Energy loss of fast quarks in nuclei

TL;DR

This paper analyzes how fast quarks lose energy while traveling through nuclei by examining Drell-Yan dimuon production, finding evidence for nonzero energy loss in nuclear matter using a light-cone formalism.

Contribution

It introduces a consistent light-cone formulation for nuclear dependence of Drell-Yan processes and measures the first nonzero energy loss of partons in nuclei.

Findings

Determined the energy loss rate as -dE/dz = 2.32 GeV/fm.

Shadowing effects are calculated without free parameters.

First experimental evidence of parton energy loss in nuclear matter.

Abstract

We report an analysis of the nuclear dependence of the yield of Drell-Yan (DY) dimuons from the 800 GeV/c proton bombardment of $^2H$, C, Ca, Fe, and W targets. A light-cone formulation of the DY process is employed in the rest frame of the nucleus. In this frame, for $x_2\ll x_1$, DY production appears as bremsstrahlung of a virtual photon followed by decay into dileptons. We treat the two sources of nuclear suppression, energy loss and shadowing, in a consistent formulation. Shadowing, involving no free parameters, is calculated within the light-cone dipole formalism. Initial-state energy loss, the only unknown in the problem, is determined from a fit to the nuclear-dependence ratio versus $x_1$. With the assumption of constant energy loss per unit path length, we find $-dE/dz = 2.32 \pm 0.52\pm 0.5$ GeV/fm. This is the first observation of a nonzero energy loss of partons traveling in nuclear environment.