1. 1 Jet medium interactions Pawan Kumar Netrakanti (For the STAR Collaboration) Purdue University, USA  Motivation  Parton energy loss  Medium response to energetic partons  Summary Outline Workshop on Hot & Dense Matter in the RHIC-LHC Era February 21-14, 2008 TIFR

2. 2 Motivation Medium propertiesPhysical phenomenonExperimental probes Energy densityParton E loss in the mediumHigh p T particle production,  and  correlations Velocity of soundMach cones3-particle correlations Partonic interactions Mechanism of E loss Non-Abelian features of QCD - Color factor effects, path length effects of E loss Jet-medium coupling High p T particle production  and  correlations, correlations with respect to reaction plane Collectivity and Thermalization Partonic collectivity, viscosity and interactions Azimuthal anisotropy Medium effect on particle production mechanism Parton recombination, modified/vacuum fragmentation Identified particle correlations Correlations play a significant role in understanding medium properties

3. 3 Basic approach Look for modification Is there any modification in heavy ion collisions ? Calibrated probe Near side Leading/trigger particle Away side  near away Associated particles Absence of medium STAR : PRL 97 (2006) 252001 STAR : PLB 637 (2006) 161 Medium formed in heavy-ion collisions Jet and high p T particle production in pp understood in pQCD framework STAR Preliminary New STAR high p T p+p results

4. 4 Advantage of di-hadron correlations y (fm) x (fm) Less surface bias Single Di-hadron y (fm) x (fm) Limited sensitivity of R AA to P(  E,E) T. Renk, PRC 74 (2006) 034906 T. Renk and Eskola,hep-ph/0610059 Di-hadron correlations more robust probes of initial density ~ H. Zhong et al., PRL 97 (2006) 252001  2 IAA  2 RAA

5. 5 Current observations in STAR Away side yield modification Parton E loss High p T suppression STAR : PLB 655 (2007) 104 STAR : PRL 97 (2006) 152301 STAR : PRL 91 (2003) 072304 Reappearance of di-jets STAR : PRL 97 (2006) 162301 p Tlp : 4 - 6 GeV/c p Tasoc : 2 GeV/c - p Tlp Away side shape modification d+Au Enhanced correlated yield at large  on near side Medium response STAR : J. Putschke, QM2006 STAR : M. J. Horner, QM2006 2.5 < p T trig < 4 GeV/c 1< p T assoc < 2.5 GeV/c p T trig =3-6 GeV/c, 2 GeV/c <p T assoc < p T trig Au+Au STAR: PRL 95 (2005) 152301 J.G. Ulery, QM 2005 How can we understand these features ?

6. 6 Do they give answers to … Mechanism of energy loss in medium -  Few hard interactions or multiple soft interactions ?  What is the Path length dependence of energy loss ? - L 2 or L  What is the probability distribution of parton energy loss?  Do partons loose energy continuously or discretely? Where does the energy from the absorbed jets go or how are they distributed in the medium?  Shock waves in recoil direction  Coupling of radiation to collective flow

7. 7 Di-hadron fragmentation function (Away side) z T =p T assoc /p T trig Denser medium in central Au+Au collisions compared to central Cu+Cu z T distributions similar for Au+Au and Cu+Cu for similar N part STAR Preliminary 1/N trig dN/dz T I AA zTzT 6< p T trig < 10 GeV Inconsistent with PQM calculations Modified fragmentation model better STAR Preliminary H. Zhong et al., PRL 97 (2006) 252001 C. Loizides, Eur. Phys. J. C 49, 339-345 (2007) N part I AA

8. 8 Di-hadron correlations w.r.t reaction plane out-of-plane  S =90 o in-plane  S =0 3< p T trig < 4 GeV/c, p T assoc : 1.0- 1.5 GeV/c trigger in-plane trigger out-of-plane 20-60% : away-side : from single-peak (φ S =0) to double-peak (φ S =90 o ) Top 5% : double peak show up at a smaller φ S At large φ S, little difference between two centrality bins Observations : Au+Au 200 GeV STAR Preliminary d+Au 20-60% top 5%

9. 9 Path Length Effects Au+Au 200 GeV 3< p T trig < 4 GeV/c 1.0 < p T asso < 1.5 GeV/c In-plane: similar to dAu in 20-60%. broader than dAu in top 5%. Out-of-plane: not much difference between the two centrality bins. Away-side features reveal path length effects RMS =  i (  i -  ) 2 y i  i y i RMS STAR Preliminary v 2 {4} v 2 {RP} v 2 sys. error

