J/psi production in proton-nucleus collisions at 158 and 400 GeV

TL;DR

This study investigates J/psi production in proton-nucleus collisions at 158 and 400 GeV, revealing nuclear suppression effects that vary with energy and parton momentum fraction, providing insights into nuclear matter effects.

Contribution

It provides new measurements of J/psi suppression at different energies and explores the dependence on parton momentum fraction, enhancing understanding of nuclear effects in fixed-target experiments.

Findings

Significant nuclear suppression of J/psi yield observed.

Greater suppression at lower incident energy.

Dependence of suppression on parton momentum fraction x_2.

Abstract

The NA60 experiment has studied J/psi production in p-A collisions at 158 and 400 GeV, at the CERN SPS. Nuclear effects on the J/psi yield have been estimated from the A-dependence of the production cross section ratios sigma_{J/psi}^{A}/sigma_{J/psi}^{Be} (A=Al, Cu, In, W, Pb, U). We observe a significant nuclear suppression of the J/psi yield per nucleon-nucleon collision, with a larger effect at lower incident energy, and we compare this result with previous observations by other fixed-target experiments. An attempt to disentangle the different contributions to the observed suppression has been carried out by studying the dependence of nuclear effects on x_2, the fraction of nucleon momentum carried by the interacting parton in the target nucleus.