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High p T Charged Hadron Suppression at  s =200 GeV

High p T Charged Hadron Suppression at  s =200 GeV. Jiangyong Jia State University of New York at Stony Brook. Introduction Detectors Charged hadron analysis Background Correction High p T Results and Discussion Charged Hadron Spectra and Suppression

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High p T Charged Hadron Suppression at  s =200 GeV

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  1. High pT Charged Hadron Suppression at s =200 GeV Jiangyong Jia State University of New York at Stony Brook • Introduction • Detectors • Charged hadron analysis • Background • Correction • High pT Results and Discussion • Charged Hadron Spectra and Suppression • d-Au results: Suppression is Final State Effect • Details of the Suppression Patterns • Collision Geometry and Jet absorption • Summary and outlook

  2. Quark Gluon Plasma RHIC • Achieve in the laboratory by colliding heavy-ions • Relativistic Heavy Ion Collider at BNL • Estimate from measured transverse energy ET Formation time t0 = 0.3-1fm/c  i ~ 5 - 15 GeV/fm3 Tc ~ 250-350 MeV • QCD coupling constant is “asymptotically free” • as 0 as r  0 • Lattice QCD predicts a deconfined phase • Quarks and gluons are freed Quark Gluon Plasma • TC ~ 155-175 MeV eC ~ 0.3-1.0 GeV/fm3 • How can we confirm the existence and study the properties of QGP?

  3. The Experimental Probe for QGP proton proton p+p->p0 + X s= 200 GeV schematic view of jet production hadrons leading particle • Jet dominate pT>2 GeV/c • Calibrated probe: Jet cross section can be calculated in pQCD for nucleon-nucleon collisions q q hadrons leading particle • Use Hard Scattering or “Jets” as the probe • Example : p—p collisions

  4. Calibrated probe • Incoming quarks and gluons (a,b) • described by Parton Distribution Function • PDF deduced from experimental data • Scatter with large momentum transfer“Hard scattering” and create c,d • Early in the collision (t ~ 1/Q2) • With large momentum (jets) • Calculable in pQCD • c,d fragment and create hadrons • Fragmentation functions from data • Fragmentation Theorem AB hXfa/A(xa,Q2a)fb/B(xb,Q2b) a b cdDh/c(zc,Q2c)

  5. Medium Modification of Jets jet production in quark matter jet production in quark matter hadrons hadrons leading particle leading particle q q • Created early t0~1/E~0.2fm/c for 1 GeV parton • Experience the full time scale of the medium • Strongly interact and lose significant amount of energy (~ GeV/fm) • Attenuation or absorption of jets “jet quenching” q q hadrons leading particle • Suppression of high pT hadrons • By definition, processes that scale with Nbinary will produce RAA=1. Participants • Initial production rate is proportional to the number of independent binary nucleon nucleon collisions Nbinary spectators A A

  6. High pT suppression at s=130 GeV • Detailed pT and centrality dependence of charged hadrons • PLB 561 (2003) 82 • Peripheral RAA 1 • Central RAA saturates ~ 0.6 at pT >2GeV/C • First observation of high pT hadron suppression in Au-Au at s = 130 GeV • PHENIX collaboration PRL 88 (2002) 22301 130GeV PHENIX More statistics from RUN-2. Higher in pT and more detailed centrality dependence

  7. Pioneering High Energy Nuclear Interaction eXperiment (PHENIX)@Relativistic Heavy Ion Collider (RHIC) • 2 counter-circulating rings, 3.8 km circumference • Any nucleus on any other. • Top energies (each beam): • 100 GeV/nucleon Au-Au. • 250 GeV polarized p-p. • Maximal Set of Observables • Photons, Electrons, Muons, ID-hadrons • Highly Selective Triggering • High Rate Capability. • Rare Processes.

