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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?. RHIC The STAR Detector First Run in 2000 Results on Particle Spectra and Ratios HBT Flow High-pt Conclusions. Enrico Fermi Insitute, Chicago, IL Feb 26, 2001. Relativistic Heavy Ion Physics: Soft and Hard.

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

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  1. The STAR Experiment at RHIC:What have we learnt so far? RHIC The STAR Detector First Run in 2000 Results on Particle Spectra and Ratios HBT Flow High-pt Conclusions Enrico Fermi Insitute, Chicago, IL Feb 26, 2001

  2. 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 @ 11 - 14 GeV/u • SPS/CERN p, O, S, Pb beams @ 60 – 200 GeV/u • 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

  3. 2 concentric rings of superconducting magnets 3.8 km circumference counter-rotating beams of ions from p to Au O STAR Long Island RHIC @ Brookhaven National Laboratory Relativistic Heavy Ion Collider h Thomas Ullrich

  4. RHIC – Machine Parameters • L = 2  1026 cm-2 s-1 in Au+Au • L = 1  1031 cm-2 s-1 in pp • L  s Thomas Ullrich

  5. The Collaboration STAR The STAR Collaboration > 400 collaborators 34 institutions 8 countries Brazil: Sao Paolo China: IHEP - Beijing, IPP - Wuhan England: Birmingham France: IReS - Strasbourg, SUBATECH-Nantes Germany: Frankfurt, MPI - Munich Poland: Warsaw University, Warsaw U. of Technology Russia: MEPHI - Moscow, JINR - Dubna, IHEP - Protvino U.S.: Argonne, Berkeley, Brookhaven National Laboratories, UC Berkeley, UC Davis, UCLA, Creighton, Carnegie-Mellon, Indiana, Kent State, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas, Texas A&M, Washington, Wayne, Yale University Thomas Ullrich

  6. STAR Physics Program • Relativistic Heavy Ion Physics • High Density QCD Matter • QCD Deconfinement Phase Transition • Chiral Phase Transition • Polarized Proton-Proton Interactions • Spin Structure of the Nucleon • 2-Photon Physics • Intense EM Fields of Passing Nuclei •  Coherent Source of ’s •  Photon, pomeron, meson interactions Thomas Ullrich

  7. Time Projection Chamber FTPCs (1 +1) Vertex Position Detectors The STAR Detector (Year-by-Year) • Year 2000, year 2001,year-by-year until 2003, installation in 2003 Magnet Coils Silicon Vertex Tracker * TPC Endcap & MWPC ZCal ZCal Endcap Calorimeter Barrel EM Calorimeter Central Trigger Barrel + TOF patch RICH * yr.1 SVT ladder Thomas Ullrich

  8. Au on Au Event at CM Energy ~ 130 A-GeV Peripheral Event From real-time Level 3 display. Thomas Ullrich

  9. Au on Au Event at CM Energy ~ 130 A-GeV Mid-Central Event From real-time Level 3 display. Thomas Ullrich

  10. Au on Au Event at CM Energy ~ 130 A-GeV Central Event From real-time Level 3 display. Thomas Ullrich

  11. Particle ID Techniques - dE/dx & RICH RICH dE/dx s (dE/dx) = .08 protons kaons pions e RICH PID range for K//p 1 - 3 GeV/c for K/ 1.5 - 5 GeV/c for p/p dE/dx PID range: p  ~ 0.7 GeV/c for K/  ~ 1.0 GeV/c for p/p Thomas Ullrich

  12. X+ Particle ID Techniques - 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

  13. K* combine all K+ and p- pairs (x 10-5) 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 Combinatorics Ks p+ + p-f  K+ + K- L  p + p-L  p + p+ Thomas Ullrich

  14. L0 Trigger for Run 2000 Summer 2000 Triggers • “Minimum Bias” ZDC East and West thresholds set to lower edge of single neutron peak. REQUIRE: Coincidence ZDC East and West • “Central” CTB threshold set to upper 15% REQUIRE: Min. Bias + CTB over threshold ~30K Events |Zvtx| < 200 cm Thomas Ullrich

  15. Data Taking: Summer Run 2000 • RHIC Operation: • “rose to the occasion”, great job !!! • reached 10% design luminosity • Magnetic Field: • half field: 0.25 T • Detectors: • TPC (100% uptime), RICH, 1 ladder SVT, ZDC, CTB • Trigger: • L0 & few days L3 ( |z-vertex|<80 cm) • 844k central trigger 15% of geo (331k were 5% of geo) • 761k minimum bias • 20k peripheral () • DAQ: • bandwidth to RCF (~20 MB/s) Thomas Ullrich

