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Jet Physics at RHIC

This paper discusses the physics of jets, quarks, gluons, and confinement in the context of the Relativistic Heavy Ion Collider (RHIC). It explores the "coulomb" type of potential that leads to QCD bound states and the properties of the Quark-Gluon Plasma (QGP). The goal is to study the existence and behavior of the QGP, as well as its role in QCD confinement and hadronization. The paper can be found at: https://www.phenix.bnl.gov/WWW/p/talk/papers.php.

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Jet Physics at RHIC

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  1. Jet Physics at RHIC Jiangyong Jia Every paper can be found at: https://www.phenix.bnl.gov/WWW/p/talk/papers.php

  2. Quarks, gluons and Confinement “coulomb” type of potential leads to QCD bound states QCD QED V(r) Hydrogen atom r No free quark.QCD is a “confining” gauge theory,with an effective potential: “Coulomb” “Confining” Jiangyong Jia

  3. Confining Potential: k r r Now image collide two high energy quarks q q q q Jet : the collection of particles from the “same” quark/gluon leading particle hadrons hadrons leading particle Energy used to separate quarks is converted to potential, which excites from the vacuum.   String with tension k ~ 1 GeV/fm  faster slower Jiangyong Jia

  4. Plasma Quark Gluon Plasma Normal Nuclear matter Heat to 170 MeV or 2x1012 Full melting Strong QCD field Hot plasma of p, e, photon Hydrogen gas Heat to 13.6 eV or 120K Full ionization Strong EM field Jiangyong Jia

  5. The Quark Gluon Plasma “Lattice QCD” predicts a transition to a Quark Gluon Plasma. e/T4 Transition values: T = 170 MeV e = 0.8 GeV/fm3 Assumes thermal system. hadrons quark/gluon T/Tc Energy density for “g” massless d.o.f, g = 3 for normal nuclear matter g = 37 for Quark Gluon Plasma (gluons, quarks, spin, color) Jiangyong Jia

  6. One Head on Au + Au Collision at RHIC 1000’s of particles Au Au sNN = 200 GeV (center-of-mass energy per nucleon-nucleon collision) Jiangyong Jia

  7. Space-time Evolution of Collisions p+ L e p0 jet p K J/Y g Freeze-out Hadronization QGP Thermaliztion Our interest Hard Scattering Au Au time  Expansion  space Jiangyong Jia

  8. Goals of heavy-ion collisions  • Create QGP as transient state in heavy-ion collisions • Verify existence of QGP • Study properties of QGP • Study QCD confinement and how hadrons get their masses   Jiangyong Jia

  9. Questions z y x • Have we created a matter? Is there a well-defined • Energy density e • Temperature T • Chemical potential m • Size R • What is the collective behavior of the matter? • Expansion velocity v • Elliptic flow v2 • It’s viscosity h Have we created a quark gluon matter? • What is the dynamical properties of the matter? • Opacity • Debye (color) screening in quark gluon state Jiangyong Jia

  10. Tools p K p J/ p p p q cc p p q p p p p p p p e+ p g e- • Deduce from particles emitted by the matter • hadrons p, K, p frequent, produced “late” when particles stop to interact, temperature of late stage • electro-magnetic radiation g, e+e-, m+m- rare, emitted “any time”; reach detector unperturbed by strong final state interaction temperature of plasma stage • Using penetrating probes • “hard” probes: Jets, J/psi very rare, created “early” before QGP formation, penetrate hot and dense matter. Jiangyong Jia

  11. Energy Density e = E/V pR2 2ct0 • For 0 = 0.2 fm/ceBj = 23 GeV/fm3 !!! • For 0 = 1 fm/c eBj = 4.6 GeV/fm3 !!! Energy density far above transition value predicted by lattice Bjorken hydrodynamics: Time to thermalize the system PHENIX: Central Au+Au yields PRL 87 052301 (2001) Phys. Rev. C 71, 034908 (2005) Jiangyong Jia

