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High-p T results from STAR – what did we learn?

High-p T results from STAR – what did we learn?. Jana Bielcikova for the STAR Collaboration NPI ASCR and Center for physics of ultra-relativistic heavy-ion collisions, Prague, Czech Republic.

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High-p T results from STAR – what did we learn?

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  1. High-pT results from STAR – what did we learn? Jana Bielcikova for the STAR Collaboration NPI ASCR and Center for physics of ultra-relativistic heavy-ion collisions, Prague, Czech Republic

  2. Outline: • Introduction • Baryon/meson enhancement, quark vs gluon energy loss • Di-hadron correlations: system size dependence • “Jet”-medium interaction via 2- and 3-particle correlations - conical emission - ridge - path length effects • Emerging and future studies: g-jet, full jet reconstruction • Summary 4th workshop "High-pT at LHC", Prague

  3. Probing QCD matter with high-pT particles and jets Au+Au p+p What happens to high-pT particles/jets which pass through the medium? Are they similar to p+p or modified by the medium? See also talks by: • Tools: • inclusive pT spectra • di-hadron correlations • multi-hadron correlations • jets, g-jets C. Natrass O. Barannikova J. Putschke A. Hamed 4th workshop "High-pT at LHC", Prague

  4. Baryon/meson ratios at RHIC d+Au, Au+Au: STAR, PRL 97 (152301) 2006 p+p: P. Fachini (STAR), QM2008 M. Lamont (STAR), SQM2006 • Au+Au: p/ ~ 1 Λ/K0S ~ 1.8 • p+p: p/ ~ 0.3 Λ/K0S ~ 0.6 • e++e-: p/ ~ 0.1-0.2 • large enhancement of B/M ratio in Au+Au relative to p+p collisions • - reaches maximum at pT~3 GeV/c • particle production via parton coalescence/recombination 4th workshop "High-pT at LHC", Prague

  5. Gluon vs quark energy loss (I) D µ a 2 ˆ E C q L s R Gluon jet contribution factor increases from , K, p towards: e.g. pT = 8 GeV/c: 50% for p 90% for p If and At high pT for same beam energy, system and centrality: RCP() > RCP(p) RCP(K) > RCP() B. Mohanty (STAR), arXiv: 0705.0953 AKK (Albino-Kniehl-Kramer): NPB 734, 50 (2006) 4th workshop "High-pT at LHC", Prague

  6. Gluon vs quark energy loss (II) I. Vitev, QM2008 B. Mohanty, P. Fachini (STAR), QM2008 High-pT (pT > 6 GeV/c): RCP()~RCP(p) no color factor effect of 9/4 observed up to pT ~ 12 GeV/c ? non-asymptotic limit: q and g losses are closer to each other 4th workshop "High-pT at LHC", Prague

  7. System size dependence of di-hadron yields 6 < pTtrig < 10 GeV/c, pTassoc >3 GeV/c Near-side peak Away-side peak O. Catu (STAR), QM08 zT=pTassoc/pTtrig Parton Quenching Model (PQM): BDMPS energy loss, Glauber geometry, rbin scaling C. Loizides, Eur. Phys. J. C 49, 339 (2007) Modified Fragmentation Model: NLO, higher twist, hard sphere geometry, rpart scaling Zhang, Owens, Wang, Wang, PRL 98, 212301 More model calculations needed to disentangle effects fromenergy loss and density scaling/profile 4th workshop "High-pT at LHC", Prague

  8. 40-60% Preliminary 0-12% Conical emission in A+A collisions? 2.5 < pTtrig< 4 GeV/c and 1< pTassoc < 2.5 GeV/c • Mach cone in heavy-ion physics introduced • in1970’s (Hofmann, Stöcker, Heinz, Scheid, Greiner) • a supersonic parton creates shock waves: • - hydrodynamics • Stöcker et al., NPA750 (2005) 121 • Casalderrey-Solana et al., NPA774 (2006) 577 • Renk, Ruppert, PRC73 (2006) 011901 • - colored plasma • Ruppert, Mueller, PLB618 (2005) 123 • - AdS/CFT • Gubser, Pufu, Yarom, PRL100, (2008) 012301 • Čerenkov gluon radiation by a superluminal parton • Dremin, NPA750 (2006) 233 • Koch et. al., PRL96 (2006) 172302 M. Horner (STAR), J.Phys.G34, S995,2007 To distinguish from other mechanisms 3-particle correlation studies needed 4th workshop "High-pT at LHC", Prague

