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Identified Particles in Au+Au Collisions at s NN = 200 GeV

This collaborative study presents measurements of identified particles in gold-gold collisions at an energy of 200 GeV. The experiment focuses on particle ratios, system properties at freeze-out, baryon transport, and energy dependence of ratios. Detailed particle identification is based on dE/dx measurements. Results reveal antiparticle-to-particle ratios along with corrections and high-precision measurements of particle yields. The study also explores energy evolution, centrality, and pT dependence of particle ratios.

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Identified Particles in Au+Au Collisions at s NN = 200 GeV

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  1. Identified Particles in Au+Au Collisions at sNN = 200 GeV Barbara Wosiek Institute of Nuclear Physics, Kraków, Poland for the Collaboration Barbara Wosiek/INP

  2. Collaboration ARGONNE NATIONAL LABORATORYBirger Back, Alan Wuosmaa BROOKHAVEN NATIONAL LABORATORY Mark Baker, Donald Barton, Alan Carroll, Nigel George, Stephen Gushue, George Heintzelman, Burt Holzman, Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov INSTITUTE OF NUCLEAR PHYSICS, KRAKOWAndrzej Budzanowski, Roman Hołyński, Jerzy Michałowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Woźniak MASSACHUSETTS INSTITUTE OF TECHNOLOGYMaartin Ballintijn,Wit Busza (Spokesperson), Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Jang Woo Lee, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Carla Vale, Gerrit van Nieuwenhuizen, Gábor Veres, Robin Verdier, Bernard Wadsworth, Bolek Wysłouch NATIONAL CENTRAL UNIVERSITY, TAIWANChia Ming Kuo, Willis Lin, Jaw-Luen Tang UNIVERSITY OF ILLINOIS AT CHICAGORussell Betts, Edmundo García, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer UNIVERSITY OF MARYLANDAbigail Bickley, Richard Bindel, Alice Mignerey, Marguerite Belt Tonjes UNIVERSITY OF ROCHESTERJoshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs Barbara Wosiek/INP

  3. pTmeasurements with the spectrometer Z dN/dpT near mid-rapidity up to 5 GeV/c 0.03 0.2 1.0 pT, GeV/c Charge PID Mass Mass +Charge This talk Christof Roland’s talk, Sat. Barbara Wosiek/INP

  4. Outline Medium pT range pT = 0.07 – 1.0 GeV/c depending on particle MASS Antiparticle/particle ratios as a function of Npart and pT Properties of the system at freeze-out Baryon transport Low pT range pT = 0.030 – 0.200 GeV/c depending on particle MASS Yields of (+ + ) , (K+ + K), (p + p) Probing long distances (truly non-perturbative QCD regime) Radial flow Barbara Wosiek/INP

  5. Antiparticle toparticle ratios measurements 70 cm 10 cm z -x y Acceptance of the spectrometer y pT (GeV/c) B=2T  0.35 – 1.3 0.10 – 0.6 0.25 – 0.8 0.10 – 0.5 0.20 – 0.7 0.15 – 0.9 K p,p Momentum resolution 1 – 2 % Reversible 2T magnetic field Two symmetric spectrometer arms • Independent measurements • Acceptance & efficiency cancels Barbara Wosiek/INP

  6. Particle identification Based on dE/dx measurements in Si sensors (resolution 7%) p Positive charges Negative charges K+ p K— + — Barbara Wosiek/INP

  7. Ratios at sNN = 200 GeV Corrections to the measured ratios : +5.1% absorption +0.7% secondary negligible -1.2% feeddown K-/K+ -/+ p/p High precision measurements Au+Au sNN = 200 GeV,12% most central (submitted to PRC, nucl-ex/0206012) <–>/<+> = 1.025 ± 0.006(stat.) ± 0.018(syst.) <K–>/<K+> = 0.95 ± 0.03(stat.) ± 0.03(syst.) <p>/<p> = 0.74 ± 0.02(stat.) ± 0.03(syst.) Barbara Wosiek/INP

  8. Energy dependence of particle ratios A+A central collisions PHOBOS 130 GeV PRL 87,102301,2001 K–/K+ PHOBOS 200 GeV Submitted to PRC nucl-ex/0206012 p/p • Rapidly decreasing net baryon density near midrapidity Barbara Wosiek/INP

  9. Energy evolution of B Using measured <K–>/<K+>,<p>/<p> and statistical model of F. Becattiniet al.,(PRC64,024901,2001) with Tch 160 – 170 MeV Estimated baryochemical potential at sNN = 200 GeV: B = 26  2 MeV LHC ~1 MeV? Fit: P.Braun-Munzinger NP. A697,902,2002 Barbara Wosiek/INP

  10. Centrality and pT dependence Au+Au sNN = 200 GeV 10% most central  p/p K–/K+ /+  p/p K–/K+ /+ PHOBOS preliminary PHOBOS preliminary • Ratios, within the errors, are independent of pT and Npart Barbara Wosiek/INP

