$\phi$ meson production in the forward/backward rapidity region in Cu$+$Au collisions at $\sqrt{s}_NN=200$ GeV

he PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured???meson production and its nuclear modification in asymmetric Cu+Au heavy-ion collisions at?sNN????√=200?GeV at both forward Cu-going direction (1.2<y<2.2) and backward Au-going direction (?2.2<y<?1.2), rapidities. The measurements are performed via the dimuon decay channel and reported as a function of the number of participating nucleons, rapidity, and transverse momentum. In the most central events, 0\%--20\% centrality, the??meson yield integrated over?1<pT<5?GeV/c?prefers a smaller value, which means a larger nuclear modification, in the Cu-going direction compared to the Au-going direction. Additionally, the nuclear-modification factor in Cu+Au collisions averaged over all centrality is measured to be similar to the previous PHENIX result in?d+Au collisions for these rapidities.