This work presents measurements of the rapidity-window dependence of event-by-event net-proton cumulants and proton factorial cumulants in Au+Au collisions at $\sqrt{s_\mathrm{NN}}=$7.7 -- 27 GeV, using high-statistics data from RHIC BES-II. Protons and antiprotons are identified with improved detector performance within $0.4<p_\mathrm{T}<2.0$ GeV/$c$ and $|y|<0.6$, enabling a wide coverage in momentum space to probe long-range correlations near the QCD critical point. In the most central collisions, the proton number $κ_2/κ_1$ and $κ_3/κ_1$ exhibit power-law scaling with the rapidity window, but with exponents below the theoretical expectation, suggesting that the critical point, if it exists, may lie at higher baryon densities. A finite-size scaling analysis of the susceptibility and Binder cumulant study points out a critical baryon chemical potential region in 550 -- 650 MeV.
We discuss the production of $D$-mesons and $J/ψ$ in high multiplicity proton-proton and proton-nucleus collisions within the Color-Glass-Condensate (CGC) framework. We demonstrate that the modification of the LHC data on $D$ and $J/ψ$ yields in high multiplicity events relative to minimum bias events arise from a significant enhancement of the gluon saturation scales of the corresponding rare parton configurations in the colliding protons and nuclei. For a given event multiplicity, we predict these relative yields to be energy independent from $\sqrt{s}=200$ GeV at RHIC to the highest LHC ene…
Multiplicity and pseudorapidity ($η$) density ($dN_{\rm ch}/dη$) distributions of charged hadrons provide key information towards understanding the particle production mechanisms and initial conditions of high-energy heavy-ion collisions. However, detector constraints limit the $η$-range across which charged particle measurements can be carried out. Extrapolating the measured distributions to large $η$-range by parameterizing measured distributions and by using calculations from event generators, we characterize the production of charged particles over the full kinematic range. In the present …
The exploration of the QCD phase diagram has been one of the main drivers of contemporary nuclear physics. The Relativistic Heavy Ion Collider (RHIC) at BNL is uniquely suited for this task through its Beam Energy Scan (BES) program which allowed for a large range in baryon chemical potential $μ_B$ as was successfully demonstrated after the completion of Phase 1 in 2014. Phase 2 of the BES at RHIC is scheduled to start in 2019 and will explore with precision measurements the intermediate-to-high $μ_B$ region of the QCD phase diagram, five energies $\sqrt{s_{NN}}$ from 7.7 to 19.6 GeV in collid…
Recently, Chatterjee et al used a hadronic transport model to estimate the resolution with which various experimental quantities select the impact parameter of relativistic heavy ion collisions at collision energies relevant to the Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider (RHIC). Measures based on particle multiplicity at forward rapidity were found to be significantly worse than those based on midrapidity multiplicity. Using the same model, we show that a slightly more sophisticated measure greatly improves the resolution based on forward rapidity particles; this …
Fluctuations and correlations of conserved quantities (baryon number, strangeness, and charge) can be used to probe phases of strongly interacting QCD matter and the possible existence of a critical point in the phase diagram. The cumulants of the multiplicity distributions related to these conserved quantities are expected to be sensitive to possible increased fluctuations near a critical point and ratios of the cumulants can be directly compared to the ratios of the susceptibilities from Lattice QCD calculations. In these proceedings, the measurements of the cumulants of net-proton multiplic…
We report results of $v_1(y)$ and $dv_1/dy$ near mid-rapidity for $π^{\pm}$, $K^{\pm}$, $K_s^0$, $p$, $\overline{p}$, $Λ$, $\overlineΛ$ and $ϕ$ 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 $π^{\pm}$, $K^{\pm}$ and $K_s^0$ mesons remains negative over all beam energies. The $dv_1/dy$ of $p$ and $Λ$ baryons shows a sign change around 10 - 15 GeV, while net baryons (net p and net $Λ$) indicate a double sign change. The $dv_1/dy$ of $\overline{p}$, $\overlineΛ$ and $ϕ$ show a similar trend for $\sqrt{s_{NN}}>$ 14.5 G…
In these proceedings, we present the higher-order cumulants of proton multiplicity distributions of the fixed-target (FXT) run in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 3.0 GeV. The cumulant ratios are presented as a function of centrality and collision energy. The proton cumulant ratio C4/C2 is consistent with fluctuations driven by baryon number conservation and indicates an energy regime dominated by hadronic interactions. These data imply that the QCD critical point could exist at energies higher than 3 GeV if created in heavy-ion collisions.
Centrality definition in A$+$A collisions at colliders such as RHIC and LHC suffers from a correlated systematic uncertainty caused by the efficiency of detecting a p$+$p collision ($50\pm 5\%$ for PHENIX at RHIC). In A$+$A collisions where centrality is measured by the number of nucleon collisions, $N_{\rm coll}$, or the number of nucleon participants, $N_{\rm part}$, or the number of constituent quark participants, $N_{\rm qp}$, the error in the efficiency of the primary interaction trigger (Beam-Beam Counters) for a p$+$p collision leads to a correlated systematic uncertainty in $N_{\rm par…
Probing the nature of the QCD phase transition with higher-order net-proton number fluctuation and local parton density fluctuation measurements at RHIC-STAR
