# Presentation: 666920

## Charged Hadron pT Spectra from PHOBOS in Au+Au Collisions at 62.4 GeV

- Charged Hadron pT Spectra from PHOBOS in Au+Au Collisions at 62.4 GeV

##              Collaboration (April 2004)

**Birger Back,**** ****Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, ****Abigail Bickley****, **
**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 Hołyński, 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 Woźniak, Alan Wuosmaa, 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**

- Gábor I. Veres

## The PHOBOS Detector (2004)

**The 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**

- Gábor I. Veres

## Motivation for energy scan at RHIC

-        **R****AA**** <<1 **
**at 200 and 130 GeV**

**Shown to be final state effect (Au+Au vs. d+Au)**

**Search for the onset of high-p****T**** suppression**

- Gábor I. Veres

## Number of binary collisions

**Number of binary collisions**

**Glauber Monte Carlo**

**Au+Au**

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

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

**“****Participants”**

**“****Collisions”**

- Gábor I. Veres

## Au+Au 62.4 GeV pT spectra vs. centrality

***PHOBOS preliminary***

-  acceptance
-  efficiency
-  feed-down
-  secondaries
-  momentum resolution
-  ghosts
-  bin width
-  dead channels

- Corrections:

- Gábor I. Veres

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

***PHOBOS preliminary***

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

- p+p reference data at 62.4 GeV: ISR SFM, 0.5<η<1
- (acceptance correction with PYTHIA)

**PLB 578297, 2004**

- Gábor I. Veres

## Energy dependence of RAA in pT bins

***PHOBOS preliminary***

***PHOBOS preliminary***

- Gábor I. Veres

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

**Npart**

**Yields normalized by N****part**** are more centrality-independent**

- Gábor I. Veres

## Evolution with centrality... universal?!

- Gábor I. Veres

## Scaling violated in Ncoll

**Scaling violated in N****coll**

***PHOBOS preliminary***

- Gábor I. Veres

## Closer look at the peripheral bin

***PHOBOS preliminary***

**Closer look at the peripheral bin**

- N**part** scaling is more precise than N**coll** scaling

- Gábor I. Veres

## Summary

-  **Charged hadron p****T**** spectra measured in Au+Au@62.4 GeV**
** ****For p****T****>2 GeV/c,  R****AA ****is significantly larger than at 200 GeV**
** ****Yields/N****part**** smoothly evolve from peripheral to central**

** ****This evolution is independent of collision energy!**
** ... ****and that is not true for yields normalized by N****coll****...****            geometry (N****part****) plays an important role!**

**...****but surprisingly...**

- Gábor I. Veres