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Paper proposal for kaon anti-flow

Updated on Fri, 2024-11-22 04:26. Originally created by liuzw on 2023-09-27 06:48.

Paper Title: Anti-flow of Kaons in Au + Au Collisions at $\sqrt{s_{NN}}$ = 3.0 - 3.9 GeV

Target journal: PRL

PAs: Xin Dong, Chitrasen Jena,  Li-Ke Liu, Zuowen Liu, Kishora Nayak, Sooraj Radhakrishnan, Sharang Rav Sharma, Shusu Shi, Guoping Wang, Xing Wu, Nu Xu
PA representative: Zuowen Liu

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Abstract:

Anisotropic flow is known to be sensitive to the medium properties in high-energy nuclear collisions. Directed flow, $v_1$, is the first harmonic coefficient in the Fourier expansion of the final state particle azimuthal distribution measured in such collisions. Due to heavier mass of the strange quarks, hadrons contain one or more strange quarks, such as kaons, are thought to be even more sensitive to the equation of state of the medium especially at the high baryon density region. In this paper, we report the first systematic measurements of transverse momentum dependence of $K^{\pm}$ and $K^0_S$ $v_1$ in Au + Au collisions at $\sqrt{s_{NN}}$ = 3.0, 3.2, 3.5, and 3.9 GeV with STAR experiment. For comparison, $\pi^{\pm}$, protons, and $\Lambda$ $v_1$ are involved. A strong transverse momentum dependence of the mid-rapidity $v_1$ slope ($dv_1/dy|_{y=0}$) of kaons is observed: while a negative $v_1$ slope has been observed in low $p_T$ region, $p_T < 0.6$~GeV/$c$, positive slopes are seen at high $p_T$ region. A similar $p_T$ dependence is also evident for $v_1$ slope of charged pions in collisions at these energies. The hadronic transport model JAM can reproduce anti-flow at low $p_T$, it is supported that the observed low $p_T$ kaon anti-flow arises from the blocking of the spectators in the non-central collisions in the high baryon density region.


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Paper figures:


Fig. 1. The efficiency uncorrected density distribution in transverse momentum ($p_T$) and particle rapidity ($y$) for $\pi^+$, $K^+$, $K^-$ and $K_S^0$ measured with STAR detectors TPC and TOF in Au + Au collisions at $\sqrt{s_{NN}}$ = 3.0, 3.2, 3.5, and 3.9 GeV. Note that the density distribution is self-normalized in each panel.

Fig. 2. Directed flow ($v_1$) of $\pi^{+}$ (solid square), $\pi^{-}$ (open square), $K^{+}$ (open triangle), $K^{-}$ (open inverted triangle), $K^{0}_S$ (solid inverted triangle), protons (solid circle), and $\Lambda$ (open circle) as function of rapidity in Au + Au 10-40\% collisions at $\sqrt{s_{NN}}$ = 3.0, 3.2, 3.5, and 3.9 GeV. Statistical and systematic uncertainties are shown as bars and gray bands, respectively. Data points of $K^{+}$ are shifted horizontally to improve visibility. The JAM calculations for $K^0_S$ and protons are represented by red and blue lines, with the dash and solid lines representing cascade and baryonic mean-field modes, respectively. Note that the mean-field mode in JAM2 is named as RQMDv.MS2.

Fig. 3. Collision energy dependence of the $v_1$ slope ($dv_1/dy|_{y=0}$) at mid-rapidity for $\pi^{\pm}$, $K^{\pm}$, $K^0_S$, protons, and $\Lambda$ in Au + Au 10-40\% collisions. Statistical and systematic uncertainties are shown as bars and gray bands, respectively. Data points are staggered horizontally to improve visibility. The JAM calculations for $\Lambda$ and protons are represented by red and blue lines, and dash and solid lines represents cascade and baryonic mean-field modes, respectively. Note that $p_T$ windows for $\pi^{\pm}$, $K^{\pm}/K_S^0$, and protons$/\Lambda$ are $0.2 < p_T < 1.6$ GeV/$c$, $0.4 < p_T < 1.6$ GeV/$c$, and $0.4 < p_T < 2.0$ GeV/$c$, respectively.

