PHOBOS WHITE PAPER REPORT

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PHOBOS WHITE PAPER REPORT
White paper report, June 2004

• Wit Busza
• on behalf of the PHOBOS Collaboration

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• We have discovered a strongly interacting medium
  with extremely high energy density whose
  description in terms of simple hadronic degrees
  of freedom is not appropriate
• Furthermore, we have discovered that much of the
  data can be expressed in terms of simple scaling
  rules which suggest the existence of strong
  global constraints or some kind of universality
  in the mechanism of the production of hadrons in
  high energy collisions (possible connection to
  ideas of parton saturation)

• To date, in Heavy Ion Collisions, there is no
  evidence for the weakly interacting QGP, as
  naively imagined by a large segment of the
  community before RHIC turn-on and concluded from
  a possible misinterpretation of the lattice
  results (80 of Stefan-Boltzmann is not weakly
  interacting)

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Key earlyPHOBOS observation
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Particle Density near Mid-Rapidity
PRL 85, 3100 (2000)
PRL 88, 22302 (2002)
PRL 91, 052303 (2003)
arXivnucl-ex/0405027
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Energy per unit volume
dNch/dh
Number of Particles Produced at y0
ltEgt 0.7 GeV
Therefore total energy released in h lt 1 is
2000GeV
Energy of Collision
relevant initial volume pR2 X (0.1fm - few
fm) X 2
Initially released energy per unit volume gt few
GeV/fm3 Note energy density inside proton 0.5
GeV/fm3
Data from PRL 85, 3100 (2000) PRL 88, 22302
(2002) PRL 91, 052303 (2003)
arXivnucl-ex/0405027
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• In AuAu Collisions at ?sNN 200 GeV
• Maximum released energy is at mid-rapidity
• In a system at rest with the center of mass
• Energy/volume gt few GeV/fm3
• It is not appropriate to describe such a
  system in terms of simple hadronic degrees of
  freedom

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AT MID-RAPIDITY THE SYSTEM IS RELATIVELY
BARYON-FREE
PRC 67, 021901R (2003)
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The high energy system is strongly interacting
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Evidence from flow
200 GeV AuAu PHOBOS preliminary
0 lt h lt 1.5
0-55 central, h h-
PRL 89, 222301 (2002) Nucl. Phys. A715, 611c
(2003)
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Evidence from the small number of particles
produced with very low pT
In a large volume, weakly interacting system you
would expect the development of particles with
long wavelength
PHOBOS PHENIX
arXivnucl-ex/0401006
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Evidence from the suppression of high-pT
particles
PHOBOS dAu 200 GeV
AuAu 0-6 200 GeV
PRL 91, 072302 (2003)
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BACK-TO-BACK JET CORRELATIONS
STAR
PRL 90, 082302 (2003)
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Discovery of simple scaling rulesin other
words, discovery of global constraints
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DISCOVERY OF SIMPLE SCALING BEHAVIORS

• UNIVERSAL TOTAL PARTICLE PRODUCTION
• ABSENCE OF BOOST INVARIANT CENTRAL PLATEAU
• UNIVERSAL SCALING ACCORDING TO LIMITING
  FRAGMENTATION
• UNIVERSAL Npart SCALING
• FACTORIZATION INTO GEOMETRIC PART AND ENERGY PART

