1. Jet-Medium Interactions from RHIC/STAR to LHC/ALICE Fuqiang Wang Purdue University What have been learnt at RHIC? What can be done at LHC?

2. 2 Jet-like angular correlations have provided valuable information at RHIC. At high pt away-side is suppressed. 4 < p T trig < 6 GeV/c p T assoc > 2 GeV/c 8 < p T trig < 15 GeV/c p T assoc > 2 GeV/c 4 < p T trig < 6 GeV/c 0.15 < p T assoc < 4 GeV/c At low pt away-side is enhanced and broadened. At higher trigger pt away-side is reappearing.

3. 3 Associated p T spectra: experimental way to study thermalization processes. syst. error 4 < p T trig < 6 GeV/c hard-soft parton interactions drive jet products and medium to equilibrate. PRL 95, 152301 (2005).

4. 4 Full reconstruction of “jet” energy pp One may construct fragmentation functions for different centralities.

5. 5 can be studied in greater detail. number correlation p T -weighted correlation Away side (GeV/c) p T trig =4-6 GeV/c p T assoc =0.15-4 GeV/c path-length effect? conical flow? deflected jets?

6. 6 centrality dependence of from away jets from medium decay Away side (GeV/c) Leading hadrons Medium away near

7. 7 baryon/meson anomaly Coalescence/recombination models are very attractive. But baryon and meson trigger correlations are not much different.

8. 8 Away-side fragmentation patterns appear unchanged with centrality. With the emerged away-side jet, we can do tri- or quad-hadron correlations! Are they the fraction of partons that escaped without interactions? Reconstruct the away-side jets including low p T. Dan Magestro

9. 9 All these studies can be carried out at LHC/ALICE, and better. ALICE best suited for “semi-hard” region: probably where most of the jet-quenching actions take place. Large p T coverage: full reconstruction of jets. Jet- fragmentation studies. background increase (x2) from RHIC to LHC. But huge increase in high-p T statistics. unique PID capabilities. larger statistics: multi- dimensional studies.

10. 10 And even better… with triggering!  (PHOS/EMC) + jet (TPC)  (EMC) +  0 (PHOS)  (PHOS) + jet (EMC) –both surface and volume emission. –full reconstruction of away-side jets. energy balance? medium-energy pick-up? –modified jet-fragmentation functions.  (PHOS/EMC) + e ± (TPC)  (PHOS) + e ± (EMC) –heavy-flavor energy loss

11. 11 PHENIX: |  |<0.35 STAR Preliminary trigger pt =2.5-4.0 GeV/c, associated pt =1.0-2.5 GeV/c Conical flow? STAR: |  |<0.35 60-80%40-60% 20-40%10-20% 0-5%5-10% Jason Ulery Mark Horner

12. 12  1  2 Three-particle correlations? away near Medium mach cone Medium away near deflected jets + SS (soft-soft correlation in Background) flow modulated background T(J+B) 1 (J+B) 2 = (TJ 1 J 2 ) + (TJ 1 )B 2 + (TJ 2 )B 1 + T(B 1 B 2 ) T(B 1 B 2 ) = B 1 B 2 = B J  1  2

13. 13 3-particle correlation analysis STAR Preliminary 3 < p T trig < 4 GeV/c, 1 < p T assoc < 2 GeV/c, Au+Au 0-10% Raw signal: T(J+B) 1 (J+B) 2 Hard-Soft-bkgd: (TJ 1 )B 2 + (TJ 2 )B 1 flow modulated background soft-soft correlation bkgd-bkgd: B 1 B 2

14. 14 effect of v 2 on 3-particle correlation correlation result is robust with v 2. 4 particle cumulant v 2 3 < p T trig < 4 GeV/c, 1 < p T assoc < 2 GeV/c, Au+Au 0-10% reaction plane v 2 average of 4 particle cumulant v 2 and reaction plane v2 1/N trig d 2 N/d( Δφ 1 )d( Δφ 2 ) STAR Preliminary

15. 15 pp and d+Au results Appears elongated along the diagonal axis in d+Au, possibly due to k T broadening Δφ 1/N trig d 2 N/d( Δφ 1 )d( Δφ 2 ) 2 < p T trig < 4 GeV/c, 1 < p T assoc < 2 GeV/c away   /2 = 0.89 ± 0.11   = 0.69 ± 0.05 near   = 0.66 ± 0.07 pp d+Au 3 < p T trig < 4 GeV/c, 1 < p T assoc < 2 GeV/c d+Au STAR Preliminary

16. 16 p T trig =3-4, p T assoc =1-2 GeV/c 2-particle corr, bg, v2 subtracted  φ 2 = φ 2 - φ trig d+Au min-bias dN 2 /d Δφ 1 d Δφ 2 /N trig  φ 1 = φ 1 - φ trig  φ 2 = φ 2 - φ trig Au+Au 10% conical flow? 3-particle correlation d+Au and Au+Au elongated along diagonal: kT effect, and deflected jets? difference in Au+Au average signal per radian 2 : center – corner = 0.3 ± 0.3 (stat) ± 0.4 (syst) center – cone = 2.6 ± 0.3 (stat) ± 0.8 (syst) Three regions on away side: center =( ,  ) ±0.4 corner =(  +1,  +1) ±0.4 x2 cone =(  +1,  - 1) ±0.4 x2 Distinctive features of conical flow are not seen in present data with these p T windows.

17. 17 Three-particle correlations can be done at LHC, also much better. may have to be limited at low-modest p T (need 2 associated particles).