Dhevan Gangadharan UCLA STAR Collaboration DNP meeting 10/25/08 1

Outline 2 Examples of Weak Parity Violation The Theory of Parity Violation in the strong interactions The STAR experimental result Outlook/Conclusions

Examples of Weak Parity Violation Beta decay of Co-60In flight Pion decay S ν μ+μ+ π+π+ e- Electrons are preferentially emitted opposite the spin of the nucleus Muons are preferentially polarized along the direction of the Pion’s motion Wu. et al. Physical Review 105(4), 1957 Garwin. et al. Physical Review, 105(4),

Spontaneous Parity Violation in Strong Interactions Vacuum Energy Topological charge This can occur through The Chiral Magnetic Effect: Kharzeev et al. arXiv: The Chiral Magnetic Effect Ingredient 1of 2 The Vacuum Structure undergoes a Transition 4 Sphaleron

The Chiral Magnetic Effect Ingredient 2 of 2 A Non-zero background Magnetic field Spectator nucleons create a Magnetic Field 5

The Chiral Magnetic Effect As a consequence: An Electric Field parallel to the Magnetic Field is created 6

The Chiral Magnetic Effect The End Result The Electric Field will cause charge separation relative to the reaction plane For a given topological charge the E-M current direction has a preference. This is Parity Violation Charge separation represents an E-M current perpendicular to the reaction plane 7

Looking for Charge Separation Vacuum Energy Topological charge Transitions to -1 Topological charge are just as likely. +1 and -1 states yield opposite E-M currents. Charge separation is given by a ≠ 0 in However, will vanish when averaged over many events because of the equal presence of +1 and -1 states. Thus, one must use correlation techniques: 8 S. A. Voloshin, Phys. Rev. C 70, (2004)

The STAR detector at RHIC Tracking of particles is done by the TPC (light grey region) AuAu 200 GeV collisions used for this analysis. 9

Opposite charge combinations show a distinctly different trend than same charge combinations. This trend is in accord with theory since should be of opposite sign than 10 STAR Preliminary More plots of this correlator with different systems and against different variables can be found at arXiv:

11 Next….. Rule out non-P violating contributions to our observable (Our correlator is a P-even quantity) Reconstructed particles (Λ, Ξ) can be used to replace particle a in: to determine whether the same asymmetry persists. This is interesting since in principle the electric field generated can affect all three constituent quarks before they coalesce. A Ξ contains 3 negative quarks whereas a Λ contains a mixture of positive and negative quarks. Ξ+Ξ+ Ξ+Ξ+ Ξ+Ξ+ Ξ-Ξ- Ξ-Ξ- Ξ-Ξ- Ψ Λ Λbar Λ Λ Ψ Λ

Conclusions 12 Heavy-Ion collisions might create Spontaneous Parity violating processes in Strong Interactions. The gross quantitative and qualitative features of the correlation used in this analysis are in accord with theoretical expectations.