1 / 48

High Momentum probes Nuclear Suppression Correlations Identified particle measurements

High Momentum probes Nuclear Suppression Correlations Identified particle measurements (for theory see lecture 5). Hadronization in QCD (the factorization theorem). hadrons. Parton Distribution Functions. hadrons. Hard-scattering cross-section. leading particle. Fragmentation Function.

wilbur
Télécharger la présentation

High Momentum probes Nuclear Suppression Correlations Identified particle measurements

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. High Momentum probes Nuclear Suppression Correlations Identified particle measurements (for theory see lecture 5)

  2. Hadronization in QCD (the factorization theorem) hadrons Parton Distribution Functions hadrons Hard-scattering cross-section leading particle Fragmentation Function High pT (> 2.0 GeV/c) hadron production in pp collisions: ~ Jet: A localized collection of hadrons which come from a fragmenting parton c a Parton Distribution Functions Hard-scattering cross-section Fragmentation Function b d “Collinear factorization”

  3. High-energy parton loses energy by rescattering in dense, hot medium. q q “Jet quenching” = parton energy loss Described in QCD as medium effect on parton fragmentation: Medium modifies perturbative fragmentation before final hadronization in vacuo. Roughly equivalent to an effective shift in z: Important for controlled theoretical treatment in pQCD: Medium effect on fragmentation process must be in perturbative q2 domain.

  4. Induced Gluon Radiation Modification according to Gyulassy et al. (nucl-th/0302077) attributable to radiative rather than collisional energy loss Induced Gluon Radiation • ~collinear gluons in cone • “Softened” fragmentation

  5. Modification of fragmentation functions(hep-ph/0005044)

  6. RAA and high-pT suppression STAR, nucl-ex/0305015 pQCD + Shadowing + Cronin energy loss pQCD + Shadowing + Cronin + Energy Loss Deduced initial gluon density at t0 = 0.2 fm/c dNglue/dy ≈ 800-1200 e≈ 15 GeV/fm3, eloss = 15*cold nuclear matter (compared to HERMES eA)(e.g. X.N. Wang nucl-th/0307036)

  7. Jet quenching I: hadrons are suppressed, photons are not

  8. Energy dependence of RAA p 0 nucl-ex/0504001 RAA at 4 GeV: smooth evolution with √sNN Agrees with energy loss models

  9. L q q g L q q Two possible mechanisms of radiative e-loss plus collisional e-loss High energy limit: energy loss by gluon radiation. Two limits: (a) Thin medium: virtuality q2 controlled by initial hard scattering (LQS, GLV) (b) Thick medium: virtuality q2 controlled by rescattering in medium (BDMPS) Trigger on leading hadron (e.g. in RAA) favors case (a). Low to medium jet energies: Collisional energy loss is competitive! Especially when the parent parton is a heavy quark (c or b).

  10. Baier, Schiff and Zakharov, AnnRevNuclPartSci 50, 37 (2000) Radiative energy loss in QCD BDMPS approximation: multiple soft collisions in a medium of static color charges Transport coefficient: Medium-induced gluon radiation spectrum: Total medium-induced energy loss: DE independent of parton energy (finite kinematics DE~log(E)) DE  L2 due to interference effects (expanding medium DE~L)

  11. Extracting qhat from hadron suppression data RAA: qhat~5-15 GeV2/fm

  12. ~RHIC data QGP Hadronic matter  R. Baier, Nucl Phys A715, 209c What does qhat measure? • Equilibrated gluon gas: • number density ~T3 • energy density e~T4 qhat+modelling  energy density Model uncertainties • pQCD result: c~2 (aS? quark dof? …) • sQGP (multiplicities+hydro): c~10

  13. RHIC data sQGP? ? QGP Pion gas Cold nuclear matter q-hat at RHIC

  14. Salgado and Wiedemann PRD68 (2003) 014008 Medium-induced radiation spectrum GLV BDMPS   Baier, Dokshitzer, Mueller, Peigne, Schiff, Armesto, Salgado, Wiedemann, Gyulassy, Levai, Vitev BDMPS(ASW) vs. GLV Rough correspondence: (Wiedemann, HP2006)  30-50 x cold matter density