  16. Negative Hadrons:  Distribution and Multiplicity dN(h-)/dh = 244  1  16 (pt > 100 MeV/c) dN(h-)/dh = 264  1  18 (extrap. to all pt) h- Increased particle production per participant pair: 43% compared to Pb+Pb @ 17.2 GeV 30% compared to pp @ 200 GeV h- Full efficiency corrections Thomas Ullrich

  17. STAR Preliminary h- NA49 UA1 Power Law A (1+pt /p0) - n h- : pt Distributions and  pt  vs. Centrality h- <pt> increases with centrality For central collisions higher than in pp collisions @ s = 1.8 TeV (CDF) Thomas Ullrich

  18. p and K-: mt Distributions vs. Centrality T = 565  40  50 MeV T = 300  15  30 MeV peripheral  central mt = (m2 + pt2)½ Thomas Ullrich

  19. mid-rapidity Tp = 565 MeV TK = 300 MeV Tp = 190 MeV p , K-, p- Spectra - mt slopes vs. Centrality • Increase with collision centrality •  consistent with radial flow. Thomas Ullrich

  20. Radial Flow: mt - slopes versus mass Naïve: T = Tfreeze-out + m  r 2 where  r  = averaged flow velocity • Increased radial flow at RHIC ßr (RHIC) = 0.6c  ßr (SPS/AGS) = 0.4 - 0.5cTfo (RHIC) = 0.1-0.12 GeV  Tfo (SPS/AGS) = 0.12-0.14 GeV Thomas Ullrich

  21. Particle Rations at RHIC • All ratios for: • Central collisions •  = 0 p/p = 0.6  0.02 (stat.)  0.06 (sys.) / = 0.73 ± 0.03 (stat.) X+/X- = 0.82 ± 0.08 (stat.) K-/K+(kink) = 0.87 ± 0.02(stat.) ± 0.05(sys.) K-/K+(dE/dx) = 0.89±0.008 (stat.) ± 0.05 (sys.) K-/p- =0.15 ± 0.02 (stat.) K*/h-= 0.06 ± 0.06 (stat.)± 0.01 (sys.) K*/h-= 0.058 ± 0.06 (stat.) ± 0.01 (sys.) Thomas Ullrich

  22. _ _ ¯ _ _ _ _ _ Anti-baryon/Baryon Ratios versus s • Baryon-pair production increases with s • Mid-rapidity region • not yet baryon-free! • Pair product is larger than baryon transport • 2/3 of protons from pair production • 1/3 from initial baryon number transported over 5 units of rapidity STAR preliminary Thomas Ullrich

  23. Chemical Fit Results Not a 4-yields fit! s  1 2  1.4 Thermal fit to preliminary data: Tch (RHIC) = 0.19 GeV  Tch (SPS) = 0.17 GeV q (RHIC) = 0.015 GeV << q (SPS) = 0.12-0.14 GeV Thomas Ullrich

  24. 250 200 150 100 50 0 Chemical Freeze-out early universe P. Braun-Munzinger, nucl-ex/0007021 LEP/ SppS RHIC quark-gluon plasma SPS AGS Lattice QCD deconfinement chiral restauration Chemical Temperature Tch [MeV] thermal freeze-out SIS hadron gas neutron stars atomic nuclei 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV] Thomas Ullrich

  25. Two-particle interferometry (HBT) • Correlation function for identical bosons: • C(p1, p2) = P(p1, p2)/ (P(p1) P(p2)) = 1 + |(q)|2 •  : Fourier transform of the density distribution • q = p1 - p2 • Here: Bertsch-Pratt parameterization • C(qout, qside, qlong) = 1 +  exp (qi2 Ri2) • 1d projections of 3d Bertsch-Pratt • 12% most central out of 170k events • Coulomb corrected • |y| < 1, 0.125 < pt < 0.225 qout STAR preliminary qlong STAR preliminary Thomas Ullrich

  26. Pion HBT Excitation Function Compilation of world 3D -HBT parameters as a function of s STAR Preliminary • Central AuAu (PbPb) • Decreasing  parameter • Increased correlation strength • less baryon resonances ? • Saturation in radii • Geometric or dynamic (thermal/flow) saturation • No jump in effective lifetime • No significant rise in size of the  emitting source • Lower energy running needed! Thomas Ullrich

