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The STAR Experiment at RHIC: What have we learnt so far?

The STAR Experiment at RHIC: What have we learnt so far?. Relativistic Heavy-Ion Physics RHIC The STAR Detector Results on Inclusive Particle Spectra and Ratios HBT and Elliptic Flow Hard Probes Summary. Stony Brook, NY April 10, 2001. Of cross-disciplinary interest:.

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The STAR Experiment at RHIC: What have we learnt so far?

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  1. Thomas Ullrich

  2. The STAR Experiment at RHIC:What have we learnt so far? Relativistic Heavy-Ion Physics RHIC The STAR Detector Results on InclusiveParticle Spectra and Ratios HBT and Elliptic Flow Hard Probes Summary Stony Brook, NY April 10, 2001

  3. Of cross-disciplinary interest: early universe “NM EOS” Collective Nuclear Phenomena Effects of the Nuclear Medium Nuclear Physics 250 quark-gluon plasma 200 “NM EOS - Matter Incompressibility” Neutron Star Stability Supernova Expansion Dynamics Astrophysics SPS Chemical Temperature Tch [MeV] 150 AGS Lattice QCD deconfinement chiral restauration 100 “QCD Phase Transition” Evolution of Early Universe Cosmology SIS hadron gas 50 atomic nuclei “Perturbative QCD Vacuum” High (Energy) Density QCD Symmetry Breaking Mechanisms Particle Physics 0 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV] Motivation for Relativistic Heavy Ion Collisions • “To understand the Equation of State of Nuclear, Hadronic & Partonic Matter” neutron stars Thomas Ullrich

  4. Temperature Since the Big Bang Thomas Ullrich

  5. beam   beam Space-Time Evolution W.A. Zajc

  6. “In high-energy physics we have concentrated on experiments in which we distribute a higher and higher amount of energy into a region with smaller and smaller dimensions. In order to study the question of ‘vacuum’, we must turn to a different direction; we should investigate some ‘bulk’ phenomena by distributing high energy over a relatively large volume.” T.D. Lee (Nobel Laureate) Rev. Mod. Phys. 47 (1975) 267. Thomas Ullrich

  7. Relativistic Heavy Ion Physics: Soft and Hard QCD is the strangest of all theories. On one hand, it is beyond any doubt the microscopic theory of the hadron world. On the other hand it has a split personality. It embodies “hard” and “soft” physics, both being hard subjects, but the softer is the harder. Y.L. Dokshitzer, 1998 • From Soft to Hard: • AGS/BNL p, Si to Au beams @ Ebeam = 11 - 14 GeV/u, s ~ 5 GeV for Au+Au • SPS/CERN p, O, S, Pb beams @ Ebeam = 60 – 200 GeV/u , s ~ 17 GeV for Pb+Pb • RHIC/BNL p to Au, s = 17 – 500 GeV, s = 200 GeV for Au+Au • LHC/CERN s = 5.5 TeV for Pb+Pb Thomas Ullrich

  8. RHIC 9 GeV/u Q = +79 U-line BAF (NASA) m g-2 High Int. Proton Source LINAC BOOSTER Pol. Proton Source HEP/NP AGS 1 MeV/u Q = +32 TANDEMS Relativistic Heavy Ion Collider Facility PHOBOS BRAHMS STAR PHENIX Design Parameters: Beam Energy = 100 GeV/u No. Bunches = 57 No. Ions /Bunch = 1  109 Tstore = 10 hours Lave = 2  1026 cm-2 sec-1 Thomas Ullrich

  9. Relativistic Heavy Ion Collider (RHIC) PHOBOS BRAHMS PHENIX STAR • Two concentric superconducting rings • Van de Graaff -> Booster -> AGS -> RHIC • Ions from A ~ 200 (Au) to protons, pA, AA, AB • Polarized-protons • Six interaction regions (with 4 detectors) • First Run: June - Sept. 2000 PerformanceAu + Aup + p Max snn 200 GeV 500 GeV L [cm-2 s -1 ] 2 x 10261.4 x 1031 Interaction rates 1.4 x 103 s -1 3 x 105 s -1 Performance (Summer 2000) Au + Au snn 130 GeV L [cm-2 s -1 ] ~ 2 x 1025Interaction rates ~ 1 x 102 s -1 Thomas Ullrich

  10. Silicon Vertex Tracker Coils Magnet EM Cal Time Projection Chamber Trigger Barrel & Time of Flight Patch Ring Imaging Cerenkov Detector Electronics Platforms Forward Time Projection Chamber The STAR Detector at RHIC “Large acceptance hadronic detector” Thomas Ullrich

  11. Time Projection Chamber Thomas Ullrich

  12. Ring Imaging Cherenkov Counter • Inclusive PID for K//p • 1-3 GeV/c for K and p • 1.5-5 GeV/c for p • C6F14 Liquid Radiator • CsI Photo Cathode • MWPC with 16,000 Pads Kp High pt Physics Thomas Ullrich