  8. PHENIX Setup for Au-Au at s = 200 GeV in Year 2001 • Trigger and Centrality • Beam-Beam Counters:BBC 3.0<|h|<3.9, = 2 • Zero-Degree Calorimeters: ZDC • |h| > 6, |Z|=18.25 m Charged particle Tracking • ||<0.35, = Drift Chamber :DC • RDC = 2-2.4 m • Pad Chamber 1:PC1 • RPC1 = 2.4 m Background Rejection and Subtraction Pad Chamber 2:PC2 RPC1 = 4.2 m Pad Chamber 3:PC3 RPC1 = 4.9 m Ring Image Cerenkov Detector:RICH RRICH = 2.5-4.1 m

  9. Centrality Selection Define centrality classes: ZDC vs BBC EZDC b • Centrality classes defined by cut on the BBC_Q and ZDC_E • Extract Npart, Ncoll from Glauber model simulation QBBC 15-20% 10-15% 5-10% 0-5% 0-5% • BBC charge is  participants • ZDC energy is sensitive to spectators. 27 million minimum bias events used

  10. Track reconstruction by DC-PC1 y r x • PC1 hits combined with the collision vertex fix the polar angle q. • Measured momentum resolution is r 0 z • Drift Chamber measure trajectory in (x,y) plane • Give the bending angle a after magnetic field

  11. Backgrounds in Charged Hadron measurement • Backgrounds include • e+/e- from conversion of g in materials • Weak decays, mostly K± • These tracks have small a, consequently large apparent pT • Tracks with matching cut at PC2 and PC3 • Overwhelmed by background at high pT

  12. Background under the matching distribution a) Define the shape from a sample of background b) Normalize the background outside the matching window c) Subtract to get the signal Different charge bend in opposite direction • Matching in r-f plane at PC • Plot the residual distribution • Tails are the background • Asymmetric shape due to residual bend • e produce Cerenkov light in RICH, and detected by PMT. • Tracks can be divided into two categories according to RICH response: • NPMT >0 ( e background and high pTp ) • NPMT <0 (decay background and high pT k,p )

  13. Conversion Background Estimate • e background subtraction from the matching distribution • Require NPMT>4 to tag pure electron backgrounds • Normalize electron background and subtract it • Monte-Carlo reproduce the conversion background matching distribution. • Tracks with RICH hit contains both electron background and primary pions • eNPMT follows Poisson distribution with mean of 4.5 • Pions begin to fire RICH at pT >4.8 GeV/c, <NPMT> < 3 at pT <10 GeV/c 6<pT<7GeV/c

  14. Decay Background Estimate • Tracks do not fire RICH (NPMT<0)contains decay background and primary K±,P± • Tracks at pT >10 GeV/c are dominated by decay background • This sample of tracks gives the background matching distribution • For each pTbin, normalize to background in 3-9 s region and subtract • Monte-Carlo reproduce the decay background matching distribution 6<pT<7GeV/c

  15. Signal/background ratio • Signal/All-bg ~ 1 at 7 GeV/c and ~0.3 at 10GeV/c. Signal Conversion Decay Signal/bg

  16. Corrections • Embed single particle into real events to estimate occupancy correction • correction for most central collision is 1.35 ± 6% • pT and centrality dependence factorize • Monte-Carlo simulation of single particles through PHENIX detector • Plateau is given by geometrical acceptance and efficiency • yellow band show the systematic error • At high pT dominated by background subtraction

  17. Charged hadron spectra and evolution • Ratio of each centrality to minimum bias spectra • Peripheral  central Concave  Convex • High pT shape is almost centrality independent • pT spectra out to 10 GeV/c • Characteristic power-law tail “Central” Nuclear Physics Particle Physics “Peripheral”

  18. Suppression of charged hadron in Central collisions • Peripheral RAA ~ 1 • Consistent with hard-scattering • Central RAA suppressed by factor of 4.5 *

  19. Suppression: An Initial State Effect? xG(x,Q2) x QS • Multiple elastic scatterings (Cronin effect) • Wang, Kopeliovich, Levai, Accardi • Nuclear enhancement observed in pA and AA at lower energies • Nuclear shadowing • Relevant for x<0.01 • Not reached at RHIC • Gluon Saturation (CGC) • Wavefunction of low x gluons overlap; Gluon fusion ggg saturates the density of gluons in the initial state. (gets Nch right!) Broaden pT : Gribov, Levin, Ryshkin, Mueller, Qiu, Kharzeev, McLerran, Venugopalan, Balitsky, Kovchegov, Kovner, Iancu …

  20. Jet Quenching: A Final State Effect? RdAu~ 0.7 D.Kharzeev et al., hep-ph/0210033 d+Au is the “control” experiment Final state effect: no suppression Initial state effect: suppression Gluon saturation model:: Hadron gas • Hadronic absorption of fragments: • Gallmeister, et al. PRC67,044905(2003) • Fragments formed inside hadronic medium • Energy loss of partons in dense matter • Gyulassy, Wang, Vitev, Baier, Wiedemann…