  27. Emission duration for transparent sources: STAR Preliminary The ROut/RSide Ratio Tomášik, Heinz nucl-th/9805016 =0.0 =0.5 opaqueness Small radii + short emission time + opaqueness  short freeze-out Thomas Ullrich

  28. STAR Preliminary Radius Fits STAR NA49 áfBE;flowñ T0=94.3 MeV T0=89.7 MeV áfBE;no flowñ T0=99.5 MeV T0=94.3 MeV T0=89.7 MeV The  Phase Space Density pion occupation of cell in coordinatemomentum space: • “Universal” phase space density observed at SPS appears to hold at RHIC as well • Consistent with thermal distribution (T94MeV) and strong collective flow ( 0.58) • Fundamental phase space saturation may relate increases in geometry, temperature, multiplicity Thomas Ullrich

  29. Elliptic Flow: A schematic view of v2 Origin: spatial anisotropy of the system when created and rescattering of evolving system spatial anisotropy  momentum anisotropy v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane Almond shape overlap region in coordinate space Thomas Ullrich

  30. Hydro Calculation of Elliptic Flow P. Kolb, J. Sollfrank, and U. Heinz Equal energy density lines • Elliptic flow observable sensitive to early evolution of system • Large v2 is an indication of early thermalization Thomas Ullrich

  31. Charged particle v2 versus centrality Hydro Calculations STAR || < 1.3 0.1 < pt < 2.0 PRL 86 (2001) 402 First time in Heavy-Ion Collisions a system created which approaches hydrodynamic model predictions for v2 for mid-central collisions Thomas Ullrich

  32. Identified Particles: Elliptic Flow of Pions and Protons • Hydro calculations: P. Huovinen, P. Kolb and U. Heinz Mass dependence of v2(pt) shows a behavior in agreement with hydro calculations Thomas Ullrich

  33. Elliptic Flow Excitation Function STAR, PRL 86 (2001) 402 Thomas Ullrich

  34. vacuum QGP Hard Probes in Heavy-Ion Collisions • “hard” probes: cc, bb and jets • during formation phase parton scattering processes with large Q2 • create high mass or high momentum objects • penetrate hot and dense matter • sensitive to state of hot and dense matter • a) formation phase • parton scattering • b) hot and dense phase • Quark Gluon Plasma • Hadron Gas • c) freeze-out • emission of hadrons color screening: J/y suppression dE/dx  jet quenching Thomas Ullrich

  35. Results from the SPS Nihard = ipp TAB Npart/Nbin RAA exhibits amplified “Cronin effect” behavior Parton energy loss,if any,is overwhelmed by initial state soft multiple collisions at SPS! Thomas Ullrich

  36. Inclusive pt-Distribution in pp • Data available over wide range of s, but not for 130 GeV Power law: E d3/dp3 = A (1+pt/p0) –n interpolate A, p0, n to 130 GeV Thomas Ullrich

  37. 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 NA49 <pt> = 0.414 ± 0.004 GeV/c UA1 <pt> = 0.392 ± 0.003 GeV/c STAR preliminary Thomas Ullrich

  38. Au+Au/pp: Compare pt - distributions • “Hard” Scaling • Nuclear Overlap Integral • TAA = 26 mb-1 for 5% most central • NAA / Npp= Nbin coll = 1050 • “Soft” Scaling • NAA / Npp= ( 344 / 2 ) STAR preliminary Jet Quenching: First hint for QGP formation at RHIC ? Thomas Ullrich

  39. v2(pt) for high pt particles M. Gyulassy, I. Vitev and X.N. Wang, nucl-th/00012092 Thomas Ullrich

  40. Charged particle anisotropy 0 < pt < 4.5 GeV/c Around pt > 2 GeV/c the data starts to deviate from hydro. However, v2 stays large. Only statistical errors Systematic error 10% - 20% for pt = 2 – 4.5 GeV/c Thomas Ullrich

  41. Conclusions • STAR Detectors (TPC, RICH, Triggers) working well to better than specifications • Mapping out “Soft Physics” Regime • Net-baryon  0 at mid-rapidity! ( y = y0-ybeam ~ 5 ) • Chemical parameters Tch (RHIC) = 0.19 GeV  Tch (SPS/AGS) = 0.17 GeV q (RHIC) = 0.015 GeV << q (SPS/AGS) • Kinetic parameters ßr (RHIC) = 0.6c  ßr (SPS/AGS) = 0.4-0.5c Tfo (RHIC) = 0.1-0.12 GeV  Tfo (SPS/AGS) = 0.12-0.14 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 ever hoped for after the first run !!! Thomas Ullrich

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