  13. Trigger Au Au Zero-Degree Calorimeter (ZDC East) Zero-Degree Calorimeter (ZDC West) Central Trigger Barrel (CTB) L0 trigger: initial event acceptance (ZDC  CTB) L1 and L2: not used (designed for topology, more complex algorithms) L3 trigger: fast online event reconstruction on processor farm (30 Hz) Thomas Ullrich

  14. nch - number of primary tracks in |h| < 0.75 ~ 90% of all hadronic Au+Au interactions Reconstructed vertex events 5% Central central collisions  Geometry Trigger and Multiplicity Cuts Data Summer 2000  2.0 M total trigger events taken, 844 K central (top 15%)  331 K good (top 5%) central for physics analysis  458 K good min bias events for physics analysis Thomas Ullrich

  15. Particle ID Techniques - dE/dx & RICH dE/dx s (dE/dx) = .08 RICH dE/dx PID range: p  ~ 0.7 GeV/c for K/  ~ 1.0 GeV/c for p/p RICH PID range for K//p 1 - 3 GeV/c for K/ 1.5 - 5 GeV/c for p/p Thomas Ullrich M. Horsley, B. Lasiuk & J. Dunlop (Yale) M. Calderon (Yale)

  16. X+ Particle ID Techniques - Topology topology Decay vertices Ks p + + p - L  p + p - L  p + p + X - L + p - X +L + p + W  L + K - L Vo “kinks”: K  +  Thomas Ullrich

  17. K* combine all K+ and p- Combinatorics pairs (x 10-5) Ks p + + p - f  K + + K - L  p + p - L  p + p + [ r  p + + p -] [D  p + p -] f from K+ K- pairs dn/dm m inv (GeV) background subtracted Breit-Wigner fit Mass & width consistent w. PDG m inv dn/dm K+ K- pairs same event dist. mixed event dist. m inv Particle ID Techniques Combinatorics Z. Xu (Yale) central collisions Thomas Ullrich

  18. Strange Particle Decay Firsts So Far in Thomas Ullrich

  19. mt - slopes vs mass Increased transverse flow at RHIC? SPS fit Thomas Ullrich

  20. Y X XZ-plane - the reaction plane P.F. Kolb, et al, (QM99) Elliptic Flow - A Sensitive Probe of Early Dynamics Elliptic flow measures:  response of the system to early pressure  the system’s ability to convert original spatial anisotropy into momentum anisotropy • Elliptic flow predictions from hydro/transport models • sensitive to early dynamics of initial system Thomas Ullrich

  21. Hydrodynamic Calculation of Elliptic Flow P. Kolb, J. Sollfrank, and U. Heinz Equal energy density lines Thomas Ullrich

  22. Azimuthal Asymmetries in Non-Central Collisions P. Jacobs and G. Cooper, nucl-ex/0008015 Almond shape overlap region in coordinate space Momentum space Thomas Ullrich

  23. data Hydro central collisions  Elliptic Flow - Centrality Dependence Elliptic flow of charged particles in STAR v2: 2nd Fourier harmonic coefficient of azimuthal distribution of particles with respect to the reaction plane STAR, PRL 86 (2001) 402 0.1 < pt < 2.0 h < 1.3 Thomas Ullrich

  24. Elliptic Flow Excitation function STAR, PRL 86 (2001) 402 RHIC CERN SPS BNL AGS Thomas Ullrich

  25. schematic view of jet production hadrons leading particle q q hadrons leading particle High Transverse Momentum at RHIC • New opportunity using Heavy Ions at RHICHard Parton Scattering • sNN = 130 GeV at RHIC (17 GeV at CERN SPS) • Jets and mini-jets • ~30-50 % of particle production • high pt leading particles • azimuthal correlations • Extend into perturbative regime • Calculations reliable (?) • Scattered partons propagate through matter • radiate energy (dE/dx ~ x2) in colored medium • interaction of parton with partonic matter • suppression of high pt particles “jet quenching” • suppression of angular correlation Vacuum QGP Thomas Ullrich

  26. Inclusive pt-distributions in p-p Well Known • Data available over wide range of s = 20 - 2000 GeV, but not for 130 GeV ! • Good power law fits: • pp = d2N/dpt2 = A (p0+pt)-n • interpolate A, p0, n to 130 GeV A.Dress QM01 Thomas Ullrich

  27. Negative Hadrons: pt - distributions Power Law A (1 + pt /p0) - n p0 = 2.74 ± 0.11 GeV/c n = 13.65 ± 0.42 STAR <pt> = 0.514 ± 0.012 GeV/c horizontal error bars indicate bin width NA49 <pt> = 0.414 ± 0.004 GeV/c UA1 <pt> = 0.392 ± 0.003 GeV/c h- |h| < 0.1 Preliminary Thomas Ullrich

