Azimuthal charged-particle correlations and possible local strong parity violation.

Area of Science:

• High-energy nuclear physics
• Quantum Chromodynamics (QCD)
• Particle physics

Background:

• Relativistic heavy-ion collisions may create parity-odd domains, influencing the QCD vacuum.
• These domains are theoretically predicted to cause charge separation along the system's orbital momentum axis.

Purpose of the Study:

• Investigate charge separation effects in relativistic heavy-ion collisions.
• Utilize a three-particle azimuthal correlator, a parity-even observable sensitive to charge separation.
• Search for evidence of parity violation in Au + Au and Cu + Cu collisions.

Main Methods:

• Measurements of charged hadrons near center-of-mass rapidity.
• Utilized the STAR detector at Brookhaven National Laboratory.
• Analyzed data from gold-gold (Au + Au) and copper-copper (Cu + Cu) collisions at a center-of-mass energy of 200 GeV per nucleon pair.

Main Results:

• A signal consistent with theoretical predictions for charge separation was detected.
• The observed signal aligns with expectations related to parity-odd domains.
• The study identified potential contributions from non-parity-violating effects.

Conclusions:

• The experiment provides evidence supporting the existence of charge separation phenomena in heavy-ion collisions.
• The findings offer a potential probe for nontrivial topological structures in the QCD vacuum.
• Further investigation is needed to disentangle parity-violating signals from other contributions.