1. Jet Studies in STAR via Di-jet Triggered (2+1) Multi-hadron Correlations Kolja Kauder for the STAR collaboration Kolja Kauder for the STAR collaboration, QM2009 1 Jet quenching in heavy ion collisions Statistical studies of di-jets: 2+1 correlation technique Analysis technique Jet shapes, Spectra, and Fragmentation functions Symmetric trigger results Asymmetric trigger results Outlook Outline

2. Jet-medium interaction Kolja Kauder for the STAR collaboration, QM2009 2 3<p T,trig <4 GeV/c 1.3<p T,assoc <1.8 GeV/c M. Horner QM ‘06 3 < p T,trig < 4 GeV/c J. Putschke QM ‘06 Double-hump structure Near-side ridge Di-hadron (1+1) correlation analysis: a high-p T trigger particle associated with lower p T particles

3. Kolja Kauder for the STAR collaboration, QM2009 3 Au+Aucentral STAR, PRL102.052302 Away side: Δ ϕ -Δ ϕ correlation P. Netrakanti QM’08 Near-side: Δη-Δη correlations 3-particle correlations Experimental indication of conical emission No apparent substructure 200 GeV 3<p T Trig <10 GeV/c 1<p T Asso <3 GeV/c

4. 2+1 correlation technique Kolja Kauder for the STAR collaboration, QM2009 4 Use ‘di-jets’ to study jet-medium effects “pin” the ‘jet axis’ selecting back- to-back triggers study correlation w.r.t. this axis Courtesy of R.Hollis “jet-axis” trigger (T2) primary trigger (T1) associates | Δ ϕ -π | < α (=0.2) Trigger-trigger correlation T1: 5 GeV/c < p T < 10 GeV/c T2: 4 GeV/c < p T < p T T1 Au+Au Central (12%) Capitalize on PRL 97 (2006) 162301

5. Signal construction One trigger, Au+Au Central (12%) Kolja Kauder for the STAR collaboration, QM2009 5 Mixed-event backgroundRaw 2D signal T1: 4 GeV/c < p T < 10 GeV/c A1: 1.5 GeV/c <p T < 4GeV/c Au+Au Central (12%)

6. Background contributions Kolja Kauder for the STAR collaboration, QM2009 6 Correlated Background Accounting for correlated background on T1 and T2 side Correlated background approximated by di-hadron correlations Uncorrelated Background Elliptic flow term Normalization: ZYAM vs. Absolute T1: 5 GeV/c < p T < 10 GeV/c T2: 4 GeV/c < p T < p T T1 A1: 1.5 GeV/c < p T < 4 GeV/c Au+Au Central (12%) T2A1 T1A1 Absolute vs. ZYAM background

7. Symmetric Triggers Results: 2+1 correlation Kolja Kauder for the STAR collaboration, QM2009 7 Kinematic constraints: T1: 5 GeV/c < p T < 10 GeV/c T2: 4 GeV/c < p T < p T T1 A1: 1.5 GeV/c < p T < 4 GeV/c d+Au √S NN =200 GeV Errors are statistical

8. Symmetric Triggers Results: 2+1 correlation Kolja Kauder for the STAR collaboration, QM2009 8 Kinematic constraints: T1: 5 GeV/c < p T < 10 GeV/c T2: 4 GeV/c < p T < p T T1 A1: 1.5 GeV/c < p T < 4 GeV/c Au+Au 12% Central √S NN =200 GeV Errors are statistical

9. Kolja Kauder for the STAR collaboration, QM2009 9 Symmetric Triggers Associated hadron spectra Jet region: | Δη | < 0.5 Au+Au 12% Central, √S NN =200 GeV d+Au √S NN =200 GeV Significantly harder than uncorrelated background No appreciable difference between same side and away side Jet region: | Δη | < 0.5 | Δ ϕ | < 0.5 - - - - Background Errors are statistical Kinematic constraints: T1: 5 GeV/c < p T < 10 GeV/c T2: 4 GeV/c < p T < p T T1 A1: 1.5 GeV/c < p T < 4 GeV/c

10. Kolja Kauder for the STAR collaboration, QM2009 10 Symmetric Triggers and yield No appreciable change in No appreciable change in Yield modification not significant within systematic errors No difference same away Kinematic constraints: T1: 5 GeV/c < p T < 10 GeV/c T2: 4 GeV/c < p T < p T T1 A1: 1.5 GeV/c < p T < 4 GeV/c Jet region: | Δη | < 0.5 | Δ ϕ | < 0.5 d+Au Au+Au T1>5,T2>4 T1>5,T2>4 d+Au Au+Au T1>5,T2>4 T1>5,T2>4 Errors are statistical - - - - Background

11. Kolja Kauder for the STAR collaboration, QM2009 11 Symmetric Triggers Fragmentation function estimates Approximate fragmentation functions via Away/Same Au+Au Central 12% d+Au No significant modification of fragmentation functions STAR Preliminary Errors are statistical Same side: p T,T1 Away side: p T,T2

12. Asymmetric Triggers 2+1 correlation Kolja Kauder for the STAR collaboration, QM2009 12 Au+AuHT-triggered √S NN =200 GeV STAR Preliminary Errors are statistical Kinematic constraints: T1: 8 GeV < E T < 15 GeV T2: 4 GeV/c < p T < min{p T T1,10 GeV/c} A1: 1.5 GeV/c < p T < 10 GeV/c

13. Kolja Kauder for the STAR collaboration, QM2009 13 Asymmetric Triggers Associated hadron spectra Kinematic constraints: T1: 8 GeV < E T < 15 GeV T2: 4 GeV/c < p T < min{p T T1,10 GeV/c} A1: 1.5 GeV/c < p T < 10 GeV/c Au+AuHT-triggered √S NN =200 GeV d+Au Au+Au Au+Au T1>5,T2>4 T1>5,T2>4 T1>8,T2>4 d+Au Au+Au Au+Au T1>5,T2>4 T1>5,T2>4 T1>8,T2>4 Errors are statistical

14. Kolja Kauder for the STAR collaboration, QM2009 14 deposition for back-to-back jets Model Predictions T. Renk PRC78, 014903 (2008) Charged hadron Sum-p T in correlation peaks: Σ p T = Σ p T,assoc + p T,trig ± 0.35 [GeV/c]  d + Au)  = 1.64 ± 0.35 [GeV/c].50 ± 0.31 [GeV/c]  Au + Au)  = 1.50 ± 0.31 [GeV/c].3 ± 0.1 [GeV/c]  Au + Au)  = 4.3 ± 0.1 [GeV/c] Symmetric Asymmetric  = Σ p T (same)-Σ p T (away)

15. Kolja Kauder for the STAR collaboration, QM2009 15 Summary Studied dijet properties using 2+1 correlation technique Symmetric trigger pairs: Similar spectra for central Au+Au and d+Au collisions No measurable modifications in correlations, fragmentations functions, Σp T Asymmetric trigger pairs: Similar peaks on same side and away side Softer away side spectrum Σp T  Estimate for energy loss

16. Back-Up Kolja Kauder for the STAR collaboration, QM2009 16

17. Kolja Kauder for the STAR collaboration, QM2009 17 Asymmetric Triggers Fragmentation function