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for the Collaboration

Results from the PHOBOS experiment at RHIC. Adam Trzupek The Henryk Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences Kraków, Poland. for the Collaboration.

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for the Collaboration

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  1. Results from the PHOBOS experiment at RHIC Adam Trzupek The Henryk Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences Kraków, Poland for the Collaboration The 2007 Europhysics Conference on High Energy Physics Manchester, England, 19-25 July 2007  

  2. PHOBOS 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 LABORATORYINSTITUTE OF NUCLEAR PHYSICS PAN MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

  3. Outline • PHOBOS detector • Data: p+p, d+Au, Cu+Cu, Au+Au at 20 – 200 GeV • Charged particle multiplicities • Factorization of energy and centrality dependence in Au+Au and Cu+Cu collisions • Azimuthal anisotropy of produced particles in Au+Au and Cu+Cu collisions • Participant eccentricity scaling • pT- Spectra of identified particles • Very low pT data – a handle on radial flow • Summary

  4. PHOBOS Detector • Multiplicity Detector (Octagon, Rings) -5.4 <  < 5.4 , 0 <  < 2  Octagon Ring Counters 1m Ring Counters

  5. PHOBOS Detector • MultilayerSpectrometer,TOF midrapidity,0.03 GeV/c< pT< 5 GeV/c ZDC Triggering TOF 1m Spectrometer Triggering ZDC

  6. Charged hadron dNch/dh distribution (PHOBOS) 19.6 GeV 62.4 GeV 130 GeV 200 GeV centrality Au+Au Cu+Cu preliminary preliminary d+Au • Energy dependence: • Height increases • Width increases (in space) • Centrality dependence: • Height increases • Species dependence: • Same systematic trends PRL 91 (2003) 052303, PRC 74 (2006) 021901, PRC 72 (2005) 031901

  7. Au+Au and Cu+Cu at the same Npart ( = 200 GeV) Npart - number of participating nucleons For the same Npart(system size) dNch/d shape is verysimilar forAu+AuandCu+Cu collisions PHOBOS: NPA774 (2006) 113 Cu+Cu midcentral Preliminary 15-25%, Npart = 61 Au+Au peripheral 45-55%, Npart = 56 Cu+Cu central Preliminary 3-6%, Npart = 100 Au+Au midcentral 35-40%, Npart = 99

  8. Charged particle yields in Au+Au and Cu+Cu at midrapidity Ratio of charged hadron yield at 200 GeV to yields at lower energies (200/X) Particle density perparticipant pair PRC 74 (2006) 021901, NPA774 (2006) 113 s PHOBOS preliminary • No centrality dependence for Npart > 40 • Energy and centrality dependences of • charged hadron yields factorize Increase in particle production per participant with Npart

  9. Charged Particle pT Spectra Ratio of charged hadron yields at 200 and 62.4 GeV midrapidity PRL 94, 082304 (2005), PRL 96 (2006) 212301 <pT> = 0.25 GeV/c <pT> = 1.25 GeV/c <pT> = 2.5 GeV/c <pT> = 3.88 GeV/c <pT> = 3.38 GeV/c Au+Au Cu+Cu p+p No centrality dependence for pT = 0.2 – 4 GeV/c Factorization of energy and centrality dependence is valid at different transverse momenta.

  10. Extended longitudinal scaling NPA774 (2006) 113 Energy independence of charged particle yields from moderate to high rapidities

  11. Azimutal anisotropy of produced particles z Reaction plane M. Kaneta y x • Pressure gradients lead to azimuthal anisotropy • Elliptic flow is the second harmonic in the Fourier expansion of azimuthal particle distribution dN/d(f-Y0) = N0 (1 + 2v1cos (f-Y0) + 2v2cos (2(f-Y0)) + ... )

  12. v2in Au+Auand Cu+Cu( dependence) 0-40%, charged particles • broad h range • several energies Au+Au Centrality: 0-40% PRL 98 (2007) 242302, PRC 72 (2005) 051901, PRL 94 (2005) 122303 Cu+Cu • for Cu+Cu v2 is largeand grows with energy • shape (in ) for Au+Au andCu+Cu similar

  13. v2 in Au+Au and Cu+Cu (centrality dependence) Charged particles, || < 1 PRL 98 (2007) 242302, PRC 72 (2005) 051901 • decreases with centrality • for central collisions v2 is non-zero (larger in Cu+Cu)

  14. Standard and Participant eccentricity Initial overlap geometry Visible in final measured particle azimuthal angular distributions Standard eccentricity: minor axis along b, (bx) Participant eccentricity: 0 Au+Au for the same b, interaction points vary from event-to-event b minor axis not along b, (bx)

  15. Does usingmake a difference?YES 200 GeV PRL 98 (2007) 242302 • increases for smaller systems • For central Cu+Cu: >>

  16. Eccentricity scaled v2in Au+Au and Cu+Cu v2 scaled by standardeccentricity v2 scaled by participant eccentricity 200 GeV Cu+Cu Cu+Cu Au+Au Au+Au PRL 98 (2007) 242302 unifies average v2 in Au+Auand Cu+Cu

  17. Eccentricity scaled v2in Au+Au and Cu+Cu v2 scaled by standardeccentricity v2 scaled by participant eccentricity 200 GeV Cu+Cu Cu+Cu Au+Au Au+Au PRL 98 (2007) 242302 unifies average v2 in Au+Auand Cu+Cu

  18. pT dependence of v2/ unifies v2(pT) in Au+Au and Cu+Cu Au+Au and Cu+Cu at matched Npart midrapidity nucl-ex/0701051

  19. Pseudorapidity dependence of v2/ Au+Au and Cu+Cu at matched Npart unifies v2() in Au+Au and Cu+Cu The collision geometry controls the dynamical evolution of heavy ion collisions More information on the dynamical evolution can be obtained from identified particle pT spectra

  20. PHOBOS Particle Identification 70 60 50 + - K K K+K 40 30 0 5 4 2 3 1 p (GeV/c) Particle ID from low to high pT PRC 70 (2004) 051901, PRC 75 (2007) 024910  p+p p 1/v (ps/cm) p  ++-  Eloss(MeV) p (GeV/c) Stopping particles dE/dx TOF 3.0 0.3 0.03 pT (GeV/c)

  21. Identified particle pT-spectra, Au+Au at 62.4 GeV Time-of-Flight measurement extends pT reach to 3 GeV/c for protons y0 • Smooth evolution with centrality • Proton spectra are harder thanthe meson spectra PRC 75 (2007) 024910 

  22. Particle production at very low pT 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 PRC 75 (2007) 024910  y0 PHOBOS Au+Au 62.4 GeV • No enhanced production at very low pT • pT-spectra consistent with transverse expansion of the system

  23. mT -scaling in d+Au vs. central Au+Au J.Phys.G 30 S1143-S1147 (2004 ) PRC 70 (2004) 051901(R) mT - Scaling  the same slope of mT –spectra PRC 70 (2004) 051901, PRC 75 (2007) 024910  Lack of mT scaling in central heavy ion collisions

  24. Summary • dNch/d for Au+Au and Cu+Cu • Similar at the same Npart • Factorization of centrality and energy dependence • Extended longitudinal scaling • Elliptic Flow • v2 for A+A is large and continues to grow with energy • Participant eccentricity is relevant for the azimuthal anisotropy • Scaling of v2/ part for Cu+Cu and Au+Au • pT -Spectra of Identified Particles • No enhanced production at very low pT in central Au+Au collisions • Lack of mT scaling in central Au+Au collision consistent with transverse expansion of the system The collision geometry controls the dynamical evolution of heavy ion collisions

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