# Presentation: 899110

## Results and Perspectives

**Results and Perspectives**

**G****á****bor I. Veres**
**E****ö****tv****ö****s Lor****á****nd University, Budapest *****and***** **
**Massachusetts Institute of Technology, Cambridge**
- for the                      collaboration
***RHIC & AGS Annual Users’ Meeting***
***June 23, 2005***

**PHOBOS Workshop talks:**
**	****George Stephans****	****- Femtoscopy (Tue 6/21)**
**	****Zhengwei Chai ****	****- Multiplicity Fluctuations (Tue 6/21)**

**PHOBOS Posters by: ****Abigail Bickley, Richard Hollis, Carla Vale**

## Another year of spectacular achievement for RHIC & C-AD  THANKS!!!

- Run 5 is the most diverse run so far:
-  9 weeks of Cu+Cu at 200 GeV (6 nb-1)
-  2 weeks of Cu+Cu 62.4 GeV (0.25 nb-1)
-  2 days of Cu+Cu 22.5 GeV
-  few hours of p+p at 410 and 200 GeV

- Mark D. Baker

## The			 Collaboration (June 2005)

- Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel, Wit Busza (Spokesperson), Zhengwei Chai, Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Ian Harnarine, Conor Henderson,
- David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane,
- Piotr Kulinich, Chia Ming Kuo, Wei Li, Willis Lin, Steven Manly, Alice Mignerey,
- Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed,
- Eric Richardson, Christof Roland, Gunther Roland, Joe Sagerer, Iouri Sedykh, Chadd Smith,
- Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov, Artur Szostak,
- Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres,
- Peter Walters, Edward Wenger, Donald Willhelm, Frank Wolfs,  Barbara Wosiek, Krzysztof Woźniak, Shaun Wyngaardt, Bolek Wysłouch
- 	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

- Mark D. Baker

## Outline

- What did we learn in the five years of PHOBOS history?
- Results since the last Users’ Meeting
- Plans and perspectives of PHOBOS

- Mark D. Baker

## 5 years of PHOBOS...

**Data we took in various ****r****u****n****s****:**

|  | p+p | d+Au | Cu+Cu | Au+Au |
| --- | --- | --- | --- | --- |
| 410 | 5 |  |  |  |
| 200 | 2,3,4,5 | 3 | 5 | 2,4 |
| 130 |  |  |  | 1 |
| 62.4 |  |  | 5 | 4 |
| 55.9 |  |  |  | 1 |
| 22.5 |  |  | 5 |  |
| 19.6 |  |  |  | 2 |

- Mark D. Baker

## PHOBOS: number of events on tape...

|  | p+p | d+Au | Cu+Cu | Au+Au |
| --- | --- | --- | --- | --- |
| 410 | 20 |  |  |  |
| 200 | 100 | 150 | 400 | 250 |
| 130 |  |  |  | 4.3 |
| 62.4 |  |  | 110 | 22 |
| 55.9 |  |  |  | 1.8 |
| 22.5 |  |  | 20 |  |
| 19.6 |  |  |  | ~1 |

**[in millions]**

- Mark D. Baker

## Evolution of the detector – Pre-run 1: AuAu

- Evolution of the detector – Pre-run 1: AuAu

- Mark D. Baker

## Run 1: Au+Au

- Mark D. Baker

## Run 2: Au+Au and p+p

## Run 3: d+Au and p+p

- Mark D. Baker

## Run 4 and 5: Au+Au, Cu+Cu

- Mark D. Baker

## Run 4 and 5: p+p

- Mark D. Baker

## Run 6...

- Mark D. Baker

## Data rate and number of events taken

- Continuous DAQ upgrades!

- Over a billion events taken

- Mark D. Baker

## The PHOBOS computing architecture

- ... to cope with _*hundreds of millions*_* of events*

**CatWeb ****–**** ****data management**** (650k files, 400 TByte)**
-  **Easy www interface to stage HPSS********RCF**
**API for access to functionality from ROOT/PhAT**

**AnT – Analysis Tree DST format**
-  **ROOT Tree based, fast ****access to subsets of data**
** ****Well structured, links hits to tracks etc.**

**PROOF – Parallel ROOT Facility**
-  **Parallel ****interactive**** analysis, over ****x100 speed-up****!**
** ****Co-exist with regular batch usage**

