Kent Riley Yale University 6/25/2012

Transcription

1 Kent Riley Yale University 6/25/2012

2 Motivation Azimuthal correlations of charged particles A probe for Local Parity Violation (LPV) Charge separation effects due to the Chiral Magnetic Effect (CME) should be reflected in P-even correlations <cos(φ a +φ b -2ψ RP )> = (<cosδφ a cosδφ b > - <sinδφ a sinδφ b >) Paper on subject published on 2004 data B. I. Abelev, et al., Phys. Rev. C 81, (2010) Kaon-Pion analysis is a next step 2

3 Motivation CME Separation of charged quarks due to strong magnetic field right after collision Strong interaction effects or CME Kaon-Pion correlations Majority of charged particles are pions many pion pairs are produced later in the hadronization process after flow is established Leads to Pi-Pi pairs being produced at small angles clouds signal Naïve assumption of CME is similar in K-Pi and all-charge combinations 3

4 Measuring the Charge Separation 2-particle correlator: <cos(φ a +φ b -2ψ RP )> = (<cosδφ a cosδφ b > - <sinδφ a sinδφ b >) Image from: STAR collaboration arxiv: v2 [nucl-ex] 4

5 Measuring the Charge Separation <cos(φ a +φ b -2ψ RP )> = (<cosδφ a cosδφ b > - <sinδφ a sinδφ b >) <cos Δφ a cosδφ b > In-plane term: Positive for particles emitted in the same direction in plane Negative for particles emitted in the opposite direction in plane <sinδφ a sinδφ b > Out-of-plane term: Positive for particles emitted in the same direction out of plane Negative for particles emitted in the opposite direction out of plane The correlator looks at whether particles are emitted in the same or opposite directions But its difficult to distinguish between whether its in or out of plane 5

6 Measuring the Charge Separation Reaction Plane <cos(φ a +φ b -2ψ RP )> > 0 Reaction Plane <cos(φ a +φ b -2ψ RP )> < 0 6

7 Measuring the Charge Separation Can t actually measure the reaction plane Must estimate => event plane (EP) <cos(φ a +φ b -2ψ RP )> = <cos(φ a +φ b -2ψ EP )>/<cos(2(ψ EP -ψ RP ))> where <cos(2(ψ EP -ψ RP ))> is the full event plane resolution Another method The 3-particle correlator <cos(φ a +φ b -2φ c )>/v 2 = <cos(φ a +φ b -2ψ RP )> Will use instead of 2-particle correlator here 7

8 Comparing 3-particle correlations - a,b,c are charged particles STAR Preliminary 160M (2011) vs 83M (2010) vs 14M (2004) LPV signal => oppo same 200 GeV per nucleon gold-gold collisions 8

9 K-Pi correlation K-Pi motivation If background is mostly late stage creation of Pi-Pi pairs after the flow has been generated, this background should have a smaller effect in K-Pi correlations Naïve expectation of CME is similar in K-Pi and all-charge combinations 9

10 PID Cuts Pion < m 2 < 0.1 (GeV/c 2 ) < p t, p < 1.6 GeV/c n σπ < 2 (after passing TOF m 2 cuts) Kaon 0.2 < m 2 < 0.3 (GeV/c 2 ) < p t, p < 1.6 GeV/c n σk < 2 (after passing TOF m 2 cuts) Plots from 2010 run

11 K-Pi correlation vs centrality STAR Preliminary Hollow points: (~160M) <cos(φ a +φ b -2φ c )>/v 2 - a,b,c are charged particles Solid points: (~83M) <cos(φ a +φ b -2φ c )>/v 2 - a particle is pion - b particle is kaon - c is charged particle 200 GeV per nucleon gold-gold collisions 11

12 Modifications according to flow <cos(φ a +φ b -2φ c )>/v 2 = <cos(φ a +φ b -2ψ RP )> = (<cosδφ a cosδφ b > - <sinδφ a sinδφ b >) Reaction Plane (<cosδφ a cosδφ b >(1-v 2 ) - <sinδφ a sinδφ b >(1+v 2 )) = = (<cosδφ a cosδφ b > - <sinδφ a sinδφ b >) - v 2 (<cosδφ a cosδφ b > - <sinδφ a sinδφ b >) = (<cos(φ a +φ b -2φ c )>/v 2 - v 2 <cos(φ a -φ b )>) To reduce the effects of the elliptic flow on the correlator As suggested by S. Pratt (2010) 12

13 Modifications according to flow - a,b,c are charged particles STAR Preliminary Solid points: <cos(φ a +φ b -2φ c )>/v 2 Hollow points: <cos(φ a +φ b -2φ c )>/v 2 - v2<cos(φ a -φ b )> 200 GeV per nucleon gold-gold collisions 13

14 K-Pi correlation vs modified - a particle is pion - b particle is kaon - c is charged particle STAR Preliminary Solid points: <cos(φ a +φ b -2φ c )>/v 2 Hollow points: <cos(φ a +φ b -2φ c )>/v 2 - v2<cos(φ a -φ b )> 200 GeV per nucleon gold-gold collisions 14

