N. N. Ajitanand Nuclear Chemistry, SUNY Stony Brook For the PHENIX Collaboration

1. Investigation of Parity Violation at RHIC with the PHENIX Detector N. N. Ajitanand Nuclear Chemistry, SUNY Stony Brook For the PHENIX Collaboration RHIC & AGS Users Meeting June 7-11 2010

2. L or B It has been proposed [1] that in heavy ion collisions, metastable domains may be created in which parity and CP symmetries are violated. A combination of a net chirality of quarks within a domain and the extremely strong magnetic field in a heavy ion collision could lead to the manifestation of parity violation as a separation of charges along the angular momentum vector of the collision system [2]. 1.D. Kharzeev, R. D. Pisarski, and M. H. G. Tytgat, Phys. Rev. Lett. 81, 512 (1998). 2.D. Kharzeev and R. D. Pisarski, Phys. Rev. D 61, 111901 (2000). Local Parity Violation at RHIC N. N. Ajitanand RHIC-AGS 2010

3. Azimuthaldistributionw.r.tthereactionplane N(φ ) = N0 (1+2v2cos(2φ)+2v4cos(4φ)+ 2a1sin(φ)) a1>0 a1<0 φ φ - - B B ++ ΨRP ΨRP Positive charges favor B Negativecharges favor B - - ++ Chargeseperationalong B fieldresultsfromparitybreakingterm a1 Detection of azimuthal charge-asymmetry is a pre-requisite for evidence of Parity Violation

4. Charged Particle Tracks |η|<0.35, π/2 x 2 arms Central Arm Spectrometer (DC,PCs) Mid Reaction Plane 1.0<|η|<2.8, 0<φ<2π Reaction Plane Detector (RXN) Charge asymmetry determined for azimuthal distribution of charged hadrons in the central arms w.r.t Reaction Plane determined by RXN

5. The two-particle correlation – an extension of the STAR method Proposed and used by ShinIchiEsumi

6. L or B Two-particle correlation Method Reaction plane Y Reaction Plane X v1=0 , Bin ≈ Bout Averaging is performed over all pairs in a given event and then over all events with a given centrality • acceptance correction accounted for • with event mixing Signal proportional to square of ‘a1’ • reaction plane resolution correction

7. L or B Two-particle correlation Method Technical details for experimentalists • Event mixing in • centrality: 10 bins [0-100%] • z-vertex: 10 bins [-30~30cm] • reaction plane: 50 bins [] (50, 49, 48, …) x /50 • Mixed event within the same • event class of (cent, z-vtx, R.P.) • in order to take into account the • acceptance as well as residual • flow effects to be removed. • Measure • FAB=<cos(A+B-2R.P.)> and for F, Fand F for both real and mixed events • Take a difference between real and mixed, then correct for R.P. resolution: (Freal-Fmixed) / ResR.P. (1, 2, 3, …) x /50

8. Two-particle correlation Results Signal is sensitive to collision centrality N. N. Ajitanand RHIC-AGS 2010

9. Two-particle correlation Results Signal grows with centrality and pT N. N. Ajitanand RHIC-AGS 2010

10. Two-particle correlation Results Relatively good agreement between PHENIX & STAR N. N. Ajitanand RHIC-AGS 2010

11. A new multi-particle correlation method Proposed and used by N. N. Ajitanand

12. Multi-particle correlation: Construction of mixed event Event with p positively charged hadrons and n negatively charged hadrons 1 2 3 4 ---- p p positives 1 2 3 4 ---- n n negatives Construction of statistically matched mixed event 1 2 3 4 ---- p p random choices 1 2 3 4 ---- n n remaining

13. Evaluate real event averages of S = average S over the ppositively charged hadrons in the event = average S over the nnegatively charged hadrons in the event Evaluate mixed event averages of S = average S over p randomly chosen hadrons in the same event = average S over n remaining hadrons in the same event The new multi-particle correlator

14. Properties of Cp Simulated Results a1 > 0 in all events (Blue points) N (Red points) S Cp Numerator shifted to the right Cpshows positive slope S N. N. Ajitanand RHIC-AGS 2010

15. Properties of Cp Simulated Results a1 < 0 in all events (Blue points) (Red points) N S Cp Numerator shifted to the left Cpshows negative slope S N. N. Ajitanand RHIC-AGS 2010

16. Properties of Cp Simulated Results a1 changes sign from event to event (Blue points) N (Red points) S S Cp Numerator slightly broader Cpconcave and symmetric N. N. Ajitanand RHIC-AGS 2010

17. Properties of Cp Simulated Results Cp is an in-event correlator  Several benefits Flow : Yes Parity violating signal : No Decay : No Flat response to flow Cp S Cp Jet : Yes Parity violating signal : No Decay : No Flat response to jets S Cp insensitive to flow and jets

18. Properties of Cp Simulated Results Cp is an in-event correlator  Several benefits Flow : Yes Parity violating signal : Yes Decay : No Concave response to parity violation S Flow: Yes Parity violating signal : No Decay : Yes Convex response to decays Cp Cp S N. N. Ajitanand RHIC-AGS 2010

19. Multi-particle correlation Results Concave shape validates charge asymmetry

20. Concavity also observed for more central events Simulation fits favor a lower value of a1 N. N. Ajitanand RHIC-AGS 2010

21. Summary • PHENIX measurements of azimuthal charge-asymmetry presented for two separate methods • Azimuthal charge-asymmetry observed by both methods • Extracted signals in general agreement with STAR N. N. Ajitanand RHIC-AGS 2010