Measurement of electrons from heavy-flavor decays from p+p, d+Au, and Cu + Cu collisions in the PHENIX experiment

Abstract

Charm and bottom quarks are formed predominantly by gluon fusion in the initial hard scatterings at RHIC, making them good probes of the full medium evolution. Previous measurements at RHIC have shown large suppression and azimuthal anisotropy of open heavy-flavor hadrons in Au+Au collisions at $\sqrt{s_{NN}}=200~{\rm GeV}$. Explaining the simultaneously large suppression and flow of heavy quarks has been challenging. To further understand the heavy-flavor transport in the hot and dense medium, it is imperative to also measure cold nuclear matter effects which affect the initial distribution of heavy quarks as well as the system size dependence of the final state suppression. In this talk, new measurements by the PHENIX collaboration of electrons from heavy-flavor decays in $p$+$p$, $d$+Au, and Cu+Cu collisions at $\sqrt{s_{NN}}=200~{\rm GeV}$ are presented. In particular, a surprising enhancement of intermediate transverse momentum heavy-flavor decay leptons in $d$+Au at mid and backward rapidity are also seen in mid-central Cu+Cu collisions. This enhancement is much larger than the expectation from anti-shadowing of the parton distributions and is theoretically unexplained.