15 K-Pi correlation vs Δη - a,b,c are charged particles - a particle is pion - b particle is kaon - c is charged particle STAR Preliminary 2004 data (30-50%) 2011 data (30-50%) Graph from: STAR collaboration arxiv: v2 [nucl-ex] 200 GeV per nucleon gold-gold collisions 15

16 K-Pi correlation vs Δp T - a,b,c are charged particles - a particle is pion - b particle is kaon - c is charged particle STAR Preliminary 2004 data 2011 data 2004 data (30-50%) 2011 data (30-50%) Graph from: STAR collaboration arxiv: v2 [nucl-ex] 200 GeV per nucleon gold-gold collisions 16

17 K-Pi correlation vs <p T > - a,b,c are charged particles - a particle is pion - b particle is kaon - c is charged particle STAR Preliminary 2004 data (30-50%) 2011 data (30-50%) Graph from: STAR collaboration arxiv: v2 [nucl-ex] 200 GeV per nucleon gold-gold collisions 17

18 Measuring the Charge Separation <cos(φ a -φ b )> < 0 Reaction Plane <cos(φ a +φ b -2ψ RP )> > 0 <cos(φ a -φ b )> > 0 <cos(φ a -φ b )> > 0 Reaction Plane <cos(φ a +φ b -2ψ RP )> < 0 <cos(φ a -φ b )> < 0 18

19 Comparing 2-particle correlations - a,b are charged particles STAR Preliminary 200 GeV per nucleon gold-gold collisions 19

20 K-Pi correlation vs centrality STAR Preliminary Hollow points: (~160M) <cos(φ a +φ b -2φ c )>/v 2 - a,b,c are charged particles Solid points: (~83M) <cos(φ a +φ b -2φ c )>/v 2 - a particle is pion - b particle is kaon - c is charged particle 200 GeV per nucleon gold-gold collisions 20

21 K-Pi correlation vs Δη, Δp T,<Δp T > <cos(φ a -φ b )> - a particle is pion - b particle is kaon STAR Preliminary STAR Preliminary STAR Preliminary 21

22 Summary K-Pi correlations exhibit characteristic LPV signal Flow modifications (the v 2 <cos(φ a -φ b )> term) are smaller in K-Pi correlations compared to using all charges in opposite pairs As expected from removing late-stage pion pair production To Do: Removing K* resonances preliminary simulations show no effect Run Pi-Pi correlations K-K correlations many opp charge pairs produced in early stages of collision statistics 22

23 Backup Backup Backup Backup Backup - Backup - Backup Backup Backup Backup 23

24 200GeV Dataset and Cuts Production Trigger setup Vertex Cuts Trigger ID Events P11id AuAu200_production _2011 VertexZ < 30cm VertexR < 2cm VpdZ VertexZ < 4cm ~160M all charge ~83M K-Pi Cuts Primary tracks 15 < # of hits < < # of hits / # of possible hits 0.15 < p t < 2.0 GeV/c Eta_a,b,c < 1 (Using bad runs list in StRefMultCorr) Centrality bins* (Alex & Hiroshi) StRefMultCorr * StRefMultCorr dependent on RefMult, Z-vertex, Luminosity v2 average of 2- and 4-particle cumulant flow 24

25 200GeV Dataset and Cuts Production Trigger setup Vertex Cuts Trigger ID Events P11id AuAu200_production _2011 VertexZ < 30cm VertexR < 2cm VpdZ VertexZ < 4cm ~160M all charge ~83M K-Pi Cuts Primary tracks 15 < # of hits < < # of hits / # of possible hits 0.15 < p t < 2.0 GeV/c Eta_a,b,c < 1 (Using bad runs list in StRefMultCorr) Centrality bins* (Alex & Hiroshi) StRefMultCorr * StRefMultCorr dependent on RefMult, Z-vertex, Luminosity v2 average of 2- and 4-particle cumulant flow 25

26 K-Pi simulation (50M events) 0.2 < p t < < p t < < p t < < p t < < p t < < p t < 1.6 Random particles with elliptic flow 26

27 K-Pi simulation (50M events) 0.2 < p t < < p t < < p t < < p t < < p t < < p t < 1.6 After re-centering procedures 27

28 K-Pi simulation (50M events) 0.2 < p t < < p t < < p t < < p t < < p t < < p t < 1.6 After re-centering procedures, signal on 28

29 K-Pi correlation Pions ~10B Pion leakage <0.5% of total pions are readout as kaons Corresponds to <5% of total kaons 200 GeV per nucleon gold-gold collisions 29

30 K-Pi correlation vs centrality Kaon PID cuts ~97.5% of tracks <cos(φ a +φ b -2φ c )>/v 2 - a&c particles are pions - b particle is kaon 200 GeV per nucleon gold-gold collisions 30

31 K-Pi correlation vs centrality Kaon PID cuts ~97.5% of tracks <cos(φ a -φ b )> - a particle is pion - b particle is kaon 200 GeV per nucleon gold-gold collisions 31