# Presentation: 896371

## The 4 Phases of Phobos

- RHIC Users Meeting, May 2008

- Wit Busza

## Phobos a Success Story for 

- RHIC Users Meeting, May 2008

- Phobos a Success Story for

- The RHIC Management
- The PAC
- The Accelerator Department
- The DoE
- HEP/NP Collaboration
- The Phobos Collaboration

## Origins of PHOBOS Collaboration

- RHIC Users Meeting, May 2008

- NP:   Phase Diagram and
-            Properties of Hot QCD Matter ?
- HEP: Mechanism of Multiparticle
-            Production ?

- New
- Phobos

## Physics Expectations and Prejudices in late 1980’s and early 1990’s were very different from those today.  We were driven by the possibility that there will be a 

- RHIC Users Meeting, May 2008

- Physics Expectations and Prejudices in late 1980’s and early 1990’s were very different from those today.  We were driven by the possibility that there will be a

- Discontinuity of observables as a function of energy and system size
- Very significant increase in multiplicity and expansion of produced system
- Possible production of disoriented chiral condensate & of large number of very low pT particles

- Management showed wisdom & foresight to encourage a highly varied research program, including large & small experiments

## PAC came to our rescue by rejecting this proposal

- RHIC Users Meeting, May 2008

## From MARS Proposal:

- RHIC Users Meeting, May 2008

## Fermilab E178 (PR D22 (1980) 13)) 

- RHIC Users Meeting, May 2008

- Fermilab E178 (PR D22 (1980) 13))

- PHOBOS

## 13 June 2000:

- Wit Busza

- RHIC Users Meeting, May 2008

- 19 July 2000:

- Management & DoE came to our rescue by not giving us enough money in the early phases of PHOBOS and thus prevented us from first using it at the AGS.  However Management did give us enough to be ready on day one at RHIC.

- First result & it has withstood the test of time!

## Pre-RHIC theoretical predictions

- RHIC Users Meeting, May 2008

- First RHIC
- result

- PHOBOS, Nucl. Phys. A747, 28 (2003)

- Phobos data

**Notes:**
First a quick look back in the history.
Before RHIC turned on there was a large number of theoretical predictions for the multiplicity of particles emitted at mid-rapidity in 200 GeV Au+Au collisions.
The predictions varied by up to a factor of two as illustrated here.
In retrospect we see that the experimental value for 200 GeV lies in in the lower range of the predictions.
In fact, the increase in charged particle multiplicity at eta=0 with energy turns out to be only logarithmic as shown in the right panel.

## PHOBOS Detector

- RHIC Users Meeting, May 2008

- Unique low-pT measurements

- Large acceptance for Nch -5.4 < η < 5.4  (0.5o < θ < 179.5o )0 < φ < 2π

- First
- Quarter
- of
- Phobos

##           Collaboration

- RHIC Users Meeting, May 2008

-           Collaboration

- B.Alver, B.B.Back, M.D.Baker, M.Ballintijn, D.S.Barton, S.Basilev, R.Baum, B.Becker, R.R.Betts, A.A.Bickley, A.Białas, R.Bindel, W.Bogucki, A.Budzanowski, W.Busza*, A.Carroll, M. Ceglia, Z.Chai, Y.-H.Chang, A.E.Chen, V.Chetluru, T.Coghen, C.Conner, W.Czyż, B.Dąbrowski, M.P.Decowski, M.Despet, P.Fita, J.Fitch, M.Friedl, K.Gałuszka, R.Ganz, E.García, T.Gburek, N.George, J.Godlewski, C.Gomes, E.Griesmayer, K.Gulbrandsen, S.Gushue, J.Halik, C.Halliwell, J.Hamblen, P.Haridas, I.Harnarine, A.S.Harrington, M.Hauer, A.Hayes, G.A.Heintzelman, C.Henderson, D.J.Hofman, R.S.Hollis, R.Hołyński, B.Holzman, A.Iordanova, E.Johnson, J.L.Kane, J.Katzy, N.Khan, W.Kita, J.Kotuła, H.Kraner, W.Kucewicz, P.Kulinich, C.M.Kuo, C.Law, J.W.Lee, M.Lemler, W.Li, J.Ligocki, W.T.Lin, C.Loizides, S.Manly, D.McLeod,  J.Michałowski, A.Mignerey, J.Mülmenstädt, M.Neal, R.Nouicer, A.Olszewski, R.Pak, I.C.Park, M.Patel, H.Pernegger, M.Plesko, C.Reed, L.P.Remsberg, M.Reuter, E.Richardson, C.Roland, G.Roland, D.Ross, L.Rosenberg, J.Ryan, J.Sagerer, A.Sanzgiri, P.Sarin,  P.Sawicki, J.Scaduto, H.Seals, I.Sedykh, J.Shea, J.Sinacore, W.Skulski, C.E.Smith, M.A.Stankiewicz, S.G.Steadman, P.Steinberg, G.S.F.Stephans, A.Strączek, M.Stodulski, M.Stręk, Z.Stopa, A.Sukhanov, K.Surowiecka, A.Szostak, J.-L.Tang, R.Teng, M.B.Tonjes, A.Trzupek, C.Vale, G.J.van Nieuwenhuizen, S.S.Vaurynovich, R.Verdier, G.I.Veres, B.Wadsworth, P.Walters, E.Wenger, D.Willhelm, F.L.H.Wolfs, B.Wosiek, K.Woźniak, A.H.Wuosmaa, S.Wyngaardt, B.Wysłouch, K.Zalewski, J.Zhang, P.Żychowski
- 	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
- *spokesperson