  15. What do we learn from RAA? GLV formalism BDMPS formalism ~15 GeV Wicks et al, nucl-th/0512076v2 Renk, Eskola, hep-ph/0610059 DE=15 GeV Energy loss distributions very different for BDMPS and GLV formalisms But RAA similar! Need more differential probes

  16. RAA for p0: medium density I I. Vitev C. Loizides hep-ph/0608133v2 W. Horowitz Use RAA to extract medium density: I. Vitev: 1000 < dNg/dy < 2000 W. Horowitz: 600 < dNg/dy < 1600 C. Loizides: 6 < < 24 GeV2/fm Statistical analysis to make optimal use of data Caveat: RAA folds geometry, energy loss and fragmentation

  17. Binary collision scaling p+p reference Application to Heavy Ion Collisions: Initial Results Strong suppression in Au+Au collisions, no suppresion in d+Au: Effect is due to interactions between the probe and the medium Established use as a probe of the density of the medium Conclusion (at the time): medium is dense (50-100x nuclear matter density) PHENIX: Phys. Rev. Lett. 91 (2003) 072301 STAR: Phys. Rev. Lett. 91 (2003) 072304 PHOBOS: Phys. Rev. Lett. 91 (2003) 072302 BRAHMS: Phys. Rev. Lett. 91 (2003) 072303

  18. Central RAA Data Increasing density The Limitations of RAA: “Fragility” K.J. Eskola, H. Honkanken, C.A. Salgado, U.A. Wiedemann, Nucl. Phys. A747 (2005) 511 Surface bias leads effectively to saturation of RAA with density Challenge: Increase sensitivity to the density of the medium A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38(2005) 461

  19. PHENIX p0 Spectrum What can we learn about Energy Loss? Fractional effective energy loss: Sloss(MJT) “Effective” because of surface bias when analyzing single particle spectra PHENIX, nucl-ex/0611007 Renk and Eskola, hep-ph/0610059 8 < pT < 15 GeV/c

  20. Calibrated Interaction? Grey Probes Wicks et al, nucl-ex/0512076 • Problem: interaction with the medium so strong that information lost: “Black” • Significant differences between predicted RAA, depending on the probe • Experimental possibility: recover sensitivity to the properties of the medium by varying the probe

  21. Interpreting Correlations T. Renk, nucl-ex/0602045 Geometric biases:Hadrons: surface Di-hadrons: tangential, but depending on Eloss can probe deeply Charm-hadron, and especially Beauty-hadron(B): depends on Eloss Note: b and c produced in pairs, B and C decay into multiple hadrons Gamma-hadrons: Precise kinematics, back to surface Beyond reaction of probe to medium, also reaction of medium to probe

  22. Escaping Jet “Near Side” Lost Jet “Far Side” pedestal and flow subtracted Di-Jets through Hadron-Hadron Correlations “Disappearance of away-side jet” in central Au+Au collisions 4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig 0-5% STAR, PRL 90 (2003) 082302 IAA (Jet-correlated Yield in AA) / (Jet-correlated Yield in pp)

  23. pedestal and flow subtracted Evolution of Jet Structure M. Horner, QM 2006 At higher trigger pT (6 < pT,trig < 10 GeV/c), away-side yield varies with pT,assoc 4 < pT,trig< 6 GeV/c, 2 < pT,assoc< pT,trig For lower pT,assoc (1.3 < pT,assoc <1.8 GeV/c), away-side correlation has non-gaussian shape  becomes doubly-peaked for lower pT,trig

  24. “Reappearance of away-side jet” With increasing trigger pT, away-side jet correlation reappears STAR, Phys. Rev. Lett. 97 (2006) 162301 4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig

  25. Dijets from dihadrons 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV STAR PRL 97 (2006) 162301 d+Au Au+Au 20-40% Au+Au 0-5% 1/Ntrig dN/d(Df) • NOT background subtracted: no ambiguities from background model • At high trigger pT, high associated pT: • clear jet-like peaks seen on near and away side in central Au+Au

  26. Surface Bias of Di-Jets? STAR, Phys. Rev. Lett. 97 (2006) 162301 8 < pT,trig< 15 GeV/c Renk and Eskola, hep-ph/0610059 8 < pT,trig< 15 , 4< pT,assoc< 6 GeV/c