  21. First d-Au Results from RHIC d-Au control experiment: Initial state effects present in Au nucleus Medium volume too small for jet quenching PHENIX d-Au Result: No suppression of high pt hadron yields Pronounced “Cronin enhancement” RHIC at too high x for shadowing and gluon saturation! *

  22. Centrality Dependence A.Accardi Au + Au Experiment d + Au Control Experiment Different and opposite centrality evolution of Au+Au experiment from d+Au control Centrality dependence is consistent with Cronin effect nucl-ex/0308006 Preliminary Data Jet suppression is clearly a final state effect *

  23. Beam Energy Dependence • Expect xT scaling for hard processes: • Spectrum shape depends only on • Normalization by • Empirically n=6.3 Compilation of neutral pion data

  24. Test xT Scaling for Au-Au • Compare data from 130 and 200 GeV beam energy • Central & peripheral p0 data consistent with n=6.3 • Peripheral h data consistent with n=6.3 • Small deviation for central h data consistent with proton enhancement Expected s dependence for hard scattering processes

  25. Particle Composition: Charged-to-Pion Ratio • Intermediate pT region • h/p centrality dependent • ~ 1.6 for peripheral collisions • Reaches ~ 2.5 for central events Proton enhancement in central collisions • High pT region (pT > 4.5 GeV/c) • h/p ~ 1.6 • Independent of centrality • Same value as found in pp protons hard Particle composition like Jet fragmentation

  26. soft hard Centrality Dependence of Jet Quenching • Hard region: pT > 4.5 GeV/c • Suppression depends on centrality but not on pT • Characteristic features of jet fragmentation independent of centrality • xT scaling • h/p0 constant • pQCD spectral shape Have jet quenching but particle production from jet fragmentation • Soft and intermediate region: pT < 4.5 GeV/c • Extends > 2 GeV/c into pQCD region • Changing particle composition unlike jet fragmentation • pT dependent suppression

  27. Centrality Dependence of Suppression(I) • High pT yield per binary collision: • pT > 4.5 GeV/c • continuous decrease with centrality • Identical for charged hadrons and p0 • peripheral to central factor ~ 4 • High pT yield per participant • pT > 4.5 GeV/c • Initially increases like collision scaling • Decreases above Npart~100 by ~1.5 Approximate participant scaling??? *

  28. Centrality Dependence of Suppression(II) • Hadron yield above 4.5 GeV/c • peripheral data scale with Ncoll • deviation for Npart > 50 Energy loss (B.Mueller, nucl-th/0208038) Energy loss (X.N.Wang,nucl-th/0307036) jet absorption with Woods-Saxon geometry (next) STAR data from nucl-ex/0305015 Jet absorption + nuclear geometry suggested by Bjorken 1982 Surface emission gives approximate Npart scaling: *

  29. Number of hard scattering proportional to collision density rNcoll (x,y) Number of collisions determined from the nuclear overlap Woods-Saxon nuclear density distribution Project into plane transverse to beam and divide by transverse area Peripheral collisions (75-80%) Ncoll ~ 10 very dilute surface rmax<1/fm2 Modeling the Hard Scattering Central collisions (0-5%) Ncoll ~ 1000 rmax~17/fm2 probability of hard scattering  rNcoll (x,y)

  30. Matter density proportional to participant density rNpart (x,y) Number of participants calculated from collision geometry Participant density related to energy density Peripheral collisions (75-80%) Npart ~ 10 rmax<0.7/fm2 Modeling the Matter Density Central collisions (0-5%) Npart ~ 350 rmax~4/fm2

  31. Jet Absorption Picture • Jets are absorbed in dense reaction volume according to: Interpretation: - static source absorption  l • Neglect any pT dependence and jet fragmentation k is the absorption parameter (only free parameter) fix k to give f = 0.22 for central collisions in static limit k corresponds to absorption length l ~ 2.9 fm • Generate dijet isotropicly according to binary collision profile rNcoll(x,y) • Density of matter in transverse plane determined by participant density rNpart(x,y)

  32. Centrality Dependence of High pT Yields • static source absorption  l • static source absorption  l2 • expanding source absorption  l • Compare to jet absorption picture • describes centrality dependence of yield • Not very sensitive to absorption pattern used • Centrality dependence consistent with jet absorption in extremely opaque medium • Centrality dependence of yield reflects mostly collision geometry *