**Distributed disks**
-  **100 TByte, fast access**
** ****ALL**** physics ****data**** is stored on disks!**

- Mark D. Baker

## PHOBOS physics publications

**The PHOBOS Perspective on Discoveries at RHIC****Scaling of Charged Particle Production in d+Au Collisions at sqrt(s_NN)=200 GeV****Charged antiparticle to particle ratios near midrapidity in p+p collisions at sqrt(s_NN) = 200 GeV****Transverse momentum and rapidity dependence of HBT correlations in Au+Au collisions at sqrt(s_NN) = 62.4 and 200 GeV****Centrality and pseudorapidity dependence of elliptic flow for charged hadrons in Au+Au collisions at sqrt(s_NN)= 200 GeV****Energy dependence of elliptic flow over a large pseudorapidity range in Au+Au collisions at RHIC****Pseudorapidity dependence of charged hadron transverse momentum spectra in d+Au collisions at sqrt(s_NN)=200 GeV****Collision Geometry Scaling of Au+Au pseudorapidity density from sqrt(s_NN) = 19.6 to 200 GeV****Centrality dependence of charged hadron transverse momentum spectra in Au+Au collisions from sqrt(s_NN) = 62.4 to 200 GeV****Particle production at very low transverse momenta in Au+Au collisions at sqrt(s_NN)=200 GeV****Pseudorapidity Distribution of Charged Particles in d+Au collisions at sqrt(s_NN)=200 GeV****Centrality dependence of charged antiparticle to particle ratios near mid-rapidity in d+Au collisions at sqrt(s_NN)=200 GeV****Centrality Dependence of the Charged Hadron Transverse Momentum Spectra in d+Au Collisions at  sqrt(s****NN****)=200 GeV****Charged hadron transverse momentum distributions in Au+Au collisions at sqrt(s_NN) = 200 GeV****Comparison of the Total Charged-Particle Multiplicity in High-Energy Heavy Ion Collisions with e+e- and pp/pbar-p Data****Significance of the fragmentation region in ultrarelativistic heavy ion collisions****Ratios of charged antiparticles to particles near mid-rapidity in Au+Au collisions at sqrt(s****NN****)=200 GeV****Pseudorapidity and centrality dependence of the collective flow of charged particles in Au+Au collisions**** at sqrt(s****NN****)=130 GeV ****Centrality Dependence of the Charged Particle Multiplicity near Mid-Rapidity in  Au+Au Collisions at sqrt(s****NN****)=130 and 200 GeV ****Energy dependence of particle multiplicities near mid-rapidity in central Au+Au collisions ****Centrality Dependence of Charged Particle Multiplicity at Midrapidity in Au+Au Collisions at sqrt(s****NN****)=130 GeV ****Charged-particle pseudorapidity density distributions from Au+Au collisions at sqrt(s****NN****)=130 GeV ****Ratios of charged particles to antiparticles near mid-rapidity in Au+Au collisions at sqrt(s****NN****)=130 GeV ****Charged particle multiplicity near mid-rapidity in central Au+Au collisions at sqrt(s) = 56 and 130 AGeV **

- 24 papers, including 12 in Phys. Rev. Letters

- Mark D. Baker

## “White Paper”: summary of PHOBOS results

- We have created a state of matter at RHIC with high energy-density, that is nearly net-baryon free and  interacting very strongly.
- Transition to this high-energy state of matter does not create abrupt changes in observables at RHIC energies.
- The data exhibit “simple” scaling behavior and factorization.  → suggests strong _global constraints_ and illustrates the importance of the _collision geometry_ in the initial state and the early evolution of the colliding system.

- _nucl-ex/0410022, Nucl. Phys. A 757, 28_

- Mark D. Baker

## High energy density & nearly baryon-free matter

- _Energy Density Estimate:    _******RHIC** > 3 GeV/fm3

-  Energy density ~6x that of nucleons (20x that of nuclei)

- _Particle Ratios:_
- Approaching Unity

- B at full RHIC energy is a factor ~10 smaller than at SPS.

**(Our new result is p+p@200GeV)**

- Mark D. Baker

## Strongly interacting matter...

- Strongly interacting matter...

