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Anti-particle to particle ratios in p+p, Cu+Cu and Au+Au collisions at RHIC

for the collaboration. Anti-particle to particle ratios in p+p, Cu+Cu and Au+Au collisions at RHIC. G á bor I. Veres E ötvös Loránd University, Budapest Massachusetts Institute of Technology, Cambridge. Quark Matter 2006 Conference, Shanghai, November 19, 2006.

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Anti-particle to particle ratios in p+p, Cu+Cu and Au+Au collisions at RHIC

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  1. for the collaboration Anti-particle to particle ratios in p+p, Cu+Cu and Au+Au collisions at RHIC Gábor I. Veres Eötvös Loránd University, Budapest Massachusetts Institute of Technology, Cambridge Quark Matter 2006 Conference, Shanghai, November 19, 2006 Quark Matter 2006, Shanghai, November 14-20, 2006

  2. Collaboration Burak Alver, Birger Back,Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel, Wit Busza (Spokesperson), Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Joshua Hamblen, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Christof Roland, Gunther Roland, Joe Sagerer, Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, 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 9 ongoing PhD thesis studies Quark Matter 2006, Shanghai, November 14-20, 2006

  3. Outline PHOBOS detector and PID methods Particle ratios: • ratios in central Au+Au vs. s • Cu+Cu ratios vs. centrality at 200 and 62 GeV • comparison of p+p, Cu+Cu and Au+Au ratios vs. Npart Particle spectra: • Au+Au PID spectra at 62.4 GeV • low-pT particle yields • baryon/hadronratios • mT scaling • centrality dependence of the net proton yield Summary Quark Matter 2006, Shanghai, November 14-20, 2006

  4. Motivation Particle ratios: • are influenced by baryon pair production, baryon number transport, and final state interactions • show how close the system is to ideal baryon-free plasma • provide input to quantitative analysis of chemical equilibrium in thermal models z -x y Quark Matter 2006, Shanghai, November 14-20, 2006

  5. The detector Time of Flight 1m Spectrometer Quark Matter 2006, Shanghai, November 14-20, 2006

  6. 70 60 50 + - K+K 40 30 0 5 4 2 3 1 p (GeV/c) Particle ID from low to high pT PHOBOS PID Capabilities p+p 1/v (ps/cm) ++- Eloss(MeV) p (GeV/c) Stopping particles dE/dx TOF 3.0 0.3 0.03 pT (GeV/c) Quark Matter 2006, Shanghai, November 14-20, 2006

  7. PID cuts K p d p e Analysis techniques • Particles identified via dE/dx • in the spectrometer • Monte Carlo studies • to estimate corrections acceptance fficiency, corrections acceptance in y and pT : 0 < y < 1.5 0.2 < pT< 0.8 GeV/c p [GeV/c] Quark Matter 2006, Shanghai, November 14-20, 2006

  8. h– h– h+ Z h+ Z h– h+ h+ h– B– B+ Controlling systematic uncertainties by changing the polarity of the magnetic field Geometrical acceptance drops out of the ratios: Ratios measured independently for different:• bending directions• spectrometer arms Quark Matter 2006, Shanghai, November 14-20, 2006

  9. Absorption coefficient _ p p pT [GeV/c] DCA{ DCA{ GEANT Monte Carlo (FLUKA+Geisha)/2 Corrections Absorption• GEANT used • 4% for p/p• 1.5% for K–/K+ _ Feed-down • daughters of weakly decaying particles (,, –)•HIJING particle yields are used• track DCA cut (3.5 mm!) keeps correction small• 2% for p/p, <1% for K–/K+ and –/+ _ Secondary particles • GEANT used• 1% for p/p, 2% for –/+ _ Quark Matter 2006, Shanghai, November 14-20, 2006

  10. Errors on the ratios • Statistical errors: 1% (tens of millions of events analyzed) • Systematic errors (90% C.L.): pKp+ Quark Matter 2006, Shanghai, November 14-20, 2006

  11. Results: energy dependence arXiv:nucl-ex/0610001submitted to PRC stat.errors only New results at 62.4 GeV fit smoothly into the energy evolution of antiparticle/particle ratios Quark Matter 2006, Shanghai, November 14-20, 2006

  12. _ • p/p ratios: little, if any, centrality dependence • (still not understood theoretically) Cu+Cu ratios, all 3 species vs. Npart • Integrated over pT and y y0 • Similarly to Au+Au, strong • collision energy dependence 200 GeV 62.4 GeV Quark Matter 2006, Shanghai, November 14-20, 2006

  13. Comparison of systems at 200 GeV _ • p/p ratios do not • depend strongly on • - system size • - centrality y0 • The study is being currently extended to 62.4 GeV p+p: Phys.Rev. C71, 021901 (2005) Quark Matter 2006, Shanghai, November 14-20, 2006

  14. Ratios of different species Ratios of different species (like p/p) are of significant interest: they are used to study the baryon excess observed at higher RHIC energies in the 2 – 4 GeV/c pT range.  For that, identified spectra of all species were analyzed. Quark Matter 2006, Shanghai, November 14-20, 2006

  15. Identified particle pT-spectra, Au+Au at 62.4 GeV Time-of-Flight measurement extends the pT reach to 3 GeV/c for protons Proton spectra are harder than the meson spectra arXiv:nucl-ex/0610001submitted to PRC y0 Smooth evolution with centrality Quark Matter 2006, Shanghai, November 14-20, 2006

  16. y0 arXiv:nucl-ex/0610001submitted to PRC PHOBOS Au+Au 62.4 GeV Particle production at very low pT Low pT spectra carry information about radial flow, possible anomalous enhancement at very low pT, quantum mechanical effects, scaling laws T = 1026 MeV bsurface = 0.760.02 T = 1016 MeV bsurface = 0.720.02 T = 1036 MeV bsurface = 0.780.02 • Unique low-pT coverage of PHOBOS Quark Matter 2006, Shanghai, November 14-20, 2006

  17. arXiv:nucl-ex/0610001submitted to PRC J.Phys.G 30 S1143-S1147 (2004 ) PRC 70 (2004) 051901(R) mT -scaling in d+Au vs. Au+Au at 200 GeV Lack of mT scaling in heavy ion collisions Quark Matter 2006, Shanghai, November 14-20, 2006

  18. Central A+A y0 pp+ crossing ArXiv:nucl-ex/0610001submitted to PRC Smooth energy dependence of pT where p/p+1 (Anti)proton/hadron ratios for the two charge signs p>++K+ PHOBOS y0 arXiv:nucl-ex/0610001submitted to PRC Baryon excess approached at about pT3 GeV/c Quark Matter 2006, Shanghai, November 14-20, 2006

  19. _ y0 arXiv:nucl-ex/0610001submitted to PRC The net proton yield is proportional to Npart! p/p centrality independent  p and p Npart as well _ _ Net protons (p–p) Quark Matter 2006, Shanghai, November 14-20, 2006

  20. Summary • New results from PHOBOS: • antiparticle/particle ratios in Cu+Cu collisions • p(p)/h± ratios, identified spectra in 62.4 GeV Au+Au collisions • What have we learned? • Centrality-independence:• p/p ratios• net proton, p and p yield per participant(still not fully understood theoretically) • baryon excess in Au+Au collisions at 62.4 GeV • mT-scaling holds in d+Au but violated in Au+Au _ _ _ Quark Matter 2006, Shanghai, November 14-20, 2006

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