Bedanga Mohanty Medium properties and response of the medium to highly energetic partons Bedanga Mohanty (For the STAR Collaboration) Variable Energy Cyclotron Centre, Kolkata Outline Motivation Parton Energy Loss Medium Response to Energetic Partons Summary

Motivation Medium Properties Physical phenomenon Experimental probes Bedanga Mohanty Motivation Medium Properties Physical phenomenon Experimental probes Energy Density Parton Eloss in the medium high pT particle production,  and  correlations Velocity of sound Mach cones 3-particle correlations Partonic interactions Mechanism of Eloss Non-Abelian features of QCD - Color factor effects, path length effects of Eloss Jet-medium coupling High pT 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

Is there any modification in Heavy Ion Collisions ? Bedanga Mohanty Basic approach Calibrated probe Look for modification Near side Leading/trigger particle Away side Dj near away Associated particles Absence of medium Medium formed in Heavy-ion collisions STAR : PRL 97 (2006) 252001 STAR : PLB 637 (2006) 161 Jet and high pT particle production in pp understood in pQCD framework Is there any modification in Heavy Ion Collisions ?

Advantage of di-hadron correlations Bedanga Mohanty Advantage of di-hadron correlations y (fm) x (fm) Less surface bias Single Di-hadron Di-hadron correlations more robust probes of initial density ~ 1.6 - 2.1 GeV/fm H. Zhong et al., PRL 97 (2006) 252001 Limited sensitivity of RAA to P(E,E) T. Renk, PRC 74 (2006) 034906

Current Observations in STAR Bedanga Mohanty Current Observations in STAR High pT suppression Away side yield modification Parton Eloss pTlp : 4 - 6 GeV/c STAR : PLB 655 (2007) 104 STAR : PRL 97 (2006) 152301 STAR : PRL 91 (2003) 072304 pTasoc : 2 GeV/c - pTlp Away side shape modification d+Au, 40-100% Enhanced correlated yield at large  on near side Medium Response STAR : J. Putschke, QM2006 STAR : M. J. Horner, QM2006 Reappearance of di-jets STAR : PRL 97 (2006) 162301 What does these features reveal about the medium ?

Do they give answers to … Bedanga Mohanty Do they give answers to … Mechanism of energy loss in medium - What is the Path length dependence of energy loss ? - L2 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? Few hard interactions or multiple soft interactions ? 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

Results on Partonic Eloss Bedanga Mohanty Results on Partonic Eloss Parton Eloss Medium response Reappearance of di-jets Results to be discussed in this talk : System size dependence of Eloss : Dihadron Fragmentation functions Oana Catu (Parallel talk on 8th Feb) Path length effects on parton Eloss : Di-hadron correlations with respect to reaction plane Aoqi Feng (Parallel Talk on 5th Feb) Is there a difference in quark and gluon Eloss ? Zhangbu Xu (Plenary Talk on 5th Feb)

Di-hadron Fragmentation Function Bedanga Mohanty Di-hadron Fragmentation Function zT=pTassoc/pTtrig 6< pT trig < 10 GeV Inconsistent with PQM calculations Modified fragmentation model better STAR Preliminary Denser medium in central Au+Au collisions compared to Cu+Cu zT distributions similar for Au+Au and Cu+Cu for similar Npart STAR Preliminary Au+Au 0-12% H. Zhong et al., PRL 97 (2006) 252001 Dense medium formed in Au+Au collisions with energy loss parameter ~ 1.6-2.1 GeV/fm Oana Catu, Parallel Talk, 8th February

Di-hadron correlations w.r.t Reaction Plane Bedanga Mohanty Di-hadron correlations w.r.t Reaction Plane trigger in-plane out-of-plane in-plane fS=0 3< pTtrig < 4 GeV/c, pTasso : 1.0- 1.5 GeV/c out-of-plane fS=90o 20-60% STAR Preliminary top 5% Au+Au 200 GeV STAR Preliminary Observations : 20-60% : away-side : from single-peak (φS =0) to double-peak (φS =90o) Top 5% : double peak show up at a smaller φS At large φS, little difference between two centrality bins Aoqi Feng, Parallel Talk, 5th February

Path Length Effects away-side features reveal path length effects Bedanga Mohanty Path Length Effects Au+Au 200 GeV 3< pTtrig < 4 GeV/c 1.0 < pTasso < 1.5 GeV/c STAR Preliminary At small φS ~ 0 (in-plane): similar to dAu in 20-60%. broader than dAu in top 5%. At large φS ~ 90o (out-of-plane): not much difference between the two centrality bins. trigger in-plane out-of-plane The RMS increases with phiS. away-side features reveal path length effects Aoqi Feng, Parallel Talk, 5th February

