2020/11/30 by Yicheng Feng, Y. Feng, J. Zhao +5
Physics and Astronomy · #Hadron #High-Energy Particle Collisions Research #Observable #Particle physics #Particle physics theoretical and experimental studies #Physics #Quantum Chromodynamics and Particle Interactions #Quantum mechanics #nucl-ex #nucl-th
paper · pdf · doi:10.1103/physrevc.103.034912
published as Phys. Rev. C 103, 034912 (2021) · 18 pages, 13 figures
openalex created_date 2020/11/09 · openalex publication_date 2021/03/29 · arxiv created 2021/04/01 · arxiv updated 2021/04/07 · openalex updated_date 2026/08/05
Background: The chiral magnetic effect (CME) is extensively studied in heavy-ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). An azimuthal correlator called R_\mathrm\ensuremathΨm was proposed to measure the CME. By observing the same R_\mathrm\ensuremathΨ2 and R_\mathrm\ensuremathΨ3 (convex) distributions from A Multi-Phase Transport (ampt) model, by contrasting data and model as well as large and small systems and by event shape engineering (ESE), a recent preprint (arXiv:2006.04251v1) from STAR suggests that the R_\mathrm\ensuremathΨm observable is sensitive to the CME signal and relatively insensitive to backgrounds, and their Au+Au data are inconsistent with known background contributions.Purpose: We examine those claims by studying the robustness of the R_\mathrm\ensuremathΨm observable using ampt as well as toy model simulations. We compare R_\mathrm\ensuremathΨm to the more widely used \mathrm\ensuremathΔ\ensuremathγ azimuthal correlator to identify their commonalities and differences.Methods: We use ampt to simulate Au+Au, p+Au, and d+Au collisions at √sNN=200\phantom\rule4.pt0exGeV, and study the responses of R_\mathrm\ensuremathΨm to anisotropic flow backgrounds in the model. We also use a toy model to simulate resonance flow background and input CME signal to investigate their effects in R_\mathrm\ensuremathΨ2. Additionally we use the toy model to perform an ESE analysis to compare with STAR data as well as predict the degree of sensitivity of R_\mathrm\ensuremathΨ2 to isobar collisions with the event statistics taken at RHIC.Results: Our ampt results show that the R_\mathrm\ensuremathΨ2 in Au+Au collisions is concave and apparently different from R_\mathrm\ensuremathΨ3, in contradiction to the findings in STAR's preprint, while the R_\mathrm\ensuremathΨ2 in p+Au and d+Au collisions are slightly concave. Our toy model ESE analysis indicates that the R_\mathrm\ensuremathΨ2 is sensitive to the event-by-event anisotropy q2 as well as the elliptic flow parameter v2. The toy model results further show that R_\mathrm\ensuremathΨ2 depends on both the CME signal and the flow backgrounds, similar to the \mathrm\ensuremathΔ\ensuremathγ observable. It is found that the R_\mathrm\ensuremathΨ2 and \mathrm\ensuremathΔ\ensuremathγ observables show similar sensitivities and centrality dependencies in isobar collisions.Conclusions: Our ampt results contradict those from a recent preprint by STAR. Our toy model simulations demonstrate that R_\mathrm\ensuremathΨ2 is sensitive to both the CME signal and physics backgrounds. Toy model simulations of isobar collisions show similar centrality dependence and magnitudes for the relative R_\mathrm\ensuremathΨ2 strengths as well as the relative \mathrm\ensuremathΔ\ensuremathγ strengths. We conclude that R_\mathrm\ensuremathΨ2 and the inclusive \mathrm\ensuremathΔ\ensuremathγ are essentially the same.