Abstract
The effects of parton energy loss in nuclear matter on the Drell-Yan process in pA and πA collisions at fixed-target energies are investigated. Calculations are based on the Baier-Dokshitzer-Mueller-Peigné-Schiff (BDMPS) framework embedded in a next-to-leading order calculation, using the transport coefficient extracted from J/ψ measurements. Model calculations prove in good agreement with preliminary measurements by the E906 experiment, despite a slightly different magnitude, supporting a consistent picture between Drell-Yan and J/ψ data. Predictions for the COMPASS future measurements in πA collisions at sqrt{s}=18.9 GeV are also performed. At higher collision energy ( sqrt{s}=38.7 GeV), Drell-Yan measurements are only slightly affected by energy loss effects. On the contrary, the E906 results turn out in clear disagreement with nuclear PDF effects alone. The comparison of E772, E866, and E906 measurements indicates for the first time a clear violation of QCD factorization in Drell-Yan production in pA collisions.
Highlights
The latter, fully coherent radiative energy loss, arises from the interference of gluon emission amplitudes off an ‘asymptotic’ incoming particle, produced long before entering the medium, and an asymptotic outgoing particle [7,8,9,10,11]
Calculations are based on the Baier-Dokshitzer-Mueller-Peigne-Schiff (BDMPS) framework embedded in a next-toleading order calculation, using the transport coefficient extracted from J/ψ measurements
The effects of parton energy loss on Drell-Yan production in pA and πA collisions at fixedtarget energies has been investigated, based on a BDMPS energy loss framework embedded in a next-to-leading order (NLO) calculation
Summary
We consider the inclusive production of Drell-Yan lepton pairs of large invariant mass,. The xF-differential production cross section in a generic h1h2 collision reads dσ(h1h2) = dxF dM i,j=q,q,g dx. The single differential cross section dσ/dxF is obtained by integrating (2.1) over the dilepton mass range, here between the charmonium and bottomonium resonances. In this analysis we are interested in the production of Drell-Yan pairs using either a proton or a pion beam on nuclear targets, pA and πA collisions. In the absence of nuclear effects, eq (2.3) may differ from unity because of the differences between proton and neutron parton densities. Fqn fqp, resulting in rather small isospin effects. Isospin effects are more important in low energy πA collisions, mostly sensitive to the valence up and down quark distribution in the nucleus
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