## PHOBOS Achievements

- RHIC Users Meeting, May 2008

- 4π coverage allowed unique study of global properties
- Discovery of simplicity and scaling of global properties
- Npart scaling
- Logarithmic rise of mid rapidity particle density
- Extended longitudinal scaling of dn/dη and ν2
- Observation that over entire RHIC energy range no signs of discontinuity in global observables
- No signs of increase in particle production at low pT
- Extensive studies of correlations and fluctuations (still continuing), in particular related to eccentricity fluctuations
- Phobos results have been shown to be reliable.

- Full Moon
- Phobos

## PHOBOS Results on Pseudorapidity Distributions 

- RHIC Users Meeting, May 2008

- PHOBOS Results on Pseudorapidity Distributions

- * PHOBOS  PRL 91,52303 (2003)

- 19.6 GeV

- 200 GeV Cu+Cu

- 200 GeV Au+Au

- 130 GeV

- 62.4 GeV

- 22.4 GeV
- PHOBOS

- 62.4 GeV

- 200 GeV d+Au

- 25-35%
- 35-45%
- 45-55%

- 0-6%
- 6-15%
- 15-25%

- 10-20%
- 20-40%
- 40-60%
- 60-80%
- 80-100%

- PRL 91, 052303 (2003)
- PRC 74, 021901 (2006)
- PRC 72, 031901 (R)(2005)
- arXiv:0709.4008 [nucl-ex]

**Notes:**
This slide shows the complete set of multiplicity data for Au+Au collisions published by PHOBOS.
We also have measurements for Au+Au at 62.4 GeV and Cu+Cu at 200 GeV, which are present being analyzed and prepared for publication.
Note the very modest increase in the height of the mid-rapidity plateau with beam energy.
Note the increase in width of the distributions with collision energy.The latter is largely responsible for accounting for the factor 10 increase in energy between 20 and 200 GeV, because it becomes increasingly expensive to emit particles at large pseudorapidities because of the cosh_eta term in the energy of such particles.
Also note that for 20 GeV we see an ABSOLUTE increase in particle production in the wings of the distribution when going to more peripheral collisions. We believe that this growth reflects emission from spectator fragments. Simple model of such emission patterns support this hypothesis.

## Phobos results on elliptic flow of charged particles

- RHIC Users Meeting, May 2008

- Data

- Au+Au

- 19.6 GeV

- 62.4 GeV

- 130 GeV

- 200 GeV

- preliminary

- preliminary

- PHOBOS

- Cu+Cu

- AuAu:  PHOBOS: PRL 94 122303 (2005)
- CuCu: PHOBOS: PRL 98, 242302 (2007)

## Extended longitudinal scaling – Au+Au

- RHIC Users Meeting, May 2008

- PHOBOS Phys. Rev. Lett. 91, 052303 (2003) / Nucl. Phys. A757, 28 (2005)

