PHOBOS WHITE PAPER REPORT
Wit Buszaon behalf of the PHOBOS
Collaboration
White paper report, June 2004
• 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)
…Key earlyPHOBOS observation…
Particle Density near Mid-Rapidity
PRL 88, 22302 (2002)PRL 91, 052303 (2003)
PRL 85, 3100 (2000)
Models prior to RHIC
arXiv:nucl-ex/0405027
Initially released energy per unit volume > few GeV/fm3
Note: energy density inside proton ≈ 0.5 GeV/fm3
Energy per unit volume:
11
45
1000~alld
dN
Therefore total energy released in || < 1 is ~2000GeV
Num
ber
of P
artic
les P
r odu
ced
at y
=0
Energy of Collision
dNch
/d
“relevant” initial volume ~ R2 X (0.1fm - few fm) X 2
<E> ~ 0.7 GeV
Data from: PRL 85, 3100 (2000); PRL 88, 22302 (2002); PRL 91, 052303 (2003); arXiv:nucl-ex/0405027
In Au+Au Collisions at sNN = 200 GeV
• Maximum released energy is at mid-rapidity
• In a system at rest with the center of mass
Energy/volume > few GeV/fm3
It is not appropriate to describe such a system in terms of simple hadronic degrees of freedom
AT MID-RAPIDITY THE SYSTEM IS RELATIVELY BARYON-FREE
PRC 67, 021901R (2003)
…The high energy system is strongly interacting…
Evidence from flow:
200 GeV Au+Au PHOBOS preliminary
0 < < 1.50-55% central, h+ + h-
PRL 89, 222301 (2002)Nucl. Phys. A715, 611c (2003)
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
arXiv:nucl-ex/0401006
PHOBOS PHENIX
Evidence from the suppression of high-pT particles:
Au+Au
0-6%
200 GeV
PHOBOS d+Au 200 GeV
PRL 91, 072302 (2003)
STAR
BACK-TO-BACK “JET” CORRELATIONS
PRL 90, 082302 (2003)
Discovery of simple scaling rules…
…in other words,
discovery of global constraints
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
UNIVERSAL TOTAL PARTICLE PRODUCTION
pp pX pp X
provided Mx2 is the same
Brenner et al
In pp collisions, on average, approximately half the energy goes into the leading baryon
A.Brenner et a., Phys.Rev.D26 (1982) 1497l
Relevant energy for comparisons of Au+Au, p+p, and d+Au
arXiv:nucl-ex/0301017
arXiv:nucl-ex/0403033
arXiv:nucl-ex/0301017
ABSENCE OF BOOST INVARIANT CENTRAL PLATEAU
E895 E895 E8953.0 GeV Au+Au
BRAHMS
prel.NA49 NA49
3.6 GeV Au+Au
4.1 GeV Au+Au
8.8 GeV Pb+Pb
17.3 GeV Pb+Pb
200 GeV Au+Au
PHOBOS
Plateau in pseudorapidity distributions is misleading
Rapidity distributions of pions are gaussians
PRL 91, 052303 (2003)
arXiv:nucl-ex/0403050
PHOBOS Preliminary v2200
PHOBOS v2130
No boost-invariant central plateau for v2
PRL 89, 222301 (2002)
UNIVERSAL SCALING ACCORDING TO “LIMITING
FRAGMENTATION”
6% central
Au+Au
beamy
dNch
/d
/<N
part>/
2
PRL 91, 052303 (2003)
Rest frame of A Rest frame of p or d
PHOBOS
arXiv:nucl-ex/0403033
To be submitted PRL June 2004
Energy and pseudorapidity dependence of v2
To be submitted PRL June 2004
Limiting fragmentation seen in v2
Elliptic flow:
To see the limiting behavior, imagine that RHIC collided beams with asymmetric energy, with ´ = -2 corresponding to y = 0.
PRL 91, 052303 (2003)
Universal Npart scaling
Npart scaling for:
pA, dA, AA
10 GeV to 200 GeV
Npart from 2 to 350
E178: J.E.Elias et al., Phys.Rev.D22(1980) 13 arXiv:nucl-ex/0403033
Phobos and E178 data
Preliminary
pp chosen to have the same available energy
FACTORIZATION INTO GEOMETRIC PART AND
ENERGY PART
Preliminary
arXiv:nucl-ex/0403033
Example of factorization into geometric part and energy part:
arXiv:nucl-ex/0403033
SAME SEEN IN p+A AT ALL ENERGIES
Nucl.Phys. A715 (2003) 65-74PRL 91, 052303 (2003)
Phobos
Centrality Dependence at | < 1
PRC 65, 061901R (2002)
arXiv:nucl-ex/0405027
Ratio of 200/130 and 200/19.6
Energy and geometry factorize
arXiv:nucl-ex/0405003
• 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)
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
SPARES
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 LABORATORYINSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY
NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGOUNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER
Collaboration (May 2004)
dN/d
UA5
beamy
• In a wide variety of systems (hadron + A to A+A) 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 p+p, while in A+A, the constant of proportionality is the multiplicity produced in e+e- annihilations or in p+p 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 eta’=eta-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.