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Where did the energy go?

Where did the energy go?. – OUTLINE – motivation analysis results summary. Fuqiang Wang Purdue University. Physics motivation. Quantum Chromo dynamics predicts phase transition between hadrons and Quark-Gluon Plasma at high energy density. The goal of RHIC is to create QGP –

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Where did the energy go?

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  1. Where did the energy go? – OUTLINE – motivation analysis results summary Fuqiang Wang Purdue University International CCAST Summer School and Workshop on QCD and RHIC Physics

  2. Physics motivation QuantumChromodynamicspredicts phase transition between hadrons and Quark-Gluon Plasma at high energy density. The goal of RHIC is to create QGP – a state of deconfined, thermalized quarks and gluons Lattice QCD prediction: F. Karsch, Nucl. Phys. A698, 199c (2002) (1) energy density? (2) thermalization? TC ~ 170  8 MeV eC ~ 0.5 GeV/fm3 International CCAST Summer School and Workshop on QCD and RHIC Physics

  3. ? To probe energy density self-generated, penetrating probe: large pT hadrons, jets Gluon bremsstrahlung Jet quenching: X.-N. Wang et al. • they are generated early (by hard-scatterings); • they need time to escape the collision zone; • during this time, a QGP (or whatever medium) is formed; • they interact with the medium, losing energy, thus giving us information about the medium. Can also come from initial state suppression? e.g. PDF different in Au and deuteron International CCAST Summer School and Workshop on QCD and RHIC Physics

  4. strongabsorption High pT suppression • suppression of high pT hadron yield • suppression of back side angular correlation • no suppression in d+Au  Final state interaction in Au+Au, consistent with energy loss by high pT particles – jet quenching. International CCAST Summer School and Workshop on QCD and RHIC Physics

  5. Energy density inferred from models X.-N. Wang, PLB 579 (04) 299 pQCD calculations: x30 gluon density x100 energy density in central Au+Au collisions Bjorken estimate: 4 - 20 GeV/fm3 (t=0.2-1 fm/c) High pT particles (partons/hadrons) lose energy. Where did the energy do? International CCAST Summer School and Workshop on QCD and RHIC Physics

  6. Pal, Pratt, PLB 574 (2003) 21 To measure energy loss … by going to low pT. S. Pal, S. Pratt, PLB574 (2003) 21. X.-N. Wang, PLB 579 (2004) 299, nucl-th/0307036. C.A. Salgado, U.A. Wiedemann, hep-ph/0310079. M. Gyulassy, I. Vitev, X.-N. Wang, B.-W. Zhang, nucl-th/0302077. …… • How is energy distributed? • amount of energy loss? • contribution from medium? International CCAST Summer School and Workshop on QCD and RHIC Physics

  7. High pT particle STAR Preliminary High pT particle p+p Jet-like structures Au+Au p+p (1/Ntrig) dN/d(Df) Signal Au+Au top 5% background Df Reconstructing low pT associated particles • Select a leading particle 4<pT<6 GeV/c, |h|<0.75. • Associate other particles(0.15<pT<4 GeV/c,|h|<1.1)with the leading particle.FormDf,Dh correlations. • Background from mix- events. v2 modulation on background. Normalize in0.9<|Df|<1.3. • Efficiency corrections are applied to associated particles. • Take difference and normalize per trigger. International CCAST Summer School and Workshop on QCD and RHIC Physics

  8. High pT: M.G. Albrow et al. NPB145, 305 (1978) p+p, 53 GeV Low pT: 1/Ntrigger dN/d(Df) D f (radians) Azimuth angular correlations near side: |Df|<1.1, |Dh|<1.4away side: |Df-p|<2, |h|<1.1 International CCAST Summer School and Workshop on QCD and RHIC Physics

  9. STAR Preliminary s RMS “Jet” sizes near: |Df|<1.1, |Dh|<1.4 away: |Df-p|<2, |h|<1.1 bkgd subt. Au+Au top 5% (1/Ntrig) dN/d(Df) Df near (1/Ntrig) dN/d(Dh) • With increasing centrality: • Near side broadens in h but not f. • Away side modest increase in size. Dh International CCAST Summer School and Workshop on QCD and RHIC Physics

  10. radial flow p + p S.A. Voloshin, nucl-th/0312065 Longitudinal broadening N.Armesto, C.A.Salgado, U.A.Wiedemann, hep-ph/0405301 long. flow International CCAST Summer School and Workshop on QCD and RHIC Physics

  11. p+p “Jet” charge multiplicity and “energy” STAR Preliminary With the same final leading particle, we are selecting a larger energy jet in central AA than in pp. International CCAST Summer School and Workshop on QCD and RHIC Physics

