# Presentation: 666918

## First Results from the 62.4 GeV Run

**Gunther Roland**
**for the **
**PHOBOS Collaboration**

**Centrality Dependence of Charged Hadron Transverse Momentum Spectra in Au+Au Collisions from sqrt(s)= 62.4 to 200 GeV**

## Thanks to CAD!

**Thanks to CAD!**

**62 GeV run great success**
** ****for the machine!**

**time**

**Collision rate**

**65% uptime!**

**9 days**

## PHOBOS 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**

**PHOBOS Collaboration (May 2004)**

## Dense Matter at RHIC

## Dense Matter at RHIC

**High density, largely equilibrated state**
**Small mean free path, large opacity**

**Suppression of hadron **
**production at large p****T**** **

## Energy Dependence of High pT Suppression

**Energy Dependence of High p****T**** Suppression**

## Connection between dN/d and RAA?

**R****AA**** much steeper than dN/d******
**Onset vs smooth evolution of R****AA****?**

**WA98**

-                           ]

## 62 GeV Predictions (0)

**62 GeV Predictions (********0****)**

**WA98**

-                           ]

**Vitev**

**Vitev, nucl-th/0404052 **

## 62 GeV Predictions, part II

**X.N.Wang, nucl-th/0307036 **

**62.4 GeV**

**X.N.Wang , private communication **

## PHOBOS Detector (2004)

- Au+Au 62.4 GeV

**Spectrometer**

**Octagon**

**Paddle Trigger Counter**

**137000 Silicon Pad Channels**

**NIM A 499, 603-623 (2003)**

**SpecTrig**

**TOF**

**T0 counter**

**PHOBOS Detector (2004)**

## Centrality Determination in Au+Au

**b (fm)**

**Centrality Determination in Au+Au**

**<N****coll****>**

**<N****part****>**

**<N****coll****>**

**<N****part****>**

**200 GeV**

**62 GeV**

**Paddle Counter Signal**

**# of Participants (N****part****)**

**top 50% of cross-section**

**<N****part****> 61 to 335**

## Centrality Scaling

**Glauber Monte Carlo**

**Au+Au**

**N****coll****= # of NN collisions: ****~A****4/3**

**N****part****/2 ~ ****A**

**“****Participants”**

**“****Collisions”**

**Centrality Scaling**

## Charged Hadron Spectra at 62.4 GeV

***PHOBOS***

** ****Acceptance**
** ****Efficiency**
** ****Feed-down**
** ****Secondaries**
** ****Momentum resolution**
** ****Ghosts**
** ****Bin width**
** ****Dead channels**

- Corrections:

**Charged Hadron Spectra at 62.4 GeV**

## p+p reference at 62.4 and 200 GeV

**Z Phys. C 69, 55 (1995)**

**Nucl. Phys. B 207, 1 (1982)**

**Phys. Lett. B 83, 257 (1979)**

**Nucl. Phys. B 335, 261 (1990)**

**p+p reference at ****62.4**** and ****200**** GeV**

**SFM @ISR**

## RAA at 62.4 and 200 GeV

***PHOBOS***

**At 62.4 GeV, significantly higher R****AA**** than at 200 GeV**

**PLB 578297, 2004**

**R****AA**** at 62.4 and 200 GeV**

## Energy Dependence of RAA

***PHOBOS preliminary***

**Energy Dependence of R****AA**

## Energy Dependence of RAA

***PHOBOS preliminary***

**Energy Dependence of R****AA**

**Vitev**

## Energy Dependence of RAA

**PHOBOS 62.4 GeV**

**X.N.Wang, nucl-th/0307036 **

## Centrality Dependence of RAA

***PHOBOS***

**PLB 578297, 2004**

**Centrality Dependence of R****AA**

**Large variation of R****AA **** with centrality**
**<N****part****> from 61 to 335**
**<N****coll****> from 76 to 820**
**Similar at both energies?**

## Npart scaling relative to p+p

**Keep p+p as denominator**
**Scale with <N****part****> instead of <N****coll****>**

## RAA      at 200 and 62.4 GeV (Au+Au) 

**R****AA****     **** at 200 and 62.4 GeV (Au+Au) **

**N****part**

**Yields normalized by ****N****part****  less centrality-dependent**

## Centrality Evolution in Au+Au

**Centrality Evolution in Au+Au**

**Use **_***central***_** A+A as denominator**
**Scale with 1/<N****part****>**
**Allows comparison between different experiments**

## RPC  vs. pT, PHOBOS and STAR, 200 GeV

**PLB 578297, 2004**
**PRL 91, 172302, 2003**

**N****part**

## Energy-Independent Centrality Evolution?

**Energy-Independent Centrality Evolution?**

**Yield/participant changes by less than 25% for all p****T**
**Same shape evolution for 62.4 and 200**

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

## Collision Scaling vs Centrality

**Collision Scaling vs Centrality**

## RPC vs RPC

**R****PC**** vs R****PC**

**N****part**

**N****coll**

## Centrality and Energy Evolution

**Centrality and Energy Evolution**

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

## Summary

**First results from 62.4 GeV run**
**Smooth decrease of R****AA**** for central Au+Au with sqrt(s) for p****T**** up to 4 GeV/c**
** ****Large change of R****AA**** with centrality**
**Centrality evolution energy independent **
**< N****part****> from 61 to 335**
**Yield/< N****part****> varies by less than 25%**
**Same shape evolution for 62.4 and 200 GeV data  **