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Paul Constantin Iowa State University

Extraction of Jet Properties via Two-Particle Azimuthal Correlations in pp and AuAu Collisions at s NN =200 GeV. Paul Constantin Iowa State University. Outline. Hadronic Jets as investigation tool of bulk soft QCD states Properties of hadronic jets

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Paul Constantin Iowa State University

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  1. Extraction of Jet Properties via Two-Particle Azimuthal Correlations in pp and AuAu Collisions at sNN=200 GeV Paul Constantin Iowa State University

  2. Outline • Hadronic Jets as investigation tool of bulk soft QCD states • Properties of hadronic jets • High-pT hadron inclusive cross section at RHIC – discovery of jet quenching • Two-hadron azimuthal correlations – detailed study of hadronic jet properties Iowa State University

  3. q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q Quark-Gluon Plasma (QGP) • QCD Lattice - hadronic systems undergo a double phase transition • at TC~150-180 MeV: • deconfined quark&gluon matter (QGP) – long range confining force is screened • chiral symmetry restoration – quarks become massless Iowa State University

  4. 250 200 QGP 150 RHIC Temperature (MeV) SPS deconfinement chiral restauration 100 thermal freeze-out AGS 50 hadron gas SIS nuclei neutron stars 0 0 200 400 600 800 1000 1200 Baryonic Potential B (MeV) QCD Phase Diagram However,the QGP hadronizes very quickly: one can observe only signatures of its existence (jet quenching, J/ suppression, strangeness enhancement, large collective flow, dilepton production, direct photon production, etc.) Iowa State University

  5. Jet event in a hot QCD medium Quenching of Hadronic Jets in QGP Bulk soft QCD particle production from vacuum: dnch/dh|h=0= 670, about 15,000 quarks in the final state and about 1,200 quarks in the initial state: 92% of all quarks are from vacuum ! Jet (hard) QCD particle production : -from partonic hard scattering (primarily gluons); - high-Q2 processes with calculable cross section (S(Q2)<<1) produced early (<1fm); - interact strongly with the bulk QGP:loose energy via gluon radiation  jet quenching Observed via: - leading (high-pT) hadron cross section; - two-hadron azimuthal correlations at high-pT. Iowa State University

  6. proton • power law cross section: proton schematic view of jet production hadrons leading particle q q hadrons leading particle Hadron High pT Cross Section in pp collisions (I) High pT hadron production has been well studied in pp, p and p collisions : • fragmentation of partons from hard scattering; • tends to cluster in phase space forming jets; • has a Q2-independent and universal • fragmentation function D(z), zpThadron/pTparton. Iowa State University

  7. N.A.McCubbin, Rep. Prog. Phys. Vol.44, No.10 (1981) Hadron High pT Cross Section in pp collisions (II) Kourkoumelis et al. Z. Phys.C5(1980)95 n(xT,s)  94 and decreases with both xT and s Iowa State University

  8. High pT Cross Section - pQCD collinear factorization Production yield in hard-scattering regime factorizes in the leading order AB hXfa/A(xa,Q2a)fb/B(xb,Q2b)a b cdDh/c(zc,Q2c) Fragmentation function Parton distribution function Dh/c(zc,Q2c) production probability of hadron h (momentum fraction zc = pTh/pTc) from parton c Iowa State University

  9. semi-classical QCD field • collinear factorization breaks • “analytic” solution Initial State Effects in Nuclear Media • Gluon Saturation (Color Glass Condensate) • Cronin Effect (pT broadening due to multiple scatterings) Iowa State University

  10. Final State Effects in Nuclear Media – Partonic Energy Loss energy loss kT broadening transport coefficient (medium effects) Gyulassy, Wang, Vitev, Levai et al Baier, Dokshitzer, Muller, Peigne, Schiff nontrivial consequence ofnon-abelian nature of QCD Iowa State University

  11. <kTy> Jet Fragments Azimuthal Distribution (I) • Kinematical parameters used to describe dijet events: • parton fragmentation parameters: • parton acoplanarity parameters: Iowa State University