  11. Particle measurements at very low pT F E D C B A X[cm] Beam pipe Z[cm] Search for particles ranging out in the 5th spectrometer plane Mass measurements (‘energy-range’ method) 20 • Eloss=dE • Mp= <dE/dx>Eloss m • (1/2) ( m2) 10 0 • Cuts on dE/dxper plane • ”MASS HYPOTHESIS” 0 10 20 Z [cm] P Ek=21 MeV • Cuts on Eloss(Ek=kinetic energy) • ”MOMENTUM HYPOTHESIS” K Ek=19 MeV dE/dx  Ek= 8 MeV • Corrections acceptance efficiency background A B C D E silicon plane Barbara Wosiek/INP

  12. Particle mass measurements at very low pT Results Au+Au sNN=200 GeV 15% central Test of the method: Reconstruction of low momentum MC particles (p,p) (p,p) Eloss <dE/dx>[10-3GeV2/cm] Eloss <dE/dx>[10-3GeV2/cm] (K+,K–) (K+,K–) (+,) (+,) MC DATA Eloss [MeV] Eloss [MeV] Barbara Wosiek/INP

  13. Invariant yields ofvery low pTparticles Analysis details: Au+Au sNN=200 GeV 15% central -0.1< y <0.4 • Particle momenta calibrated with reconstr.GEANT tracks • (pT resolution ~5%) • Data corrections: •  acceptance & efficiency • (embedding single tracks) •  background corrections: • feeddown, secondaries, • misID, ghosts; • (p+p) 41±8% • (K++K–) 16±11% • (++) 39±3% • based on DCA distributions & • rescaled HIJING • Current systematic errors 20%() ~40%(K) ~50%(p) (++) (K++K–) 1/ (2pT)d2N/dydpT (p+p) PHOBOS preliminary pT [GeV/c] Barbara Wosiek/INP

  14. sNN = 200 GeV:Comparison to models Au+Au yields scaled by 1/<Npart/2> HIJING RQMD HYDRO+THERMAL W.Broniowski,W.Florkowski (PRL87,2001,272302;PRC65,2002,064905) (++) (K++K–) (p+p) 10 10 10 1 1 1 1/ (2mT) d2N/dydmT 1/<Npart/2> 10-1 10-1 10-1 PHOBOS preliminary PHOBOS preliminary PHOBOS preliminary 10-2 10-1 1 10-2 10-1 1 10-2 10-1 1 mT – m0 PHENIX 130 GeV PRL88,2002,242301 (p+p) corrected for feeddown • very low pT • (p+p):models differ by a factor 2 to 6 Barbara Wosiek/INP

  15. SUMMARY Au+Au at sNN= 200 GeV: Medium pT range • p/p ratio increases to 0.74 at 200 GeV • 3/4 of protons are from antibaryon-baryon pair production • B = 26  2 MeV, ~50% smaller than at 130 GeV • Ratios are approximately constant as a function of pT and Npart Au+Au at sNN= 200 GeV: Low pT range • No enhancement in low pT yields • Effect of strong radial flow for (p+p) seen below pT 200 MeV/c • Model constraints – dynamics has largest effect on low pT protons & antiprotons Barbara Wosiek/INP

  16. Backup slides Barbara Wosiek/INP

  17. Ratios: cross-checks • Ratio particles at opposite field polarities which bend in the same direction • Acceptance and efficiency cancels • Independent measurements • Systematic Checks B1: Beam Orbit 1 B2: Beam Orbit 2 FB: Forward Bending BB: Backward Bending Barbara Wosiek/INP

  18. Determination of B B = 26±2 MeV Redlich, QM2001 Presentation Barbara Wosiek/INP

  19. Comparison of dE/dx distributions for low momentum reconstructedpions Plane A Plane B Plane C Plane D Plane E DATA HIJING Barbara Wosiek/INP

  20. Comparison of dE/dx distributions for low momentum reconstructedprotons Plane A Plane B Plane C Plane D Plane E DATA HIJING Barbara Wosiek/INP

  21. Background estimates for (p+p) Barbara Wosiek/INP

  22. sNN = 200 GeV:Comparison to models Au+Au yields scaled by 1/<Npart/2> HIJING RQMD HYDRO+THERMAL W.Broniowski,W.Florkowski (PRL87,2001,272302;PRC65,2002,064905) (++) (K++K–) (p+p) 10 10 10 1 1 1 1/ (2pT) d2N/dydpT 1/<Npart/2> 10-1 10-1 10-1 PHOBOS preliminary PHOBOS preliminary PHOBOS preliminary 0.2 0.4 0.6 0.2 0.4 0.6 0.2 0.4 0.6 pT PHENIX 130 GeV PRL88,2002,242301 (p+p) corrected for feeddown • very low pT • (p+p):models differ by a factor 2 to 6 Barbara Wosiek/INP

  23. Acceptance plots Barbara Wosiek/INP

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