1 STAR results on Medium Properties and Response of the Medium to Energetic Partons Bedanga Mohanty (For the STAR Collaboration)‏ Variable Energy Cyclotron Centre, Kolkata  Motivation  Parton Energy Loss  Medium Response to Energetic Partons  Summary Outline

2 Motivation Azimuthal anisotropyPartonic collectivity, viscosity and interactions Collectivity and Thermalization Identified particle correlations Parton recombination, modified/vacuum fragmentation Medium effect on particle production mechanism High p T particle production  and  correlations, correlations with respect to reaction plane Non-Abelian features of QCD - Color factor effects, path length effects of E loss Jet-medium coupling Partonic interactions Mechanism of E loss 3-particle correlationsMach conesVelocity of sound High p T particle production,  and  correlations Parton E loss in the mediumEnergy density Experimental probesPhysical phenomenonMedium properties Correlations play a significant role in understanding medium properties

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) STAR : PLB 637 (2006) 161 Medium formed in heavy-ion collisions Jet and high p T particle production in pp understood in pQCD framework Higher the trigger particle p T more probable it is from a jet and more well defined is the jet axis STAR Preliminary New STAR high p T p+p results

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) T. Renk and Eskola,hep-ph/ Di-hadron correlations more robust probes of initial density ~ H. Zhong et al., PRL 97 (2006)  2 IAA  2 RAA

5 Current Observations in STAR Away side yield modification What does these features reveal about the medium ? Parton E loss High p T suppression STAR : PLB 655 (2007) 104 STAR : PRL 97 (2006) STAR : PRL 91 (2003) Reappearance of di-jets STAR : PRL 97 (2006) p Tlp : 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, QM < 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) J.G. Ulery, QM 2005

6 Do they give answers to … Mechanism of energy loss in medium - What is the Path length dependence of energy loss ? - L 2 or L Do we see a Color charge dependence of energy loss ? 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 Few hard interactions or multiple soft interactions ?

7 Results on Partonic E loss Parton E loss Reappearance of di-jets Medium response Is there a difference in quark and gluon E loss ? Patricia Fachini (Parallel Talk on 5th Feb), Zhangbu Xu (Plenary Talk on 5th Feb)‏ Path length effects of parton E loss : Dihadron Fragmentation functions Oana Catu (Parallel talk on 8th Feb)‏ Di-hadron correlations with respect to reaction plane Aoqi Feng (Parallel Talk on 5th Feb)‏ Probability distribution of parton E loss :  -hadron correlations A. Hamed (Parallel Talk on 8th Feb) Results to be discussed in this talk :

8 Is there a difference in q, g E loss Color factor effects of the type 9/4 not observed in pion, (anti-)proton ratios and R cp upto p T ~ 12 GeV/c STAR : PLB 637 (2006) 161STAR : PRL 97 (2006) STAR : PLB 655 (2007) 104 Patricia Fachini, Parallel Talk, 5th February Baryon & meson NMF STAR Preliminary Anti-Baryon to meson ratio STAR Preliminary EgEg EqEq ~ 9/4 Anti-particle to particle ratio X.-N. Wang, PRC 70 (2004) STAR Preliminary 2 L C E s   ^

9 Away-side Di-hadron Fragmentation Function Oana Catu, Parallel Talk, 8th February 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) C. Loizides, Eur. Phys. J. C 49, (2007)‏ N part I AA

10 Aoqi Feng, Parallel Talk, 5th February 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 asso : 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%

11 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 Aoqi Feng, Parallel Talk, 5th February RMS =  i (  i -  ) 2 y i  i y i RMS STAR Preliminary v 2 {4} v 2 {RP} v 2 sys. error

12 E loss probability distribution :  -hadron correlation Provides constraints on E loss probability distributions Possibly gives full accounting of jet energy loss T. Renk : PRC 74 (2006) Jet Prompt  1 st measurement of away-side  -h correlations Suppression similar level as inclusives in central collisions Note : E jet = E  A. Hamed (Parallel Talk on 8th Feb) X.-N. Wang et al PRL 77(1996)231

13 Results on Medium Response Parton E loss Reappearance of di-jets Medium response Results to be discussed in this talk : Conical Emission : Final 3-particle results with higher p T trigger, PID correlations Jason Ulery (Plenary Talk on 8th Feb), Gang Wang (Parallel Talk on 8th Feb), Guoliang Ma (Poster), Jiaxu Zuo (Poster), Quan Wang (Poster)‏ Ridge in heavy ion collisions : Identified particle correlations, 3-particle correlations Correlations w.r.t RP Pawan Netrakanti (Plenary Talk on 5th Feb), Aoqi Feng, Parallel Talk, 5th Feb, Christine Nattrass (Parallel Talk on 8th Feb), Jiaxu Zuo (Poster), Cristina Suarez (Poster), Betty Abelev (Poster), Navneet Kumar (Poster)

14 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 See also Jason Ulery - Plenary Talk on 8th February, (  1 -  2 )/2 3 <p T-trig < 4 GeV/c 1 < p T-assoc < 2 GeV/c Gang Wang (Parallel Talk on 8th Feb e-h correlation STAR Preliminary dAu Central Au+Au 0-12% STAR Preliminary

15 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) 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)‏

16 Ridge in Heavy Ion Collisions What does these features reveal about the medium ? Perhaps tells us how the energy lost by partons are distributed in the medium d+Au, % Au+Au, 0-5% 3 < p T (trig) < 6 GeV 2 < p T (assoc) < p T (trig)‏ d+Au Au+Au

17 Features of the Ridge (at QM2006) ‏ Yield at large  independent on  Indication of two contributions Jet contribution + contribution arising due to jet Propagating in the medium What could be the different physics possibilities ? STAR Preliminary Ridge persists up to high p T -trig T Ridge ~ T inclusive < T jet STAR Preliminary STAR : J. Putschke, QM2006

