Paper: Cold Nuclear Matter Effect on the Inclusive $J/\psi$ Production in p+Au Collisions at $\sqrt{s_\text{NN}}$ = 200 GeV with

Updated on Tue, 2025-07-01 01:05. Originally created by zyzhang on 2024-03-16 09:43.

Title:
Cold Nuclear Matter Effect on the Inclusive J/ψ Production in p+Au Collisions at √(s_NN) = 200 GeV with the STAR Experiment

List of PAs:
Ziyue Zhang, Zaochen Ye, Zhenyu Ye

Target Journal:
PRC

Abstract
In this paper, the measurement of Cold Nuclear Matter (CNM) Effects on the production of inclusive J/ψ in p+Au collisions at √(s_NN) = 200 GeV is reported, and a combined J/ψ→e⁺e^- cross section in p+p at √s = 200 GeV from STAR is calculated. The CNM effects in p+Au collisions are quantified by the Nuclear Modification Factor (R_pAu), defined as the ratio of the yield of the inclusive J/ψ in p+Au collisions to that in the p+p collision, scaled by the average number of binary nucleon-nucleon collisions. The R_pAu is derived as a function of transverse momentum (p_T) in the range 4 - 12 GeV/c and is averaged within the rapidity (y) and azimuthal angle (φ) coverage of |y|<1, 0 ≤ φ < 2π. The result is consistent with unity, suggesting negligible modification on the yield by the CNM effects in this kinematic region. Various model calculations are in agreement with R_pAu measurement, yet calculations of yields in p+p and p+Au collisions are less satisfactory in describing the data. This analysis has improved the measurement precision in p+p cross section, p+Au invariant yield and consequently R_pAu in the covered kinematic region.

Figures:

Fig. 1 Signal Extraction
Caption: The invariant mass distributions of unlike-sign (US) dielectron pairs after subtraction of like-sign (LS) dielectron pairs (the combinatorial background) in p+p and p+Au collisions. The vertical bars represent statistical uncertainties. The US – LS mass distributions (black circles) are fit with a function (black lines) which is the sum of 2 contributions: i. templates from simulation representing the signal (red lines); ii. an exponential function to model the residual background empirically (blue dashed lines). The open black circles are excluded from the fit to reduce potential influence from the ψ(2S) meson. The green dashed lines are the default lower and upper limits for the mass window over which the integral is evaluated.
Plot:

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Fig.2 Inclusive J/ψ→e⁺e^- cross section as a function of p_T in p+p collisions at √(s) = 200 GeV. This result is compared to the STAR J/ψ→μ⁺μ^- measurement for |y| < 0.5 at the same √(s), and to various model calculations for |y| < 0.5. The “*” indicates that the dimuon measurement is corrected for the rapidity coverage from |y| < 0.5 to |y| < 1 based on calculations of the Improved Color Evaporation Model (ICEM) as a function of pT. This analysis (2015) is combined with 2 other published STAR J/ψ→e⁺e^- results with data taken in 2009 and 2012. The vertical bars represent the statistical uncertainties, while the brackets and transparent boxes represent the systematic uncertainty that is uncorrelated and correlated between p_T bins, respectively. The horizontal bars represent the bin width. The dashed line is a fit to the combined J/ψ→e⁺e^- result.

Plot:

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Fig. 3 p+Au invariant yield
Caption: Inclusive J/ψ→e⁺e⁻ invariant yield as a function of p_T in p+Au collisions at √(s_NN) = 200 GeV. This resut is compared to the STAR J/ψ→μ⁺μ⁻ measurement for |y| < 0.5 at the same √(s_NN), and to various model calculations. The dashed line is a combined fit to dielectron and dimuon channel results, covering ranges 4 < p_T < 12 GeV/c and 0 < p_T < 4 GeV/c, respectively. The representation of uncertainties and bin width is identical to Fig. 2
Plot:

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Fig. 4 RpAu
Caption: Inclusive J/ψ→e⁺e⁻ R_pAu compared to the J/ψ→μ⁺μ⁻ R_pAu, as well as the R_AA in 0-20% central Au+Au collisions at the same √(s_NN). The second panel shows comparison of the J/ψ R_pAu measurements for the dielectron and dimuon channels with various model calculations. The representation of uncertainties and bin width is identical to Fig. 2, except that uncertainties correlated between p_T bins are represented by the boxes of the corresponding color around unity.

Plot:

Tables:
Table 2: Summary table of the systematic uncertainties in this analysis, quoted as percentages. Values for 3 physics observables are quoted. The p_T dependent uncertainties are quoted as a range. The quadrature sums of all p_T dependent uncertainties and p_T independent uncertainties are quoted separately.

Footnote a. The N_mb^eqv.* is the quadrature sum of contributions from the N_mb^eqv., Trig.Bias and vertex finding efficiency estimation and is dominated by the former 2.

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Table 3: Uncertainties of dielectron measurements (4 < p_T < 10 GeV/c), quoted as the percentage of the central value within overlapping p_T range. The 10 < p_T < 12 GeV/c bin is not included due to the fact that the sum of certain systematic uncertainties was extrapolated from lower p_T ranges in 2012 results, inhibiting the comparison. The asymmetric uncertainties from the raw yield estimation in 2009 results were averaged in order to provide a direct comparison with other years. “-” indicates the lack of an estimation in the original publication; “N/A” indicates that the source is not involved in the analysis; the total uncertainty listed in the table for each individual measurement considers all the statistical and systematic uncertainties including those that are missing in the original analysis and taken from the other measurements.