Color Factors and q,g Eloss Bedanga Mohanty Color Factors and q,g Eloss QCD : For SU(3) : Nc = 3 CA = 3 (gluons), CF = 4/3 (quarks) S = 0.119 SU(3) is the gauge group for QCD Eg Eq ~ 9/4 2 L <q> C E s a  D ^ An opportunity to relate experimental observable (of Eloss) to basic ingredient of QCD - Gauge Group through Color Factors i,j represent fermion field indices and a,b gauge field indices

Is there a difference in q, g Eloss Bedanga Mohanty Is there a difference in q, g Eloss Anti-particle to particle ratio Baryon & meson NMF Eg Eq ~ 9/4 Anti-Baryon to meson ratio Color factor effects not observed in pion, (anti-)proton ratios and Rcp upto pT ~ 10 GeV/c STAR : PLB 637 (2006) 161 STAR : PRL 97 (2006) 152301 STAR : PLB 655 (2007) 104

Future studies in STAR for color charge effect Bedanga Mohanty Future studies in STAR for color charge effect With Full TOF sketch With HFT N. Armesto et al., PRD 71 (2005) 05427 Similar idea can also applied for R (/h) With LHC B. Mohanty (for STAR) nucl-ex/0705.9053

Results on Medium Response Bedanga Mohanty Results on Medium Response Parton Eloss Medium response Reappearance of di-jets Results to be discussed in this talk : Conical Emission : Final 3-particle results with higher pT 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), Christine Nattrass (Parallel Talk on 8th Feb), Jiaxu Zuo (Poster), Cristina Suraze (Poster), Betty Abelev (Poster) , Navneet Kumar (Poster)

Conical Emission vs Deflected Jets Bedanga Mohanty Conical Emission vs Deflected Jets Medium away near deflected jets Conical emission or deflected jets ? away near Medium Conical Emission Associated pT dependence of Cone angle distinguishes different conical emission scenarios Cone angle reflects time integrated speed of sound in the medium

3-particle  Correlations Bedanga Mohanty 3-particle  Correlations dAu dAu STAR Preliminary STAR Preliminary (1-2)/2 (1+2)/2 Experimental evidence of Conical emission Central Au+Au 0-12% Central Au+Au 0-12% STAR Preliminary STAR Preliminary (1+2)/2 (1-2)/2 Jason Ulery - Plenary Talk on 8th February

Mach-cone or Cerenkov Gluons Bedanga Mohanty Mach-cone or Cerenkov Gluons STAR Preliminary STAR Preliminary Mach-cone: angle independent of associated pT Cerenkov gluon radiation: decreasing angle with associated pT Although pT dependence hints at Mach-cone picture, observed cone angle ~ 1.4 radians leads to very small (time averaged) velocity of sound in the medium

Conical Emission: Species dependence Bedanga Mohanty Conical Emission: Species dependence Different particles possibly decouple at different times Does Conical emission effect particle ratios Does the correlation shape vary with particle mass (like in flow) |Dh|<1.0 peripheral central protons 3<pt-trig<6GeV/c 0.15<pt_asso<0.5GeV/c Electron-hadron STAR Preliminary

Ridge in Heavy Ion Collisions Bedanga Mohanty Ridge in Heavy Ion Collisions d+Au, 40-100% Au+Au, 0-5% 3 < pT(trig) < 6 GeV 2 < pT(assoc) < pT(trig) What does these features reveal about the medium ? Perhaps tells us how the energy lost by partons are distributed in the medium

Features of the Ridge (at QM2006) Bedanga Mohanty Features of the Ridge (at QM2006) STAR Preliminary STAR Preliminary Yield at large  Independent on  Ridge persists up to high pT-trig TRidge ~ Tinclusive < Tjet Indication of two contributions Jet contribution + contribution arising due to jet Propagating in the medium STAR Preliminary What could be the different physics possibilities ?

Different physics possibilities Bedanga Mohanty Different physics possibilities Coupling of induced radiation to longitudinal flow N.Armesto et.al Phys.Rev.Lett. 93(2007) 242301 Turbulent color fields A.Majumder et.al Phys. Rev. Lett.99(2004)042301 Anisotropic Plasma S.A.Voloshin, Phys.Lett.B. 632(2007)490 E.Shuryak, hep-ph:0706.3531 Jet quenching and radial flow V.S. Pantuev hep-ph:0710.1882 Recombination of locally thermally enhanced patrons C.Y. Wong hep-ph:0712.3282 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

Ridge : Identified Particles Bedanga Mohanty Ridge : Identified Particles pT assoc >3 GeV STAR Preliminary Near-side jet yield independent of colliding system, Npart and trigger particle type Higher pT-trigleads to higher jet yields Supports : Parton fragmentation after parton Eloss in the medium Ridge yield increases with Npart Oana Catu, Parallel Talk, 8th February Cristine Nattrass, Parallel Talk, 8th February