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UNIVERSAL TOTAL PARTICLE PRODUCTION
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Relevant energy for comparisons of AuAu, pp,
and dAu
In pp collisions, on average, approximately half
the energy goes into the leading baryon
A.Brenner et a., Phys.Rev.D26 (1982) 1497l
arXivnucl-ex/0301017 arXivnucl-ex/0403033
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arXivnucl-ex/0301017
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ABSENCE OF BOOST INVARIANT CENTRAL PLATEAU
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PHOBOS
Plateau in pseudorapidity distributions is
misleading Rapidity distributions of pions are
gaussians
PRL 91, 052303 (2003) arXivnucl-ex/0403050
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No boost-invariant central plateau for v2
PHOBOS Preliminary v2200
PHOBOS v2130
PRL 89, 222301 (2002)
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UNIVERSAL SCALING ACCORDING TO LIMITING
FRAGMENTATION
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PRL 91, 052303 (2003)
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Rest frame of A
Rest frame of p or d
arXivnucl-ex/0403033
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(No Transcript)
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Energy and pseudorapidity dependence of v2
To be submitted PRL June 2004
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Limiting fragmentation seen in v2
To be submitted PRL June 2004
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Elliptic flow
PRL 91, 052303 (2003)
To see the limiting behavior, imagine that RHIC
collided beams with asymmetric energy, with h
-2 corresponding to y 0.
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Universal Npart scaling
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Npart scaling for pA, KA, pA, dA, AA 10 GeV to
200 GeV Npart from 2 to 350
Preliminary
Phobos and E178 data
pp chosen to have the same available energy
E178 J.E.Elias et al., Phys.Rev.D22(1980) 13
arXivnucl-ex/0403033
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FACTORIZATION INTO GEOMETRIC PART AND ENERGY PART
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arXivnucl-ex/0403033
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Example of factorization into geometric part and
energy part
SAME SEEN IN pA AT ALL ENERGIES
arXivnucl-ex/0403033
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Phobos
PRL 91, 052303 (2003)
Nucl.Phys. A715 (2003) 65-74
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Centrality Dependence at h lt 1
Ratio of 200/130 and 200/19.6
PRC 65, 061901R (2002) arXivnucl-ex/0405027
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Energy and geometry factorize
arXivnucl-ex/0405003
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• We have discovered a strongly interacting medium
  with extremely high energy density whose
  description in terms of simple hadronic degrees
  of freedom is not appropriate
• Furthermore, we have discovered that much of the
  data can be expressed in terms of simple scaling
  rules which suggest the existence of strong
  global constraints or some kind of universality
  in the mechanism of the production of hadrons in
  high energy collisions

• To date, in Heavy Ion Collisions, there is no
  evidence for the weakly interacting QGP, as
  naively imagined by a large segment of the
  community before RHIC turn-on and concluded from
  a possible misinterpretation of the lattice
  results (80 of Stefan-Boltzmann is not weakly
  interacting)

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WE DO NOT CLAIM THE FOLLOWING

• Phenomena unique to RHIC
• - could be similar to the
  story of jets
• Color deconfinement
• - exact nature of system
  unknown
• Chiral symmetry restoration

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SPARES
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Collaboration (May 2004)
Birger Back, Mark Baker, Maarten Ballintijn,
Donald Barton, Russell Betts, Abigail Bickley,
Richard Bindel, Wit Busza (Spokesperson), Alan
Carroll, Zhengwei Chai, Patrick Decowski,
Edmundo García, Tomasz Gburek, Nigel George,
Kristjan Gulbrandsen, Clive Halliwell, Joshua
Hamblen, Adam Harrington, Michael Hauer, Conor
Henderson, David Hofman, Richard Hollis, Roman
Holynski, Burt Holzman, Aneta Iordanova, Jay
Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo,
Willis Lin, Steven Manly, Alice Mignerey, Gerrit
van Nieuwenhuizen, Rachid Nouicer, Andrzej
Olszewski, Robert Pak, Inkyu Park, Heinz
Pernegger, Corey Reed, Christof Roland, Gunther
Roland, Joe Sagerer, Helen Seals, Iouri Sedykh,
Wojtek Skulski, Chadd Smith, Maciej Stankiewicz,
Peter Steinberg, George Stephans, Andrei
Sukhanov, Marguerite Belt Tonjes, Adam Trzupek,
Carla Vale, Sergei Vaurynovich, Robin Verdier,
Gábor Veres, Peter Walters, Edward Wenger, Frank
Wolfs, Barbara Wosiek, Krzysztof Wozniak, Alan
Wuosmaa, Bolek Wyslouch ARGONNE NATIONAL
LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITU
TE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS
INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL
UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT
CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF
ROCHESTER
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dN/dh
UA5
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• In a wide variety of systems (hadron A to AA)
  the total number of emitted charged particles
  appears to scale linearly with the number of
  participants.
• The total multiplicity of charged particles
  emitted in hadron A is equal to the number of
  participants times the multiplicity observed in
  pp, while in AA, the constant of
  proportionality is the multiplicity produced in
  ee- annihilations or in pp at twice the center
  of mass energy. This is suggestive of a universal
  energy dependence of charged particle
  multiplicities in strong interactions.
• In the forward region, the pseudorapidity
  densities, when measured as a function of the
  shifted variable etaeta-ybeam appear not to
  depend on beam energy. The precise form of the
  distribution depends on the impact parameter, but
  again in an energy- independent way. No evidence
  is seen for a boost invariant central plateau.