Cosmic-ray Research Division
Institute for Space–Earth Environmental Research, Nagoya University

Transverse large asymmetry observed in neutral pion production at polarized proton-proton collisions

The RHICf collaboration, which Professor Yoshitaka Itow, Assistant Professor Hiroaki Menjo and some students in CR-lab join, had a press-release about their experimental result. The RHICf experiment performs measurements of very forward neutral particles, photons, neutrons and etc., emitted at proton-proton collisions provided by Relativistic Heavy Ion Collider (RHIC) located in Brookhaven National Laboratory, USA. The RHIC accelerator can align the spin direction of accelerated protons, and collide two beams at interaction points. This provides a unique opportunity of spin asymmetry measurements on particle productions using polarised beams. Spin asymmetry measurements of neutral pion production have been performed at several experiments, however, the acceptance of the measurements were limited such as perpendicular direction of collisions. The RHICf experiment firstly measured the asymmetry on neutral pion productions at very forward region including zero degree of collisions and reported unexpected large asymmetry.

This result was published on Physical Review Letters (Online on June 22, 2020, Vol. 124, 252501).

Our laboratory members are actively working for both the RHICf experiment and the LHCf experiment (a similar experiment at LHC, CERN). Details of the experiments are in the linked page.

Fig. Neutral pion production at a proton-proton collision。The upward arrow represents the spin direction.