18 Different Physics Possibilities Qualitatively consistent with the features of ridge Following are the new approaches attempted to disentangle different physics possibilities - 3-particle correlation - Identified particle correlation - Di-hadron correlation with respect to reaction plane - System size dependence QCD bremsstrahlung radiation boosted by transverse flow S.A.Voloshin, Phys.Lett.B. 632(2007)490 E.Shuryak, hep-ph: Broadening of quenched jets in turbulent color fields A.Majumder et.al Phys. Rev. Lett.99(2004) Recombination between thermal and shower partons at intermediate p T R.C. Hwa & C.B. Chiu Phys. Rev. C 72 (2005) In medium radiation and longitudinal flow push N.Armesto et.al Phys.Rev.Lett. 93(2007) Momentum Kick Model C.Y. Wong hep-ph:

19 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 Oana Catu, Parallel Talk, 8th FebruaryChristine Nattrass, Parallel Talk, 8th February

20 Particle Ratios and v 2 : Jet & Ridge Cristina Suarez - Poster, 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 Jiaxu Zuo - Poster Ridge vs. Inclusive STAR Preliminary Jet Cone vs. Inclusive STAR Preliminary Jet ridge Paul Sorenson - Talk 9th Feb, Navneet K. Pruthi - Poster v 2 modulated background + ridge + jet inferred v 2 of events with ridge pair ~ inclusive inferred v 2 of events with jet pair < inclusive

21 Ridge : Di-hadron Correlation w.r.t RP jet ridge Observations : Ridge:decreases with φ S. Little ridge at larger φ S. Jet:slightly increases with φ S. General agreement with d+Au Interpretation : Strong near-side jet-medium interaction in reaction plane, generating sizable ridge Minimal near-side jet-medium interaction perpendicular to reaction plane Aoqi Feng, Parallel Talk, 5th February STAR Preliminary 3< p T trig < 4 GeV/c, p T asso : GeV/c Au+Au 200 GeV 20-60%

22 Uniform overall excess of associated particles not due to correlated emission + = Ridge : 3-particle Correlation In-medium radiated gluons diffused in  Jets Pawan K. Netrakanti, Plenary Talk, 5th February In-medium radiated gluons still collimated Jet fragmentation and diffused gluons dAu : Jets AuAu : 200 GeV 3<p T Trig <10 1<p T Asso <3 |  |<0.7 STAR Preliminary

23 Outlook : Di-Jets and Jet Reconstruction Parton E loss Reappearance of di-jets Medium response Results to be discussed in this talk : Di-jets triggered correlations - Olga Barannikova, Parallel Talk on 8th February Multi-hadron cluster triggered correlations Brooke Haag - Poster

24 Observation of di-jets Di-Jets Triggered Correlations Di-jet trigger T2 A1 T1 What happens to these features if we trigger on di-jets ? T1: p T >5GeV/c T2: p T >4GeV/c A1: p T >1.5GeV/c

25 Di-Jets Triggered Correlations Au+Au 12% central |  |<0.7 T2A1_T1 T1A1_T2  _dN_ N trig d  )‏ STAR Preliminary 0 No Away-side suppression, No Shape modification, no ridge Olga Barannikova, Parallel Talk, 8th February 200 GeV Au+Au, 12% central T1: p T >5GeV/c T2: p T >4GeV/c A: p T >1.5GeV/c T2A1_T1 T2A1  _dN_ N trig d  )‏ -2 4 STAR Preliminary 12% Central 40-60% MB 60-80% MB T2A1_T1 STAR Preliminary Au+Au d+Au  _dN_ N trig d  )‏ STAR Preliminary GeV Au+Au & d+Au 1 _dN_ N trig d  )‏ 

Multi-hadron Cluster Triggered Correlations R Seed Secondary Seeds Associated track Multi-hadron trigger Motivation: Explore jet-biases in di-hadron correlations Start developing jet reconstruction Use cluster energy for trigger: - R = p T,seed > 5 GeV - p T,sec seed > 3 GeV Away-side spectrum Single-hadron and multi-hadron triggers give similar result Re-confirms single high p T triggered correlation results probes jet-like correlations 0-12% Au+Au Add GeV trigger STAR Preliminary Brooke Haag - Poster

27 Summary : Parton E loss Differences (due to color factor) in energy loss between quarks and gluons not observed in the measured p T range Dense medium formed in Au+Au collisions compared to central Cu+Cu collisions Cu+Cu and Au+Au : z T distributions similar for collisions with similar N part - feature not consistent with PQM calculations Path length effects observed : Broader RMS for away-side distribution in di-hadron correlations from in-plane to out-of-plane 1st measurement of away-side suppression in  -h correlation STAR Preliminary

28 Jet Cone vs. Bulk 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 o Particle ratios in ridge similar to inclusive measurements o Di-hadron correlations with respect to reaction plane indicates - ridge is dominated in-plane, consistent with medium density effect o 3-particle correlations : jet fragmentation + an overall uniform excess of associated particles not due to correlated emission Ridge vs. Bulk STAR Preliminary dAu AuAu

29 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

30 Color Factors and q,g E loss i,j represent fermion field indices and a,b gauge field indices QCD : For SU(3) : N c = 3 C A = 3 (gluons), C F = 4/3 (quarks)‏ SU(3) is the gauge group for QCD  S = EgEg EqEq ~ 9/4 2 L C E s   ^ An opportunity to relate experimental observable (of E loss ) to basic ingredient of QCD - Gauge Group through Color Factors ALEPH : ZPC 76 (1997) 1 OPAL :EJPC 20 (2001) 601