  9. near near near Medium Medium Medium away away π away di-jets 0 π 0 deflected jets mach cone Conical flow or deflected jets? (I) cartoons of 3-particle azimuthal correlations (1 trigger + 2 associated particles) di-jets conical emission deflected jets (by the collective movement, “flow”, of the expanding medium) Armesto , Salgado, Wiedemann, PRL 93, (2004) 242301 courtesy to J. Ulery 4th workshop "High-pT at LHC", Prague

  10. C3  STAR Preliminary  Subtraction of v2v2v4 terms using v2 = 0.06 Subtraction of v2v2v4 term using v2 = 0.12 Conical flow or deflected jets? (II) • STAR uses 2 methods: • 1. Jet+flow background - model dependent analysis • evidence for conical emission • 2. Cumulantmethod • C. Pruneau (STAR),J.Phys.G34 (667),2007; • C. Pruneau, PRC 74 (2006) 064910 • unambiguous evidence • for 3-particle correlations • strength and shape of away-side • structures depend on magnitude • of flow coefficients • no conclusive evidence for • conical emission • an improved analysis with • rotating EP shows conical • structures d+Au central Au+Au Note: Large and complicated backgrounds Abelev et al (STAR), arXiv:0805.0622 3 < pT,trig < 4 GeV/c 1 < pT,assoc < 2 GeV/c central Au+Au central Au+Au STAR Preliminary 

  11. pT dependence of cone angle Cone angle independent of pTassoc STAR preliminary Cone angle (radians) Koch, Majumder, Wang, PRL96 172302 (2006) pT(GeV/c) Čerenkov gluon emission: cone angle decreases with pTassoc BUT! Hydro: expects pT dependence as well (G. Torrieri, priv.comm.) 4th workshop "High-pT at LHC", Prague

  12. Momentum conservation in correlation analyses C3 cumulant pTconservation 3-particle correlation Calculation for: <pT,trig > = 3.2 GeV/c <pT,assoc >= 1.2 GeV/c N. Borghini, PRC 75 (2007) 021904 Calculation by N. Borghini: momentum conservation  sizable correlation between pairs or triplets of high-pT particles in central Au+Au collisions at RHIC  C3(pT) ~ C3(flow)  jet “distorts” the event Data: possibly a fraction of stat. conservation: assuming bkg follows exp. drop  a small effect for pTtrig~3-4 GeV/c 2-particle correlation after v2 subtraction N. Borghini, arXiv:0710.2588 4th workshop "High-pT at LHC", Prague

  13. Centrality and φS dependence: • 20-60% : away-side evolves from single (φS=0o) to double peak (φS=90o) • 0-5% : double peak shows up at smaller φS • at large φS there is little difference between two centrality bins Away-side peak: path-length effects? 3< pTtrig < 4 GeV/c, pTassoc=1.0-1.5 GeV/c trigger in-plane out-of-plane fS=90o in-plane fS=0o Au+Au 200 GeV 20-60% STAR Preliminary d+Au d+Au RMS trigger out-of-plane shoulder Au+Au 200 GeV STAR Preliminary 0-5% A.Feng (STAR), QM2008 4th workshop "High-pT at LHC", Prague

  14. Di-hadron correlations: path-length effects STAR Preliminary 3< pTtrig < 4 GeV/c, pTassoc=1.0-1.5 GeV/c v2 syst. error Au+Au 200 GeV “shoulder” v2{EP} v2{4} A.Feng (STAR), QM2008 A.Feng (STAR), QM2008 in-plane: similar to d+Au in 20-60% broader than d+Au in central collisions out-of-plane: small difference between the two centralities Yield in shoulder region independent of fs Yield in peak region decreases with fs Away-side features reveal path-length effects 4th workshop "High-pT at LHC", Prague

  15. A closer look at the near-side peak … pTtrig=3-4 GeV/c, 2 GeV/c <pTassoc< pTtrig d+Au, 200 GeV Au+Au, 200 GeV STAR preliminary “jet” ridge Additional near-side correlation in  observed in central Au+Au collisions • The ridgeology … • 1) Medium heating and parton recombination • Chiu & Hwa PRC 72 (2005) 034903 • 2) Radial flow + high-pT trigger particle • Shuryak, Phys.Rev.C76 (2007) 047901 • Voloshin, nucl-th/0312065 NPA 749, (2005) 287 • Gavin, Pruneau, Voloshin , NPA 802, 107 (2008) • 3) Parton radiation and its coupling • to the longitudinal flow • Armesto, Salgado, Wiedemann, PRL 93 (2004) 242301 4) Momentum broadening in anisotropic QGP Romatschke, PRC 75 (2007) 014901 5) Longitudinal broadening of quenched jets in turbulent color fields Majumder, Mueller, Bass, PRL99 (2007) 042301 6) Momentum kick imparted on partons in medium Wong, PRCPRC76 (2007) 054908 7) Glasma flux tubes Dumitru, Gelis, McLerran, Venugopalan, arXiv: 0804.3858 … 4th workshop "High-pT at LHC", Prague

