1. Conor Henderson, MIT 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. Conor Henderson, MIT 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 LABORATORYBROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOWMASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWANUNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLANDUNIVERSITY OF ROCHESTER

3. Conor Henderson, MIT The PHOBOS Detector Time-Of-Flight SpecTrig T0 Detectors Spectrometer

4. Conor Henderson, MIT The PHOBOS Spectrometer 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 z -x 10 cm y 70 cm B=2T

5. Conor Henderson, MIT 1 23 4 50 p (GeV/c) 30 40 50 60 70 1/v (ps/cm) Particle Identification in PHOBOS Three techniques for Particle ID: Stopping Particles (0.05 < p T < 0.2 GeV/c) Silicon dE/dx (0.3 < p T <1.3 GeV/c) Time-Of-Flight (0.5 < p T < 4 GeV/c)

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

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

8. Conor Henderson, MIT Au+Au Low-p T Particle Yields ++++ K + +K – p+p arXiv:nucl-ex/0401006 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 Au+Au  s NN = 200 GeV

9. Conor Henderson, MIT Au+Au Low-p T Results -1 for mesons +1 for baryons Au+Au  s NN = 200 GeV PHENIX - open symbols PHOBOS –closed symbols Solid line = fit to PHENIX spectra Dashed line = extrapolation of fit This fit extrapolates smoothly to the low-p T points  No enhancement of low-p T particle yields  No evidence of unusual long-wavelength physics PHENIX spectra for m T < 1GeV/c 2 fit with:

10. Conor Henderson, MIT Antiparticle/ Particle Ratios near mid-rapidity Z Field Polarity: B -  - -  + +  - -  + + 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 Particles identified by Si dE/dx

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

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

13. Conor Henderson, MIT Particle Ratios in p+p and d+Au …  s NN = 200 GeV arXiv:nucl-ex/0309013

14. Conor Henderson, MIT … And Compared to Au+Au  s NN = 200 GeV arXiv:nucl-ex/0309013

15. Conor Henderson, MIT 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. Conor Henderson, MIT The PHOBOS Spectrometer Trigger TOF Trigger High-p T 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. Conor Henderson, MIT Time-of-Flight Spectra Analysis Momentum slices are fitted to extract the yields of each particle species 1 23 4 50 p (GeV/c) 30 40 50 60 70 1/v (ps/cm) Yields corrected for geometrical acceptance and tracking efficiency; no feed-down correction applied

18. Conor Henderson, MIT Identified Particle p T Spectra from TOF d+Au  s NN = 200 GeV

19. Conor Henderson, MIT Particle Composition in d+Au d+Au  s NN = 200 GeV

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

21. Conor Henderson, MIT m T -scaling in d+Au ? … d+Au  s NN = 200 GeV Kaon yields scaled by 2 x 2

22. Conor Henderson, MIT … But Not in Au+Au? Spectra normalized at 2 GeV/c  1.26  0.86 Au+Au  s NN = 200 GeV Spectra normalised at p T = 2 GeV/c (Different norm. factors for kaons and protons) m T -scaling violated at low m T in Au+Au Consistent with transverse expansion of Au+Au collision system

23. Conor Henderson, MIT PHOBOS Strangeness Summary Three techniques for particle ID from low to high p T : stopping particles; Si dE/dx and Time-Of-Flight Au+Au results: –Low-p T yields  no evidence of unusual long-wavelength physics; violation of m T -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 m T -scaling p+p results: –Preliminary particle ratios similar to d+Au

24. Conor Henderson, MIT Strangeness Outlook from PHOBOS Au+Au identified particle spectra from TOF d+Au low-p T particle yields Particle ratios in Au+Au at 62.4 GeV Low p T  yields in Au+Au

25. Conor Henderson, MIT Back-up Slides

26. Conor Henderson, MIT Stopping Particles Acceptance

27. Conor Henderson, MIT Low-p T Yields Compared to Models Event generators unable to consistently describe low p T yields. HIJING overpredicts yields at low p T. Ratio of measured to HIJING yields averaged over low p T range:

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

29. Conor Henderson, MIT TOF and Spec PID Acceptances

30. Conor Henderson, MIT d+Au pbar/p compared to models

31. Conor Henderson, MIT TOF Particle Ratios

32. Conor Henderson, MIT Particle Composition vs.  s in p(d)+A Collisions