PHENIX Measurements of dN(ch)/d eta in small systems

Abstract

The PHENIX experiment has excellent data for small systems including p+Au, d+Au, He-3+Au at 200 GeV as well as the d+Au beam energy scan down to 19.6 GeV. We present new measurements of dN(ch)/d eta for all of these systems over a broad range in pseudorapidity -3 < eta < +3 and event multiplicity. These measurements provide key constraints of baryon stopping models and are compared with various theoretical calculations. The measurements are also compared with flow observables as a function of pseudorapidity to explore scaling relations. In particular measurements as a function of collision energy provide key inputs for calculations for the upcoming A+A beam energy scan at RHIC in terms of particle production and baryon rapidity shifts.