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for the Collaboration

Low-p T Spectra of Identified Charged Particles in s NN = 200 GeV Au+Au Collisions from PHOBOS Experiment at RHIC. Adam Trzupek Institute of Nuclear Physics, Kraków, Poland. for the Collaboration. International Europhysics Conference on High Energy Physics

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  1. Low-pT Spectra of Identified Charged Particles in sNN = 200 GeV Au+Au Collisions from PHOBOS Experiment at RHIC Adam Trzupek Institute of Nuclear Physics, Kraków, Poland for the Collaboration International Europhysics Conference on High Energy Physics EPS (July 17th-23rd 2003) in Aachen, Germany

  2. Particle pT distributions at RHIC Au+Au sNN=200 GeV PHOBOS preliminary • RHIC experiments measured particle spectra at pT > 0.2 GeV/c => jet quenching • PHOBOS has a unique capability to measure particles down to very small • transverse momenta << 0.2GeV/c Adam Trzupek

  3. Why production of particles with very low pT is interesting? for pT << mh Enhanced production of low pT particles is expected due to the presence of NEW long wave-length phenomena, e.g. large volume of the system at freeze-out should lead to an increase of low pT particle yields Enhanced yield of pions with pT < 0.2 GeV/c with respect to the B-E distribution may occur when disoriented chiral condensates (DCC) are formed Mass-dependent suppression at low pT due to the collective transverse expansion of the system is expected Adam Trzupek

  4. 70 cm 10 cm z -x y F E D C X[cm] B A . . Be pipe 0 10 20 Z [cm] . pT and PID measurement in PHOBOS spectrometer • PHOBOS Spectrometer (2001) • two arms at mid rapidity • dipole magnetic field of 2T at maximum • 16 layers of silicon wafers • fine/optimal pixelization, precise dE measurement • pT > 0.2 GeV/c • track curvature in B field => MOM • dE/dx in Si, ToF => PID • pT = 0.03 - 0.2 GeV/c • low pT particles stop • in silicon wafers => PID, MOM • B field negligible • ( layers A-F ) (++-) => (K++ K-) (p + p) Adam Trzupek

  5. Particle identification at very low pT P Ek=21 MeV K Ek=19 MeV  Ek= 8 MeV A B C D E silicon layer Candidates should have dE/dx values within dE/dx bands for (++-), (K++K-) and (p+p) Eloss =  dEi , i = A, ... ,E Mp = < Eloss dE/dx >  mh ( mh2) (1/2) Bethe-Bloch function 1 bands Mp (p+p) dE/dx [MeV] (K++K-) MC (++-) Eloss [MeV] Correction for energy loss in layer E was applied under the assumption that particle stops in this layer. This correction procedure and energy loss fluctuations in beam pipe and Si lead to a correlation Mp vs Eloss Adam Trzupek

  6. (p+p) Experimental data sample • Sample used for this analysis: • 15% most central • Au+Au events • of sNN = 200 GeV • Number of events used: • 400,000 out of 2M available • for final results Preliminary Mp (K++K-) (++-) DATA Eloss [MeV] Adam Trzupek

  7. Momentum distributions: Acceptance & efficiency corrections embedding single MC tracks into experimental events Background corrections: feeddown, secondaries, misID, ghosts; (p +p) 41±8% (K++K-) 16±11% (++-) 39±3% based on track vertex distributions (DCA) and rescaled HIJING with detector (Geant) simulations Current systematic errors 20%() ~40%(K) ~50%(p) Centrality 0-15% sNN=200 GeV Au+Au y= -0.1 — 0.4 (++-) (K++K-) (p+p) PHOBOS preliminary pT [GeV/c] Adam Trzupek

  8. Comparison to other RHIC experimentsT. Ullrich Nucl.Phys.A 715,p.399c(2003) • Yields at lowest pT at RHIC are measured with the PHOBOS spectrometer • Uncertainties in fit extrapolations to pT =0 are reduced • Flattening of proton spectra indicates strong collective radial expansion Adam Trzupek

  9. B-E fit, pT = 0.2 - 0.7 GeV/c Pion mT distributions: Bose - Einstein distribution: mT = pT2+mh2 • Pion low pT yields are well described by Bose - Einstein function extrapolated from higher pT (>0.2GeV/c) • Excess in low pT pion production below 0.2 GeV/c predicted by DCC models is not observed J. Randrup Nucl.Phys. A681 (2001) 100c Adam Trzupek

  10. Models constraints HIJING RQMD HYDRO+THERMAL W.Broniowski,W.Florkowski (PRL87,2001,272302) P. Kolb and R. Rapp; PRC 67 (2003) 044903 (p+p)  1/(2mT) d2N/dydmT /<Npart/2> PHOBOS preliminary H Model predictions differ from data by factors 2-6 at loo pT Hydrodynamic simulation with (initial) transverse boost describes data well from the very low pT up to 1.5 GeV/c Adam Trzupek

  11. Summary • Algorithm was developed to determine yields of (++-), (K++ K-) and (p + p) at very low pT ( 0.03 - 0.2 GeV/c ) using the PHOBOS spectrometer • No enhancement in low pT yields for pions is observed • Flattening of (p+p) spectra down to very low pT indicates strong radial flow in the system • Models should account for the dynamics ( rescattering, expansion ) which has largest effect on low pT (p + p) yields Adam Trzupek

  12. Collaboration (May 2003) Birger Back,Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Becker, Russell Betts, Abigail Bickley, Richard Bindel, Andrzej Budzanowski, Wit Busza (Spokesperson), Alan Carroll, Patrick Decowski, Edmundo Garcia, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Stephen Gushue, Clive Halliwell, Joshua Hamblen,Adam Harrington,Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova,Erik Johnson, Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo,Jang Woo Lee, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Aaron Noell, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Louis Remsberg, Christof Roland, Gunther Roland, Joe Sagerer, Pradeep Sarin, Pawel Sawicki, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Peter Steinberg, George Stephans, Andrei Sukhanov, Ray Teng, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Robin Verdier, Gábor Veres, Bernard Wadsworth, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Alan Wuosmaa, Bolek Wysłouch, Jinlong Zhang ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER Adam Trzupek

  13. Backup slides Adam Trzupek

  14. 1m • PHOBOS Detector (2001) • Triggering • Scintillator Paddles • Zero Degree Calorimeter • 4p Multiplicity Array • - Octagon, Vertex & Ring Si Counters • Two Mid-rapidity Spectrometers • TOF wall for High-Momentum PID Adam Trzupek

  15. 1/(2pT)d2N/dydpT acceptance & efficiency corrections embedding single MC tracks into experimental events in phase space cells: pT, y, Zver , (- + +) Adam Trzupek

  16. Model Constraints HIJING RQMD HYDRO+THERMAL W.Broniowski,W.Florkowski (PRL87,2001,272302;PRC65,2002,064905) (Au+Au yields )/<Npart/2> (++) (K++K–) (p+p) 10 10 10 PHOBOS preliminary PHOBOS preliminary 1 1 1 1/(2mT) d2N/dydmT /<Npart/2> 10-1 10-1 10-1 PHOBOS preliminary 10-2 10-1 1 10-2 10-1 1 10-2 10-1 1 mT – m0 PHENIX 130 GeV Adam Trzupek

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