10. 10 Two component approach -Correlated to trigger (jets..) - Uncorrelated to trigger (except via anisotropic flow) Bkg normalization 3-particle ZYAM STAR Preliminary Conical emission or deflected jets ? Conical Emission Medium away near deflected jets away near Medium Conical Emission Experimental evidence of Conical emission (  1 -  2 )/2 3 <p T-trig < 4 GeV/c 1 < p T-assoc < 2 GeV/c dAu Central Au+Au 0-12% STAR Preliminary

11. 11 Mach Cone or Cerenkov Gluons Mach-cone: Angle independent of associated p T Cerenkov gluon radiation: Decreasing angle with associated p T Naively the observed cone angle ~ 1.36 radians leads to very small (time averaged) velocity of sound in the medium STAR Preliminary Strength and shape of away side structures observed depends on assumed magnitude of flow coefficients In cumulant approach: no conclusive evidence for conical emission so far Claude Pruneau : STAR : QM2008(Poster), PRC 74 (2006) 064910 C3C3  Subtraction of v 2 v 2 v 4 terms using on v 2 = 0.06 Subtraction of v 2 v 2 v 4 term using v 2 = 0.12 STAR Preliminary Cone angle (radians) p T (GeV/c)

12. 12 Ridge in Heavy Ion Collisions What does these features reveal about the medium ? Can we get an idea about the energy lost by partons in the medium? d+Au, 40-100% Au+Au, 0-5% 3 < p T (trig) < 6 GeV 2 < p T (assoc) < p T (trig) d+AuAu+Au

13. 13 Features of the Ridge (at QM2006) Yield at large  independent on  STAR Preliminary J. Putschke (QM06) Ridge persists up to high p T -trig T Ridge ~ T inclusive < T jet STAR : J. Putschke, QM2006 Indication of two contributions Jet contribution + contribution arising due to jet propagating in the medium

14. 14 Jet and Ridge : Observations Near-side jet yield independent of colliding system, N part and trigger particle type High p T-trig leads to higher jet yields Supports : Parton fragmentation after parton E loss in the medium Ridge yield increases with N part

15. 15 Particle Ratios: Jet & Ridge Ratios in cone smaller than inclusive Ratios in ridge similar to inclusive Jet :  /K 0 s ~ 0.5 < inclusive Ridge :  /K 0 s ~ 1 ~ inclusive Ridge vs. InclusiveJet Cone vs. Inclusive STAR Preliminary Jet ridge

16. 16 Theoretical model interpretations 2)Transverse flow boost S.A.Voloshin, Phys.Lett.B. 632(2006)490 E.Shuryak, hep-ph:0706.3531 1)In medium radiation + longitudinal flow push N.Armesto et.al Phys.Rev.Lett. 93(2004) 242301 3)Turbulent color fields A.Majumder et.al Phys. Rev. Lett.99(2004)042301 4)Momentum Kick C.Y. Wong hep-ph:0712.3282 5)Recombination between thermal and shower partons R.C. Hwa & C.B. Chiu Phys. Rev. C 72 (2005) 034903 Can we discriminate between these physics interpretations?  3-particle Correlation in 

17. 17 Motivation for 3-particle correlation in   1  2 T : Trigger particle A1: First Associated particle A2: Second Associated particle 1) Jet fragmentation in vacuum STAR TPC acceptance for 3-particle correlation in  (|  |<1 and full azimuth) 2) In medium radiated gluons diffused in  3)In medium radiated gluons still collimated 4) Combination between jet fragmentation and diffused gluons   = A1-T   = A2-T

18. 18 Au+Au and d+Au at  s NN = 200 GeV Trigger : 3<p T <10 GeV/c, |  |<1 Associated : 1< p T <3 GeV/c, |  |<1 Select both associated particles Near Side: |  | <0.7 Away Side: |  -  |<0.7 Mixed events to obtain background : (a) Min-bias events with same centrality (b)  (primary vertex z) < 1 cm (c) Same magnetic field configuration Analysis techniques STAR Preliminary

19. 19 3-particle correlation background  Raw  Raw  Raw signal  Raw  Bkg  Hard-Soft  Bkg1  Bkg1  Bkg1  Bkg2 correlated Soft-Soft - -

