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Medium properties and response of the medium to highly energetic partons

This talk discusses the motivation, parton energy loss, and medium response to energetic partons in heavy-ion collisions. It explores di-hadron correlations as robust probes of initial density and presents observations and results on partonic energy loss and medium response.

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Medium properties and response of the medium to highly energetic partons

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  1. 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

  2. Motivation Correlations play a significant role in understanding medium properties

  3. Leading/trigger particle Associated particles Near side Absence of medium Dj Away side away near Basic approach Calibrated probe Look for modification 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 ?

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

  5. Enhanced correlated yield at large  on near side Away side shape modification d+Au, 40-100% Medium Response STAR : J. Putschke, QM2006 STAR : M. J. Horner, QM2006 Reappearance of di-jets STAR : PRL 97 (2006) 162301 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 What does these features reveal about the medium ?

  6. 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? Do they give answers to … 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

  7. Results on Partonic Eloss Parton Eloss Reappearance of di-jets Medium response 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)

  8. 6< pT trig < 10 GeV STAR Preliminary STAR Preliminary • Inconsistent with PQM calculations • Modified fragmentation model better Au+Au 0-12% • Denser medium in central Au+Au collisions compared to Cu+Cu • zT distributions similar for Au+Au and Cu+Cu for similar Npart Di-hadron Fragmentation Function zT=pTassoc/pTtrig 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

  9. trigger in-plane 20-60% top 5% trigger out-of-plane Di-hadron correlations w.r.t Reaction Plane in-plane fS=0 3< pTtrig < 4 GeV/c, pTasso : 1.0- 1.5 GeV/c out-of-plane fS=90o STAR Preliminary 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

  10. trigger in-plane trigger out-of-plane 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. away-side features reveal path length effects Aoqi Feng, Parallel Talk, 5th February

  11. Eg ~ 9/4 Eq 2 D E <q> ^ L  a C s An opportunity to relate experimental observable (of Eloss) to basic ingredient of QCD - Gauge Group through Color Factors 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 i,j represent fermion field indices and a,b gauge field indices

  12. Eg ~ 9/4 Eq Is there a difference in q, g Eloss Anti-particle to particle ratio Baryon & meson NMF 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

  13. With Full TOF Future studies in STAR for color charge effect 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

  14. Results on Medium Response Parton Eloss Reappearance of di-jets Medium response 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)

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

  16. 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

  17. Mach-cone or Cerenkov Gluons • Mach-cone: angle independent of associated pT • Cerenkov gluon radiation: decreasing angle with associated pT STAR Preliminary STAR Preliminary 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

  18. |Dh|<1.0 central |Dh|<1.0 peripheral 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) protons 3<pt-trig<6GeV/c 0.15<pt_asso<0.5GeV/c Electron-hadron STAR Preliminary

  19. d+Au, 40-100% Au+Au, 0-5% 3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig) 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

  20. 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 ?

  21. Different physics possibilities N.Armesto et.al Phys.Rev.Lett. 93(2007) 242301 Coupling of induced radiation to longitudinal flow 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 C.Y. Wong hep-ph:0712.3282 Recombination of locally thermally enhanced patrons 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

  22. 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

  23. STAR Preliminary STAR Preliminary Jet Ridge vs. Bulk Jet Cone vs. Bulk ridge STAR Preliminary STAR Preliminary Baryon/Meson in Jets in Ridges 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

  24. jet ridge Ridge : di-hadron correlation w.r.t RP 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

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

  26. 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 η Width Amplitude 200 GeV 62.4 GeV cos(2φΔ): “elliptic flow” Expected behavior: binary collision scaling from Kharzeev and Nardi model Areal Particle Density = Sharp steps observed in mini-jet parameters and beam energy scaling with transverse density

  27. Results on di-jets and -jets Parton Eloss Reappearance of di-jets Medium response 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

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

  29. 1 _dN_ Ntrigd(Df ) 12% Central 40-60% MB 60-80% MB 200 GeV Au+Au & d+Au 1 _dN_ Ntrigd(Df ) 1 _dN_ Ntrigd(Df ) STAR Preliminary Au+Au d+Au 2 T1A1_T2 T2A1_T1 3 2 0 2 STAR Preliminary 1 1 _dN_ Ntrigd(Dh ) 0 T1: pT>5GeV/c T2: pT>4GeV/c A: pT>1.5GeV/c T2A1_T1 T1A1_T2 Au+Au 12% central |Df |<0.7 0 STAR Preliminary 2 -2 -2 -2 -1 -1 -1 2 2 0 1 3 4 0 1 3 4 5 5 0 1 3 4 5 0 STAR Preliminary -1 -1.5 0.5 0 -0.5 1.5 1 Df Df Df Dh Di-Jets triggered correlations 200 GeV Au+Au, 12% central No Away-side suppression, No Shape modification, no ridge Olga Barannikova, Parallel Talk, 8th February

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

  31. dN Y-axis: () 1 Ntrg Gamma-jet correlation in STAR 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

  32. Summary : Parton Eloss 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

  33. 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

  34. Thanks Thanks to STAR Collaboration

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