Spectra of identified particles, geometry categorization and bias and global observables in d+Au collisions

Abstract

Abstract Geometry selection in d + Au / p + Pb collisions is crucial for understanding the physics underlying modified nuclear parton distribution functions, gluon saturation or shadowing, initial state energy loss, and possible hydrodynamic flow in these small systems. The PHENIX Collaboration tests for auto-correlation biases in the geometry determination in small collision systems. These biases are well understood and an order of magnitude smaller at RHIC as compared to the LHC. As a result, auto-correlation biases are unable to describe the suppression of high transverse momentum ( p T ) π 0 's seen in the ratio of central-to-peripheral d + Au collisions. The centrality dependent d + Au pion, kaon and proton yields relative to binary collision-scaled p + p yields are also reported, including the high p T π 0 and K S 0 . At intermediate p T , between 2 and 5 GeV / c , baryons are enhanced in central d + Au collisions. The baryon enhancement is present in d + Au and Au + Au collisions and increases with centrality. We compare identified particle yields in peripheral Au + Au collisions to central d + Au collisions that have a comparable number of participants and binary collisions. The p T dependence of this ratio is strikingly similar for mesons and baryons.