20. 20 STAR Preliminary dAu AuAu 40-80% AuAu 0-12% 2-particle Correlation STAR Preliminary 3-particle correlation (|  |<0.7) STAR Preliminary dAu AuAu 40-80% AuAu 0-12% 3<p T Trig <10 GeV/c 1<p T Asso <3 GeV/c Shaded : sys. error. Line : v2 uncer. STAR Preliminary dAu AuAu 40-80% AuAu 0-12% STAR Preliminary dAu AuAu 40-80% AuAu 0-12% 0.7<R<1.4

21. 21 Comparison (Projections) 3<p T Trig <10 GeV/c 1<p T Asso <3 GeV/c |  | <0.7 AuAu 0-12% is higher than dAu and AuAu 40-80% 0.7<R<1.4 STAR Preliminary

22. 22 Summarizing … 3-particle correlation in  Ridge is uniform event by event. 3<p T Trig <10 GeV/c, 1<p T Asso <3 GeV/c, |  |<0.7  The ridge is approximately uniform or broadly falling with .  No significant structures along diagonals or axes. STAR Preliminary dAu AuAu 40-80% AuAu 0-12% + = Jet Ridge

23. 23 Potential for away-side analysis 3<p T Trig <10 GeV/c 1<p T Asso <3 GeV/c |  -  | <0.7 Study the ridge with the help of Di-hardon correlation w.r.t. reaction plane. Another tool to study Ridge STAR Preliminary 3<p T trig <4GeV/c 1.0<p T asso <1.5GeV/c STAR Preliminary

24. 24 Summary : Medium Response Strong jet-medium interaction observed. Signals of conical emission observed in central Au+Au collisions at 200 GeV in 2-component approach Medium responds through ridge formation. New observations should provide significant constrains on the mechanism of ridge formation Particle ratios in ridge similar to inclusive measurements Di-hadron correlations with respect to reaction plane indicates - ridge is dominated in-plane, consistent with medium density effect STAR Preliminary Jet Cone vs. Bulk Ridge vs. Bulk STAR Preliminary

25. 25 Summary: Meduim Response  Three-particle correlation in  -  can potentially identify the underlying physics of the ridge.  Correlation peak at  =  ~0, characteristic of jet fragmentation, is observed in d+Au, Au+Au 40-80% and central Au+Au 0-12%.  The peak sits atop of pedestal in central Au+Au. This pedestal, composed of particle pairs in the ridge, is approximately uniform or broadly falling with  in the measured acceptance. No significant structures along diagonals or axes.  Significant step forward in experimental study. Quantitative theoretical calculations are needed for further understanding.

26. 26 Thanks Thanks to STAR Collaboration Argonne National Laboratory Institute of High Energy Physics - Beijing University of Birmingham Brookhaven National Laboratory University of California, Berkeley University of California - Davis University of California - Los Angeles Universidade Estadual de Campinas Carnegie Mellon University University of Illinois at Chicago Creighton University Nuclear Physics Inst., Academy of Sciences Laboratory of High Energy Physics - Dubna Particle Physics Laboratory - Dubna Institute of Physics. Bhubaneswar Indian Institute of Technology. Mumbai Indiana University Cyclotron Facility Institut Pluridisciplinaire Hubert Curien University of Jammu Kent State University University of Kentucky Institute of Modern Physics, Lanzhou Lawrence Berkeley National Laboratory Massachusetts Institute of Technology Max-Planck-Institut fuer Physics Michigan State University Moscow Engineering Physics Institute City College of New York NIKHEF and Utrecht University Ohio State University Panjab University Pennsylvania State University Institute of High Energy Physics - Protvino Purdue University Pusan National University University of Rajasthan Rice University Instituto de Fisica da Universidade de Sao Paulo University of Science and Technology of China Shanghai Institue of Applied Physics SUBATECH Texas A&M University University of Texas - Austin Tsinghua University Valparaiso University Variable Energy Cyclotron Centre. Kolkata Warsaw University of Technology University of Washington Wayne State University Institute of Particle Physics Yale University University of Zagreb

27. 27 Back up

28. 28 Black : Raw signal Pink : Mixed-event background Blue : Scaled bkgd by ZYA1 Red : Raw signal – bkgd 2-particle correlation AuAu ZDC central (0-12%) triggered data, 3<p T Trig <10 GeV/c, 1<p T Asso <3 GeV/c  acceptance corrected STAR Preliminary |  |<0.7 Ridge