Baryon/Meson in Jets in Ridges Bedanga Mohanty Baryon/Meson in Jets in Ridges Jet Cone vs. Bulk STAR Preliminary Ridge vs. Bulk STAR Preliminary Jet ridge Jet : /K0s ~ 1 Ridge : /K0s ~ 2 ~ bulk Baryon/Meson ratios in cone smaller than inclusive Baryon/Meson ratios in ridge similar to inclusive Jiaxu Zuo - Poster Christina Suraze - Poster

Ridge : di-hadron correlation w.r.t RP Bedanga Mohanty Ridge : di-hadron correlation w.r.t RP jet ridge STAR Preliminary Observations : Ridge: decreases with φS. Little ridge at larger φS. Jet: slightly increases with φS. 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

Ridge : 3-particle correlation Bedanga Mohanty Ridge : 3-particle correlation Turbulent color fields Jets Jets Data : 200 GeV STAR Preliminary Turbulent color fields ? STAR Preliminary Coupling of induced radiation to longitudinal flow Pawan K. Netrakanti, Plenary Talk, 5th February

Observations from un-triggered correlations Bedanga Mohanty Observations from un-triggered correlations p+p minijet reference: cos(2fD) + 2D gaussian r - r D r same mixed = r r mixed ref Primary contributions in Au+Au collisions include: minijets (jet correlations with no trigger particle) quadrupole (flow) Au+Au 200 GeV Areal Particle Density = Amplitude η Width 200 GeV 62.4 GeV cos(2φΔ): “elliptic flow” Expected behavior: binary collision scaling from Kharzeev and Nardi model Sharp steps observed in mini-jet parameters and beam energy scaling with transverse density

Results on di-jets and -jets Bedanga Mohanty Results on di-jets and -jets Parton Eloss Medium response Reappearance of di-jets Results to be discussed in this talk : Di-jets triggered correlations - Olga Barannikova Parallel Talk on 8th February Probability distribution of Eloss : hadron correlations - Ahmed H. Hamed Parallel Talk on 8th February

Di-Jets triggered correlations Bedanga Mohanty Di-Jets triggered correlations Observation of di-jets T1: pT>5GeV/c T2: pT>4GeV/c A: pT>1.5GeV/c associates primary trigger (T1) “jet-axis” trigger (T2) What happens to these features if we trigger on di-jets ?

Di-Jets triggered correlations Bedanga Mohanty Di-Jets triggered correlations 200 GeV Au+Au, 12% central 12% Central 40-60% MB 60-80% MB Df -1 -2 1 2 3 4 5 1 _dN_ Ntrig d(Df ) STAR Preliminary T1: pT>5GeV/c T2: pT>4GeV/c A: pT>1.5GeV/c Au+Au d+Au 200 GeV Au+Au & d+Au T1A1_T2 T2A1_T1 Df -1 -2 1 2 3 4 5 1 _dN_ Ntrig d(Df ) STAR Preliminary Au+Au 12% central |Df |<0.7 T2A1_T1 T1A1_T2 Dh -1 -1.5 1 -0.5 0.5 1.5 1 _dN_ Ntrig d(Dh ) STAR Preliminary No Away-side suppression, No Shape modification, no ridge Olga Barannikova, Parallel Talk, 8th February

Eloss Probability distribution : Gamma-jet correlation Bedanga Mohanty Provides constraints on Eloss probability distributions Possibly gives full accounting of jet energy loss T. Renk : PRC 74 (2006) 034906

Gamma-jet correlation in STAR Bedanga Mohanty 1 Ntrg dN () Y-axis: Au+Au 200 GeV 0 0-5% 20-80% pTassoc>4GeV/c  STAR Preliminary STAR Preliminary /c (rad) (rad) Central Au+Au events : Away side more suppressed Cu+Cu collisions : Similar away side shape for 0 and  Reduction in yields for  compared to 0 in near side Ahmed M. Hamed, Parallel Talk, 8th February

Summary : Parton Eloss Dense medium formed in Au+Au collisions Bedanga Mohanty H. Zhong et al., PRL 97 (2006) 252001 Dense medium formed in Au+Au collisions with energy loss parameter ~ 1.6-2.1 GeV/fm Medium less dense in Cu+Cu collisions Differences (due to color factor) in energy loss between quarks and gluons not observed in the measured pT range Path length effects observed : Broader RMS of away-side distribution in di-hadron correlations from in-plane to out-of-plane STAR Preliminary STAR Preliminary

Summary : Medium Response Bedanga Mohanty Summary : Medium Response Strong jet-medium interaction observed. Signals of conical emission observed in central Au+Au Collisions at 200 GeV Medium responds through ridge formation. New observations reveals Particle ratios in ridge similar to inclusive measurements Di-hadron correlations with respect to reaction plane indicates - strong jet-medium interaction may be causing the ridge formation 3-particle correlations suggests picture closer to a Turbulent Color fields scenario STAR Preliminary Ridge vs. Bulk STAR Preliminary Jet Cone vs. Bulk STAR Preliminary STAR Preliminary STAR Preliminary STAR Preliminary

Bedanga Mohanty Thanks Thanks to STAR Collaboration