Color transparency in $\pi^-$-induced dilepton production on nuclei

Abstract

We argue that the observation of the color transparency effect in the semiexclusive $A(\pi^-,l^+ l^-)$ process is important for determining whether it is possible to extract the generalized parton distributions of the nucleon from the elementary reaction $\pi^- p \to l^+ l^- n$ at $p_{\rm lab}=15-20$ GeV/c at small $|t|$ and large invariant mass of the dilepton pair $l^+ l^-$. Assuming that the transverse size of the pionic $q \bar q$ pair in the hard interaction point is similar to the one in the reaction $\gamma^* p\to \pi^+ n$ studied at JLab we predict large color transparency effects in the discussed kinematic range. We also suggest that the semiexclusive $\rho^0$ production in $\pi^-$-induced reactions in the same beam momentum region may provide new information on the dynamics of the interaction in the non-vacuum channel, while the $J/\psi$ production can be used to get information on $J/\psi N$ total interaction cross section.,