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 ($1.4<\eta<2.4$, $p$-going direction) and backward rapidity ($-2.2<\eta<-1.2$, $A$-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.
Highlights
Measurements of particle production in heavy-ion collisions enable the study of properties of a hot and dense nuclear medium called the quark-gluon plasma (QGP) [1,2,3,4]
We present nuclear modification factors of charged hadron in p + Al and production at forward p + Au collisions at a√ndsNbNa=ckw20a0rd rapidity GeV of various multiplicities
There is no significant modification of charged hadron production observed in peripheral p + Al and p + Au collisions in either rapidity region
Summary
Measurements of particle production in heavy-ion collisions enable the study of properties of a hot and dense nuclear medium called the quark-gluon plasma (QGP) [1,2,3,4]. An initial striking observation at the Relativistic Heavy Ion Collider (RHIC) was that production of high transverse momentum (pT ) hadrons in Au + Au collisions is strongly suppressed compared to that in p + p collisions scaled by the number of binary collisions. This suppression indicates that partons experience substantial energy loss as they traverse the QGP, a phenomenon called jet-quenching [5]. A control experiment involving a deuteron projectile on a heavy-ion target, d + Au, was carried out to test whether the feature of strong energy loss is still present in a collision system of much smaller size. In the ten years because these initial measurements, indications of QGP formation in smaller collision systems including d + Au have been found, though without evidence of jet quenching phenomena [7]
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