Correlations for Jet Probes of Quark-Gluon Plasma leading particle hadrons q q hadrons leading particle Olga Evdokimov University of Illinois at Chicago.
Download ReportTranscript Correlations for Jet Probes of Quark-Gluon Plasma leading particle hadrons q q hadrons leading particle Olga Evdokimov University of Illinois at Chicago.
Correlations for Jet Probes of Quark-Gluon Plasma leading particle hadrons q q hadrons leading particle Olga Evdokimov University of Illinois at Chicago (some) RHIC Discoveries Strongly interacting medium with partonic degrees of freedom • Strong collective flow • Constituent number scaling Jet quenching • “Missing” high-pT hadrons • Novel “landscape” in hadron correlations NNPSS 2011 2 R Elliptic Flow Fourier expansion for angular distributions: d 3N 1 d 2N E 3 1 2vn cosn …d p 2 pT dpT dy n1 v2 - elliptic flow Initial state spatial anisotropy Pressure gradient anisotropy Final state momentum anisotropy Elliptic flow is developed at early stage NNPSS 2011 Time 3 Perfect Fluid Hydro model v2(pt) and mass dependence - best described by ideal hydrodynamics! Ideal hydro “Perfect” liquid: equilibrium, zero mean free path, low viscosity Note: strange, multi-strange, charm hadrons -- flow! NNPSS 2011 4 Partonic Degrees of Freedom Pressure gradients converting work into kinetic energy KET m( T 1) mT m Baryons Mesons v2 appears to scale with the number of constituent quarks. Quark coalescence NNPSS 2011 5 Hard Probes for QGP Ideal - use calibrated external probes to study medium properties X-ray Strongly-interacting perfect fluid source with partonic degrees of freedom Courtesy of J. Klay For HI collisions use self-generated (in)medium probes Hard probes (jets)! NNPSS 2011 6 Hard Probes “Hard” == large scale suitable for perturbative QCD calculations Hard parton scattering leading particle hadrons high momentum transfer Q2 high transverse momentum pT high mass m q q hadrons leading particle perturbative Hard probes = PDF pQCD FF non-perturbative non-perturbative Assumptions: Factorization assumed between the perturbative and non-perturbative parts Universal fragmentation and parton distribution functions NNPSS 2011 7 hadrons The reference leading particle q q hadrons p+p→0+X leading particle Simon, private communication S.S. Adler et al, PRL 91 241803 F. Simon p+p→0+X KKP: B. Kniehl, G. Kramer, P¨otter, Nucl. Phys. B597, 337 (2001) AKK: S. Albino, B Kniehl, G. Kramer, arXiv: 0803.2768v2 DSS: D. de Florian, W. Vogelsang, F. Wagner, arXiv: 0708.3060v3 NNPSS 2011 8 Medium properties via jets leading particle Jet Tomography: calibrated (?) probes hadrons What happens if partons traverse a high energy density colored medium? q q Energy loss mechanisms hadrons leading particle Path length effects non-trivial: Flavor/color-charge dependence of parton-medium coupling In-medium fragmentation/ hadronization NNPSS 2011 Hard probes! 9 Define “hard” In pp: inclusive cross-section is dominated by jet production above ~4 GeV/c CDF PRD 65, 072005, 2002. NNPSS 2011 What about RHIC/LHC matter? Probably, > 6GeV/c (but soft part cannot be dropped) 10 QGP101-Jets are quenched PHENIX (2011) @ 200 GeV ALICE PLB 696 30-39 0 Nuclear Modification Factors R AA Jet quenching evident in strong suppression of high pT hadrons Multiple models provide a successful descriptions of the suppression levels Most include radiative and collisional energy loss coll rad rad+coll Fits: G. Qin