  28. STAR Preliminary Negative Hadrons: Compare topp pt - distributions • “Hard” Scaling • Binary collisions • Nuclear Overlap Integral • TAA = 26 ± 2 mb-1 • NAA / Npp= Nbin coll = 1050 • “Soft” Scaling • Wounded nucleon • NAA / Npp= ( 344 / 2 ) • Statistical errors negligible • Errors on points: • systematic error on STAR data • Gray bars: cumulative • error including UA1 scaling Thomas Ullrich

  29. AA AA 4 Comparing CERN-SPS Pb-Pb to p-p • RAA exhibits amplified Cronin Enhancement at SPS energies • RAA» (RpA ) 2 • Parton energy loss, if any, is overwhelmed • by initial state soft multiple collisions at SPS! Thomas Ullrich

  30. f Azimuthal Anisotropy • Anisotropy in geometry: • Anisotropy in jet quenching: • hydro valid up to some pt • without dE/dx v2  0 • with finite dE/dx anisotropy in geometry  v2 > 0 nucl-th/0009019 X.Y. Wang path lenght  Thomas Ullrich

  31. Azimuthal anisotropy • at low pT provides • control of geometry • Different pathlength • as function of f • leads to f anisotropy • from partonic energy loss f Partonic Energy Loss Predictions: Azimuthal Anisotropy Thomas Ullrich

  32. Charged Particle Anisotropy • STAR data: only statistical errors plotted. Systematic error 10% - 20% for pt = 2 – 4.5 GeV/c • Hydro + hard scattering: M. Gyulassy, I. Vitev and • X.N. Wang, nucl-th/00012092, PRL • Azimuthal angular correlation measured by v2: • hydrodynamic behavior up to ~1.5 GeV • followed by saturation Thomas Ullrich

  33. Comparison of Measued pt Distributions with Theory • calculation compatible with • anisotropy measurement • and pt - spectra Hydro + hard scattering: M. Gyulassy, I. Vitev and X.N. Wang, nucl-th/00012092 Thomas Ullrich

  34. Chemical Freeze-out Temperature and Chemical Equilibrium ? • Statistical Model: • Assume: • thermally and chemically equilibrated fireball at hadro-chemical freeze-out • law of mass action is applicable !!! • Recipe: • grand canonical ensemble to describe partition function  density of particles of species i • fixed by constraints: Volume V, , strangeness chemical potentialS,isospin • input: measured particle ratios • output: temperature T and baryo-chemical potential B Thermal fit to preliminary data (here D. Magestro, PBM, JS): Not a 4-yields fit !!! 2  1.14 Compare to QCD on Lattice: Tc = 154±8 MeV (Nf=3) Tc = 173±8 MeV (Nf=2) (ref. Karsch QM01) Thomas Ullrich

  35. early universe 250 RHIC/STAR data quark-gluon plasma 200 SPS AGS Lattice QCD deconfinement chiral restauration 150 Chemical Temperature Tch [MeV] thermal freeze-out 100 SIS hadron gas 50 neutron stars atomic nuclei 0 200 400 600 800 1000 1200 0 Baryonic Potential B [MeV] Chemical Freeze-out Thomas Ullrich

  36. Hidden Strangeness:   K+K- • Pb+Pb or Au+Au • pp preliminary Less radial flow ! preliminary preliminary preliminary Thomas Ullrich

  37. Elliptic Flow: Identified Particles preliminary Thomas Ullrich

  38. Conclusions • STAR Detectors (TPC, RICH, Triggers) worked well to specifications • Mapping out “Soft Physics” Regime • Very small net-baryon density but still  0 at mid-rapidity! ( y = y0-ybeam ~ 5 ) • Models suggest for chemical parameters Tch (RHIC) = 175 GeV Tch (SPS/AGS) = 0.17 GeV B (RHIC) = 50 MeV <<B (SPS/AGS) • Kinetic parameters ßr (RHIC) = 0.6c  ßr (SPS/AGS) = 0.4-0.5c Tfo (RHIC) = 100-120 MeV  Tfo (SPS/AGS) = 120 -140 GeV • Unexpected small HBT radii (or maybe not) • Strong radial and elliptic flow • Pion phase-space density at freeze-out seems to be universal • Promising results from “Hard Physics” • pt spectra from central collisions show clear deviation from p-p extrapolation • high-pt data are consistent with “jet quenching” predictions ! More than we hoped for so shortly after startup … Thomas Ullrich

  39. Outlook • Upcoming Run (FY01/FY02): • Starts in May/June • Hope to reach design luminosity • 12 weeks Au+Au @ sNN = 200 GeV • 5 weeks polarized pp @ s= 200 GeV • Vary species and energy … • … until February/March • STAR getting closer to its final design configuration • Inner Tracker (3 layer SDD) • East and West Foeward TPCs • 20% barrel EMC • ToF patch • New Physics • Rare multi-strange baryons () • High-pt, jets, ° Thomas Ullrich

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