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Strangeness Production in PHOBOS

Strangeness Production in PHOBOS. C o nor Henderson Massachusetts Institute of Technology For the PHOBOS Collaboration RHIC/AGS Users’ Meeting, 14 May 2004 Brookhaven National Laboratory. Collaboration.

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Strangeness Production in PHOBOS

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  1. Strangeness Production in PHOBOS Conor Henderson Massachusetts Institute of Technology For the PHOBOS Collaboration RHIC/AGS Users’ Meeting, 14 May 2004 Brookhaven National Laboratory

  2. Collaboration Birger Back,Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley, Richard Bindel, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski, Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Adam Harrington, Michael Hauer, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Joe Sagerer, Helen Seals, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Alan Wuosmaa, Bolek Wysłouch ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

  3. The PHOBOS Detector Time-Of-Flight SpecTrig Spectrometer T0 Detectors

  4. The PHOBOS Spectrometer 70 cm 10 cm B=2T z -x y • Two arms x 16 layers of silicon • Highly-segmented in x-z plane • Inner layers in zero-field region, outer layers in 2T magnetic field • Tracking within 10 cm of interaction region

  5. Particle Identification in PHOBOS 70 60 1/v (ps/cm) 50 40 30 0 5 4 2 3 1 p (GeV/c) • Three techniques for Particle ID: • Stopping Particles (0.05 < pT < 0.2 GeV/c) • Silicon dE/dx (0.3 < pT <1.3 GeV/c) • Time-Of-Flight (0.5 < pT < 4 GeV/c)

  6. Low-pT Stopping Particles F E D C X[cm] B A . . Beam pipe 0 10 20 Z [cm] . Z[cm] • Search for particles which stop in 5th Spectrometer layer • Tracks identified via energy deposition pattern • , K, p identified for • 0.05 < pT < 0.2 GeV/c • No B-field, so particle charge cannot be determined

  7. Low-pT Stopping Particles DATA Construct a mass parameter from energy deposition in each layer: p + p K+ + K- + + - Method calibrated by Monte Carlo simulation

  8. Au+Au Low-pT Particle Yields ++ K++K– p+p Au+Au sNN = 200 GeV • Yields corrected for: • Geometrical acceptance • Reconstruction efficiency • PID inefficiencies • Absorption in the beam pipe • Feed-down from weak decays • Secondaries • Mis-identified particles • Ghosts y = - 0.1— 0.4 arXiv:nucl-ex/0401006

  9. Au+Au Low-pT Results Au+Au sNN = 200 GeV PHENIX spectra for mT < 1GeV/c2 fit with: PHENIX - open symbols PHOBOS –closed symbols -1 for mesons +1 for baryons • This fit extrapolates smoothly to the low-pT points • No enhancement of low-pT particle yields • No evidence of unusual long-wavelength physics Solid line = fit to PHENIX spectra Dashed line = extrapolation of fit

  10. Antiparticle/ Particle Ratios Field Polarity: B-  -  - Z  +  + near mid-rapidity Particles identified by Si dE/dx • Invert magnetic field = interchange trajectories • Tracking efficiency and geometrical acceptance corrections cancel in ratio • Antiparticle/particle ratios then just corrected for: absorption; feed-down; secondaries

  11. A+A Particle Ratios vs. Collision Energy K- / K+ p / p Phys. Rev. C 67, 021901R (2003)

  12. Baryo-Chemical Potential At RHIC Au+Au sNN = 200 GeV Phys. Rev. C 67, 021901R (2003) With T = 165 MeV, B = 272 MeV at sNN = 200 GeV in Au+Au

  13. Particle Ratios in p+p and d+Au … sNN = 200 GeV arXiv:nucl-ex/0309013

  14. … And Compared to Au+Au sNN = 200 GeV arXiv:nucl-ex/0309013

  15. The PHOBOS Time-Of-Flight Detector • Two Time-Of-Flight walls: • TB at 45 deg, 5.4m • TC at 90 deg, 4m • 120 plastic scintillators per wall, read-out top and bottom • TOF timing resolution ~ 100 ps • Collision start-time determined from arrays of Cerenkov counters (T0s) along beam-line

  16. The PHOBOS Spectrometer Trigger TOF Trigger • High-pT tracks identified by straight-line hit combinations and online measurement of event vertex • New scintillator walls installed (the SpecTrig); online trigger decision made by programmable electronic logic module • Resulted in factor 15-20 enhancement in d+Au collisions

  17. Time-of-Flight Spectra Analysis 70 60 50 1/v (ps/cm) 40 30 0 5 4 2 3 1 p (GeV/c) • Momentum slices are fitted to extract the yields of each particle species • Yields corrected for geometrical acceptance and tracking efficiency; no feed-down correction applied

  18. Identified Particle pT Spectra from TOF d+Au sNN = 200 GeV

  19. Particle Composition in d+Au d+Au sNN = 200 GeV

  20. Centrality Dependence in d+Au No observed variation in particle composition with collision centrality in d+Au Peripheral 40-70% 20-40% Central 0-20%

  21. mT-scaling in d+Au ? … d+Au sNN = 200 GeV x 2 Kaon yields scaled by 2

  22. … But Not in Au+Au?  1.26  0.86 Spectra normalized at 2 GeV/c Au+Au sNN = 200 GeV • Spectra normalised at pT= 2 GeV/c (Different norm. factors for kaons and protons) • mT-scaling violated at low mT in Au+Au • Consistent with transverse expansion of Au+Au collision system

  23. PHOBOS Strangeness Summary • Three techniques for particle ID from low to high pT: stopping particles; Si dE/dx and Time-Of-Flight • Au+Au results: • Low-pT yields  no evidence of unusual long-wavelength physics; violation of mT-scaling observed • Particle ratios indicate B = 272 MeV at RHIC • d+Au results: • Particle ratios differ from Au+Au at same  • Preliminary identified particle spectra exhibit mT-scaling • p+p results: • Preliminary particle ratios similar to d+Au

  24. Strangeness Outlook from PHOBOS • Au+Au identified particle spectra from TOF • d+Au low-pT particle yields • Particle ratios in Au+Au at 62.4 GeV • Low pT yields in Au+Au

  25. Back-up Slides

  26. Stopping Particles Acceptance

  27. Low-pT Yields Compared to Models • Event generators unable to consistently describe low pT yields. • HIJING overpredicts yields at low pT. • Ratio of measured to HIJING yields averaged over low pT range:

  28. Comparison to Hydro. Models P. Kolb and R. Rapp, Phys.Rev. C67, 044903 (2003) Red curves: Tdec=100MeV Solid: without initial transverse boost Dashed: with initial transverse boost Blue curves: Tdec=165MeV Inclusion of an initial (pre-hydrodynamic) transverse flow better describes the spectra.

  29. TOF and Spec PID Acceptances

  30. d+Au pbar/p compared to models

  31. TOF Particle Ratios

  32. Particle Composition vs.s in p(d)+A Collisions

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