Nuclear gluon shadowing via dileptons from open charm decay in $p+A$ at $\sqrt s=200$ AGeV

Opposite-sign lepton pairs ($ee$,$e\mu$ and $\mu\mu$) from open charm decay are proposed as a measure of nuclear shadowing effects. Via an approximate scaling the ratio of the dilepton spectra from $p+A$ to those from $pp$ reflects the shadowing function well. We show that the required measurements are feasible at the Relativistic Heavy ion Collider (RHIC) by considering the backgrounds according to the proposed PHENIX detector geometry.