Three Particle Correlations

1. Three Particle Correlations Jason Glyndwr Ulery, Purdue University For the STAR Collaboration 21 October 2005 Midwest Critical Mass

2. Motivation • Interested in probing the medium. • Using jets as the probe • Can be calculated in pQCD and thus are well calibrated in a vacuum. • Are expected to be modified by the medium and can therefore give information on the properties of the medium. • Use three particle correlations to gain more information than provided by two particle correlations.

3. Is there conical flow? near near 3-4 GeV/c 1-2 GeV/c near assoc trigger Medium soft bkgd assoc Medium Medium away away mach cone away di-jets deflected jets Df2 3-particle correlation Df1 hard-soft-corr + soft-bkgd. Df2 flow modulated background: Df1 soft-soft-corr in underlying event.

4. Hard-Soft-Soft Correlation Analysis • Trigger particle chosen. • Distributions of pairs of associated particles Δφ1= φ1 -φtrigger and Δφ2 =φ2 -φtrigger • Mixed events modified by flow and subtracted 1 +2*v21v2triggercos[2(φ1 -φtrigger)] +2*v22v2triggercos[2(φ2-φtrigger)] +2*v21v22cos[2(φ1-φ2)] • Cross terms (hard-soft and soft-soft in background) is subtracted. 3<PTTrigger<4 1<PTAssociated<2 Raw Signal 1/NTrigger (dN/d(Δφ))2 Mixed Events With Flow Hard-Soft STAR Preliminary Soft-Soft Final Signal Δφ AuAu 0-10%

5. Closer Look at the Terms • Raw signal is constructed by choosing a trigger particle between 3 and 4 GeV/c then looking at Δφ1 vs Δφ2 for all n(n-1) pairs of particles between 1 and 2 GeV/c. • Random mixed events do the same process for trigger particles from 1 event and all n1*n2 from 2 other events. The flow modulation is also added in. Δφ 1/NTrigger (dN/d(Δφ))2 STAR Preliminary Δφ Δφ 1/NTrigger (dN/d(Δφ))2 STAR Preliminary Δφ • 1 +2*v21v2triggercos[2(φ1 -φtrigger)] • +2*v22v2triggercos[2(φ2-φtrigger)] • +2*v21v22cos[2(φ1-φ2)]

6. Closer Look at the Terms II • Hard-Soft term created by taking one particle from the background-subtracted 2 particle correlation and another from the background with flow. Δφ 1/NTrigger (dN/d(Δφ))2 Δφ STAR Preliminary Δφ Δφ Δφ

7. Closer Look at Terms III • Soft-soft term found by taking the trigger particle from one event and the two associated particles from another event. • Background for this term is done by taking trigger from one event and associated particle from two other events and adding in the flow between the two associated particles. Δφ Δφ STAR Preliminary 1/NTrigger (dN/d(Δφ))2

8. pp and d+Au pp 2<PTTrigger<4 1<PTAssociated<2 1/NTrigger (dN/d(Δφ))2 STAR Preliminary Δφ • Appears elongated along the diagonal axis in d+Au • Possibly kT broadening d+Au 2<PTTrigger<4 1<PTAssociated<2 Δφ Δφ Δφ d+Au 3<pTTrigger<4 1<PTAssociated<2 away sS/2 = 0.89 ± 0.11 sD = 0.69 ± 0.05 near sD = 0.66 ± 0.07 STAR Preliminary Δφ Δφ

9. Conical Flow? 3-Particle Correlation pTtrig=3-4, pTassoc=1-2 GeV/c 2-particle corr, bg, v2 subtracted d+Au min-bias Df2 p Dφ2=φ2-φtrig 0 0 p Df1 Au+Au 10% Df2 Dφ2=φ2-φtrig p dN2/dΔφ1dΔφ2/Ntrig 0 0 p Df1 Dφ1=φ1-φtrig Three regions on away side: center = (p, p) ±0.4 corner = (p+1,p+1) ±0.4 x2 cone = (p+1,p-1) ±0.4 x2 difference in Au+Au average signal per radian2: center – corner = 0.3 ± 0.3 (stat) ± 0.4 (syst) center – cone = 2.6 ± 0.3 (stat) ± 0.8 (syst) d+Au and Au+Au elongated along diagonal: kT effect, and deflected jets? Distinctive features of conical flow are not seen in present data with these pT windows.

10. 3 Particle V2 3<PTTrigger<4 1<PTAssociated<2 0-10% • Previous plots used average of 4 particle cumulant and reaction plane v2. • Correlation is robust with v2. 4 Particle Cumulant V2 STAR Preliminary Reaction Plane V2 Δφ Δφ Δφ STAR Preliminary Δφ

11. Conclusions • Three particle correlations can provide us with additional information over two particle correlations. • Elongation along Δφ1= Δφ2 in d+Au possibly due to kT broadening. • Elongation also seen along Δφ1= Δφ2 in Au+Au possibly due to the combination of kT broadening and away side jets deflected by radial flow. • No indication of conical flow seen in the present data.