  12. Jet Fragments Azimuthal Distribution (II) Experiment discovered an effect neglected by theory: back-to-back jets are not coplanar! kT properties: increases slowly with both pT and s, increases with the nuclear thickness like A1/3 (Cronin effect) jT-scaling: jT400MeV/c, independent of pT and s Angelis et al. Phys. Lett. B97(1980)163 CCOR collaboration at CERN-ISR Iowa State University

  13. High pT p-p and Au-Au 0 Spectra Run-2 p-p + Au-Au sNN= 200 GeV p-p hep-ex/0304038 Au-Au nucl-ex/0304022 Good agreement with NLO pQCD Iowa State University

  14. at high-pT: RAA > 1 kT-broadening “Cronin” RAA = 1 particle prod.  Nbinary RAA < 1 suppression The Nuclear Modification Factor RAA RAA is a relative yield with respect multiple nucleon-nucleon collisions. If there is no nuclear effect, AA is just incoherent superposition of pp then RAA = 1: nucleon-nucleon cross section Nbinary/sinelp+p Iowa State University

  15. High-pT Suppression in AuAu nucl-ex/0304022 Au-Au nucl-ex/0304022 Strong suppression in central AuAu hadron spectra! Iowa State University

  16. (h++h-)/2 dAu p0 PHENIX preliminary Cronin Effect in dAu If the suppression seen in AuAu is an initial state effect (eg., gluon saturation), it should be seen also in dAu. Cronin is the dominant initial state effect at y=0 at RHIC (x is too high for gluon saturation). The strong suppression in AuAu is a final state effect: hadronic jet quenching! Iowa State University

  17. The Suppressed Spectra xT-scale! 0 xT-scales in both peripheral and central Au+Au with same value of n=6.3 as in p-p Iowa State University

  18. PHENIX Detector • Global Event (vertex position, collision time, centrality, min bias trigger, reaction plane orientation): – Beam-Beam Counters (BB) – Zero Degree Calorimeters (ZDC) • Charged Particle Tracking: • Drift-Chambers (DC) • Pad-Chambers (PC) • Electron Identification • Ring Imaging Cherenkov Detector (RICH) • p0 via p0  gg: • Lead scintillator calorimeter (PbSc) • Lead glass calorimeter (PbGl) Iowa State University

  19. 25-30% 20-25% 15-20% 10-15% 5-10% 0-5% EZDC QBBC Centrality determination • Uses the anti-correlationbetween the • total charge deposited in the BBCs • (prop. to the number of participant • nucleons) and the total neutral energy • deposited in the ZDCs (prop. to the • number of spectator neutrons). • Npart (number of participants) and • Ncoll (number of collisions) via • Glauber model simulations. • AuAu data sample: 27M minimum • bias events • pp data sample: 134M minimum • bias events and 35M ERT triggered • events Iowa State University

  20. vertex PC1 R DC ref  z vertex Charged Hadron Tracking 1) use the vertex position and DC and PC1 hits to reconstruct the charged particles tracks. 2) use knowledge of the magnetic field to derive the kinematics (pT,,) of the particle. 3) require a tight PC3 matching cut to reduce combinatorial background. 4) veto tracks that have a RICH association to reduce conversion electron background. Iowa State University

  21. measured mixed measured/mixed |DC|>50mrad RPC1>10cm DC [rad] measured mixed measured/mixed |zDC|>0.2cm RPC3>15cm zDC [cm] Charged Hadron Pair Cuts At small relative distances/angles, various distortions appear due to detection resolution (hit merging, track splitting, etc.). A mixed event method is used to cut them out. Iowa State University

  22. CARTOON flow+jet flow N A Two-hadron azimuthal correlation function:technique We use the mixed event technique to correct the shape of the  distributions for acceptance and efficiency fluctuations: We then fit with the expected sources: C() = F(1+2V22cos(2))+ GausN(;N)+ GausA(;A) where, of course, v20 in pp and dAu and constant F is fixed by CF normalization. We extract 4 parameters: widths (N, A) and areas (SN, SA). Iowa State University

