Pion-exchange and Fermi-motion effects on the proton-deuteron Drell-Yan process

Abstract

Within a nuclear model where the deuteron has $NN$ and $\ensuremath{\pi}NN$ components, we derive a convolution formula for investigating the Drell-Yan process in proton-deuteron ($pd$) reactions. The contribution from the $\ensuremath{\pi}NN$ component is expressed in terms of a pion momentum distribution that depends sensitively on the $\ensuremath{\pi}NN$ form factor. With a $\ensuremath{\pi}NN$ form factor determined by fitting the $\ensuremath{\pi}N$ scattering data up to invariant mass $W=1.3\text{ }\text{ }\mathrm{GeV}$, we find that the pion-exchange and nucleon Fermi-motion effects can change significantly the ratios between the proton-deuteron and proton-proton Drell-Yan cross sections, ${R}_{pd/pp}={\ensuremath{\sigma}}^{pd}/(2{\ensuremath{\sigma}}^{pp})$, in the region where the partons emitted from the target deuteron are in the Bjorken ${x}_{2}\ensuremath{\gtrsim}0.4$ region. The calculated ratios ${R}_{pd/pp}$ at 800 GeV agree with the available data. Predictions at 120 GeV for analyzing the forthcoming data from Fermilab are presented.