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 International Europhysics Conference on High Energy Physics EPS (July 17th-23rd 2003) in Aachen, Germany

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

Adam Trzupek for p T << m h Enhanced production of low p T 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 p T particle yields Why production of particles with very low p T is interesting? Enhanced yield of pions with p T < 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 p T due to the collective transverse expansion of the system is expected

Adam Trzupek p T > 0.2 GeV/c track curvature in B field => MOM dE/dx in Si, ToF => PID p T = GeV/c low p T particles stop in silicon wafers => PID, MOM B field negligible ( layers A-F ) Z [cm] X[cm ] A B C D E F Be pipe... p T and PID measurement in PHOBOS spectrometer z -x 10 cm y 70 cm 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 (  + +  - ) => (K + + K - ) (p + p)

Adam Trzupek E loss =  dE i, i = A,...,E M p =  m h (  m h  2 ) (  1/  2 ) Bethe-Bloch function A B C D E  E k = 8 MeV P E k =21 MeV K E k =19 MeV silicon layer Candidates should have dE/dx values within dE/dx bands for (  + +  - ), (K + +K - ) and (p+p) Particle identification at very low p T dE/dx [MeV] E loss [MeV] (++-)(++-) (K + +K - ) (p+p) MC MpMp 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 M p vs E loss 1  bands

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

Adam Trzupek Momentum distributions: (++-)(++-) (K + +K - ) (p+p) PHOBOS preliminary p T [GeV/c] 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%  s NN =200 GeV Au+Au y= -0.1 — 0.4

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

Adam Trzupek  Pion low p T yields are well described by Bose - Einstein function extrapolated from higher p T (>0.2GeV/c)  Excess in low p T pion production below 0.2 GeV/c predicted by DCC models is not observed J. Randrup Nucl.Phys. A681 (2001) 100c B-E fit, p T = GeV/c Pion m T distributions: Bose - Einstein distribution: m T =  p T 2 +m h 2

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

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

Adam Trzupek 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 LABORATORYBROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOWMASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWANUNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLANDUNIVERSITY OF ROCHESTER

Adam Trzupek Backup slides

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

Adam Trzupek 1/(2  p T )d 2 N/dydp T acceptance & efficiency corrections embedding single MC tracks into experimental events in phase space cells:  p T,  y,  Z ver,  (  - +  + )

Adam Trzupek PHOBOS preliminary (++)(++)(K + +K – ) (p+p) m T – m HIJING RQMD HYDRO+THERMAL W.Broniowski,W.Florkowski (PRL87,2001,272302;PRC65,2002,064905) PHENIX 130 GeV 1/(2  m T ) d 2 N/dydm T / (Au+Au yields )/ PHOBOS preliminary Model Constraints