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; J H Lee; T Ljubicic; Y Makino; H Menjo; I Nakagawa; A Ogawa; J S Park; T Sako; N Sakurai; K Sato; R Seidl; K Tanida; S Torii; A Tricomi; M Ueno; Q D Zhou; RHICf Collaboration

doi:10.1103/PhysRevLett.124.252501

Transverse Single-Spin Asymmetry for Very Forward Neutral Pion Production in Polarized p+p Collisions at sqrt[s]=510 GeV

Phys Rev Lett. 2020 Jun 26;124(25):252501. doi: 10.1103/PhysRevLett.124.252501.

Authors

M H Kim^{1

2}, O Adriani^{3

4}, E Berti^{3

4}, L Bonechi⁴, R D'Alessandro^{3

4}, Y Goto^{2

5}, B Hong¹, Y Itow^{6

7}, K Kasahara⁸, J H Lee⁹, T Ljubicic⁹, Y Makino⁶, H Menjo¹⁰, I Nakagawa^{2

5}, A Ogawa⁹, J S Park^{2

11}, T Sako¹², N Sakurai¹³, K Sato⁶, R Seidl^{2

5}, K Tanida¹⁴, S Torii¹⁵, A Tricomi^{16

17}, M Ueno⁶, Q D Zhou⁶; RHICf Collaboration

Affiliations

¹ Korea University, Seoul 02841, Korea.
² RIKEN Nishina Center for Accelerator-Based Science, Wako, Saitama 351-0198, Japan.
³ Department of Physics and Astronomy, University of Florence, Sesto Florentino (FI) I-50019, Italy.
⁴ INFN Section of Florence, Sesto Florentino (FI) I-50019, Italy.
⁵ RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973-5000, USA.
⁶ Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Aichi 464-8601, Japan.
⁷ Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya, Aichi 464-8602, Japan.
⁸ Shibaura Institue of Technology, 307 Fukasaku, Minuma-ku, Saitama 337-8570, Japan.
⁹ Brookhaven National Laboratory, Upton, New York 11973-5000, USA.
¹⁰ Graduate school of Science, Nagoya University, Nagoya, Aichi 464-8601, Japan.
¹¹ Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea.
¹² Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan.
¹³ Tokushima University, Tokushima, Tokushima 770-8051, Japan.
¹⁴ Advanced Science Research Center, Japan Atomic Energy Agency, 21 2-4 Shirakata Shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan.
¹⁵ RISE, Waseda University, Shinjuku, Tokyo 162-0044, Japan.
¹⁶ Department of Physics and Astronomy, University of Catania, Catania I-95123, Italy.
¹⁷ INFN Section of Catania, Catania I-95123, Italy.

PMID: 32639790
DOI: 10.1103/PhysRevLett.124.252501

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 nonperturbative 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 nonzero 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 nonperturbative processes are expected to dominate. A non-negligible contribution from soft processes may be necessary to explain the nonzero neutral pion asymmetries.