# Presentation: 749488

## PHOBOS Discoveries at RHIC

- Wit Busza
- on behalf of the PHOBOS Collaboration

- RBRC Workshop
- 14/15 May 2004

## 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**

##  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,...

- 	**...****however,**
-  **We have *****discovered***** a strongly interacting medium with extremely **_***high energy density***_** whose description in terms of simple *****hadronic***** degrees of freedom makes no sense;**
-  **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***_**.  **

## ...Key earlyPHOBOS observation...

## Particle Density near Mid-Rapidity

**Models prior to RHIC**

**PRL 88, 22302 (2002)**

**PRL 91, 052303 (2003)**

**PRL 85, 3100 (2000) **

## 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 > 5 GeV/fm****3**
-           **It makes **_***no sense***_** to describe it in terms of      **_***simple***__** **__***hadronic degrees of freedom***_

## ...The high energy system is strongly interacting...

## Evidence from flow:

**Hit-based method**
**Track-based method**

**200 GeV Au+Au PHOBOS preliminary**

- 0 <  < 1.5

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

**200 GeV Au+Au PHOBOS preliminary**

**Nucl. Phys. A715 (2003) 611-614**

## 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 could expect the development of particles with long wavelength

**arXiv:nucl-ex/0401006**

## Evidence from the suppression of high-pT particles:

- AuAu
- 200GeV

**PHOBOS dAu 200 GeV**

**PRL 91, 072302 (2003)**

## RAA  as a function of sNN

**R****AA  ****as a function of ********s****NN**

**arXiv:nucl-ex/0405003**

## Discovery of simple scaling rules......in other words, 

**discovery of **_**global constraints**_

## Energy dependence of particle production

**Universality of total multiplicity**
** ****Limiting fragmentation**

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

**Brenner et al**

- Note: In pp collisions, on average, approximately _half the energy_ goes into the _leading baryon_

**arXiv:nucl-ex/0301017**

- A.Brenner et a., Phys.Rev.D26 (1982) 1497l

## Energy dependence of particle production

** ****Limiting fragmentation**

**Energy dependence of particle production**

## No boost invariant central plateau seen in v2 or dN/dy 

**No boost invariant central plateau seen in v****2**** or dN/dy**** **

**PRL 91, 052303 (2003)**

## No boost invariant central plateau seen in dN/dy

**No boost invariant central plateau seen in dN/dy**

- 

**19.6 GeV**

**130 GeV**

**200 GeV**

**PHOBOS**

**AuAu**

- G.Roland, QM2004

- arXiv:nucl-ex/0403033

- Prel.

**PRL 91, 052303 (2003)**

## Universal limiting fragmentation

**Universal limiting fragmentation**

**arXiv:nucl-ex/0403033**

**PRL 91, 052303 (2003)**

## PRL 91, 052303 (2003)

**PRL 91, 052303 (2003)**

## Centrality dependence

## Npart scaling for:

- pA, dA, AA
- 10 GeV to 200 GeV
- Npart  from 2 to 344

- PHOBOS 200 GeV

**arXiv:nucl-ex/0301017**

- arXiv:nucl-ex/0403033

**Phobos and E178 data**

- E178: J.E.Elias et al., Phys.Rev.D22(1980) 13

## Npart scaling for symmetric collisions:

**N****part**** scaling for ****symmetric**** collisions:**

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

**PRL 91, 052303 (2003)**

**Phobos**

**Phobos**

## Npart scaling for asymmetric collisions:

**N****part**** scaling for ****asymmetric**** collisions:**

- arXiv:nucl-ex/0403033

## arXiv:nucl-ex/0405003

**arXiv:nucl-ex/0405003**

**PHOBOS**

**62.4 GeV**
**200 GeV**

##  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,...

- 	**...****however,**
-  **We have *****discovered***** a strongly interacting medium with extremely **_***high energy density***_** whose description in terms of simple *****hadronic***** degrees of freedom makes no sense;**
-  **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***_**.  **