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High p T Probes of QCD Matter

High p T Probes of QCD Matter. Huan Zhong Huang 黄焕中 Department of Physics and Astronomy University of California, Los Angeles Department of Engineering Physics Tsinghua University. Characteristics of Interactions. Non-Abelian Nature of QCD. QED. QCD. Coupling Strength. q. q.

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High p T Probes of QCD Matter

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  1. High pT Probes of QCD Matter Huan Zhong Huang 黄焕中 Department of Physics and Astronomy University of California, Los Angeles Department of Engineering Physics Tsinghua University

  2. Characteristics of Interactions

  3. Non-Abelian Nature of QCD QED QCD

  4. Coupling Strength q q Shorter distance  q q q q (GeV) Momentum Transfer Salient Feature of Strong Interaction Asymptotic Freedom: Quark Confinement: 庄子天下篇 ~ 300 B.C. 一尺之棰，日取其半，万世不竭 Take half from a foot long stick each day, You will never exhaust it in million years. QCD Quark pairs can be produced from vacuum No free quark can be observed

  5. Quarks are Real ! e+e- qq (OPAL@LEP) p+p jet+jet (STAR@RHIC) Discovery of the Gluons ?!

  6. Number of Participants Impact Parameter Geometry of Nucleus-Nucleus Collisions Npart – No of participant nucleons Nbinary – No of binary nucleon-nucleon collisions cannot be directly measured at RHIC estimated from Woods-Saxon geometry

  7. Expectations for High pT from Au+Au Use number of binary nucleon-nucleon collisions to gauge the colliding parton flux: N-Binary Scaling  RAA = 1 N-Binary Scaling works for very rare processes i.g., Drell-Yan and direct photon production with some caveats (parton F2 and G change in A). RAA can also be measured using central/peripheral ratios !

  8. Collision Dynamics (high pT processes !)

  9. Collisions at high pT (pQCD) At sufficiently large transverse momentum, let us consider the process: p + p hadron + x • 1) f(x,m2) – parton structure function • 2) sab->cd – pQCD calculable at large m2 • 3) D(zh,m2) – Fragmentation function

  10. Kinematic Variables in 22 process

  11. Parton Distribution Function

  12. Fragmentation Function from e+e collisionscharged hadron

  13. PQCD LO Parton-Parton Cross Sections

  14. Jet prominent at high energy collisions !

  15. Jet total energy  Avoid Fragmentations !

  16. PQCD Works for p+p at RHIC

  17. You can ‘see’ jets clearly!! High Energy p+p collisions! Four Jets event possible !

  18. Jet Energy Reconstruction NOT at RHIC !

  19. Hard Scattering and Jet Quenching leading particle suppressed back-to-back jets disappear Parton Energy Loss in A+A Hard Scattering in p+p Reduction of high pT particles Disappearance of back-to-back high pT particle correlations

  20. Disappearance of back-to-back angular correlations Disappearance of back-to-back correlation ! y ptrig pss Ptrig–psssame side f correlation ptrig> 4 GeV/c, pss pos 2<pT<ptrig x Ptrig–posopposite side f corr. pos

  21. Suppression of high pT particles pT Spectra Au+Au and p+p RAA=(Au+Au)/[Nbinaryx(p+p)] Au+Au 0-5% p+p Strong high pT suppression by a factor of 4-5 in central Au+Au collisions ! The suppression sets in gradually from peripheral to central Au+Au collisions !

  22. Two Explanations for High pT Observations Energy Loss: Particles lose energy while traversing high density medium after the hard scattering. Energy loss quenches back-to-back angular correlations. J. Bjorken, M. Gyulassy, X-N Wang et al…. Parton Saturation: The parton (gluon) structure function in the relevant region (saturation scale) is modified. Not enough partons available to produce high pT particles. Parton fusion produces mono-jet with no back-to-back angular correlations. D. Kharzeev, L. McLerran, R. Venugopalan et al…..

  23. q q d+Au Collisions q q Au+Au Geometry d+Au Geometry d+Au collisions: Little energy loss from the dense medium created, But Parton saturation from Au nuclei persists!

  24. Data from d+Au collisions No disappearance of back-to-back correlations! No high pT suppression !

  25. High pT Phenomena at RHIC Very dense matter has been created in central Au+Au collisions! This dense matter is responsible for the disappearance of back-to-back correlation and the suppression of high pT particles !

  26. The Suppression is the Same for p0 and h – parton level effect No suppression for direct photons – photons do not participant !

  27. No Significant Difference BetweenQuarks and Gluons at High pT Baryons more likely from gluon fragmentations in the pQCD region

  28. Leading hadrons Medium STAR PRELIMINARY Energy Loss and Soft Particle Production

  29. High pT Physics • Energy Balance in Jet Production and Trigger pT Effect • -- Mach Shockwave Phenomenon • -- Dh and Df Correlations • Heavy Quark Energy Loss • g-jet Correlations • Di-jet Correlations • -- kT Smearing • -- Nuclear A Dependence of kT Scale • Can High pT Probes Be Sensitive to the DOF of the Dense Medium? • Color Glass Condensate

  30. Casalderrey-Solana, Shuryak, Teaney, hep-ph/0411315 pTtrig=4-6 GeV/c, pTassoc=0.15-4 GeV/c F. Wang (STAR), QM’04 talk, nucl-ex/0404010. Now published: STAR, PRL 95, 152301 (2005). STAR data motivated sonic-boom prediction Actually sonic-boom was first predicted in the 70’s by the Frankfurt school. Many recent studies: H. Stoecker, nucl-th/0406018. Muller, Ruppert, nucl-th/0507043. Chaudhuri, Heinz, nucl-th/0503028. Y.G. Ma, et al. nucl-th/0601012.

