Responses of the chiral-magnetic-effect-sensitive sine observable to resonance backgrounds in heavy-ion collisions

Abstract

A new sine observable, $R_{{\Psi }_2}(\Delta S)$, has been proposed to measure the chiral magnetic effect (CME) in heavy-ion collisions; $\Delta S=⟨\sin {\phi }_{+}⟩-⟨\sin {\phi }_{-}⟩$, where ${\phi }_{\pm }$ are azimuthal angles of positively and negatively charged particles relative to the reaction plane and averages are event-wise, and $R_{{\Psi }_2}(\Delta S)$ is a normalized event probability distribution. Preliminary STAR data reveal concave $R_{{\Psi }_2}(\Delta S)$ distributions in 200 GeV Au+Au collisions. Studies with a multiphase transport (AMPT) and anomalous-viscous Fluid Dynamics (AVFD) models show concave $R_{{\Psi }_2}(\Delta S)$ distributions for CME signals and convex ones for typical resonance backgrounds. A recent hydrodynamic study, however, indicates concave shapes for backgrounds as well. To better understand these results, we report a systematic study of the elliptic flow ($v_2$) and transverse momentum ($p_T$) dependences of resonance backgrounds with toy-model simulations and central limit theorem (CLT) calculations. It is found that the concavity or convexity of $R_{{\Psi }_2}(\Delta S)$ depends sensitively on the resonance $v_2$ (which yields different numbers of decay ${\pi }^{+}{\pi }^{-}$ pairs in the in-plane and out-of-plane directions) and $p_T$ (which affects the opening angle of the decay ${\pi }^{+}{\pi }^{-}$ pair). Qualitatively, low $p_T$ resonances decay into large opening-angle pairs and result in more `back-to-back' pairs out-of-plane, mimicking a CME signal, or a concave $R_{{\Psi }_2}(\Delta S)$. Supplemental studies of $R_{{\Psi }_3}(\Delta S)$ in terms of the triangular flow ($v_3$), where only backgrounds exist but any CME would average to zero, are also presented.

11 pages, 8 figures

References in corpus (12)

• Big-Bang Nucleosynthesis
• The Chiral Magnetic Effect
• Systematic Measurements of Identified Particle Spectra in pp, d+Au and Au+Au Collisions from STAR
• 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
• Observation of charge-dependent azimuthal correlations in pPb collisions and its implication for the search for the chiral magnetic effect
• Constraining the magnitude of the Chiral Magnetic Effect with Event Shape Engineering in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76$ TeV
• A new method for the experimental study of topological effects in the quark-gluon plasma
• A New Correlator to Detect and Characterize the Chiral Magnetic Effect
• Search for the Chiral Magnetic Effect in Relativistic Heavy-Ion Collisions
• Azimuthal angle dependence of the charge imbalance from charge conservation effects
• Chiral magnetic effect search in p+Au, d+Au and Au+Au collisions at RHIC

Cited by in corpus (11)

• Experimental searches for the chiral magnetic effect in heavy-ion collisions
• Probe Chiral Magnetic Effect with Signed Balance Function
• Search for the Chiral Magnetic Effect in Relativistic Heavy-Ion Collisions
• Impact of globally spin-aligned vector mesons on the search for the chiral magnetic effect in heavy-ion collisions
• Sensitivity analysis of the chiral magnetic effect observables using a multiphase transport model
• Charge asymmetry dependence of flow and a novel correlator to detect the chiral magnetic wave in a multiphase transport model
• Measurement of the charge separation along the magnetic field with Signed Balance Function in 200 GeV Au + Au collisions at STAR
• Decipher the $R_{{\Psi }_m}$ correlator in search for the chiral magnetic effect in relativistic heavy ion collisions
• Experimental review on the chiral magnetic effect in relativistic heavy ion collisions
• Back-to-back relative-excess observable in search for the chiral magnetic effect
• Investigation of Experimental Observables in Search of the Chiral Magnetic Effect in Heavy-ion Collisions in the STAR experiment