  16. Ridge properties • Ridge yield: • increases steeply with centrality • ~ independent of pTtrigger • baryon/meson ratios and • pT -spectra are ‘bulk-like’ • system size and • energy dependence •  see talk by C. Nattrass Ridge yield Ridge inclusive Jet STAR preliminary pTtrig (GeV/c) pTassoc> 2 GeV/c h-h, Au+Au 200 GeV Ridge: solid symbols Jet: open symbols STAR preliminary 4th workshop "High-pT at LHC", Prague

  17. Near-side peak: path-length effects? 3< pTtrig < 4 GeV/c, pTassoc=1.0-1.5 GeV/c trigger in-plane out-of-plane fS=90o in-plane fS=0o Ridge component |Dh|>0.7 trigger out-of-plane Au+Au 200 GeV “jet” part, near-side ridge part, near-side 20-60% “Jet” component ridge yield decreases with φS  ridge larger in-plane “jet” yield: slight increase with φS magnitude similar to d+Au STAR Preliminary 4th workshop "High-pT at LHC", Prague

  18. 3-particle DhxDhcorrelations d+Au Au+Au STAR Preliminary 3<pTtrig<10 GeV/c, 1<pTassoc<3 GeV/c, ||<0.7 2) In medium radiated gluons diffused in  1) Jet fragmentation in vacuum • In medium radiated gluons collimated • by longitudinal flow 4) Combination of jet fragmentation and diffused gluons Uniform overall excess of associated particles observed at intermediate pT - more data needed - studies at higher pTassoc and pTtrigger Note: Involves complicated background subtraction Data: STAR Preliminary P. Netrakanti (STAR), QM 2008 4th workshop "High-pT at LHC", Prague

  19. The ‘soft’ ridge in non-triggered correlations M. Daugherity (STAR), QM08 # correlated pairs/particle • “Minijet” near-side peak amplitude and Dh width • experience a sharp transition at ~55% centrality • for 200 GeV and ~40% for 62 GeV Au+Au data. • x • Df width is const. from mid-central to central • Au+Au collisions stat. errors only, syst.errors 9% (correlation amplitude) M. Daugherity (STAR), QM08 4th workshop "High-pT at LHC", Prague

  20. Emerging and future high-pT studies 4th workshop "High-pT at LHC", Prague

  21. Full jet reconstruction in Au+Au collisions J. Putschke (STAR) Hard Probes 2008 The first full jet reconstruction in heavy-ion collisions! 4th workshop "High-pT at LHC", Prague

  22. Jet spectrum and fragmentation function in Au+Au • Jet spectrum: need to understand • HT trigger bias • Fragmentation function: no apparent modification with respect to p+p Leading Order High Seed Cone(LOHSC) R=0.4, pT = 1 GeV/c, seed = 4.6 GeV/c See talk by J. Putschke 4th workshop "High-pT at LHC", Prague

  23. g-hadron correlations A. Hamed (STAR),QM2008 • a “golden probe” of parton energy • loss in the medium • precise measurement of the in-medium • modification of fragmentation function A. Hamed (STAR),Hard Probes 2008 STAR preliminary See talk by A. Hamed 4th workshop "High-pT at LHC", Prague

  24. STAR and RHIC upgrades TOF (Run 10): PID, clean e± μ± ID down to low pT DAQ1000 complete (Run 9): 3x improvementin sampledluminosity for rare probes (e.g. jets in p+p) RHIC upgrade, stochastic cooling Heavy Flavor Tracker (Run 13): direct measuruments of charm/bottom Projected performance forg-hadron measurement 4th workshop "High-pT at LHC", Prague

  25. Summary • Constraining medium density using combined fits to RAA and IAA • large d+Au data sample will help to reduce exp. uncertainties • Strong modification of correlation patterns in central A+A collisions at RHIC: • broadening of away-side peak with angular substructure • possible evidence for conical emission • medium responds through “ridge” formation in pseudo-rapidity • bulk-like properties (spectra, particle composition) • medium density/path length effects (dominated in the event plane) • THE future measurements: g-jets and full jet reconstruction are emerging • Stay tuned for new results coming from Run7 and Run8 + future STAR upgrades 4th workshop "High-pT at LHC", Prague

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