  31. Sonic Boom Casalderrey-Solana, Shuryak and Teaney Dumitru Linearize disturbance qM Trigger • Can hydro equation be applied to a few particles? • (2) Transverse expansion?

  32. Jet-Medium Interactions • how does a fast moving color charge influence the medium it is traversing? • can Mach-shockwaves be created? • information on plasma’s properties is contained in longitudinal and transverse components of the dielectricity tensor • two scenarios of interest: • High temperature pQCD plasma • Strongly coupled quantum liquid (sQGP) • H. Stoecker, Nucl. Phys. A750 (2005) 121 • J. Ruppert & B. Mueller, Phys. Lett. B618 (2005) 123 • J. Casalderrey-Solana, E.V. Shuryak, D. Teaney, hep-ph/0411315

  33. Wakes in the QCD Medium • High temperature pQCD plasma: • Calculation in HTL approximation • color charge density wake is a co-moving screening cloud • Strongly coupled quantum liquid (sQGP): • subsonic jet: analogous results to pQCD plasma case • supersonic jet: emission of plasma oscillations with Mach cone emission angle: ΔΦ=arccos(u/v) [v: parton velocity, u: plasmon propag. velocity] J. Ruppert & B. Mueller, Phys. Lett. B618 (2005) 123

  34. The Structure at Df Correlations in Central Au+Au High pT At Low pT ! Low pT

  35. near Df2 p Medium away 0 mach cone 0 p Df1 Df2 p 0 0 p Df1 In order to discriminate Mach-cone from deflected jets, one needs three-particle correlation. 0 1 2 2 1 2 0 near 1 2 2 Medium away 1 deflected jets

  36. pp Au+Au 80-50% Au+Au 30-10% Au+Au ZDC central (12%)data: x10 more statistics. Au+Au 10-0% d+Au Au+Au 50-30% STAR preliminary 3-particle correlation results

  37.  : System, Centrality Dependence at 200 GeV STAR preliminary 3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig) || < 0.5 Au+Au: peak broadens, height drops with centrality

  38.  : System, Centrality Dependence at 200 GeV 2 < pT(assoc) < pT(trig) || < 0.5 3 < pT(trig) < 6 GeV 6 < pT(trig) < 12 GeV •  increases from p+p to central Au+Au at lower pT(trig) • Higher pT(trig) flat across all centralities • Systematic error not assigned (fit range,  projection window)

  39. Centrality Dependence Jet-yield Ratios for baryons and mesons Observed baryon to meson ratio is higher for away-side jets

  40. Partonic Matter Hadronization • Definition of Nuclear Modification Factors and v2 • pT Scale for Fragmentation Processes • Degree of Freedom at Hadron Formation • More Identified Particles and Higher pT • Model Dependence – Recombination/Coalescence

  41. The Field & Feynman picture of cascade fragmentation Kretzer@ISMD04

  42. Baryon Production from pQCD e+e-jet fragmentation from SLD p p K K p p Normal Fragmentation Cannot Produce the Large Baryon Yield

  43. Too Many Baryons at Intermediate pT

  44. pT Scales and Physical Processes RCP Three PT Regions: -- Fragmentation -- multi-parton dynamics (recombination or coalescence or …) -- Hydrodynamics (constituent quarks ? parton dynamics from gluons to constituent quarks? )

  45. Multi-Parton Dynamics for Bulk Matter Hadronization Essential difference: Traditional fragmentation  particle properties mostly determined by the leading quark ! Emerging picture from RHIC data (RAA/RCP and v2)  all constituent quarks are almost equally important in determining particle properties ! v2 of hadron comes from v2 of all constituent quarks ! The fact that in order to explain the v2 of hadrons individual constituent quarks (n=2-meson,3-baryon) must have a collective elliptic flow v2 and the hadron v2 is the sum of quark v2  Strong Evidence for Deconfiement !

  46. Recombination+Fragmentation Model basic assumptions: • at low pt, the quarks and antiquark spectrum is thermal and they recombine into hadrons locally “at an instant”: • features of the parton spectrum are shifted to higher pt in the hadron spectrum • at high pt, the parton spectrum is given by a pQCD power law, partons suffer jet energy loss and hadrons are formed via fragmentation of quarks and gluons • shape of parton spectrum determines if recombination is more effective than fragmentation • baryons are shifted to higher pt than mesons, for same quark distribution • understand behavior of baryons!

  47. Reco: Single Particle Observables • consistent description of spectra, ratios and RAA

  48. Mesons(2 quarks): Baryons(3 quarks): F: joint distribution of partons T: thermal parton(low pt) S: shower parton(high pt) Recombination model (Hwa+Yang) • The traditional hadronization: high momentum partons fragment into hadrons • Recombination as a hadronization process: lower momentum partons recombine to a hadron. May cause higher yield at some pT region. hadron momentum Parton distribution p p q p1+p2 (recombine) (fragment)

  49. Recombination model on d+Au data p proton 0-20%/60-90% p

  50. Log10(dE/dx) Log10(p) Momentum: GeV/c dE/dx of p (K,p) separation: 2s dE/dx at higher pT

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