  23. parton transverse momentum fragmentation transverse momentum p+p p+A A+A away-side near-side Df Jet Shape Parameters jT, kT jTy - independency on pT and s in pp collisions, broadening with centrality if fragmentation is modified in AuAu collisions. kTy- dependency on pT and s in pp collisions, broadening with centrality if partons loose energy via gluon radiation in AuAu collisions. Iowa State University

  24. fraction of pairs in near/away Gaussian total number of pairs acc. and eff. correction for the associated hadron Jet Conditional Yields • Conditional yields: the number of associated hadrons per trigger Near it (=0) or Away from it (=) • Parton Fragmentation function: D(z=pTh/pTq) is the distribution of parton’s momentum among its fragments and should be a universal, Q2-independent function in vacuum. an experimental equivalent is the xE distribution of the away conditional yield with fixed trigger hadron. Iowa State University

  25. 1.0<pT<1.5 3.0<pT<6.0 Two-hadron azimuthal correlation function:pp data Examples of h-h fixed correlation functions (pTtrigg=pT) in pp collisions. Iowa State University

  26. 1/xE  -5.3 1/xE  -5.  0.4 CCOR (ISR) s = 63 GeV - Nucl Phys B209 (1982) pp Data - Parton Fragmentation Function Iowa State University

  27. final state parton distrib. extracted from PHENIX p+p0+X FF D(z) pp Data - <z> Extraction We measured xE and z = xE ztrigg Iowa State University

  28. <z> N ,A |jTy|, |kTy| in pp data PHENIX preliminary |jTy| = 35911 MeV/c |kTy| = 96449 MeV/c PHENIX preliminary Iowa State University

  29. Resonance Decay Contamination Two physical sources of background: pairs of charged particles from resonance decays and conversion electrons. Conversion electrons are vetoed using the RICH. Resonance decay pairs are identified by studying the charge dependence of the widths of the correlation function. Iowa State University

  30. Comparison to world data PHENIX preliminary Apanasevich et al Phys. Rev. D59(1999)074007 Angelis et al (CCOR) Phys. Lett. B97(1980)163 Iowa State University

  31. |kTy| from dAu data Plot provided by N. Grau. No significant kT-broadening seen in dAu data z=0.75 value taken from pp data Iowa State University

  32. y px x thermalization Global Correlations in AuAu – Elliptic Flow AuAu (1.5-3)x(3-5)GeV/c Centrality 60-90% v20.2 • Spatial azimuthal anisotropy in the initial state • pressure gradients  elliptic flow momentum pattern in the final state Iowa State University

  33. The Method of Minimum Jet Amplitude Point (I) The simple fit fails in AuAu correlationsbecause the away Gaussian broadens quickly with centrality and no longer can be distinguished from the cosine modulation (A>V2). The method of minimum jet amplitude point (MJAP) has two steps: 1) Suppose that the dominant contribution to the correlation function at the point min where the jet function (the sum of the two Gaussians) has minimum amplitude is given by the collective “flow” correlations. Extract the magnitude of the cosine modulation V2 with this assumption. 2) Fix V2 to the value extracted at step (1) and fit without assumptions. Assign systematic errors by varying V2 within its error and repeating this step. Iowa State University

  34. The Method of Minimum Jet Amplitude Point (II) Extensive simulations show that the 1st step of the MJAP procedure effectively truncates the away Gaussian parameters once its width becomes equal or larger than ~0.7-0.8 rad. However, the magnitude V2 of the cosine modulation is reliably retrieved. Iowa State University

  35. 1st step 2nd step 2nd step 2nd step Two-hadron azimuthal correlation function: AuAu data Assorted correlation functions with trigger in (3-5)GeV/c and associated hadron in (1.5-3)GeV/c Iowa State University