  12. Temperature and Chemical Potential All hadrons reach chemical equilibrium at T> 170 MeV m ~ 0, , Temperature is much higher at earlier plasma stage • Determined by statistical models: for example • Boltzmann distributions (temperature T ,chemical potential m): • One ratio determines m / T : PLB 518 (2001) 41 Jiangyong Jia

  13. Hydrodynamics of an Expanding Source purely thermal source light p+ heavy pT expanding source light T,v T heavy pT Large flow velocity: v~ 0.5-0.6c Heinz & Kolb hep-ph/0204061 More push for heavier particles Collective velocity fields superimposed on the thermal (~Boltzmann) distributions PRL 88, 242301 (2002) , PRC 69, 024904 (2004) PRC 69, 034909 (2004) Jiangyong Jia

  14. Hydrodynamics of Elliptic Flow Less matter, easy to expand, large v More matter, difficult to expand, small v azimuthal asymmetry Large v2 : v2 ~0.15 => yield in plane and out of plane differ by 50%! v2 Thermalization time t0=0.6 fm/c and e=20 GeV/fm3 And no viscosity *viscosity = resistance of liquid to shear forces (and hence to flow) perfect fluid pT Out of plane In plane White paper: NPA 757, (2005) 184 Jiangyong Jia

  15. What we know about this matter? Energy density and temperature above threshold Near 0 chemical potential: Baryon number free Strong collective flow, requires: early themalization, high energy density and perfect fluid. Quark-Gluon (partonic) Matter Jiangyong Jia

  16. Probing the QGP “matter box” Absorption or scattering pattern Calibrated source QGP But, the fleeting QGP can not be put in box. Need auto generated probe: Hard-scattered jets Leading particle hadrons hadrons leading particle “ideal” experiment N1 N2 • Generated early • Rate calculable Jiangyong Jia

  17. Calculate Hard-scattering rate: perturbative QCD • Incoming quarks and gluons (a,b) parton distribution function: fa/A fa/AAfa/p fa/BBfa/p • Parton scattering: . cross section calculable fa/A fb/B D(z) c A B a d b • D(z) : momentum dist. of particles created by outgoing quark or gluon (i.e. in a jet) : known J. Owens Rev.MP, 59 (1987) 465 Jiangyong Jia

  18. Calibrating Our Probes Produced pions Phys. Rev. Lett. 91, 241803 (2003) In A+A collisions: Scales by number of nucleon-nucleon collisions: Ncoll High Energy Probes are well described in Proton-Proton reactions by Perturbative QCD. Jiangyong Jia

  19. What happens to the jets in Medium? we produce a high energy quark or gluon. Central collisions : If the plasma is dense enough we expect the quark or gluon to be swallowed up: “Jet quenching” Peripheral collisions: escape with no or small modifications Peripheral Collision Central Collision Jiangyong Jia

  20. Au+Au 0 Spectra From PHENIX Calculations with no energy loss Calculations with energy loss RAA Observed/Expected Using p-p data as baseline Expected • Observe only 20% of expected yield @ high pT • Energy density ~15 Gev/fm3 • 100 x normal nuclear energy density!! • Reminder: critical energy density ~ 1 GeV/fm3 Transverse Momentum spectrum Jiangyong Jia

  21. PHENIX: Au+Au Final Results from 2002 Unequivocal observation of strong suppression at high p in central Au+Au collisions. RAA p (GeV/c) Jiangyong Jia

  22. PHENIX: Au+Au High-pT0 Suppression from 2005 We are now measuring out to truly high pT Jiangyong Jia

  23. PHENIX: Au+Au High-pT0 Suppression •  constancy for pT > 4 GeV/c for all centralities! Jiangyong Jia

  24. 0 Suppression: dE/dx Comparisons • Measured RAA shows little/no variation with pT up to 20 GeV/c • Consistent with energy loss calculations • Suppressed hard production over “whole” pT range? Jiangyong Jia

