a function of centrality are compared to that in pp collisions to understand the role of re-scattering and regeneration. The resonance to non-resonance particle ratios are shown as a function of collision centrality and compared with the results at lower energies.Comment: 4 pages, 8 figures (submitted CPOD 2013 proceedings

Measurement of global spin alignment of vector mesons at RHIC

We report the measurements of spin alignment ($\rho_{00}$) for $K^{*0}$, $\overline{K^{*0}}$, $K^{*+}$, and $K^{*-}$ vector mesons in RHIC isobar collisions (Zr+Zr and Ru+Ru) at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. We observe the first non-zero spin alignment for $K^{*\pm}$ in heavy-ion collisions. The $K^{*\pm}$ $\rho_{00}$ is about 3.9$\sigma$ larger than that of $K^{*0}$. The observed difference and the ordering between $K^{*\pm}$ and $K^{*0}$ are surprising, and require further inputs from theory. When comparing between the isobar and Au+Au collisions, no significant system size dependence in $K^{*0}$ $\rho_{00}$ is observed within uncertainties.Comment: Quark Matter 2022 proceeding

The First Moment of Azimuthal Anisotropy in Nuclear Collisions from AGS to LHC Energies

We review topics related to the first moment of azimuthal anisotropy ($v_1$), commonly known as directed flow, focusing on both charged particles and identified particles from heavy-ion collisions. Beam energies from the highest available, at the CERN LHC, down to projectile kinetic energies per nucleon of a few GeV per nucleon, as studied in experiments at the Brookhaven AGS, fall within our scope. We focus on experimental measurements and on theoretical work where direct comparisons with experiment have been emphasized. The physics addressed or potentially addressed by this review topic includes the study of Quark Gluon Plasma, and more generally, investigation of the Quantum Chromodynamics phase diagram and the equation of state describing the accessible phases.Comment: Accepted for publication in Advances in High Energy Physic

The study of K∗0K^{*0} meson production using a transport and a statistical hadronization model at RHIC BES energies

In this paper, we have discussed the centrality and energy dependence of $K^{*0}$ resonance production using UrQMD and thermal models. The $K^{*0}/K$ ratio obtained from the UrQMD and thermal models are compared with measurements done by the STAR experiment in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27 and 39 GeV. The $K^{*0}/K$ ratio from thermal model is consistent with data in most-peripheral collisions, however it over-predicts the ratio in central Au+Au collisions. This could be due to the fact that the thermal model does not have a hadronic rescattering phase, which is expected to be dominated in more central collisions. Furthermore, we have studied the $K^{*0}/K$ ratio from UrQMD by varying the lifetime of the hadronic medium within the range 5 to 20 fm/c. It was found that $K^{*0}/K$ ratio decreases with increasing lifetime of the hadronic medium. Comparison between data and UrQMD suggest, one needs to consider a hadronic lifetime $\sim$ 10-20 fm/c to explain data at $\sqrt{s_{NN}}$ = 7.7 - 39 GeV in Au+Au collisions. We also predict rapidity distribution of $K^{*0}$ from UrQMD which could be measured in the STAR BES-II program.Comment: 8 pages, 6 figure

Breaking of multiplicity scaling observed in K∗0/KK^{*0}/K ratio in baryon-rich QCD matter

In this study, we investigated the influence of collision energy and system size on hadronic rescattering by analyzing the production of $K^{*0}$ mesons using the Ultra Relativistic Quantum Molecular Dynamics (UrQMD) model. Analysis are done in Au+Au collisions at various center-of-mass energies ($\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, and 200 GeV), as well as in Cu+Cu and isobaric (Ru+Ru and Zr+Zr) collisions at $\sqrt{s_{NN}}$ = 200 GeV at mid-rapidity. Our findings reveal that the ratio of $K^{*0}$ mesons to charged kaons ($K^{*0}/K$) decreases as the collision multiplicity increases. Moreover, at top RHIC energies, this ratio exhibits a smooth multiplicity scaling behavior. However, this scaling can be violated due to the formation of baryon-rich matter at lower beam energies, specifically $\sqrt{s_{NN}}$ = 11.5 GeV or below. These results highlight the importance of considering the interplay between collision energy, system size, and the chemical composition of the produced matter when studying the hadronic rescattering effects in heavy-ion collisions.Comment: 5 pages, 6 figure