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

Understand

The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured $\phi$ meson production and its nuclear modification in asymmetric Cu$+$Au heavy-ion collisions at $\sqrt{s_{NN}}=200$ 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 $\phi$ meson yield integrated over $1<p_T<5$ 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.