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arXiv · 2003.04283

Transverse single-spin asymmetry for very forward neutral pion production in polarized $p+p$ collisions at $\sqrt{s} = 510$ GeV

M. H. Kim·O. Adriani·E. Berti·L. Bonechi·R. D'Alessandro·Y. Goto·B. Hong·Y. Itow·K. Kasahara·H. Menjo·I. Nakagawa·J. S. Park·T. Sako·N. Sakurai·K. Sato·R. Seidl·K. Tanida·S. Torii·A. Tricomi·M. Ueno·Y. Makino·Q. D. Zhou·J. H. Lee·T. Ljubicic·A. Ogawa
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Abstract

Transverse single-spin asymmetries of very forward neutral pions generated in polarized $p + p$ collisions allow us to understand the production mechanism in terms of perturbative and non-perturbative strong interactions. During 2017 the RHICf Collaboration installed an electromagnetic calorimeter in the zero-degree region of the STAR detector at the Relativistic Heavy Ion Collider (RHIC) and measured neutral pions produced at pseudorapidity larger than 6 in polarized $p$+$p$ collisions at $\sqrt{s}$ = 510 GeV. The large non-zero asymmetries increasing both in longitudinal momentum fraction $x_{F}$ and transverse momentum $p_{T}$ have been observed at low transverse momentum $p_{T} < 1$ GeV/$c$ for the first time at this collision energy. The asymmetries show an approximate $x_{F}$ scaling in the $p_{T}$ region where non-perturbative processes are expected to dominate. A non-negligible contribution from soft processes may be necessary to explain the nonzero neutral pion asymmetries.

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M. H. Kim, O. Adriani, E. Berti, L. Bonechi, R. D'Alessandro, Y. Goto, B. Hong, Y. Itow, K. Kasahara, H. Menjo, I. Nakagawa, J. S. Park, T. Sako, N. Sakurai, K. Sato, R. Seidl, K. Tanida, S. Torii, A. Tricomi, M. Ueno, Y. Makino, Q. D. Zhou, J. H. Lee, T. Ljubicic, A. Ogawa. 2020-03-09. Transverse single-spin asymmetry for very forward neutral pion production in polarized $p+p$ collisions at $\sqrt{s} = 510$ GeV. https://doi.org/10.1103/physrevlett.124.252501

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