  25. Jet tomography: path length dependence 30-40 % RAA PHENIX preliminary f Out of plane • Energy loss depends on path length In plane Dave’s QM proceedings https://www.phenix.bnl.gov/WWW/p/draft/winter/QM2005/Proceedings/ Jiangyong Jia

  26. Surface Emission Picture side view front view Jiangyong Jia

  27. Surface Emission Picture side view The detected high pT particles comes mainly from the surface region The away side jet is quenched by the medium The measured rate is ~ surface volume front view Jiangyong Jia

  28. Jet quenching papers • Measurements: • Discovery paper: PRL. 88, 022301 (2002) • Systematic studies: PRL. 91, 072301 (2003),  PRC 69, 034910 (2004) • Comparison with dAu: Phys. Rev. Lett. 91, 072303 (2003) • Non suppression of direct photons: Phys. Rev. Lett. 94, 232301 (2005) • QM 05 proceedings. • Theories • BDMS : hep-ph/0106347. • X.N. Wang, M. Gulassy, I. Vitev, nucl-th/0302077. • U. A. Wiedemann: hep-ph/0402251, hep-ph/0406319 . • Related: CGC, hadronic energy loss, heavy flavor energy loss. Jiangyong Jia

  29. Jets and Hard-scattering Correlate hadrons with leading particles Near side peak: same jet Away side peak: away side jet Df p+p Df hadrons Leading particle hadrons leading particle jet1 jet2 • Establish the method • Cold nuclear modification, jT, kT. xE, Pout distributions • nucl-ex/0510021 nucl-ex/0409024, ppg029 p+p Jiangyong Jia

  30. Evolution of away-side jet shape Intermediate pT high pT nucl-ex/0507004 low pT pT,assoc 0.2 GeV/c nucl-ex/0501016 Moderate high pT 4-6 x 2-4 GeV/c pT,assoc 2 GeV/c Phys. Rev. Lett. 90, (2003) Do we have a (qualitative) picture? Jiangyong Jia

  31. Di-jet correlation at moderate high pT 4-6 x 2-4 GeV/c pT,assoc 2 GeV/c Number of pairs 0º 180º Df • In Au+Au collisions we see only one “jet” at a time ! • Jet quenching! Jiangyong Jia

  32. What happens to the lost energy? Low pT→ Away-side enhancement pT,assoc 0.2 GeV/c Lost energy recovered at low pT Moderate high pT→ Away-side suppression 4-6 x 2-4 GeV/c pT,assoc 2 GeV/c How the medium responds to the jet? Jiangyong Jia

  33. How the medium responds to the jets? • Mach cone/shock wave? • Jets travel faster than the speed of sound in the medium • Create shock wave at: cos(q)=cs/c • QCD “shock wave” Triggering jet 0-5% PHENIX preliminary 2.5-4 x 1-2 GeV/c Other possible mechanisms: Cherenkov radiation, bending jet, Gluon radiation… Jiangyong Jia

  34. Di-jets at high pT:PHENIX PHENIX Near side jet yield is constant with centrality. Clear away side peak Suppression of away-side peak increases with centrality Jiangyong Jia

  35. Di-jets at high pT:STAR Away side yield is suppressed in central collisions But the amount of suppression is independent of pT,assoc for pT,assoc/pT,trig > 0.4 (i.e. large pT,assoc) Small modifications require both jets emitted from surface, results in a tangential emission pattern 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV/c Clear emergence of jet structure at the away-side Away side width consistent with constant Jiangyong Jia

  36. PHENIX: Cu+Cu high pT Jet Correlations Di-jet signal persists even for the most head-on Cu+Cu collisions. May allow better determination of matter properties! Jiangyong Jia

  37. Comparison Au + Au and Cu + Cu • Npart and Ncoll between the two are close • The comparison between the two could provide constrains on the collision geometry dependence of the modification 30-40% Au+Au Npart = 114 0-10% Cu+Cu Npart = 98 Jiangyong Jia

