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Charged Particle Multiplicities from Cu+Cu, Au+Au and d+Au Collisions at RHIC

Charged Particle Multiplicities from Cu+Cu, Au+Au and d+Au Collisions at RHIC. Aneta Iordanova University of Illinois at Chicago for the collaboration. Phobos Collaboration.

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Charged Particle Multiplicities from Cu+Cu, Au+Au and d+Au Collisions at RHIC

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  1. Charged Particle Multiplicities from Cu+Cu, Au+Au and d+Au Collisions at RHIC Aneta Iordanova University of Illinois at Chicago for the collaboration

  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 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 Aneta Iordanova

  3. PHOBOS detector Aneta Iordanova

  4. Outline • Control parameters of a heavy ion collision • Energy • 19.6 - 200 GeV • Colliding system size • centrality Npart from 3.5 (d+Au) – 360 (Au+Au) • Species • p+p, d+Au, Cu+Cu and Au+Au • Global features of charged particle production (observables) • dNch/dh shapes (particle distributions in h) • Mid-rapidity factorization Aneta Iordanova

  5. Data comparison of Au+Au and Cu+Cu d+Au and p+p

  6. Au+Au : PRL 91, 052303 (2003) Au+Au : PRC 74, 021901 (2006) d+Au : PRC 72, 031901 (2005) dN/dh distribution 19.6 GeV 62.4 GeV 130 GeV 200 GeV Charged hadron dNch/dh distribution centrality Au+Au data preliminary preliminary Cu+Cu data d+Au • With energy: • Height increases • Width increases (in h space) • With centrality(0-50% central): • Height increases • With species: • Same systematic trends Aneta Iordanova

  7. dN/dh distribution midcentral central Cu+Cu Preliminary 15-25%, Npart = 61 Au+Au 45-55%, Npart = 56 Cu+Cu Preliminary 3-6%, Npart = 100 Au+Au 35-40%, Npart = 99 Comparison of Au+Au and Cu+Cu 200 GeV • For the same collision system size (Npart) dNch/d shape is very similar for • central Cu+Cu with mid-central Au+Au collisions • mid-central Cu+Cu with peripheral Au+Au collisions Aneta Iordanova

  8. dN/dh distribution All at √s = 200 GeV Comparison of Au+Au, d+Au and p+p collisions at 200 GeV • Scale by Npart/2 • allows for a direct comparison to p+p • i.e. normalized to 1 participating pair • Multiplicity obtained at the same center-of-mass energy is similar in p+p and d+Au • Multiplicity is larger for Au+Au collisions at the same energy d+Au : PRL 93, 082301 (2004) Aneta Iordanova

  9. d+Au : PRC 72, 031901 (2005) p+p : 2004 J.Phys.G 30 S1133-1137 dN/dh distribution 2 dNch Npart dη Comparison of d+Au and p+p • More detailed comparison of d+Au and p+p shows • More peripheral collisions tend toward p+p shape PHOBOS d+Au and p+p Data at √s = 200 GeV 3 2 1 0 -6 -4 -2 0 2 4 6 η Aneta Iordanova

  10. factorization at midrapidity in energy and centrality

  11. Au+Au : PRC 74, 021901 (2006) Mid-rapidity factorization PHOBOS PHOBOS Au+Au Au+Au Cu+Cu preliminary Measured pseudorapidity density per participant pair as a function of Npart • Mid-rapidity dNch/dh • Information about the created matter →energy density • Particle production in A+A: interplay between collision centrality (geometry) and collision energy? • balance of binary/soft processes 0-50% cross-section 90 % C.L. 200 GeV (UA5) 19.6 and 62.4 GeV (ISR) Aneta Iordanova

  12. Au+Au : PRC 74, 021901 (2006) Mid-rapidity factorization Midrapidity Ratios • Data ratio 200/X • no centrality (geometry) dependence • Models • HIJING • disagrees with data • Saturation Model (KLN) • flat centrality dependence as in data HIJING PHOBOS 200/19.6 KLN Saturation 200/62.4 200/130 Cu+Cu preliminary Au+Au HIJING:Comput.Phys.Commun. 83 (1994) 307,v 1.35 KLN:Phys.Lett.B523 79 (2001) & arXiv:hep-ph/0111315 Aneta Iordanova

  13. factorization at midrapidity versus pT

  14. pT factorization Transverse Momentum Factorization • So far discussed factorization of bulk matter • ~pT<1GeV/c • Can look at differential factorization for pT bins Aneta Iordanova

  15. pT factorization Transverse Momentum Factorization • Ratio of charged hadron yields in200 and 62.4 GeV • factorization up to pT ≈ 4 GeV/c for Npart > 40 <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 Aneta Iordanova Au+Au: PRL 94, 082304 (2005)

  16. Summary • PHOBOS has measured multiplicity for • large systematic dataset • -5.4<η<5.4 • 2 to 360 participants • √s = 19.6 to 200 GeV • Au+Au and Cu+Cu data are similar at the same Npart • Scaling and factorization properties are found in the Au+Au data • extended longitudinal scaling • mid-rapidity factorization in bulk yield and versus pT • seem to persist into the Cu+Cu collision system • Observed factorization in energy and centrality is seen in multiplicity and versus pT • implies that this is set at an early stage of the collision and is connected with the geometry of the collision Aneta Iordanova

  17. The End

  18. Ratio of yield for200 and 62.4 GeV is centrality independent for all measured pT bins pT factorization Transverse Momentum Factorization Data from PRL 94, 082304 (2005) Aneta Iordanova

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