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Probe for the strong parity violation effects at RHIC with three particle correlations

Sergei A. Voloshin

TL;DR

The study addresses the potential presence of strong parity-violating effects in ultra-relativistic heavy-ion collisions by seeking charge separation along the system's orbital momentum. It employs a $\\mathcal{P}$-even three-particle azimuthal correlator, $\\langle \\cos(\\phi_\alpha + \\phi_\beta - 2\\Psi_{RP}) \\rangle$, with the reaction plane inferred from a third particle via $\\langle \\cos(\\phi_\alpha + \\phi_\beta - 2\\phi_c) \\rangle = \\langle \\cos(\\phi_\alpha + \\phi_\beta - 2\\Psi_{RP}) \\rangle v_{2,c}$. STAR measurements in Au+Au and Cu+Cu at $\\sqrt{s_{NN}} = 200$ and 62 GeV show charge-dependent signals broadly consistent with parity-violation predictions, though background contributions and the precise $p_t$-dependence require further clarification. The results imply the existence of parity-odd domains influencing charge separation and provide a direct experimental handle on the phenomenon, motivating more detailed future studies to disentangle backgrounds and refine the momentum dependence.

Abstract

In non-central relativistic heavy ion collisions, ¶-odd domains, which might be created in the process of the collision, are predicted to lead to charge separation along the system orbital momentum \cite{Kharzeev:2004ey}. An observable, ¶-even, but directly sensitive to the charge separation effect, has been proposed in \cite{Voloshin:2004vk} and is based on 3-particle mixed harmonics azimuthal correlations. We report the STAR measurements using this observable for Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$=200 and 62 GeV. The results are reported as function of collision centrality, particle separation in rapidity, and particle transverse momentum. Effects that are not related to parity violation but might contribute to the signal are discussed.

Probe for the strong parity violation effects at RHIC with three particle correlations

TL;DR

The study addresses the potential presence of strong parity-violating effects in ultra-relativistic heavy-ion collisions by seeking charge separation along the system's orbital momentum. It employs a -even three-particle azimuthal correlator, , with the reaction plane inferred from a third particle via . STAR measurements in Au+Au and Cu+Cu at and 62 GeV show charge-dependent signals broadly consistent with parity-violation predictions, though background contributions and the precise -dependence require further clarification. The results imply the existence of parity-odd domains influencing charge separation and provide a direct experimental handle on the phenomenon, motivating more detailed future studies to disentangle backgrounds and refine the momentum dependence.

Abstract

In non-central relativistic heavy ion collisions, ¶-odd domains, which might be created in the process of the collision, are predicted to lead to charge separation along the system orbital momentum \cite{Kharzeev:2004ey}. An observable, ¶-even, but directly sensitive to the charge separation effect, has been proposed in \cite{Voloshin:2004vk} and is based on 3-particle mixed harmonics azimuthal correlations. We report the STAR measurements using this observable for Au+Au and Cu+Cu collisions at =200 and 62 GeV. The results are reported as function of collision centrality, particle separation in rapidity, and particle transverse momentum. Effects that are not related to parity violation but might contribute to the signal are discussed.

Paper Structure

This paper contains 5 sections, 3 equations, 3 figures.

Table of Contents

  1. Introduction. Effect and observables.
  2. Data. Detector.
  3. Results and Discussion
  4. Other effects
  5. Summary

Figures (3)

  • Figure 1: (a) Comparison of correlations obtained using third particle in the main TPC and Forward TPCs. (b) The results after normalization to the flow of the third particle.
  • Figure 2: $\left< {\cos(\phi_a +\phi_\beta -2\Psi_{RP}) } \right>$ in Au+Au and Cu+Cu collisions at (a) $\sqrt{s_{NN}}=200$ GeV and (b) 62 GeV.
  • Figure 3: Au+Au 200 GeV. The signal dependence on (a) $|\eta_\alpha -\eta_\beta|$ and (b) $p_{t,\alpha}+p_{t,\beta}$.