  12. } DE = 1.4 – 2.2 GeV Jet quenching model X.-N. Wang, PLB 579 (2004) 299, nucl-th/0307036 with energy loss without energy loss Caution: cannot be readily compared to data yet International CCAST Summer School and Workshop on QCD and RHIC Physics

  13. Medium contribution? Total scalar pT:Initial parton energy + medium contribution? TPC acceptance of away side partner? International CCAST Summer School and Workshop on QCD and RHIC Physics

  14. Thermal-shower recombination Hwa, Yang, nucl-th/0401001 In this model, the thermal- shower recombination is the largest contribution to high pT particles. One mechanism for energy contribution from medium. International CCAST Summer School and Workshop on QCD and RHIC Physics

  15. Leading hadrons Medium To probe thermalization • Put two sources of particles together: • one from jet fragmentation that are initially hard. • the other from bulk medium that are soft. • and see how they become at end of the day. jet medium International CCAST Summer School and Workshop on QCD and RHIC Physics

  16. Near side: Overall enhancement from pp to AA larger initial parton energy (and modest energy loss) Away side: energy from the initial parton is redistributed to low pT energy loss in medium! syst. error Away Associated particles pT distributions STAR Preliminary: Quark Matter 2004 Near softening in spectra:partial equilibrationwith medium International CCAST Summer School and Workshop on QCD and RHIC Physics

  17. d+Au spectra ratio Au+Au / p+p 6<pT<10 GeV/c 4<pT<6 GeV/c Associated pT (GeV/c) Associated pT (GeV/c) Raito of d+Au spectra STAR Preliminary STAR Preliminary • Initial parton energy was larger in AA than pp  a hardening of spectra is expected. • No hardening is observed in AA  contribution of soft hadrons from energy loss. International CCAST Summer School and Workshop on QCD and RHIC Physics

  18. Leading hadrons Medium STAR Preliminary:QM 2004 Partial approach toward thermalization In central Au+Au, the balancing hadrons are greater in number, softer in pT, and distributed broadly in angle, relative to pp or peripheral Au+Au.  away-side products seem to approach equilibration with bulk medium traversed, making thermalization of the bulk itself quite plausible. International CCAST Summer School and Workshop on QCD and RHIC Physics

  19. Summary: where did the energy go? High pT suppressed. High pT partons/particles lose energy. The lost energy is redistributed at low pT. • high enough energy density?Models require x30 normal nuclear gluon density. • parton thermalization?Broader angular distribution, larger multiplicity, softer pT.Partial thermalization with bulk medium.High degree of thermalization in medium itself plausible. A new form of matter created at RHIC: dense, strongly interacting, opaque. QGP? International CCAST Summer School and Workshop on QCD and RHIC Physics

  20. International CCAST Summer School and Workshop on QCD and RHIC Physics

  21. PHENIX, PRL 91, 172301 (2003) p / p ~ 0.9 in central p / p ~ 0.3 in peripheral QM’04 p+p @ ISR Are leading particles from jets? non-frag. p / p ~ 0.6 non-frag. p / Nch ~ 0.3 pT=3-4 GeV/c: ~30% are probably from other sources. B. Alper, NPB 87 (1975) 41 International CCAST Summer School and Workshop on QCD and RHIC Physics

  22. Coalescence / recombination models Greco et al, PRC 68 (03) 34904 Fries et al, PRC 68 (03) 44902 Hwa et al, nucl-th/0401001 Coalescence / recombination models predict a range of non-fragmentation contributions. All predict a rapid drop of non-fragmentation contribution above 4 GeV/c. pT>4 GeV/c: may mainly come from jets, or related to jets. International CCAST Summer School and Workshop on QCD and RHIC Physics

  23. G. Boca et al. ZPC49, 543 (1991) p+A <ztrigger> dN/dpT2 [a.u.] STAR Preliminary p+p p+p PRELIMINARY pT (GeV/c) pT (GeV/c) Compare to pp, pA International CCAST Summer School and Workshop on QCD and RHIC Physics

  24. AA/pp vs IAA Peripheral: AA/pp=1.01 IAA=0.84 - broadening in h - pp reference - v2 - model difference Central: AA/pp=1.66 IAA=1.25 Df Df International CCAST Summer School and Workshop on QCD and RHIC Physics

  25. IAA < 1 in peripheral ? STAR Preliminary pp reference International CCAST Summer School and Workshop on QCD and RHIC Physics

  26. Hijing (no quenching) 4 < pTtrig < 6 GeV/c 0.15 < pT < 4 GeV/c 2 < pT < 4 GeV/c Df Df International CCAST Summer School and Workshop on QCD and RHIC Physics

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