  33. Jet-Jet Azimuthal Correlations(I) f • Back jet are easier to be quenched in medium f • Di-jet are correlated in azimuth direction • Leading particle + angular correlation • Strong near side and far side correlation in p-p collisions

  34. Jet-Jet Azimuthal Correlations (II) • Compare STAR data 4 < pT < 6 GeV/c to absorption picture • by construction, same side jet (Df~0) will always give unity • Away side jet (Df~p) suppression by factor ~ 7 well described by jet absorption and collision geometry • Away side jet have almost factor of 2 more suppression than single hadron suppression, consistent with surface emission Near side centrality dependence of yield reflects mostly collision geometry Away side *

  35. Azimuthal Anisotropy(I) • Centrality dependence of v2 at pT > 4 GeV/c from data • Measured v2 for different methods are quite different • v22-particle-cumulant>= v2BBC-reaction-plane> v24-particle-cumulant • The difference comes from contributions that do not correlate with reaction plane • 4 particle cumulant method is less affected by non-flow contribution In plane • Different direction have different energy loss • Jet are more likely to be emitted in plane than out of plane Out plane

  36. Azimuthal Anisotropy(II) • Comparing to jet absorption calculation • largest v2 from jet absorption picture 5-10% • 1 s from v24-particle-cumulant • Sensitive to the energy loss assumption and dynamic evolution of the medium

  37. Nuclear profile dependence • However, it misses the centrality dependence of the suppression • Woods-Saxon matter density has defuse surface • v2 increase by using hard sphere or cylindrical nuclear geometry • May imply that the medium has a different shape other than Woods-Saxon

  38. Summary • Charged hadron pT spectra measured out to 10 GeV/c with bg rejection • Rich high pT phenomena observed at RHIC Jet quenching well established experimentally • Suppression of high pT hadron yields • d-Au data indicate it is an final state effect • Consistent with jet quenching and surface emission • xT scaling of pion production similar to pp • Particle composition at high pT are like pp • pT >4-5 GeV/c, suppression is ~ constant, spectra shape like pp • Jet absorption picture and collision geometry works reasonably well • Describe general features of jet quenching • Consistent with suppression of hadron yields • Consistent with back-to-back jet correlation • Azimuthal anisotropy described qualitatively

  39. Outlook • Suppression is a well established effect. • What is future of high pT physics? • s dependence SPS s = 17.2 GeV  i =3 GeV/fm3  RHIC s = 200 GeV  i ~ 5 GeV/fm3 where the jet quenching set in? or does it already happen in SPS? • Hadron pT>20 GeV/c At certain pT, jet should penetrate the medium again. • More details on the Jet modification pattern: • RAA for baryon at high pT back-to-back correlation High pT v2 for identified particle Jet absorption

  40. Track reconstruction by DC-PC1 • PC1 hits combined with the collision vertex fix the polar angle q. • Measured momentum resolution is • Drift Chamber provides 12 hits in (x,y) plane. • Give the bending angle a after magnetic field, which provide the initial momentum measurement

  41. y x r-f PC3 PC1 PC2 DC • r-f at PC2 and PC3 are correlated • Define optimized matching variables: D+f and D-f

  42. Nucleon-Nucleon Reference • PHENIX p-p data at 200 GeV • p0 data out to 14 GeV/c • consistent with NLO pQCD calculation • charged hadron results not available yet • Comparison to fit of UA1 data • UA1 data at 200GeV • PHENIX p0 spectra scaled by 1.6(ISR result) • Charged hadron N-N reference • Use p0 data to constrain fit • systematic uncertainty ~ 20%

  43. xT-scaling in pp • Charged hadrons s = 23-1800 GeV • Approximate xT scaling with n = 6.3 • Deviation from xT scaling for pT < 1-2 GeV/c

  44. xT-scaling in pp (II) • Neutral pions s = 39-540 GeV • Approximate xT scaling with n = 6.3 • No data for pT < 1-2 GeV/c

  45. Testing xT scaling with 130 and 200 GeV Au-Au • xT scaling can be used to test pQCD in heavy-ion collisions • Shadowing and gluon saturation is basically a scaling effect • Partonic final state medium effect may or may not scale • Hadron absorption and parton coalesce probably does not scale Scaled by

  46. xT scaling power n from 200/130 ratio n=7.530.180.4 n=6.410.250.49 n=6.330.390.37 n=6.120.330.36 n= ncent-nperi = 1.410.43 proton “enhancement” up to 4 GeV

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