et al, PRL100:072301, 2008 NNPSS 2011 YieldAA/N binary AA Yieldpp 11 Jets are quenched! How? More differential measurements: Angular di- and multi-hadron correlations hadrons Reconstructed jets q Jet-jet, jet-hadron correlations leading particle q hadrons Outline: leading particle Early di-hadron correlation results Landscape details: “peaks”, “humps” and “ridges” Multi-particle correlations NNPSS 2011 12 HI collisions: the environment Jet Au+Au? Jetevent eventinin ee Data: High multiplicities → background levels → new techniques for jet studies Physics: Strongly-interacting partonic medium → modified jets NNPSS 2011 13 Jets via angular correlations Jet produces high pT particles Select a high pT particle to locate jet, look for correlated hadrons. leading particle “trigger” Measure reference, look for changes: f0 f Same-side Away-side NNPSS 2011 Correlation strength Correlated shapes Associated spectral distributions 14 But… A fly in the ointment – “backgrounds”: many processes would lead to some sort of angular correlations An example: decomposing autocorrelations from p+p: Correlation measure: NNPSS 2011 15 Signal decomposition Triggered di-hadron correlations: Azimuthal pair distribution per trigger: Two-component model: all hadrons come from jet fragmentation + “soft” processes C ( ) C pp B(1 2 vT2 v 2A cos( 2 )) common partonic hard-scattering pairs from all other sources In two-component approach one needs to know only B, and v2(pT) and assume vT v A vT v A 2 NNPSS 2011 2 2 2 16 First results Signature two-particle correlation result: “Disappearance” of the away-side jet in central Au+Au collisions (for associated hadrons pT assoc>2) Effect vanishes in peripheral/d+Au collisions Significant Energy Loss in the Medium PRL 91 (2003) 072304 NNPSS 2011 17 Are there jets? STAR PRL 97 (2006) 162301 d+Au Au+Au 20-40% Au+Au 0-5% 1/Ntrig dN/d(f) 8 < pTtrig < 15 GeV/c, pTassoc>6 GeV/c 4<pT trig<6 GeV/c 2<pT assoc<pT trig Recovering the away side: • Away-side yield suppression • Little modification of the Near-side yields • No broadening on Near- or Away-sides NNPSS 2011 18 High-pT – vacuum fragmentation? STAR PRL 97 (2006) 162301 Near > D h1h2 z T trig T ,p p trig T h1h2 d AA dpTtrig dpT h1 d AA dpTtrig pTassoc zT trig pT Near-side: Away side: NNPSS 2011 No dependence on zT in the measured range – no modification Suppression ~ level of RAA No dependence on zT in the measured range – no modification 19 Di-jets through correlations assoc. trig2 trig1 Use back-to-back (correlated) trigger pairs to pick both sides of a di-jet “2+1” correlations: Trig1 - highest pT in event, 5-10 GeV/c Trig2 - back-to-back with Trig1 pT > 4 GeV/c Associated particles pT > 1.5 GeV/c NNPSS 2011 20 Di-jet correlations 5 < pTTrig1< 10 GeV/c 4 < pTTrig2 < pTTrig1 1.5 < pTAssoc < 10GeV/c STAR K. Kauder QM’09 NNPSS 2011 21 Surface effects in di-jets 200 GeV Au+Au and d+Au same-side STAR PRC (2011) away-side associated particle pT spectra No evidence of medium modifications NNPSS 2011 Di-jets observed - all tangential? 