# Presentation: 099896

## Charged Hadron Transverse Momentum Distributions in Au+Au collisions at 200 GeV

- Charged Hadron Transverse Momentum Distributions in Au+Au collisions at 200 GeV

**C**_**o**_**nor Henderson**

- Massachusetts Institute of Technology

-  **DNP Fall Meeting 2002**
**9-12 October 2002, NSCL, MSU**

##                      Collaboration

- 	_ARGONNE NATIONAL LABORATORY_	Birger Back, Alan Wuosmaa
- 	_BROOKHAVEN NATIONAL LABORATORY _	Mark Baker, Donald Barton, Alan Carroll, Nigel George,
- 		Stephen Gushue, George Heintzelman, Burt Holzman,
- 		Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov
- 	_INSTITUTE OF NUCLEAR PHYSICS, KRAKOW_	Andrzej Budzanowski, Roman Hołyński, Jerzy Michałowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski,
- 		Adam Trzupek, Barbara Wosiek, Krzysztof Woźniak
- _	__MASSACHUSETTS INSTITUTE OF TECHNOLOGY_	Maartin Ballintijn, Wit Busza (Spokesperson), Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Jang Woo Lee, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg,
- 		Pradeep Sarin, Stephen Steadman, George Stephans,
- 		 Carla Vale, Gerrit van Nieuwenhuizen, Gábor Veres,
- 		Robin Verdier, Bernard Wadsworth, Bolek Wysłouch
- 	_NATIONAL CENTRAL UNIVERSITY, TAIWAN_	Chia Ming Kuo, Willis Lin, Jaw-Luen Tang
- 	_UNIVERSITY OF ILLINOIS AT CHICAGO_	Russell Betts, Edmundo Garcia, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer
- 	_UNIVERSITY OF MARYLAND_	Abigail Bickley, Richard Bindel, Alice Mignerey,
- 		Marguerite Belt Tonjes
- 	_UNIVERSITY OF ROCHESTER_	Joshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly,
- 		Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs

## The PHOBOS Detector

- 2-arm Silicon Spectrometer

- Event Trigger

## The PHOBOS Spectrometer

- x

- Silicon sensors
- Outer layers in 2T magnetic field
- High segmentation in bending direction
- Tracking within 10 cm of interaction point
- Coverage near mid-rapidity

## Spectrometer Performance

## Charged Hadron Spectra at 200 GeV

- 7.8M Au+Au events
- Centrality range: 0-50%
- Spectra corrected for:
-  Efficiency & acceptance
-  Momentum resolution
- Variable bin width
-  ‘Ghost’ tracks and secondaries

## Centrality, Npart and Ncoll

- Centrality, Npart and Ncoll

| Centrality | <Npart> | <Ncoll> |
| --- | --- | --- |
| 45-50% | 65 | 107 |
| 35-45% | 93 | 175 |
| 25-35% | 138 | 300 |
| 15-25% | 200 | 500 |
| 6-15% | 276 | 780 |
| 0-6% | 344 | 1050 |

** 3-6% uncertainty in <N**part**> **

- Participant nucleons and number of binary collisions related by Glauber calculation

## Spectra Relative to p+p

-  Even most peripheral has large shape difference from p+p

## Spectra Relative to Most Peripheral 

- Spectra Relative to Most Peripheral

- Spectra divided by fit to most peripheral
- Shape changes less between peripheral and central Au+Au, than between p+p and peripheral Au+Au

## Slicing spectra in pT bins...

- Slicing spectra in pT bins...

- We now study the evolution with centrality at a given pT...

## Centrality-Scaling in pT Bins

- Centrality-Scaling in pT Bins

- Relative to yield at <Npart>=65 & scaled by <Npart>
- Centrality evolution surprisingly similar at all pT

## Observed Scaling at High pT

- Observed Scaling at High pT

- Ncoll-scaling

- Normalized to yield
- at Npart = 65

- Npart-scaling

## Summary

- PHOBOS      has measured charged hadron pT spectra in Au+Au collisions at SNN=200 GeV, over the centrality range 65-344 participant nucleons, out to pT=5 GeV/c
- The ‘high-pT suppression’ observed by PHENIX & STAR is found to result in approximate Npart scaling of the particle yields, over the studied centrality range