Fig. 4. Transverse momentum ($p_T$) dependence of $v_1$ slopes ($dv_1/dy|_{y=0}$) at mid-rapidity for $\pi^{+}$ (black solid line), $K^{+}$, $K^{-}$, and $K^{0}_{S}$ in Au + Au 10-40\% collisions at $\sqrt{s_{NN}}$ = 3.0, 3.2, 3.5, and 3.9 GeV. Statistical and systematic uncertainties are shown as bars and gray bands, respectively. Data points of $K^{0}_{S}$ are shifted horizontally to improve visibility. The JAM calculations for $K^{0}$ are represented by colored dash lines, and blue and red lines represent cascade mode with and without spectators, respectively. Note that $v_1$ slopes of $\pi^{+}$ and $K^{\pm}$ are not shown at $p_T < 0.4$ GeV/$c$ due to the limit of acceptance.
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Conclusions:

In summary, we presented directed flow measurements for $\pi^{\pm}$, $K^{\pm}$, $K_S^0$, protons, and $\Lambda$ in Au + Au collisions at $\sqrt{s_{NN}}$ = 3.0, 3.2, 3.5, and 3.9 GeV. JAM model without mean-field significantly underestimates the proton $v_1$. It suggests the strong baryon mean-field plays an important role in the high baryon density region. We found the $v_1$ slopes of all measured mesons $\pi^+$, $K^{\pm}$, and $K_S^0$ show negative $v_1$ slopes at low $p_T$ ($p_T \lesssim 0.6$ GeV/$c$), which is consistent with the observation of kaon anti-flow from E895 experiment. The JAM model reproduces anti-flow of kaon at low $p_T$ without incorporating kaon potential. It indicates the anti-flow of kaons could arise from shadowing effect from spectators and is not unique to the presence of a kaon potential.

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Presentations: 

Paper proposal at FCV meeting:
https://drupal.star.bnl.gov/STAR/system/files/Kaon_antiflow_paperProposal_ver5.pdf
https://drupal.star.bnl.gov/STAR/system/files/Kaon_antiflow_paperProposal_ver4.pdf
https://drupal.star.bnl.gov/STAR/system/files/Kaon_antiflow_paperProposal.pdf

Oral talk at QM 23:
https://drupal.star.bnl.gov/STAR/system/files/QM23_AnisotropicFlow_Zuowen.pdf
Talks at STAR Collaboration Meeting:
Spring 2023: https://drupal.star.bnl.gov/STAR/system/files/lightHadrons_v1v2_FXT.pdf
Autumn 2022: https://drupal.star.bnl.gov/STAR/system/files/CollMeeting_FXT_FlowAnalysis_0.pdf

Presentations of preliminary request at FCV meeting:
3.0 GeV(Zuowen):
https://drupal.star.bnl.gov/STAR/system/files/3GeV_RequestPreliminary.pdf
https://drupal.star.bnl.gov/STAR/system/files/3GeV_piKp_K0sLam_sysmaticUncertainty.pdf
3.2 GeV (Li-ke):
https://drupal.star.bnl.gov/STAR/system/files/3p2_Official_FCVPWG_0607.pdf
https://drupal.star.bnl.gov/STAR/system/files/3p2_K0SFlow_request_preliminary.pdf
3.5 GeV(Zuowen):
https://drupal.star.bnl.gov/STAR/system/files/3p5GeV_RequestPreliminary.pdf
https://drupal.star.bnl.gov/STAR/system/files/Update_kaonAntiflow_chargedKaonProton_3and3p5GeV.pdf
3.9 GeV(Xing and Guoping):
https://drupal.star.bnl.gov/STAR/system/files/pion_flow_3.9GeV.pdf
https://drupal.star.bnl.gov/STAR/system/files/3p9GeV_ks0_lambda_request_preliminary_PWG.pdf
https://drupal.star.bnl.gov/STAR/system/files/3p9GeV_LamK0S_Systematic_uncertainties_update.pdf

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