Nuclear-modification factor of charged hadrons at forward and backward rapidity in p + Al and p + Au collisions at sNN =200 GeV

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© 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP 3 . The PHENIX experiment has studied nuclear effects in p+Al and p+Au collisions at sNN=200GeV on charged hadron production at forward rapidity (1.4<η<2.4, p-going direction) and backward rapidity (-2.2<η<-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.