J/psi Production and Nuclear Effects for d+Au and p+p Collisions at sqrt(s_NN) = 200 GeV

TL;DR

The observed nuclear dependence in d + Au collisions is found to be modest, suggesting that the absorption in the final state is weak and the shadowing of the gluon distributions is small and consistent with Dokshitzer-Gribov-Lipatov-Altarelli-Parisi-based parametrizations that fit deep-inelastic scattering and Drell-Yan data at lower energies.

Abstract

J/psi production in d+Au and p+p collisions at sqrt(s_NN) = 200 GeV has been measured by the PHENIX experiment at rapidities -2.2 < y < +2.4. The cross sections and nuclear dependence of J/ψproduction versus rapidity, transverse momentum, and centrality are obtained and compared to lower energy p+A results and to theoretical models. The observed nuclear dependence in d+Au collisions is found to be modest, suggesting that the absorption in the final state is weak and the shadowing of the gluon distributions is small and consistent with Dokshitzer-Gribov-Lipatov-Altarelli-Parisi-based parameterizations that fit deep-inelastic scattering and Drell-Yan data at lower energies.

Figures (3)

• Figure 1: (color online) (a) The 200 GeV $J/\psi$$p+p$ differential cross section times di-lepton branching ratio versus rapidity (10% overall normalization uncertainty is not included). (b) The minimum bias $R_{dA}$ versus rapidity (12% overall normalization uncertainty not included). For both panels the dashed error bars represent systematic uncertainties relevant for comparing the two rapidity bins in each muon arm, while the solid error bars represent the overall uncertainties relevant for comparing points at negative, central, or positive rapidity. The curve in (a) represents a fit as described in the text while the curves in (b) are theoretical calculations Klein:2003djVogt:2004dhKopeliovich:2001ee as described in the text.
• Figure 2: (color online) $\alpha$ versus (a) $\alpha$ versus $p_T$ compared to lower energy measurements shown for three different $x_F$ ranges. An additional overall uncertainty of 0.02 in our $\alpha$ values is not shown.
• Figure 3: (color online) (a) $\alpha$ versus $p_T$ compared to lower energy measurements, shown for three different $x_F$ ranges. The error bars have the same meaning as in Fig. \ref{['fig:sigpp_rda']}. An additional 0.02 overall uncertainty is not shown. The dashed curves are simple fits Leitch:1999ea to the lower energy results. (b) Nuclear modification factor versus centrality as given by the number of nucleon+nucleon collisions shown for three different rapidity ranges, compared to theoretical calculationsKlein:2003djVogt:2004dh including final-state absorption and EKS (solid) or FGS (dashed) shadowing. The bars at the low end of each plot represent the systematic errors between different rapidity ranges. An additional 12% global error bar is not shown. The histograms at the bottom of the lower panel indicate the distribution of the number of collisions for each of the four centrality bins.