Transcript Document
Recent advances from the STAR Experiment Highlights from Inclusive hadron spectra & Azimuthal correlations X Mexican School of Particles and Fields Playa del Cármen, México November 2, 2002 Manuel Calderón de la Barca Outline Heavy Ion Physics and QCD STAR experiment at RHIC Measurement highlights of interest to High Energy Case I : Inclusive charged hadron spectra Case II: Azimuthal anisotropy Case III: Two-particle correlations Conclusions X MSPF 2/Nov/2002 Manuel Calderón de la Barca Heavy Ions: How does nuclear matter look at high temperature? e ~ 1-3 GeV/fm3 X MSPF 2/Nov/2002 High Density QCD Matter in Laboratory Determine its properties QCD Prediction: Phase Transitions Deconfinement to Q-G Plasma Chiral symmetry restoration Relevance to other research areas? Quark-hadron phase transition in early Universe Cores of dense stars High density QCD Manuel Calderón de la Barca The Relativistic Heavy Ion Collider BRAHMS PHOBOS RHIC Two Superconducting Rings PHENIX STAR Ions: A = 1 ~ 200, pp, pA, AA, AB Design Performance Au + Au p+p Max snn 200 GeV 500 GeV L [cm-2 s -1 ] 2 x 1026 1.4 x 1031 Interaction rates X MSPF 2/Nov/2002 3 s -1 1.4 x 10 Manuel Calderón de la Barca 6 x 105 s -1 The STAR Experiment X MSPF 2/Nov/2002 Manuel Calderón de la Barca Detector components in STAR 1st year detectors (2000) 2nd year detectors Magnet 3rd year detectors Time Projection Chamber Coils Silicon Silicon Vertex Strip Tracker Detector Forward Time Projection Chambers Zero Degree Calorimeter Vertex Position Detectors TPC Endcap & MWPC Photon Multiplicity Detector Endcap Calorimeter Barrel EM Calorimeter Central Trigger Barrel + TOF patch RICH X MSPF 2/Nov/2002 Manuel Calderón de la Barca Focus on high pt We know very little about early time Au+Au collisions to study strongly interacting matter under extreme conditions Large momentum transfers early time scales Use high pt jet phenomena as probe of medium Hard scattering has been done… but not in hot medium Measurement of fragmentation products insight into gluon density1 X MSPF 2/Nov/2002 [1] R. Baier, D. Schiff, and B. G. Zakharov, Annu. Rev Part. Sci. 50, 37 (2000). Manuel Calderón de la Barca Centrality and Participants in HI Npart (Wounded Nucleons) ~ soft production spectators Nbin ~ hard processes Preliminary sNN = 200 GeV peripheral (grazing shot) participants Uncorrected Centrality classes based on mid-rapidity multiplicity X MSPF 2/Nov/2002 central (head-on) collision Manuel Calderón de la Barca Case I : Leading hadron suppression Wang and Gyulassy: DE softening of fragmentation suppression of leading hadron yield Ivan Vitev, QM02 d 2 N AA / dpT d RAA ( pT ) TAAd 2 NN / dpT d -X MSPF 2/Nov/2002 Manuel Calderón de la Barca High pT hadrons in Au+Au STAR Preliminary (nucl-ex/0206011, PRL in press) X MSPF 2/Nov/2002 Manuel Calderón de la Barca Inclusive charged hadron suppression 130 GeV normalized to NN centrality dependence 130 and 200 GeV, Central/peripheral Preliminary Clear evidence for high pT hadron suppression in central collisions significant nuclear interactions to very high pT Now seen by all 4 RHIC collaborations (BRAHMS, PHENIX, PHOBOS, STAR) X MSPF 2/Nov/2002 Manuel Calderón de la Barca Case II: Azimuthal Anisotropy, or “Elliptic Flow” Asymmetry + interactions creates final state azimuthal correlations: lab-plane elliptic flow Geometry: asymmetric initial state STAR Preliminary 130GeV Fourier analysis 1+2v2cos2(lab-plane) X MSPF 2/Nov/2002 Manuel Calderón de la Barca Case II: Azimuthal Anisotropy, or “Elliptic Flow” Asymmetry + interactions creates final state azimuthal correlations: lab-plane elliptic flow Geometry: asymmetric initial state STAR Preliminary 130GeV Finite v2 at high pt pT > 2GeV: v2 constant X MSPF 2/Nov/2002 Manuel Calderón de la Barca Method I: Direct Jet Identification jet-jet correlations in p+p? jet-jet correlations in Au+Au? Comparison statistical method X MSPF 2/Nov/2002 Manuel Calderón de la Barca Method II: High pT Correlations Statistical leading particle analysis Histogram in 2-d py px N: D vs. D project d 2 N D , D d D d D : trig , assoc trig ,trig d 2 N D , D 1 1 D D d D Ntrig e d D d D Ntrigger: Total number of trigger particles: (4<pT<6) X MSPF 2/Nov/2002 Manuel Calderón de la Barca Result: Au+Au Distribution Mid-Central Au+Au Harmonic structure Peaks at 0, || Non-zero mean value How do we extract jet signal from background? X MSPF 2/Nov/2002 Manuel Calderón de la Barca Background Subtraction di-jets Flow Combinatorial background All D