  27. Comparison of IAA to RAA D. Magestro, QM 2005 8 < pT(trig) < 15 GeV/c  = Near-side IAA  = Away-side IAA IAA = Yield(0-5% Au+Au) Yield(d+Au) In the di-jets where trigger pT is 8-15 GeV/c, the suppression is same as for single particles as a function of pT

  28. Modification of Clean Signals Away-side yield strongly suppressed (almost) to level of RAA No dependence on zT in measured range No modification in shape in transverse or longitudinal direction The jets you can see cleanly are also in some sense the least modified STAR PRL 97 (2006) 162301

  29. Near-side Yields vs. zT After subracting the Ridge M. Horner, QM 2006

  30. Away-side Yields vs. zT M. Horner, QM 2006

  31. Away-side suppression as a function of pT,trig Away-side suppression reaches a value of 0.2 for trigger pT > 4 GeV/c, similar to single-particle suppression M. Horner, QM 2006 Away-side IAA IAA (Jet-correlated Yield in AA) / (Jet-correlated Yield in pp)

  32. near STAR preliminary away AA/pp Leading hadrons pT (GeV/c) Medium Where does the energy go? • Lower the associated pT to search for radiated energy • Additional energy at low pT BUT no longer collimated into jets Active area: additional handles on the properties of the medium? Mach shocks, Cherenkov cones … e.g. Renk and Ruppert, Phys. Rev. C 73 (2006) 011901 PHENIX preliminary 0-12% 200 GeV Au+Au STAR, Phys. Rev. Lett. 95 (2005) 152301 M. Horner, QM2006

  33. d+Au, 40-100% Au+Au, 0-5% Dh-Df Correlations Phys. Rev. C73 (2006) 064907 mid-central Au+Au pt < 2 GeV • In Au+Au: broadening of the near-side correlation in  • Seen in multiple analyses • Number correlations at low pT • PRC73 (2006) 064907 • PT correlations at low pT, for multiple energies • Major source of pT fluctuations • J. Phys. G 32, L37 (2006) • J. Phys. G 34, 451 (2007) • Number correlations at intermediate pT • PRC 75, 034901 (2007) • Number correlations with trigger particles up to 8 GeV/c • D. Magestro, HP2005 • J. Putschke, QM2006 Dr/√rref 0.8< pt < 4 GeV STAR PRC 75(2007) 034901 3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)

  34. Au+Au 20-30% Near-side Correlation J. Putschke, QM 2006 Au+Au 0-10% STAR preliminary Additional long-range correlation in Dh the “ridge” Coupling of high pT partons to longitudinal expansion - Armesto et al, PRL 93 (2004) QCD magnetic fields- Majumder et al, hep-ph/0611035 In recombination framework: Coupling of shower partons to thermal partons undergoing longitudinal expansion- Chiu & Hwa Phys. Rev. C72:034903,2005 Radial flow + trigger bias – S.A. Voloshin, Nucl. Phys. A749, 287 (2005)

  35. Dh-Df Two-Component Ansatz     3<pt,trigger<4 GeV pt,assoc.>2 GeV • Study near-side yields • Study away-side correlated yields and shapes • Components • near-side jet peak • near-side ridge • v2 modulated background Au+Au 0-10% preliminary Strategy:Subtract  from  projection: isolate ridge-like correlation Definition of “ridge yield”: ridge yield := Jet+Ridge()  Jet() Can also subtract large .

  36. J = near-side jet-like corrl. R = “ridge”-like corrl. 2 (J) ||<0.7 (J) ||<0.7 1 2 const bkg. subtracted const bkg. subtracted  (J+R) - (R) (J) flow (v2) corrected (J+R) ||<1.7 (J+R) ||<1.7 no bkg. subtraction v2 modulated bkg. subtracted Extracting near-side “jet-like” yields J. Putschke, QM 2006 Au+Au 20-30%