22 Jet modifications: pT 3<pT trig<4 GeV/c 1.0 GeV/c < pT assoc 1.3<pT assoc<1.8GeV/c PHENIX PHENIX PRL 97, 052301 (2006). STAR M. v Leeuwen, Hangzhou ‘06 One high-pT, one low-pT trigger NNPSS 2011 Reappearance of the away-side jet Double-hump structure hints at additional physics phenomena 23 Away side: double-humps trigger trigger Event 1 Event 2 pTtrig=3-4 GeV/c, pTassoc=1-2.5 GeV/c trigger -1 0 1 f Double-humps or shoulders Jet deflection Mach-cone Shock wave Are these features “real”, e.g. jet-related? NNPSS 2011 24 trigger trigger Event 1 Event 2 f2= f2ftrig 3-particle correlation in f Jet deflection 0 trigger f1= f1ftrig f2 0 Mach-cone Shock wave 0 0 NNPSS 2011 f1 25 3-particle f-f correlations STAR PRL 102 52302 (2009) d+Au Au+Au central Experimental observations consistent with jet deflection conical emission (Constrains the speed of sound: qM = 1.37 ± 0.02 ± 0.06 cS ~ 0.2) NNPSS 2011 Closing the chapter? 26 Same-side excess yield PHENIX PRC 78, 014901 (2008) Increasing trigger pT Excess yield on the same-side Away-side “shoulders” magnitude • Is it related to energy loss? • Correlated with same-side excess? NNPSS 2011 Zooming in on the same side27 RHIC Signature Result: the Ridge d+Au Au+Au Near-side correlation structure: Central Au+Au: cone-like + ridge-like Ridge correlated with jet direction Approximately independent of hand trigger pT NNPSS 2011 28 Ridge in AA collisions at LHC Pb+Pb @ 2.76 TeV ptT 4-6, paT 2-4, 0-5% Long-range near-side correlation: Cone-like + ridge-like Ridge correlated with jet direction Approximately independent of h and trigger pT NNPSS 2011 29 Ridge in pair correlations M Daugherity, QM08 Au+Au 200 GeV Low pT ridge evolution 83-94% 55-65% 46-55% 0-5% Long-range near-side correlation in inclusive events NNPSS 2011 30 Transverse momentum scan Zoom in on jets: follow pT evolution pT>0.3 GeV/c pT>1.1 GeV/c pT>0.5 GeV/c STAR Preliminary pT>1.5 GeV/c Unlike-charge-sign pairs from 10% most central 200 GeV Cu+Cu data NNPSS 2011 Low pT elongation evolves into high pT ridge 31 90º Path-length effects in-plane fS=0 0º out-of-plane fS=90o 3<pTtrig<4GeV/c STAR Preliminary Same-side yield Jet: d+Au ~ Au+Au Ridge decreases from in-plane to out-of-plane Flow effects? NNPSS 2011 32 3-particle correlation in h T : Trigger particle A1: First Associated particle A2: Second Associated particle Jet fragmentation in vacuum hA2 h1=hA1-hT h2=hA2-hT In medium radiation + Longitudinal flow hA1 N.Armesto et.al Phys.Rev.Lett. 93(2004) 242301 Transverse flow boost S.A.Voloshin, Phys.Lett.B. 632(2006)490 E.Shuryak, hep-ph:0706.3531 NNPSS 2011 Turbulent color field. A.Majumder et.al Phys. Rev. Lett.99(2004)042301 33 3-particle h-h correlation d+Au 40-80% Au+Au R STAR acceptance 0-12% Au+Au x |h|<1 PRL105 (2010) 22301 No significant structures along the diagonals or axes The ridge is uniform in every event NNPSS 2011 34 Medium response = Energy loss? “Lumpy” initial conditions in individual events, breaks the symmetry NEXSPHERIO Hydrodynamics 1000 event average single event NNPSS 2011 Takahashi, et.al. PRL 103,242301 2009 No parton-medium coupling required Could explain both double-humps (and ridge) 35 Jet-medium interactions or medium flow/fluctuations? How well measured v2 describes the bulk? What about high order Fourier harmonics? v3 v2 Full correlation structure described by Fourier Coefficients v1,v2, v3,v4,v5 * Central events: v2and v3, are comparable, sizable v4 Can describe anything with enough terms vn factorization (?) NNPSS 2011 36 Summary: Hard probes are essential for understanding of QGP properties Angular correlations are powerful experimental tools for such studies Low pT High pT Disappearance of away-side peak in central Au+Au, but not in d+Au ‣ jet quenching discovery ‣ establishing “final” state effect Away-side double-hump structure ‣ mach cone ? ‣ deflected jets ? ‣ medium response/medium? Re-emerging of di-jet signal at higher pT ‣ punch through ? ‣ tangential jets ? Near-side ridge ‣ manifestation of energy loss? ‣ medium response/medium ? NNPSS 2011 How to control biases? How to decompose observed structures? 