fengyich's blog

Title: Event-by-event correlations between Λ (anti-Λ) hyperon global polarization and handedness with charged hadron azimuthal separation in Au+Au collisions at √s_NN= 27 GeV from STAR

PAs: Yicheng Feng, Evan Finch, Jie Zhao, and Fuqiang Wang

Targeted Journal: Physical Review C

Abstract: Spin-orbit interactions between Λ (anti-Λ) hyperons and the vorticity of the hot QCD medium would cause global polarization (P) of Λ (anti-Λ) in non-central heavy ion collisions. The strong magnetic field primarily created by the spectator protons in those collisions would split the Λ and anti-Λ global polarizations (ΔP = P(Λ) - P(anti-Λ) < 0). On the other hand quantum chromodynamics (QCD) predicts topological charge fluctuation in vacuum, which would result in a chirality imbalance, or parity violation in a local domain. This would give rise to an imbalanced left- and right-handed Λ (anti-Λ), Δn = (N_L - N_R)/<N_L + N_R> ≠ 0, as well as a charge separation along the magnetic field, referred to as the chiral magnetic effect (CME). The latter can be characterized by the parity-even azimuthal correlator Δγ and parity-odd azimuthal harmonic Δa₁ observables. The measurements of individual ΔP, Δγ, and Δa₁ have not led to affirmative conclusions on the CME or the effect of magnetic field, while Δn has not been measured so far. The correlations among these observables may reveal new insights. We report exploratory measurements of event-by-event correlations between ΔP and Δγ, and between Δn and Δa₁, by the STAR experiment in Au+Au collisions at √s_NN = 27 GeV. No correlations have been observed beyond statistical fluctuations.

Conclusion: This study uses a novel event-by-event correlation method to search for the CME. We report an exploratory measurement of event-by-event correlation between Δa₁ and Δn, and between Δγ and ΔP, by the STAR experiment in Au+Au collisions at 27 GeV (Run18). With the current cuts and statistics, both correlations are consistent with zero.

Status:
July, 21, 2023, published on Phys.Rev.C: journals.aps.org/prc/abstract/10.1103/PhysRevC.108.014909
April 21, 2023, submitted to Phys.Rev.C: lists.bnl.gov/mailman/private/starpapers-l/2023-April/008355.html
April 20, 2023, submitted to arXiv: arxiv.org/abs/2304.10037

Latest paper draft:
drupal.star.bnl.gov/STAR/system/files/CorrCmeLamPolKFP_v39.pdf

Latest analysis note:
drupal.star.bnl.gov/STAR/system/files/AnaNoteCorrLamCme_v39.pdf

STAR note: drupal.star.bnl.gov/STAR/starnotes/private/PSN0800

HepData preparation:
drupal.star.bnl.gov/STAR/system/files/test.zip

Journal editor comment:
June 29, 2023
→reply to comments: drupal.star.bnl.gov/STAR/system/files/Reply_PhysRevC_20230630.pdf
→revised paper draft: drupal.star.bnl.gov/STAR/system/files/CorrCmeLamPolKFP_v39.pdf
→revised analysis note: drupal.star.bnl.gov/STAR/system/files/AnaNoteCorrLamCme_v39.pdf
→figures: drupal.star.bnl.gov/STAR/system/files/CorrCmeLamPolKFP_figures.zip