Energy loss of charm quarks from $J/\psi$ production in cold nuclear matter

Abstract

$J/\psi$ suppression in p-A collisions is studied by considering the nuclear effects on parton distribution, energy loss of beam proton and the finial state energy loss of color octet $c\overline{c}$. The leading-order computations for $J/\psi$ production cross-section ratios $R_{W/Be}(x_F)$ are presented and compared with the selected E866 experimental data with the $c\overline{c}$ remaining colored on its entire path in the medium. It is shown that the combination of the different nuclear effects accounts quite well for the observed $J/\psi$ suppression in the experimental data. It is found that the $J/\psi$ suppression on $R_{W/Be}(x_F)$ from the initial state nuclear effects is more important than that induced by the energy loss of color octet $c\overline{c}$ in the large $x_F$ region. Whether the $c\overline{c}$ pair energy loss is linear or quadratic with the path length is not determined. The obtained $c\overline{c}$ pair energy loss per unit path length $\alpha =2.78\pm 0.81$ GeV/fm, which indicates that the heavy quark in cold nuclear matter can lose more energy compared to the outgoing light quark.