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.