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Recent Results from PHOBOS

This paper presents recent results from the PHOBOS detector in Au+Au collisions at different energies. The data includes charged particle production, centrality dependence, PT distribution, particle ratios, and transverse momentum distributions.

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Recent Results from PHOBOS

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  1. Recent Results from PHOBOS David Hofman – UIC For the Collaboration AGS/RHIC Users MeetingMay 15-16, 2003, BNL

  2. 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 Pradeep Sarin AGS/RHIC Users Meeting 2003

  3. The PHOBOS Detector in 2002 Spectrometer Ring Counters Octagon f Triggering -5.4 -3 0 +3 +5.4 h ZDC 137000 Silicon Pad Channels 1m Nearly 4pCoverage ZDC AGS/RHIC Users Meeting 2003

  4. PHOBOS Data on dN/dh in Au+Auvs. Centrality and s 200 GeV 19.6 GeV 130 GeV PHOBOS PHOBOS PHOBOS dN/dh Typical systematic band (90%C.L.) h h h  Extensive systematic multiplicity data set. AGS/RHIC Users Meeting 2003

  5. Charged Particle Production at Midrapidity Data is normalized by corresponding pp value for each energy. 200 GeV 130 GeV 19.6 GeV preliminary pp Energy and Centrality Dependence Midrapidity |h|<1 Au+Au 200 GeV dNch/dh 130 GeV 19.6 GeV preliminary pp two component fit with x~ 0.1  Surprising: ratio of hard/soft collisions is the same.  Published at 130 and 200 GeV: PRC 65, 061901(R) (2002); 19.6 GeV in Preparation AGS/RHIC Users Meeting 2003

  6. Charged Particle Production (dN/dh) UA5, Z.Phys.C33, 1 (1986) p + p inel. PHOBOS Au+Au dNch/dh dN/dh¢ 6% central dNch/dh ¢/<Npart>/2 PHOBOS Au+Au Systematic errors not shown Scale by <Npart>/2 & shift to h¢=h- ybeam  Growth of the Fragmentation Region with sNN  Status: In Print for PRL AGS/RHIC Users Meeting 2003

  7. Au+Au Centrality dependence of Nch Error bands due to high-h extrapolation (preliminary)  Total charged particle production ~ Npart and consistent with e+e- AGS/RHIC Users Meeting 2003

  8. Comparison <Nch> vs. Energy  Surprising agreement at high energy  nucl-ex/0301017; Submitted for Publication AGS/RHIC Users Meeting 2003

  9. Preliminaryv2200 Final v2130 Elliptic Flow (v2) at 130 and 200 GeV  130 GeV Data Published in PRL 89, 222301 (2002) <Npart>~190 v2 PRL 89, 222301 200 130 PHOBOS Au-Au h  PRELIMINARY 200 GeV results very similar to 130 GeV  See Poster by Carla Vale for 200 GeV Track-based Results AGS/RHIC Users Meeting 2003

  10. PT Distribution of Charged Particles Phobos Preliminary Systematic Errors not shown  Phobos has capabilities to measure from pT, = 0.030 – 5 GeV/c AGS/RHIC Users Meeting 2003

  11. F E D C B A X[cm] Beam pipe Z[cm] Invariant yields ofvery low pT particles pT = 0.03 – 0.20 GeV/c (++) → Mass measurement by ‘energy-range’ method in 5 planes of silicon. (K++K–) 20 1/ (2pT)d2N/dydpT 10 (p+p) 0 0 10 20 Z [cm] PHOBOS preliminary pT [GeV/c]  Unique: Can measure down to very low pT. • Status of Experimental Result: In Preparation for Publication AGS/RHIC Users Meeting 2003

  12. Interest in RHIC data is extremely high; Preliminary Data already ‘Published’ P. Kolb and R. Rapp; PRC 67 044903 AGS/RHIC Users Meeting 2003

  13. Particle Ratios: Energy dependence pT = 0.07 – 1.0 GeV/c A+A central collisions PHOBOS 130 GeV PRL 87,102301,2001 (mB~45 MeV) K–/K+ p/p PHOBOS 200 GeV (mB~27 MeV)  Rapidly decreasing net baryon density near midrapidity  200 GeV Result is published: PRC 67, 021901(R) (2003) AGS/RHIC Users Meeting 2003

  14. Transverse Momentum Distributions for Au+Au @ 200 GeV  At 200 GeV, minimum bias pp reference data exist for comparison. 0.2<yp<1.4 AGS/RHIC Users Meeting 2003

  15.  Excess yield at 2 GeV/c  BUT, at higher energy the particle yields appear to come back ‘down’ to the pp value. Comparing Au+Au spectra to pp AGS/RHIC Users Meeting 2003

  16. Ratio of Au+Au and pp spectra at 200 GeV • We observe a significant change in the spectral shape between pp and Au+Au collisions. • Central Au+Au collisions show an approximate scaling with the number of participants for low and high pT. mid-peripheral Npart = 65 ± 4 central Npart = 344 ± 12 AGS/RHIC Users Meeting 2003

  17. Evolution with Centrality (Au+Au) • Divide spectra by fit to mid-peripheral 45-50% centrality bin. • Gradual change of shape. • Peak develops at 1.5 GeV/c. • Low and high pT ‘matches’ the mid-peripheral yields. mid-peripheral Yield/<Npart/2>/ mid-peripheral fit central AGS/RHIC Users Meeting 2003

  18. Centrality scaling in pT bins (Au+Au) • Spectra normalized to a fit at mid-peripheral 45-50% bin.  Over the centrality range studied, for low and high pT, the Au+Au data scale approximately with number of participants.  nucl-ex/0302015; Submitted for Publication AGS/RHIC Users Meeting 2003

  19. This Year: PHOBOS Detector 2003 mini-pCal pCal T0  x15 high pT data  See Poster By C. Henderson, J. Kane and G. Veres Sum Energy (a.u.) T0 pCal SPECTRIG  See Posters by A. Iordanova and R. Hollis  Moved TOF walls back ~ 5 m from interaction point  Installed new spectrometer trigger detector that selects on high pT tracks  Installed new “time-zero” (T0) Cerenkov detectors to provide triggering and on-line vertexing as well as a start time for our TOF walls.  Proton calorimeter on Gold and Deuteron “going” sides for dA run AGS/RHIC Users Meeting 2003

  20. PHOBOS Preliminary Results from d+Au Transverse Momentum Distributions in d+Au 0 – 20% 0.2<h<1.4 Centrality Determination:Energy in Silicon Ring Counters 20 – 40% 40 – 70% 3.0<|h|<5.4 70 – 100% PHOBOS d+Aupreliminary Counts Energy (arb. units ) • Four centrality bins based on energy in our Silicon Ring detectors AGS/RHIC Users Meeting 2003

  21. Yield/<Npart/2>/p+p fit Yield/<Npart/2>/p+p fit PHOBOS Preliminary Results from d+Au PHOBOSpreliminary PHOBOS preliminary peripheral RdAu RdAu PHOBOS preliminary PHOBOS preliminary central AGS/RHIC Users Meeting 2003

  22. Summary and Outlook • 5 papers (3 published and 2 submitted) since last AGS/RHIC Users’ Meeting. • 5 additional papers from Au+Au data are in progress. • First look at new results for d+Au shows qualitatively different features as compared to Au+Au! • Exciting times at RHIC and PHOBOS. Many thanks to the entire RHIC crew for supplying us the beams. AGS/RHIC Users Meeting 2003

  23. 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 AGS/RHIC Users Meeting 2003

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