  37. Jet+Ridge ()Jet () Jet) preliminary yield,) Npart The h “Ridge” + “Jet” yield vs Centrality Au+Au 0-10% 3<pt,trigger<4 GeV pt,assoc.>2 GeV Jörn Putschke, QM2006 “Jet” yield constant with Npart Reminder from pT<2 GeV: h elongated structure already in minbias AuAu f elongation in p-p  to h elongation in AuAu. Dr/√rref STAR, PRC 73, 064907 (2006)

  38. “Jet” spectrum vs. “Ridge” spectrum J. Putschke, QM 2006 STAR preliminary STAR preliminary STAR preliminary “jet” slope “ridge” slope inclusive slope

  39. Ridge Yield J. Putschke, QM 2006 pt,assoc. > 2 GeV STAR preliminary Ridge yield persists up to highest trigger pT and approximately constant yield

  40. Particle production in jet distinctly different than in medium L/K~1 L/K~0.5 Associated particle production (B/M ratio) similar in ridge and medium and about a factor 2-3 different than in the jet. Ridge and medium have similar production mechanism ? Recombination ?

  41. Extending the ridge: correlations to Dh=5 Trigger: 3<pTtrig<4 GeV/c, A.FTPC: 0.2<pTassoc< 2 GeV/c, A.TPC: 0.2<pTassoc< 3 GeV/c 2.7<|hassoc|<3.9 AuAu 0-10% AuAu 0-5% AuAu 60-80% STAR Preliminary STAR Preliminary Trigger on mid-h, associated particle high h (reverse of FMS) Near-side correlation: consistent with zero (within large v2 errors) Away-side correlations are very similar (when scaled) Energy loss picture is the same for mid- and forward h? Levente Molnar, QM2006

  42. STAR preliminary near Medium away mach cone near 0-12% 200 GeV Au+Au Medium away deflected jets How to interpret shape modifications? Hard-soft: away-side spectra approaching the bulk. Deflected jets, Mach-cone shock waves, Cherenkov radiation, completely thermalized momentum conservation, or…? • M. Horner, QM2006 STAR Collaboration, PRL 95,152301 (2005)

  43. STAR preliminary near Medium away mach cone near 0-12% 200 GeV Au+Au Medium away deflected jets Hard-soft correlations 4 < pT,trig< 6 GeV/c Hard-soft: away-side spectra approaching the bulk. Inclusive in top 5%? • Three-particle correlation – N.N. Ajitanand, J. Ulery STAR, PRL 95,152301 (2005)

  44. d+Au Δ2 0-12% Au+Au 0-12% Au+Au: jet v2=0 Δ2 off-diagonal projection Δ1 Δ1 Df=(Df1-Df2)/2 Three particle correlations • Two Analysis Approaches: • Cumulant Method • Unambiguous evidence for true three particle correlations. • Two-component Jet+Flow-Modulated Background Model • Within a model dependent analysis, evidence for conical emission in central Au+Au collisions pTtrig=3-4 GeV/c pTassoc=1-2 GeV/c C. Pruneau, QM2006 J. Ulery, HP2006 and poster, QM2006

  45. 4 < pT,trig< 6 GeV/c, 2 < pT,assoc< pT,trig Out-plane In-plane STAR STAR, Phys. Rev. Lett. 93 (2004) 252301 What other handles do we have? Centrality, trigger and associated pT,….. ….Reaction plane

  46. q g Another handle: g-jet Wang et al., Phys.Rev.Lett. 77 (1996) 231-234 Increasing ratio of direct photons to decay photons with centrality due to hadron suppression at high pT PHENIX, Phys. Rev. Lett. 94, 232301 (2005) Photon-jet measurement is, in principle, sensitive to full medium Bias to where away-side jet is close to surface? Together with di-jet measurement for comparison  Another differential observable

  47. q g 1/NtrigdN/dDf Df(rad) Another handle: g-jet Current Results from Run-4 Au+Au collisions: T. Dietel, QM 2005 J. Jin, QM 2006

  48. Summary • Limited information extracted from single-particle pT spectra • Effective fractional energy loss reaches 20% for most central collisions • Initial energy density ~ 15 GeV/fm3 from radiative energy loss models • Di-Jets (those that are observed) may have less surface bias • Photon-Jet Measurement will complement the di-jet for more complete probe • Heavy-flavor suppression not consistently described by theoretical models with light meson suppression – need elastic energy loss

More Related