Abstract
In this paper, the measurement on 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 angel (φ) coverage of |y|<1, 0 ≤ φ ≤ 2π. The result is consistent with unity, suggesting negligible modification on the yield by the CNM effects. Various model calculations are in agreement with RpAu measurement, yet calculations on yields in p+p and p+Au are less satisfactory in describing the data. This measurement 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) di-electron pairs after subtraction of like-sign (LS) di-electron pairs as the combinatorial background in p+p (left) and p+Au (right) collisions. The vertical bars represent statistical uncertainties. The US – LS mass distributions (black circles) are then 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 (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 p+p cross section
Caption: Left: Inclusive J/ψ cross section as a function of pT in p+p collisions at √(s) = 200 GeV. This analysis (2015) is combined with 2 other published STAR J/ψ→e+e- results with data taken in 2009 [1] and 2012 [2] . 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. The empirical fit function takes the form of f(pT) = N*(1 + (pT/pT,0)2)-n  where N = (4.5±0.9) nb(GeV/c)2, pT,0 = (3.4±0.4) GeV/c, n = 4.9±0.5. Right: Comparison to STAR J/ψ→μ+μ- measurement for |y| < 0.5 at the same √(s) [3] and to various model calculations [4, 5, 6, 7, 8, 9].
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) [3], and to various model calculations [4, 5, 6, 7, 8, 9]. The dashed line is a mixed fit to di-electron and di-muon channel results, covering pT range of 4 – 12 GeV/c and 0 – 4  GeV/c respectively. The empirical fit function takes the form of f(pT) = N*(1 + (pT/pT,0)2)-n, where N = (3.0±0.3) *107 (GeV/c)2, pT,0 = (4.4±0.5) GeV/c, n = 6.0±0.9. The fit is for demonstration purpose only. The representation of uncertainties and bin width is identical to Fig. 2
Plot:

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Fig. 4 RpAu
Caption: Left: Inclusive J/ψ→e+e- RpAu compared to the J/ψ→μ+μ- [3] RpAu and RAA in 0-20% central Au+Au collisions at the same √(sNN) [10].  Right: comparison on RpAu between STAR J/ψ→e+e- RpAu measurements via di-electrona and di-muon channel with various model calculations [4, 5, 6, 7, 8, 9, 11, 12, 13, 14]. 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:

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Table Dielectron measurement uncertainties
Caption: Uncertainties of di-electron measurements (4 < pT < 10 GeV/c). “-” indicates lack of estimation in the original publication; “N/A” indicates the item is not involved in the analysis; “*” indicates this item is included in “**”

Paper Draft: WIP

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