Nuclear-modification factor of charged hadrons at forward and backward rapidity in $p$$+$Al and $p$$+$Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV

Abstract

The PHENIX experiment has studied nuclear effects in $p$$+$Al and $p$$+$Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV on charged hadron production at forward rapidity ($1.4<\hat{I}\cdot <2.4$, $p$-going direction) and backward rapidity ($-2.2<\hat{I}\cdot <-1.2$, $A$-going direction). Such effects are quantified by measuring nuclear modification factors as a function of transverse momentum and pseudorapidity in various collision multiplicity selections. In central $p$$+$Al and $p$$+$Au collisions, a suppression (enhancement) is observed at forward (backward) rapidity compared to the binary scaled yields in $p$+$p$ collisions. The magnitude of enhancement at backward rapidity is larger in $p$$+$Au collisions than in $p$$+$Al collisions, which have a smaller number of participating nucleons. However, the results at forward rapidity show a similar suppression within uncertainties. The results in the integrated centrality are compared with calculations using nuclear parton distribution functions, which show a reasonable agreement at the forward rapidity but fail to describe the backward rapidity enhancement.

303 authors, 66 institutions, 17 pages, 15 figures, 4 tables, 2015 data. v2 is version accepted for publication by Phys. Rev. C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html