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Title: Charge-Dependent Correlations in Relativistic Heavy Ion Collisions and the Chiral Magnetic Effect

Abstract

We provide a phenomenological analysis of present experimental searches for local parity violation manifested through the Chiral Magnetic Effect. We introduce and discuss the relevant correlation functions used for the measurements. Our analysis of the available data from both RHIC and LHC shows that the present experimental evidence for the Chiral Magnetic Effect is rather ambiguous. We further discuss in some detail various background contributions due to conventional physics, which need to be understood quantitatively in order to draw a definitive conclusion about the existence of local parity violation in heavy ion collisions.

Authors:
 [1];  [2];  [3]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  3. Indiana Univ., Bloomington, IN (United States); Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
OSTI Identifier:
1407167
DOE Contract Number:
AC02-05CH11231
Resource Type:
Book
Resource Relation:
Related Information: Book Title: Strongly Interacting Matter in Magnetic Fields
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Bzdak, Adam, Koch, Volker, and Liao, Jinfeng. Charge-Dependent Correlations in Relativistic Heavy Ion Collisions and the Chiral Magnetic Effect. United States: N. p., 2013. Web. doi:10.1007/978-3-642-37305-3_19.
Bzdak, Adam, Koch, Volker, & Liao, Jinfeng. Charge-Dependent Correlations in Relativistic Heavy Ion Collisions and the Chiral Magnetic Effect. United States. doi:10.1007/978-3-642-37305-3_19.
Bzdak, Adam, Koch, Volker, and Liao, Jinfeng. 2013. "Charge-Dependent Correlations in Relativistic Heavy Ion Collisions and the Chiral Magnetic Effect". United States. doi:10.1007/978-3-642-37305-3_19. https://www.osti.gov/servlets/purl/1407167.
@article{osti_1407167,
title = {Charge-Dependent Correlations in Relativistic Heavy Ion Collisions and the Chiral Magnetic Effect},
author = {Bzdak, Adam and Koch, Volker and Liao, Jinfeng},
abstractNote = {We provide a phenomenological analysis of present experimental searches for local parity violation manifested through the Chiral Magnetic Effect. We introduce and discuss the relevant correlation functions used for the measurements. Our analysis of the available data from both RHIC and LHC shows that the present experimental evidence for the Chiral Magnetic Effect is rather ambiguous. We further discuss in some detail various background contributions due to conventional physics, which need to be understood quantitatively in order to draw a definitive conclusion about the existence of local parity violation in heavy ion collisions.},
doi = {10.1007/978-3-642-37305-3_19},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2013,
month = 1
}

Book:
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  • Charge-dependent azimuthal particle correlations with respect to the second-order event plane in p-Pb and PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV have been studied with the CMS experiment at the LHC. We performed the measurement with a three-particle correlation technique, using two particles with the same or opposite charge within the pseudorapidity range |η|<2.4, and a third particle measured in the hadron forward calorimeters (4.4<|η|<5). We also observed differences between the same and opposite sign correlations, as functions of multiplicity and η gap between the two charged particles, and found that they were of similar magnitude in p-Pbmore » and PbPb collisions at the same multiplicities. Our results pose a challenge for the interpretation of charge-dependent azimuthal correlations in heavy ion collisions in terms of the chiral magnetic effect.« less
  • Charge-dependent azimuthal particle correlations with respect to the second-order event plane in p-Pb and PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV have been studied with the CMS experiment at the LHC. We performed the measurement with a three-particle correlation technique, using two particles with the same or opposite charge within the pseudorapidity range |η|<2.4, and a third particle measured in the hadron forward calorimeters (4.4<|η|<5). We also observed differences between the same and opposite sign correlations, as functions of multiplicity and η gap between the two charged particles, and found that they were of similar magnitude in p-Pbmore » and PbPb collisions at the same multiplicities. Our results pose a challenge for the interpretation of charge-dependent azimuthal correlations in heavy ion collisions in terms of the chiral magnetic effect.« less
  • Charge-dependent azimuthal correlations of same- and opposite-sign pairs with respect to the second- and third-order event planes have been measured in pPb collisions at sqrt(s[NN]) = 8.16 TeV and PbPb collisions at 5.02TeV with the CMS experiment at the LHC. The measurement is motivated by the search for the charge separation phenomenon predicted by the chiral magnetic effect (CME) in heavy ion collisions. Three- and two-particle azimuthal correlators are extracted as functions of the pseudorapidity difference, the transverse momentum (pt) difference, and the pt average of same- and opposite-charge pairs in various event multiplicity ranges. The data suggest that themore » charge-dependent three-particle correlators with respect to the second- and third-order event planes share a common origin, predominantly arising from charge-dependent two-particle azimuthal correlations coupled with an anisotropic flow. The CME is expected to lead to a v[2]-independent three-particle correlation when the magnetic field is fixed. Using an event shape engineering technique, upper limits on the v[2]-independent fraction of the three-particle correlator are estimated to be 6.6% for pPb and 3.8% for PbPb collisions at 95% confidence level. The results of this analysis, both the dominance of two-particle correlations as a source of the three-particle results and the similarities seen between PbPb and pPb, provide stringent constraints on the origin of charge-dependent three-particle azimuthal correlations and challenge their interpretation as arising from a chiral magnetic effect in heavy ion collisions.« less
  • Matter with chiral fermions is microscopically described by theory with quantum anomaly and macroscopically described (at low energy) by anomalous hydrodynamics. For such systems in the presence of external magnetic field and chirality imbalance, a charge current is generated along the magnetic field direction ₋ a phenomenon known as the Chiral Magnetic Effect (CME). The quark- gluon plasma created in relativistic heavy ion collisions provides an (approximate) example, for which the CME predicts a charge separation perpendicular to the collisional reaction plane. Charge correlation measurements designed for the search of such signal have been done at RHIC and the LHCmore » for which the interpretations, however, remain unclear due to contamination by background effects that are collective flow driven, theoretically poorly constrained, and experimentally hard to separate. Using anomalous (and viscous) hydrodynamic simulations, we make a first attempt at quantifying contributions to observed charge correlations from both CME and background effects in one and same framework. We discuss the implications for the search of CME.« less