Resonance decays jets Small D Subtract large D correlations Isolate intra-jet correlations Removes di-jet signal X MSPF 2/Nov/2002 Manuel Calderón de la Barca First Results: STAR 130 GeV 0-10% Most Central Significant peak remains after subtraction Jets?! X MSPF 2/Nov/2002 Manuel Calderón de la Barca Jets at 200 GeV D Near angle persists after large D subtractions X MSPF 2/Nov/2002 Manuel Calderón de la Barca Jets at 200 GeV Shape Clear near & away side signal Same sign correlation Unlikely due to resonance decays D Near angle persists after large D subtractions X MSPF 2/Nov/2002 Manuel Calderón de la Barca Jets at 200 GeV Shape Clear near & away side signal Same sign correlation Unlikely due to resonance decays di-jets in Au+Au? Near angle persists after large D subtractions X MSPF 2/Nov/2002 Manuel Calderón de la Barca D Jet Charge e e uu Measured by DELPHI Well described by LUND string model Expect opposite charge sign between leading, next-to-leading charged particles X MSPF 2/Nov/2002 Manuel Calderón de la Barca Jets at 200 GeV Charge Ordering Fragmentation well described by string model Gaussian fit to near-side: D 0.75 Ratio of Gaussian Yields System opposite/same LUND String 2.6 (0.7) p+p 2.7 (0.9) 0-10% Au+Au 2.5 (0.6) X MSPF 2/Nov/2002 Manuel Calderón de la Barca D Jets at 200 GeV Charge Ordering Fragmentation well described by string model Gaussian fit to near-side: D 0.75 Gaussian Width System opposite same p+p 0.17 (.04) 0.16 (.05) 0-10% AuAu 0.20 (.05) 0.15 (.07) X MSPF 2/Nov/2002 Manuel Calderón de la Barca D What Have we Shown? First direct evidence of jets at RHIC What about di-jets at RHIC? Study away side in Au+Au But… large D subtraction removes away side Need different method to deal with background X MSPF 2/Nov/2002 Manuel Calderón de la Barca Reference Model Incorporate known sources of signal and dominant background D model D pp B 1 2 v22 cos 2D Au+Au correlations: Jets di-jets elliptic flow multiple hardscatterings per event X MSPF 2/Nov/2002 STAR Preliminary 130 GeV Manuel Calderón de la Barca Reference Model Algorithm: D model D pp B 1 2v22 cos 2D Au+Au measurement Background term Fit B in non-jet region 0.75 D 2.25 pp measurement Add p+p to background term X MSPF 2/Nov/2002 Manuel Calderón de la Barca Data Comparison to Ref. Model Absolute scale 4/7 centrality bins Background contribution increases with centrality Other bins qualitatively, quantitatively similar Near side well matched for all centralities X MSPF 2/Nov/2002 Manuel Calderón de la Barca Data Comparison to Ref. Model Away-side suppression Suppression increases with increasing centrality Quantify with centrality: X MSPF 2/Nov/2002 Manuel Calderón de la Barca Quantify with Ratio AuAu = pp + background AuAu - background = pp AuAu - background I 1 pp Au+Au Measurement background AuAu 2 D B 1 2 v D2 2 cos 2D I AA D , D2 d D pp D1 D p+p Measurement X MSPF 2/Nov/2002 Manuel Calderón de la Barca Dissappearance of the Jets from the Far Side I AA Centrality dependent numerator Common denominator AuAu - background pp Sys. errors: v2 +5/-20% Away-side suppression in central Au+Au HIJING model: constant ratio=1 X MSPF 2/Nov/2002 Manuel Calderón de la Barca D D Suppression of away-side jet consistent with strong absorption in bulk, emission dominantly from surface X MSPF 2/Nov/2002 Manuel Calderón de la Barca s dependence (200/130) at high pT Inclusive spectra: growth with s follows pQCD prediction (XN Wang) (systematic uncertainties are correlated – better estimates in progress) v2: independent of s for pT>2 GeV/c Geometric origin of v2 at high pT? Rates change but shape does not. X MSPF 2/Nov/2002 Manuel Calderón de la Barca Away side suppression: open issues Why not 1 for peripheral? Preliminary evidently not due to experimental near side error or uncertainty not due to mismeasured v2: even v2=0 has little effect for most peripheral and central Initial state effects: away side peripheral Shadowing in Au+Au? Nuclear kT: Initial state multiple scattering D Hijing estimate: Maximum 20% effect Resolution: Need to measure in d+Au X MSPF 2/Nov/2002 Manuel Calderón de la Barca central Summary of STAR high pT measurements hadrons at pT>~3 GeV/c are jet fragments central Au+Au: strong suppression of inclusive yield at pT>5 GeV/c suppression factor ~ constant for 5<pT<12 GeV/c large elliptic flow, finite for non-central to pT~6 GeV/c strong suppression of back-to-back hadron pairs Possible interpretation: Hard scattered partons (or their fragments) interact strongly with