Back-to-back relative-excess observable in search for the chiral magnetic effect

Abstract

$\text{Background:}$ The chiral magnetic effect (CME) is extensively studied in heavy-ion collisions at RHIC and LHC. In the commonly used reaction plane (RP) dependent, charge dependent azimuthal correlator ($\Delta \gamma$), both the close and back-to-back pairs are included. Many backgrounds contribute to the close pairs (e.g. resonance decays, jet correlations), whereas the back-to-back pairs are relatively free of those backgrounds. $\text{Purpose:}$ In order to reduce those backgrounds, we propose a new observable which only focuses on the back-to-back pairs, namely, the relative back-to-back opposite-sign (OS) over same-sign (SS) pair excess ($r_{\text{BB}}$) as a function of the pair azimuthal orientation with respect to the RP (${\phi }_{\text{BB}}$). $\text{Methods:}$ We use analytical calculations and toy model simulations to demonstrate the sensitivity of $r_{\text{BB}}({\phi }_{\text{BB}})$ to the CME and its insensitivity to backgrounds. $\text{Results:}$ With finite CME, the ${\phi }_{\text{BB}}$ distribution of $r_{\text{BB}}$ shows a clear characteristic modulation. Its sensitivity to background is significantly reduced compared to the previous $\Delta \gamma$ observable. The simulation results are consistent with our analytical calculations. $\text{Conclusions:}$ Our studies demonstrate that the $r_{\text{BB}}({\phi }_{\text{BB}})$ observable is sensitive to the CME signal and rather insensitive to the resonance backgrounds.

arXiv comment6 pages, 4 figures, 1 table

References in corpus (37)

• Big-Bang Nucleosynthesis
• The effects of topological charge change in heavy ion collisions: "Event by event P and CP violation"
• Systematic Measurements of Identified Particle Spectra in pp, d+Au and Au+Au Collisions from STAR
• Azimuthal anisotropy in Au+Au collisions at sqrtsNN = 200 GeV
• Azimuthal Charged-Particle Correlations and Possible Local Strong Parity Violation
• Suppressed pi^0 Production at Large Transverse Momentum in Central Au+Au Collisions at sqrt(s_NN) = 200 GeV
• Identified particle distributions in pp and Au+Au collisions at sqrt{s_NN}=200 GeV
• Possibility of spontaneous parity violation in hot QCD
• Parity violation in hot QCD: how to detect it
• Observation of charge-dependent azimuthal correlations and possible local strong parity violation in heavy ion collisions
• Charge separation relative to the reaction plane in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV
• Beam-energy dependence of charge separation along the magnetic field in Au+Au collisions at RHIC
• Charge conservation in RHIC and contributiuons to local parity violation observables
• rho^0 Production and Possible Modification in Au+Au and p+p Collisions at sqrt(s_NN) = 200 GeV
• Effects of Cluster Particle Correlations on Local Parity Violation Observables
• Observation of charge-dependent azimuthal correlations in pPb collisions and its implication for the search for the chiral magnetic effect
• Azimuthal correlations from transverse momentum conservation and possible local parity violation
• Remarks on possible local parity violation in heavy ion collisions
• Constraints on the chiral magnetic effect using charge-dependent azimuthal correlations in pPb and PbPb collisions at the LHC
• Effects of Momentum Conservation and Flow on Angular Correlations at RHIC
• Azimuthal anisotropy of neutral pion production in Au+Au collisions at sqrt(s_NN) = 200 GeV: Path-length dependence of jet quenching and the role of initial geometry
• Resonance decay effects on anisotropy parameters
• Measurement of Charge Multiplicity Asymmetry Correlations in High Energy Nucleus-Nucleus Collisions at 200 GeV
• Experimental searches for the chiral magnetic effect in heavy-ion collisions
• Constraining the magnitude of the Chiral Magnetic Effect with Event Shape Engineering in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76$ TeV
• Measurements of Dielectron Production in Au$+$Au Collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV from the STAR Experiment
• Importance of isobar density distributions on the chiral magnetic effect search
• On the Charge Separation Effect in Relativistic Heavy Ion Collisions
• Studying Parton Energy Loss in Heavy-Ion Collisions via Direct-Photon and Charged-Particle Azimuthal Correlations
• Varying the chiral magnetic effect relative to flow in a single nucleus-nucleus collision
• Challenges in flow background removal in search for the chiral magnetic effect
• Search for the Chiral Magnetic Effect in Relativistic Heavy-Ion Collisions
• Event-by-event background in estimates of the chiral magnetic effect
• Measurements of the chiral magnetic effect with background isolation in 200 GeV Au+Au collisions at STAR
• Medium-modified Jets and Initial State Fluctuations as Sources of Charge Correlations Measured at RHIC
• Responses of the chiral-magnetic-effect-sensitive sine observable to resonance backgrounds in heavy-ion collisions
• Chiral magnetic effect search in p+Au, d+Au and Au+Au collisions at RHIC

Cited by in corpus (1)

• Experimental review on the chiral magnetic effect in relativistic heavy ion collisions