Abstract
In this paper, the measurement of Cold Nuclear Matter (CNM) Effects on the production of inclusive J/ψ in p+Au collisions at √(sNN) = 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 (RpAu), defined as the ratio of the yield of the inclusive J/ψ against that in the p+p collision, scaled by the average number of binary nucleon-nucleon collisions. The RpAu is derived as a function of transverse momentum (pT) between 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 RpAu measurement, yet calculations on 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 RpAu in the kinematics coverage. 

Figures:

Fig. 1 Signal Extraction
Caption: The invariant mass distributions of unlike-sign (US) dielectron pairs after subtraction of like-sign (LS) dielectron pairs as 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) summed up by 2 contributions: a. templates from simulation representing the signal (red lines); b. an exponential function in an attempt to model the residual background empirically (blue dashed lines). The open black circles are excluded from the fit to reduce potential ψ(2S) influence. The green dashed lines are the default lower and upper limits for yield integral.
Plot:

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Fig.2 Inclusive J/ψ→e+e- cross section as a function of pT in p+p collisions at √(s) = 200 GeV and comparison to STAR J/ψ→μ+μ- measurement for |y| < 0.5 at the same √(s) and to various model calculations for |y| < 0.5. Notice the “*” marker 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 pT bins, respectively. The horizontal bars represent the bin width. The dashed line is a fit to the combined.
Plot:

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

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Fig. 4 RpAu
Caption: IInclusive J/ψ→e+e− RpAu compared to the J/ψ→μ+μ− RpAu as well as the RAA in 0-20% central Au+Au collisions at the same √sNN, and comparison on RpAu between STAR J/ψ RpAu measurements via dielectron and dimuon channel with various model calculations. The representation of uncertainties and bin width is identical to Fig. 2, with the exception of correlated uncertainties between pT 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 in percentage. Values for 3 physics observables are quoted. The pT dependent uncertainties are quoted as a range. The Nmbeqv.* is the quadrature sum of contributions from the Nmbeqv., Trig.Bias and vertex finding efficiency estimation and is dominated by the former two. The quadrature sum of all pT dependent uncertainties and pT independent uncertainties are quoted separately.

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Table 3: Uncertainties of dielectron measurements (4 < pT < 10 GeV/c) in percentage of the central value within overlapping pT range. The 10 < pT < 12 GeV/c bin is not included due to the fact that the sum of certain systematic uncertainties was extrapolated from lower pT ranges in 2012 results and hard to be compared with. The asymmetric uncertainties from raw yield estimation in 2009 results were averaged in order to provide direct comparison with others. “-” indicates lack of estimation in the original publication; “N/A” indicates the source is not involved in the analysis; “*” indicates this source is included in “**”; the total uncertainty listed in the table for each individual measurement has included the assigned complementary value to the lack of estimation entries.

 

Paper Draft: v0, v1, v2, v2.1, v2.2, v2.3,  

Paper Draft Diff: diff_2.1_2

PWGC Preview: slide, notes and response

PWG Review Comments and Response: draft_v0+anaNote_v3, draft_v1+anaNote_v4 

GPC:
03/11/2025: PA
04/02/2025: CodeQA PA