# Presentation: 671415

## PHOBOS WHITE PAPER REPORT

- Wit Busza
- on 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***** *****Q****G****P****, 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 earlyPHOBOS observation...

## Particle Density near Mid-Rapidity

**PRL 88, 22302 (2002)**

**PRL 91, 052303 (2003)**

**PRL 85, 3100 (2000) **

**arXiv:nucl-ex/0405027**

## Note: energy density inside proton ≈ 0.5 GeV/fm3 

- Note: energy density inside proton ≈ 0.5 GeV/fm3

**Energy per unit volume:**

**Therefore total energy released in**
** ****|********| < 1 is ~2000GeV**

**Number of Particles Produced at y=0**

**Energy of Collision**

**dN****ch****/d******

- “**relevant” initial volume ~ ********R****2 **** 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/fm****3**
-       **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:

**Evidence from ****flow:**

**200 GeV Au+Au PHOBOS preliminary**

- 0 <  < 1.5

- 0-55% central, h+ + h-

**PRL 89, 222301 (2002)**
**Nucl. Phys. A715, 611c (2003)**

## Evidence from the small number of particles produced with very low pT:

**Evidence from the small number of particles produced with very ****low p****T****:**

**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

**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 N****part**** SCALING**
**FACTORIZATION INTO GEOMETRIC PART AND ENERGY PART**

## UNIVERSAL TOTAL  PARTICLE PRODUCTION

## In pp collisions, on average, approximately half the energy goes into the leading baryon

- 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

**arXiv:nucl-ex/0301017**

## ABSENCE OF BOOST INVARIANT CENTRAL PLATEAU

## Plateau in pseudorapidity distributions is misleading

**PHOBOS**

**Plateau in pseudorapidity distributions is misleading**
**Rapidity distributions of pions are gaussians**

**PRL 91, 052303 (2003)**
**arXiv:nucl-ex/0403050**

## No boost-invariant central plateau for v2

-  * **PHOBOS Preliminary**** *****v****2****200**

* **PHOBOS**** *****v****2****130**

**No boost-invariant central plateau for v****2**

**PRL 89, 222301 (2002)**

## UNIVERSAL SCALING ACCORDING TO “LIMITING FRAGMENTATION”

## PRL 91, 052303 (2003)

**PRL 91, 052303 (2003)**

## Rest frame of A

**Rest frame of p or d**

**arXiv:nucl-ex/0403033**

## Slide 24

## Energy and pseudorapidity dependence of v2

**To be submitted PRL June 2004**

**Energy and pseudorapidity dependence of v****2**

## Limiting fragmentation seen in v2

**To be submitted PRL June 2004**

**Limiting fragmentation seen in v****2**

## Elliptic flow:

**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:

- 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

## 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**

## Phobos

**Nucl.Phys. A715 (2003) 65-74**

**PRL 91, 052303 (2003)**

**Phobos**

## Centrality Dependence at | < 1

**Centrality Dependence at |******** < 1**

**PRC 65, 061901R (2002)**
**arXiv:nucl-ex/0405027**

**Ratio of ****200/130**** and 200/19.6**

## Energy and geometry factorize

**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***** *****Q****G****P****, 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

## Collaboration (May 2004)

**Richard Bindel****, ****Wit**** Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski, **
**Edmundo Garc****í****a, 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**
**	****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**

## dN/d

**dN/d**********

**UA5**

## 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. 

- 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.