3gevflow

Updated on Mon, 2021-04-19 22:30. Originally created by slan on 2020-06-02 20:49.

Title: Disappearance of partonic collectivity in $\sqrt{s_{NN}}$ = 3 GeV Au+Au collisions at RHIC

PAs: Xin Dong, Shaowei Lan, Yue-Hang Leung, Sooraj Radhakrishnan, Shusu Shi, Yang Wu, Yaping Wang, Guannan Xie, Nu Xu, Yingjie Zhou

Target Journal: Phys. Rev. Lett.

Paper draft: https://drupal.star.bnl.gov/STAR/blog/slan/3-gev-paper-draft
Analysis note: https://drupal.star.bnl.gov/STAR/blog/slan/3-gev-analysis-note
GPC comments: https://drupal.star.bnl.gov/STAR/blog/slan/gpc-comment-0764

Abstract:

We report the measurements of directed and elliptic flows ($v_1$ and $v_2$) for identified hadrons ($\pi^{\pm}$, $K^{\pm}$, $K_{s}^0$, $p$, $\phi$ and $\Lambda$) from Au+Au collisions at a center-of-mass-energy \snn = 3\,GeV and $v_{2}$ of ($\pi^{\pm}$, $K^{\pm}$, $p$ and $\bar{p}$) at 27\,GeV and 54.4\,GeV with the STAR experiment. It is found that at the two higher collision energies, in the mid-central collisions, the number-of-constituent-quark (NCQ) scaling holds and is consistent with previous measurements at similar collision energies. On the other hand, in \snn = 3\,GeV collisions, the mid-rapidity $v_{2}$ is negative for all hadrons and the NCQ scaling, observed in high collision energy, is absent. In addition, the mid-rapidity slopes d$v_{1}$/dy$|_{y=0}$ for almost all observed hadrons are found to be positive implies dominant repulsive baryonic interactions. The features of negative $v_2$ at midrapidity and positive $v_1$ slope at 3 GeV can be reproduced with a baryonic mean-field in transport model calculations. These results imply a medium, different from the partonic equation-of-state at higher energy collisions, has been produced in the 3 GeV Au+Au collisions at RHIC.

Figures:

Fig.1

FIG. 1: The transverse momentum ($p_{T}$) versus the identified particle rapidity (y) for $\pi^{+}$, $K^{+}$, $\phi$, $p$, $\Lambda$ and $\Xi^{-}$ measured by STAR detector TPC and TOF in Au+Au collisions at \snn = 3 GeV, with the fixed-target mode of beam energy 3.85 GeV per nucleon. The target is located at y = -1.045.

Fig. 2

FIG. 2: Rapidity(y) dependence of $v_{1}$ (top panels) and $v_{2}$ (bottom panels) of proton and $\Lambda$ baryons (left panels), pions (middle panels) and kaons (right panels) in 10-40\% centrality for the \snn = 3 GeV Au+Au collisions. Statistical and systematic uncertainties are shown as bars and gray bands, respectively. The UrQMD results are shown as bands: red and blue band stand for mean-field and cascade mode, respectively. The parameter of the impressibility $\kappa$ = 380 MeV is used in the mean-field option.

Fig. 3

FIG . 3: Scaled $v_2$ by number of constituent quarks, $v_2/n_{q}$, as a function of scaled transverse kinetic energy ($(m_{T}-m_{0})/n_{q}$) for pion, kaon and proton from Au+Au collisions in 10-40\% centrality at \snn = 3 GeV, 27 GeV, and 54.4 GeV for positive charged particles (panel a) and negative charged particles (panel b). Colored dash lines represent the fit to data in 200 GeV - 7.7 GeV collisions from STAR experiment at RHIC. Statistical and systematic uncertainties are shown as bars and gray bands, respectively.

Fig.4

FIG. 4: Collision energy dependence of (panel a) directed flow slope $dv_{1}/dy|_{y=0}$ for $p$, $\Lambda$, $\pi$(combined from $\pi^{\pm}$), $K$(combined from $K^{\pm}$ and $K^{0}_{S}$), $\phi$ and $\Xi^{-}$ and (panel b) elliptic flow $v_2$ for $p$, $\pi$(combined from $\pi^{\pm}$) in heavy-ion collisions. All collision centrality from RHIC is 10-40\% except 4.5 GeV where 10-30\% for $dv_{1}/dy|_{y=0}$ and 0-30\% for $v_{2}$. Statistical and systematic uncertainties are shown as bars and gray bands, respectively. The UrQMD results are shown as colored bands: solid- and shaded-bands stand for mean-field and cascade mode, respectively. With the mean-field option with $\kappa=380$ MeV, the model predicted positive values of $dv_{1}/dy|_{y=0}$ and negative values of $v_2$ for all baryons. For clarity the x-axis value of the data points have been shifted.

Conclusions:

In summary, we report the differential and integral measurements of directed flow v1 and elliptic flow v2 of identified hadrons from the 10-40% Au+Au collisions at √sNN = 3 GeV and the high statistic data of v2 of pion, kaon and proton at √sNN = 27 GeV and 54.4 GeV.

Consistent with previous results, the number of constituent quark (NCQ) scaling of v2 is observed in the high energy collisions.

At 3 GeV, on the other hand, the flow coefficients (v1 and v2) are determined by the first order event plane. The mid-rapidity elliptic flow of all hadrons are negative and the NCQ scaling is absent. The mid-rapidity slope directed flow of all hadrons except pi+ are found to be positive.

In addition, the UrQMD model calculations with baryonic mean-field qualitatively reproduced these observations.

Due to the formation of the QGP, at the center mass collision energy larger than 10 GeV, one finds that all hadron's v2 are positive while all all slope of v1 are negative. In the Au+Au collisions at 3 GeV, we observe the total opposite behavior that implies a different EOS dominated by the nucleon interactions at the high baryon density region.

Support Documents:

QM19_poster (27 and 54.4 GeV): https://drupal.star.bnl.gov/STAR/system/files/QM19_poster_shaowei_v6.pdf
DNP 2020_presentation (3 GeV): https://drupal.star.bnl.gov/STAR/system/files/DNP2020_Shaowei.pdf
CPOD 2021: https://indico.cern.ch/event/985460/contributions/4264583/attachments/2207921/3736131/CPOD21_Shaowei.pdf

Presentations:
27 and 54.4 GeV:
https://drupal.star.bnl.gov/STAR/system/files/PID_flow_0716.pdf
https://drupal.star.bnl.gov/STAR/system/files/PIDflow_1213.pdf
https://drupal.star.bnl.gov/STAR/system/files/bulkcor_0522.pdf

3 GeV:
https://www.star.bnl.gov/protected/heavy/xgn1992/run18/20200610_BulkCor_GXie.pdf
https://drupal.star.bnl.gov/STAR/system/files/shaowei_0603.pdf
https://drupal.star.bnl.gov/STAR/system/files/shaowei_0715.pdf
https://drupal.star.bnl.gov/STAR/system/files/0930_shaowei.pdf
https://drupal.star.bnl.gov/STAR/system/files/1007_shaowei.pdf
https://drupal.star.bnl.gov/STAR/system/files/YueHangLeung-bulkcorr20200722.pdf
https://drupal.star.bnl.gov/STAR/system/files/210224_3GeV_Xiv1.pdf
https://drupal.star.bnl.gov/STAR/system/files/210407_3GeV_Xiv1_pwg.pdf