Spontaneous Parity Violation in Strong Interactions

1. Spontaneous Parity Violation in Strong Interactions Dhevan Gangadharan (UCLA) On behalf of the STAR Collaboration WWND 2009

2. Parity and How it’s Violated • Parity transformation – a spatial inversion of a system’s coordinates. Two classes of Parity Violation: • Explicit parity violation • Occurs in Weak Interactions • Confirmed • Spontaneous parity violation • Predicted to occur in Strong Interactions • Not yet confirmed (that’s what we are working on)

3. Parity Violation in Weak Interactions Co-60 beta decay Experimentally observed Not Experimentally observed e- e- P transformation S S e- e- This is an Explicit parity violation because a parity violating term is explicitly seen in the Weak Lagrangian

4. Parity Violation in Strong Interactions First Ingredient: Vacuum Transition Potential Energy of the Gluon Field NCS= -2 -1 0 1 2 • NCS is the Chern-Simons number and it characterizes the particular gluon field configurations we may create at RHIC. • The potential energy of the gluon field is periodic in one direction and oscillator-like in all other directions in functional space.

5. Parity Violation in Strong Interactions Second Ingredient: An Extremely Large Magnetic Field • Spectator nuclei create a very large magnetic field in the QGP region. • STAR TPC Magnetic field is only .5 T • Largest steady magnetic field created by man ~ 15 T • Spectator magnetic field @ (1 fm/c and b=4fm) ~ 1012 T = 1 Trillion Tesla

6. Parity Violation in Strong Interactions The Chiral Magnetic Effect Ingredient 1 + Ingredient 2 -> Electric field Ey An Ey will then produce charge separation. • Kharzeev et al. • arXiv : • 0406.125v2 • 0706.1026v2 • 0711.0950v1 • 0808.3382v1 De-confinement is a must! This is Spontaneous parity violation since the sign of Ey goes according to the spontaneously chosen sign of NCS and is not determined by the initial conditions of the collision

7. Looking For Charge Separation For this analysis we are particularly interested in a1

8. Looking for Charge Separation • 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 NCS states.

9. S. A. Voloshin, Phys. Rev. C 70, 057901 (2004) Looking for Charge Separation • Thus, one must use correlation techniques: • This correlator is P-even. It is therefore susceptible to non-parity violating processes. Typically we scale this by v2,c

10. A Theoretical Prediction for AuAu 130 GeV Kharzeev et al. arXiv: 0711.0950v1 This plot represents just one possible experimental result and based on some assumptions such as the magnitude of the: Vacuum transition rate Magnetic field strength Experimental result in 200 GeV AuAu roughly obeys this trend and order of magnitude

11. Cuts Applied to Data • -30 cm < Primary Vertex Z < 30 cm • -1 < eta < 1 • Pt > .15 GeV/c • Pt < 2 GeV/c for Pt integrated plots • At least 15 TPC hit points required • #hit points/#possible hit points > .52 There are many independent STAR analyses on this subject which are consistent with each other. The work presented here represents only a small selection of our results

12. Other Contributions to our Correlator P-even processes may make a Contribution • Flowing Resonances • A resonance may be flowing elliptically (in-plane) and decay into 2 charged particles which may exhibit charge separation. • Jets • Since they are clusters of correlated charged particles, jets may fake a signal. Acceptance Effects may make a Contribution • Re-Centering • The effect of this type of acceptance correction will be demonstrated in this talk.

13. Background Contributions 1. Flowing Resonances may fake a signal We take the contribution from flowing resonances to our correlator to be We estimate the average over resonances from an upper estimate of non-flow azimuthal correlations in 200 GeV AuAu data from . And the total contribution is found to be less than 1% of a1 fres represents the fraction of charged particles coming from a resonance. STAR Collaboration, J. Adams et al., Phys. Rev. Lett. 92, 062301 (2004). Too small to fake a signal

14. Background Contributions • Jets may fake a signal We take the contribution from jets to our correlator to be We estimate the first term from distributions in 200 GeV AuAu data. And the total contribution is found to be ≈10-7 Too small to fake a signal

15. Our Correlator in Simulated Data Preliminary result • None of these models incorporate correlations generated by the Chiral Magnetic Effect! • Study done by : Evan Finch (Yale), Ilya Selyuzhenkov (Indiana), Sergei Voloshin (Wayne State)

16. Acceptance Correction Study in Simulated Data Before Re-Centering After Re-Centering Preliminary result Preliminary result Centrality Bin Centrality Bin The act of Re-Centering, i.e. , does not remove the signal Study done by Alexei Chikanian (Yale)

17. Acceptance Correction Study with Identified Pions in AuAu200 Electrons Rejected After Corrections Before Corrections Preliminary result Preliminary result Study done by Jim Thomas(LBNL)

18. Conclusions • Heavy Ion Collisions at RHIC might produce spontaneous parity violation of the strong interactions . • The magnitude and gross features of a theoretical prediction have been presented. However, more theoretical calculations of the expected signal would be very helpful. • So far, no P-even processes which could masquerade as the result we see have been identified.

19. The STAR parity-v group • Indiana: I. Selyuzhenkov • BNL: V.Dzhordzhadze, R. Longacre, Y. Semertzidis, P. Sorensen • LBNL: J. Thomas • Yale: J. Sandweiss, E. Finch, A. Chikanian, R. Majka • UCLA: G. Wang, D. Gangadharan • Wayne State: S. Voloshin More information about this analysis can be found in Sergei Voloshin’s QM08 Poster “Probe for the (Strong Interaction) parity violation effects in heavy ion collisions with three particle correlations”