**Notes:**
I’ll now return to Au+Au collisions and see what we can learn from studying the wings of the distributions.
Again, in pp collisions it has been known for a long time that the particle production seen in the rest frame of one of the collision partners is essentially independent of the collision energy. This phenomenon has been given the term “limiting fragmentation scaling”
 For dN/deta distributions in Au+Au collisions we also observe this scaling feature. i.e. when the distributions are plotted istead againsy the parameter η’= η +- ybeam they line up with an astonishing degree of accuracy over a certain region before peeling off as the mid-rapidity plateau is approached.
The reason that this works also for dN/deta distributions is that dN/dy and dN/deta distributions are the same away from mid-rapidity as long as a small shift ln(pT/mT) is applied
Note again the contribution of spectator emission for the peripheral collisions at 20 GeV 

## Extended longitudinal scaling – Au+Au, Cu+Cu, d+Au and p+A    

- RHIC Users Meeting, May 2008

- Extended longitudinal scaling – Au+Au, Cu+Cu, d+Au and p+A

- PHOBOS, arvix:0709.4008 [nucl-ex]

- PHOBOS, Phys. Rev. C72,  031901(R) (2005)

## PHOBOS: PRL 94, 122303 (2005)

- PHOBOS
- 40% most central   Au+Au

- Extended longitudinal scaling seen in elliptic flow!

## Factorization of centrality and energy dependence

-                            PRC70,021902(R) (2004);
-                            PRC65, 061901(R) (2002)
- Figure: B.Back, Big Sky (2007)

- Wit Busza

- RHIC Users Meeting, May 2008

- |η|<1

- Nucl.Phys. A715 (2003) 65-74
- PRL 91, 052303 (2003)

## Npart Scaling holds in AA collisions                     Universality of

- RHIC Users Meeting, May 2008

- arXiv:0709.4008 [nucl-ex]

- PHOBOS

- Npart Scaling holds in AA collisions                     Universality of

## Antiparticle to particle ratios

- PRC: accepted for publication

## UNIQUE PHOBOS measurements on energy and centrality dependence of the low-pT spectra

- RHIC Users Meeting, May 2008

- UNIQUE PHOBOS measurements on energy and centrality dependence of the low-pT spectra

- Au+Au 62.4 GeV
- PHOBOS

- Phys. Rev. C75, 024910 (2007)

- No anomalous low pT enhancement

- Au+Au 200 GeV  0-6%

- PHOBOS preliminary

- Phobos, Gburek, QM 2008

## PHOBOS RESULTS THAT WILL HAVE LASTING VALUE AND WHICH NEED TO

- BE UNDERSTOOD AND EXPLAINED
**Simplicity and universality of Global Data - often data is simpler than the explanations!**
**Geometry of the collision plays a crucial role in determining a surprising number of particle production properties**
**Many phenomena can be factorized into an energy and centrality part **
**Number of participants plays a crucial role in determining the integral of the distributions (participant scaling)**
**Extended longitudinal scaling (including v****2****)**
**Importance of participant eccentricity in determining flow**

##              CURRENT PHASE OF PHOBOS

- Last
- Quarter of
- Phobos

**             ****CURRENT PHASE OF PHOBOS**
**STUDY OF FLUCTUATIONS AND CORRELATIONS**

## PHOBOS Flow Fluctuation Studies

- RHIC Users Meeting, May 2008

- CGC: Drescher & Nara arXiv:0707.0249

- Au+Au
- 200GeV

## Phobos Studies of Two-Particle Correlations

- RHIC Users Meeting, May 2008

## Phobos Ridge Studies

- RHIC Users Meeting, May 2008

- Near-side
- |Δφ|<1

- =

- - a (

- )

- -4 < Δη < -2
- |Δφ| < 1

## Summary

- RHIC Users Meeting, May 2008

**Phobos refereed**
**publications**
- PRL - 13
- PRC (RC) - 14
- PRC - 4
- Phys Lett - 1
- Nucl Phys A - 1_x0010__x0010_
- Physics total - 33
- NIM - 7
**PHOBOS citations**
- Total = 2152
- 1 Famous (>250)
- 8 Very well-known (>100)
- 5 well-known (>50)

## We wish to thank 

- RHIC Users Meeting, May 2008

- We wish to thank

- RHIC management
- RHIC Accelerator & RCF staff
- DoE

- For all the help and support you have given to PHOBOS.

## Where is the PHOBOS detector now?