-  Elliptic flow reaches hydro limit
-  Suppressed high-pT production
-  No enhanced low-pT production

**PHOBOS nucl-ex/0407012**

**...****flow**

**PHOBOS PRC 70, 051901(R)**

**...****low-p****T**

**...****high-p****T**

**PHOBOS PRL 91, 072302**

**200 GeV ****Au+Au****, 0-50%**

**hydro**

**200 GeV ****Au+Au**

- Mark D. Baker

## Slide 20

- Mark D. Baker

## Recent theoretical interest at low pT

**data: (**********************
**Au+Au 15% central**

***(George Stephans’ talk)***

**J. G. Cramer et al., Phys. Rev. Lett. 94, 102302 (2005)**

- and PHOBOS comment: nucl-ex/0506008

- Mark D. Baker

## Transition is gradual, not abrupt...

- Transition is gradual, not abrupt...

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

**PHOBOS ****PRL 94, 082304**** **

- ...vs. energy

**Au+****Au**

- ...vs. centrality

- Mark D. Baker

## Extended longitudinal scaling...

**PHOBOS PRL 94, 122303**

**PHOBOS nucl-ex/0409021**

- ...in dN/dp+p, d+Au, Au+Au):

- ...in v2 (elliptic flow):

- Mark D. Baker

## Universality of Nch

- PHOBOS  nucl-ex/0301017 &  Nucl. Phys. A 757, 28

- Npart scaling: Au+Au, d+Au

- e+e-, p+p, A+A data
- produces the same Nch

- d+Au

- p+p

- Au+Au

- Mark D. Baker

## Factorization of geometry and energy

- Ratio of dN/d=0 at different energies:

- Also differentially,
- at various pT values:

- Mark D. Baker

## Our most recent results: dN/d in Au+Au at 62.4 GeV

-  **most recent Au+Au run**
** ****B field off**
** ****2 centrality methods****: **
**scint. paddles at 3.2<********<4.5**
**octagon |********|<3**
** ****3 different dN/d******** methods:**** **
**	****analog, digital, ‘tracklets’**

- Mark D. Baker

## The most central data compared to other energies

- Mark D. Baker

## Our new 64.2 GeV point fits into the trend

-  Mid-rapidity yields in
-  ~6% most central events
-  Logarithmic rise

**PHOBOS**
***preliminary***

- Mark D. Baker

## Factorization of beam energy and collision geometry is also valid at 62.4 GeV

-  **at higher energies, hard collisions **
**	****should be more dominant**
** ****N****coll****/N****part**** increases with centrality**
** ****still, ****energy-independent **
**                         ****centrality evolution**

- Factorization of energy
- and collision geometry

- Mark D. Baker

## Extended longitudinal scaling of charged hadrons

- (Also in d+Au and in v2)

- Mark D. Baker

## RPC is precisely energy independent

- Npart

**Ratio of 0-6% and 35-40% centrality bins, each normalized by N****part**

- Mark D. Baker

## Total charged particle yields: Npart scaling

- Total charged particle yields: Npart scaling

- Error bands from the
- extrapolation to high 

**PHOBOS **
***preliminary***

-  **Integrated**** over the full ******** range**
** ****N****ch**** is ****linearly**** increasing with N****part**
** “****wounded nucleon ****scaling****”**
** ****Scaled multiplicity is higher than in p+p**

- Mark D. Baker

## Plans, Perspectives

- Data taking for PHOBOS has ended, but...
- ...lots of data on tape, still to be analyzed in the next years:

** ****Charged hadron spectra in Cu+Cu, p+Au, n+Au collisions**
** ****Identified spectra and particle/antiparticle ratios (Cu+Cu, Au+Au)**
** ****Particle production at very low p****T**** (*****G. Stephans’ talk*****)**
** ****Measurement of the Φ meson**
** ****Multiplicity analysis using ‘tracklets’ and digital/analog method**
** ****Event-by-event multiplicity fluctuations ****(*****Z. Chai’s talk*****)**
** ****Two-particle correlations in d+Au collisions**
** ****Elliptic and directed flow measurements**
** ****Rare event searches**
** ****etc... **

- More news to come!

- Mark D. Baker

## Summary

- Another great year for RHIC (& PHOBOS)
- “White Paper” reviews from the four experiments
- Spectacular and diverse run with many different collisions, and upgraded DAQ and computing
- Luminosities even exceeding the goals
- Multiplicity measurement at 62.4 GeV
- Fits into the known evolution with energy
- Various scaling features observed/confirmed
- Data are simpler than the models!
- Lot of data is still preliminary/in the works:
- Much more results to come in the (near) future!

- ...see you in Budapest!

- Mark D. Baker

## Slide 35

- Mark D. Baker

## Slide 36

- Mark D. Baker