  38. One of the possible picture? Low pT Intermediate pT Moderate high pT high pT Shock wave or cherenkov? Thermallized gluon radiation Punch through jets or tangential contribution? Away jet Trigger and associated pT Jiangyong Jia

  39. The picture High pT trigger hadron selects surface emission. Thus, away side partner has maximum path through the medium. Jiangyong Jia

  40. The picture Jet correlations in proton-proton reactions. Strong back-to-back peaks. Azimuthal Angular Correlations Jiangyong Jia

  41. The picture Jet correlations in proton-proton reactions. Strong back-to-back peaks. Jet correlations in central Gold-Gold. Away side jet disappears for particles pT ~ 2 GeV Jet correlations in central Gold-Gold. Away side jet reappears at lower pT Azimuthal Angular Correlations Jiangyong Jia

  42. The picture Jet energy is transported to the medium along certain directions Some punch through jet might remains Azimuthal Angular Correlations Jiangyong Jia

  43. “Double trigger bias” High pT trigger hadron selects surface emission. Requiring second high pT hadron bias second hadron to surface Because di-jets are back-to-back, both jets has to be tangential. the number of initial di-jets satisfying such condition is significantly reduced. But the away side jet shape can have a peak structure Jiangyong Jia

  44. Much more • Direct photons yield not quenched • Jet quenching is due to energy loss in final state • Charm quarks also are quenched • And show rapid thermalization! • Large charm quark elliptic flow signal • Can only be established at the quark level. • J/Psi is suppressed similar as in SPS! • Large baryon excess for 2 < pT < 5 GeV/c and quark number scaling of elliptic flow. • Hadron formation by quark recombination. • Many of these has been studied as function of collisions system and collision energies • Au+Au @ 62 GeV, Cu+Cu @ 62, 200 GeV • With accurate baseline measurements in p+p and d+Au Full list: https://www.phenix.bnl.gov/WWW/p/talk/papers.php Jiangyong Jia

  45. Summary • We have successfully created “matter” that exhibits bulk thermodynamic properties • Density and temperature exceeds the condition required for QGP formation. • final state particle flavor compositions consistent with “freeze-out” from chemically equilibrated system • Collective behavior well described by hydrodynamics • Strongly interacting fluid with small viscosity: sQGP • Remarkable properties of the “matter” revealed with high pT particle (i.e. jet) rate and di-jet correlation. • Strong suppression of single particle rate : jet quenching @ RHIC • Suppression consistent with energy-loss calculations. • Which requires ~ 100x energy density of normal nuclei • Di-jet correlation reveals complicated interaction between jet and medium in central Au+Au • Away side jet quenched, it’s lost energy create low pT particles, and also used to excite shock wave in the medium. Jiangyong Jia

  46. It’s In The News

  47. What happens to photons in the Medium? Jet g Sometimes a high energy prompt photon is created in the collision. We expect it to pass through the plasma without pause. Produced in hard scattering processes But, no final-state effects, emitted from the whole region Jiangyong Jia

  48. The production rate is known Well described in Proton-Proton reactions by NLO Perturbative QCD. Jiangyong Jia

  49. PHENIX: Au+Au direct photon Results Quarks and gluons disappear into medium, except consistent with surface emission. High-pT hadron suppression must be due to jet quenching (from quark and gluon jets) Scaling of photons shows excellent calibrated probe. Calculations of hard scattering rates in A+A collisions OK Survival Probability Jiangyong Jia

  50. Collision Geometry Impact parameter b Spectators Participants Spectators • Key quantities • Impact parameter: b • Number of participating nucleons: Npart • Number of binary nucleon-nucleon collisions: Ncoll • Small b ~ large Npart, Ncoll ~ more particles • Express impact parameter b in terms of “centrality” • Total cross section 4pR2. • 0-10% most central: [0, b], where pb2 / 4pR2 =0.1 • Connection to yield or probability of physics process • Soft process (large cross section) ~ Npart • Hard process (small cross section) ~ Ncoll Jiangyong Jia

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