Nuclear matter effects on $J/\psi$ production in asymmetric Cu+Au   collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV
  We report on $J/\psi$ production from asymmetric Cu+Au heavy-ion collisions at $\sqrt{s_{_{NN}}}$=200 GeV at the Relativistic Heavy Ion Collider at both forward (Cu-going direction) and backward (Au-going direction) rapidities. The nuclear modification of $J/\psi$ yields in Cu$+$Au collisions in the Au-going direction is found to be comparable to that in Au$+$Au collisions when plotted as a function of the number of participating nucleons. In the Cu-going direction, $J/\psi$ production shows a stronger suppression. This difference is comparable in magnitude and has the same sign as the difference expected from shadowing effects due to stronger low-$x$ gluon suppression in the larger Au nucleus. The relative suppression is opposite to that expected from hot nuclear matter dissociation, since a higher energy density is expected in the Au-going direction. 
C. Aidala, N.N. Ajitanand, Y. Akiba, R. Akimoto, J. Alexander, K.   Aoki, N. Apadula, H. Asano, E.T. Atomssa, T.C. Awes, B. ...
nucl-ex