  36. Results AuAu – Jet Shape Parameters • some amount of truncation is indeed present; • jTy is centrality independent and agrees • with its corresponding value in pp (red • band); • ztrigg·kTy broadens strongly with centrality • In the skin jet emission scenario, which • implies a trigger bias on the fragmentation • part of the correlation function, the above means that kTy broadens strongly with centrality, a final state energy loss signal! 1st step 2nd step Iowa State University

  37. Results AuAu – Jet Conditional Yields 1st step 2nd step near 2nd step A slight increase in the conditional yields with centrality is observed for trigger hadrons in (3-5)GeV/c and associated hadrons in (1.5-3)GeV/c. away Iowa State University

  38. Adams et al., Phys. Rev. Let. 91 (2003) Adler et al., PRL90:082302 (2003), STAR 1/NtriggerdN/d() di-hadron Background subtracted STAR away-side quenching • pp – dijets • dAu – dijets • AuAu peripheral – dijets • AuAu central – monojet! • Near-side agreement • across system size (pp, • dAu, AuAu periph., • AuAu central) • Strong suppression of back-to-back • correlations in central Au+Au Iowa State University

  39. ? STAR STAR away-side quenching Hint of surface emission ? Nucl-ex/0210033 Iowa State University

  40. Summary and Conclusions • In pp collisions, we measured the vacuum fragmentation function, • the jT (which scales with pT and s), and kTy = 964  49 MeV/c; • In AuAu collisions, we found significantkT – broadening with • centrality, while jT is approximately independent on centrality – • skin jet emission with strong broadening of back-to-back partner; • Yield of away side associated hadrons is suppressed at pT>3GeV/c • and shows rising trend with Npart below 3GeV/c. Remnant of high-pT • jets – hint of jet-quenching balance. Iowa State University

  41. Backup Slides Iowa State University

  42. ERT Bias Study Iowa State University

  43. Combinatorial Background Iowa State University

  44. Single hadron correction function Iowa State University

  45. Systematic pp Iowa State University

  46. RHIC The Relativistic Heavy Ion Collider at BNL • Two independent rings 3.83 km in circumference • 120 bunches/ring • 106 ns crossing time • Maximum Energy per N-N collision • s = 500 GeV p-p • s = 200 GeV Au-Au • Design Luminosity • Au-Au 2x1026cm-2s-1 • p - p 2x1032cm-2s-1(polarized) • Full operation started at 2000 and since then: • 3 AuAu runs s = 130 and 200 GeV • 2 polarized pp runs at s = 200 GeV • 1 dAu runat s = 200 GeV Iowa State University

  47. syst. error Away pT distributions on near and away side Away side: energy from initial parton seems to be converted to lower pT particles reminiscent of energy loss predictions Near side: Overall enhancement from pp to AA Apparent modification of the fragmentation function ? Iowa State University

  48. ~z=pTh/pTq Q2-independence of the Fragmentation Function Angelis et al. Phys. Scripta19(1979)116 CCOR collaboration at CERN-ISR Iowa State University

  49. 1 + (g pQCD direct x Ncoll) / gphenix backgrd Vogelsang NLO 1 + (g pQCD direct x Ncoll) / gphenix backgrd Vogelsang, mscale = 0.5, 2.0 1 + (g pQCD direct x Ncoll) / (gphenix pp backgrd x Ncoll) Direct Photon Measurement - Central 0-10% PHENIX Preliminary PbGl / PbSc Combined AuAu 200 GeV Central 0-10% Theory curves include PHENIX gexpected background calculation based on p0: (g direct + gexp. bkgd.) / gexp. bkgd. = 1 + (gdirect/gexp. bkgd.) Iowa State University

  50. Centrality Dependence Au + Au Experiment d + Au Control Final Data Preliminary Data • Dramatically different and opposite centrality evolution of Au+Au experiment from d+Au control. • Jet Suppression is clearly a final state effect. Iowa State University

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