37 Back Up NNPSS 2011 38 Why QGP? To test and understand QCD: Strong interaction, Confinement, Mass, Chiral symmetry. Few microseconds after the Big Bang the entire Universe was in a QGP state. NNPSS 2011 39 What is QGP? Lattice QCD prediction F. Karsch, hep-lat/0401031 (2004) Nuclear Matter TC~170 8 MeV~1012 K QGP eC~0.5 GeV/fm3~1012 kg/cm3 QGP a thermally equilibrated deconfined quarks and gluons, where color degrees of freedom become manifest over nuclear, rather than nucleonic, volumes. NNPSS 2011 40 Making a Big Bang How to create Quark Gluon Plasma? T ~170 MeV Quark-Gluon Plasma 5-10 NNPSS 2011 r/r0 41 Making a Big Bang to create Quark Gluon Plasma (QGP) – a deconfined state of quarks and gluons T ~170 MeV Quark-Gluon Plasma Heavy Ion Collisions 5-10 NNPSS 2011 r/r0 42 Collision Centrality Number of Participants Impact Parameter Npart = # of participant nucleons Nbin= # of binary collisions centrality NNPSS 2011 (Estimated by Glauber Model) 43 Away-side scan PHENIX PRC 78, 014901 (2008) Associated pT dependence: NNPSS 2011 Recovering the away side Development of “doublehumps” or “shoulders” 44 What is same-side ridge? p+p 7 TeV Jet modified medium? Ridge in high multiplicity p+p at LHC! Ridge pT-spectra and particle ratios are ‘bulk-like’ Ridge diminishes(?) with pTtrig How is it related to jets? NNPSS 2011 45 Low pT ridge M Daugherity, QM08 Low pT ridge evolution 83-94% peak amplitude STAR Preliminary 200 GeV 62 GeV 55-65% 46-55% peak η width STAR Preliminary Transverse particle density NNPSS 2011 0-5% Low pT “ridge” – part of “minijet” peak evolution Sharp transition in both amplitude and width at ρ ~ 2.5 46 Surface effects in di-jets 200 GeV Au+Au and d+Au same-side STAR PRC (2011) away-side associated particle pT spectra No evidence of medium modifications NNPSS 2011 Di-jets observed - all tangential? 47 Misbalanced triggers 8 < ETTrig1< 15 GeV/c 4 < pTTrig2 < 10 GeV/c 1.5 < pTAssoc < 10GeV/c STAR H. Pei DNP’09 NNPSS 2011 48 NNPSS 2011 49 PID for Trigger hadrons Inclusive, raw n < C, pion-depleted sample a. u. n > C, 95% pure pion sample π K P Au+Au NNPSS 2011 0-10% central, Trigger is highest pT track 4 < pT,trigger < 6 GeV/c pt,assoc. > 1.5 GeV/c 50 PID-dependent correlations ± trigger Large jet-like cone, small ridge from pion triggers (P±+K±) trigger Smaller cone, large ridge from P+K triggers Au+Au NNPSS 2011 4 < pT,trigger < 6 GeV/c pt,assoc. > 1.5 GeV/c 51 Projections – Au+Au |h|<1.0 Trigger: ± (P±+K±) Charged h Consistent with previous results – but that is a function of projection range! Does not reveal entire structure Au+Au NNPSS 2011 4 < pT,trigger < 6 GeV/c pt,assoc. > 1.5 GeV/c |f|<0.73 hreveals rich trigger PID dependent structure: Higher jet-like amplitude for pions Ridge predominantly contributed by nonpion-triggered events 52 4 < pT,trigger < 6 GeV/c pt,assoc. > 1.5 GeV/c Raw PID Correlations Large h: Ridge difference evident in raw correlations. Not reconcilable with symmetric backgrounds. Before background subtraction Full h range: Difference in awayside structures. Au+Au 0.7<|h|<1.5 d+Au MB NNPSS 2011 Trigger: ± (P±+K±) Charged h Au+Au 0 <|h|<1.5 53