Charmonium suppression in fixed target proton-nucleus collisions

Abstract

In this article, we perform a systematic investigation of cold nuclear matter (CNM) effects operative on charmonium ($J/ψ$, $ψ(2S)$) production in fixed target proton-nucleus (p+A) collisions. Influence on charmonium production cross section due to the interplay of three different plausible CNM effects namely the initial-state parton energy loss, nuclear shadowing, and final-state absorption of the resonant states, are evaluated in detail. The available data on charmonium production in fixed target p+A collision experiments from SPS, Fermilab and HERA-B are examined for this purpose. The energy dependence of the observed $J/ψ$ production patterns are utilized to anticipate level of "normal" absorption in the upcoming proton induced collisions by NA60+ experiment at CERN SPS and CBM experiment at FAIR SIS100 accelerator facilities.

Figures (11)

• Figure 1: $x$ dependence of the shadowing parameter for gluons, valance up quarks and valence down quarks inside W nucleus evaluated using EPPS21NLO nPDF package at a momentum scale $Q=3.1$ GeV, suitable for $J/\psi$ production.
• Figure 2: Variation of the shadowing ratio at mid-rapidity ($y_{cms}$ =0.0) as a function of centre-of-mass energy ($\sqrt{s_{\rm NN}}$) for p+W collisions. The blue (dot-dashed) line, magenta (solid dashed) line and the orange (dotted) line respectively denote evaluation of $c\bar{c}$ production cross section without any initial state energy loss and with BH and BDMPS schemes of beam parton energy loss. All the calculations are done using central sets of the CT18ANLO free proton PDF and EPPS21NLO nuclear PDF.
• Figure 3: Variation of the shadowing ratio for p+W collisions as a function of centre-of-mass rapidity $(y_{cms})$ at different beam energies relevant for existing or upcoming fixed target experiments in absence of any initial state parton energy loss effect. The dotted (blue) line corresponding to the $gg \rightarrow c\bar{c}$ fusion contribution, the dashed (orange) line correspond to the $q\bar{q} \rightarrow c\bar{c}$ annihilation and the solid (magenta) line is the sum of these two leading order processes. All the calculations are done using central sets of the CT18ANLO free proton PDF and EPPS21NLO nuclear PDF.
• Figure 4: Variation of the shadowing ratio for p+W collisions as a function of centre-of-mass rapidity $(y_{cms})$ relevant for existing or upcoming fixed target experiments after accounting for energy loss of projectile partons prior to hard interactions. The dotted (blue) line corresponding to no initial state energy loss scenario, the dashed (orange) line corresponds to the linear path length dependence of energy loss following BH scheme and the solid (magenta) line corresponds to quadratic path length dependence of energy loss following BDMPS scheme. All the calculations are carried out with the CT18ANLO free proton PDF and EPPS21NLO nuclear PDF.
• Figure 5: Variation of the mid-rapidity shadowing ratio as a function of target mass (A) in fixed target p+A collisions with incident proton beam energies ranging between 30 - 800 GeV relevant for available and upcoming measurements. The dotted (blue) line corresponding to no initial state energy loss scenario and incorporates only the effect of modified parton densities in the target. The dashed (orange) line corresponds to the linear path length dependence of energy loss following BH scheme and the continuous (magenta) line corresponds to quadratic path length dependence of energy loss following BDMPS scheme. All the estimations are evaluated with the CT18ANLO free proton PDF and EPPS21NLO nuclear PDF.