kshen's blog

We present the measurements of inclusive J/psi production at midrapidity (|y| < 1.0) in Au+Au collisions at √s_NN = 54.4 GeV with the STAR detector at the Relativistic Heavy Ion Collider. A suppression of J/psi production is observed in Au+Au collisions at √s_NN = 54.4 GeV comparing to the scaled production in p+p collisions. The dependences of nuclear modification factor (R_AA) on centrality and transverse momentum (p_T) are measured with improved precision compared to previous measurements at 39 and 62.4 GeV. No significant energy dependence of R_AA is found within uncertainties up to 200 GeV. The comparision to model calculations is presented and its physical implications are discussed

Figures:

Figure 1. Invariant mass distributions of J/psi candidates for 0 < p_T < 10 GeV/c reconstructed via the di-electron channel for | y | < 1. The black open circles are unlike sign from same event; The blue triangles are like sign from same event; The red line stands for the combinatorial background from unlike-sign mixed-event, and the black full squares are di-electron signal with the combinatorial background subtracted. The J/psi signal shape from embedding with additional momentum smearing is used to fit the di-electron signal and the residual background is described by a straight line.

Figure 2. J/psi invariant yields in Au+Au collisions at √s_NN = 54.4 GeV as a function of p_T for different centralities. The error bars represent the statistical uncertainties. The boxes represent the systematic uncertainties. A pT > 0.2 GeV/c cut is added to exclude coherent photon induced production.

Figure 3. The R_AA of inclusive J/psi as a function of N_part in Au+Au collisions at different collision energies at mid-rapidity. The error bars represent the statistical uncertainties. The boxes represent the systematic uncertainties. The shaded bands on the data points indicate the uncertainties from the nuclear overlap function T_AA. The bands around unity indicate the uncertainties from the p+p baselines. Suppression of the J/psi production is observed in Au+Au collisions at 54.4 GeV with improved precision compared to previous results at 39 and 62.4 GeV.

Figure 4. The R_AA of J/psi as a function of collision energy for central collisions, in comparison with model calculations. The error bars represent the statistical uncertainties and the boxes represent the systematic uncertainties, including those from p+p baselines and uncertainties from T_AA. There is no significant energy dependence within uncertainties from SPS to RHIC top energy.

Figure 5a. The inclusive J/psi R_AA as a function of p_T in Au+Au collisions for different collision energies in 0-60% centrality. Figure 5b. The inclusive J/psi R_AA as a function of p_T in Au+Au collisions for different centrality bins at 54.4 GeV. The error bars represent the statistical uncertainties. The boxes represent the systematic uncertainties. The bands around unity indicate the uncertainties from the T_AA and the p+p baselines. A larger suppression is observed at lower pT and towards more central collisions.

Figure 7. The inclusive J/psi r_AA as a function of N_part in different collision systems at mid-rapidity. The error bars represent the statistical uncertainties. The boxes represent the systematic uncertainties. The r_AA distribution at 54.4 GeV follow the trend of collision energy dependence.

Summary:

In summary, we report on measurements of J/psi meson production in Au+Au collisions at √s_NN = 54.4 GeV with the STAR detector at RHIC.

The N_part dependence of R_AA show a suppression in central Au+Au collisions at √s_NN = 54.4 GeV

Newly measured R_AA for J/psi meson at √s_NN = 54.4 GeV is shown as s function of N_part and p_T with improved precision compared to previous measurements at 39 and 62.4 GeV