medium Observed fragments are emitted from the surface of the hot & dense zone created in the collision X MSPF 2/Nov/2002 Manuel Calderón de la Barca ? And back to our original question… If partons absorbed: large DE large gluon But have not yet proven partonic DE: where does absorption occur? •Is it an initial state, partonic effect, or late hadronic effect? • theory input: what are experimental handles to distinguish hadronic from partonic absorption? (e.g. correlation function widths) JETS JETS X MSPF 2/Nov/2002 Manuel Calderón de la Barca Extra Slides X MSPF 2/Nov/2002 Manuel Calderón de la Barca Look for partonic energy loss in dense matter Thick plasma (Baier et al.): DEBDMS 2 Debye qˆ S glue glue Gluon bremsstrahlung Thin plasma (Gyulassy et al.): DEGLV C R s 2 ~ qˆL v 4 2 E jet CR dglue , r Log 2 L 3 S Linear dependence on gluon density glue: • measure DE gluon density at early hot, dense phase High gluon density requires deconfined matter (“indirect” QGP signature) X MSPF 2/Nov/2002 Manuel Calderón de la Barca Future Coming run: 50% of full barrel Electromagnetic Calorimeter • triggers: high tower, ET, jet • jets, 0, g, electrons d+Au: • Cronin effect/nuclear <kT> •enhancement of inclusive yield • suppression of back-to-back pairs • gluon shadowing Long term: • g-jet coincidences (“ultimate” jet energy loss experiment) • heavy quark jets (dead cone effect) • surprises…. X MSPF 2/Nov/2002 Manuel Calderón de la Barca Soft Physics Chemical Freezeout ~ 170 MeV Lattice 160 - 180 MeV Collective motion Large “Elliptic flow” • Large pressure gradients in the system System seems to approach thermodynamic equilibrium Kinetic freezeout ~ 110 MeV Freezeout seems to be very fast, almost explosive X MSPF 2/Nov/2002 Manuel Calderón de la Barca Energy loss in cold matter Wang and Wang, hep-ph/0202105 F. Arleo, hep-ph/0201066 Modification of fragmentation fn in e-A: dE/dx ~ 0.5 GeV/fm for 10 GeV quark X MSPF 2/Nov/2002 x1 Drell-Yan production in -A: dE/dx <0.2 GeV/fm for 50 GeV quark Manuel Calderón de la Barca Inclusive hadron suppression at RHIC Phenix 0: peripheral and central over measured p+p X MSPF 2/Nov/2002 Manuel Calderón de la Barca STAR charged hadrons: central/peripheral v2: comparison to parton cascade Parton cascade (D. Molnar) Detailed agreement if: • 5x minijet multiplicity from HIJING or • 13x pQCD gggg cross section extreme initial densities or very large cross sections X MSPF 2/Nov/2002 Manuel Calderón de la Barca v2: centrality and pT dependence Preliminar y broad plateau, v2 finite at pT~10 GeV/c except for most central collisions significant in-medium interactions to very high pT Shuryak (nucl-th/0112042): plateau exhausts initial spatial anisotropy X MSPF 2/Nov/2002 Manuel Calderón de la Barca Near-angle correlations at high pT • Jet core: D x D ~ 0.5 x 0.5 look at near-side correlations (D~0) of high pT hadron pairs • Complication: elliptic flow • high pT hadrons that are correlated with reaction plane orientation are also correlated with each other (~v22) • but elliptic flow has long range correlation (D > 0.5) • Solution: compare azimuthal correlation functions for D<0.5 and D>0.5 X MSPF 2/Nov/2002 Manuel Calderón de la Barca Non-flow effects? • Non-flow: few particle correlations not related to reaction plane • jets, resonances, momentum conservation,… contrast v2 from reaction plane and higher-order cumulants (Borghini et al.) Preliminary • Non-flow effects are significant • 4th order cumulants consistent with other non-flow estimates • But large finite v2 and saturation persist at high pT X MSPF 2/Nov/2002 Manuel Calderón de la Barca Single Particle Selection 2 pT 6 GeV 0 2 0.7 ln tan 2 0.7 beam X MSPF 2/Nov/2002 0.7 1.4 Manuel Calderón de la Barca Away side suppression and nuclear kT same thresholds for AuAu and pp nuclear <kT>: Preliminary near side enhances near-side in Au+Au suppress away-side in Au+Au similar centrality dependence away side peripheral central Stronger near-side correlation for pTtrig>3 GeV/c than pTtrig>4 GeV/c X MSPF 2/Nov/2002 Manuel Calderón de la Barca Full dataset: 4<pt(trig)<6 GeV/c X MSPF 2/Nov/2002 Manuel Calderón de la Barca Central Au+Au: 6<pT(trigger)<8 GeV/c Stronger signal but limited statistics in non-central bins X MSPF 2/Nov/2002 Manuel Calderón de la Barca Combinatorial Background p+p: 1 hard scattering per event Expect peak at 0, || zero background Au+Au: many hard scatterings per event Expect peak at 0, || Flat, non-zero background X MSPF 2/Nov/2002 Manuel Calderón de la Barca