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

1
Charged Hadron Transverse Momentum Distributions
in AuAu collisions at 200 GeV

• Conor Henderson

Massachusetts Institute of Technology
DNP Fall Meeting 2002 9-12 October 2002, NSCL,
MSU
2
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
Holynski, Jerzy Michalowski, Andrzej Olszewski,
Pawel Sawicki, Marek Stodulski, Adam Trzupek,
Barbara Wosiek, Krzysztof Wozniak 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
Wyslouch 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
3
The PHOBOS Detector
2-arm Silicon Spectrometer
Event Trigger
4
The PHOBOS Spectrometer

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

x
5
Spectrometer Performance
6
Charged Hadron Spectra at 200 GeV

• 7.8M AuAu events
• Centrality range 0-50
• Spectra corrected for
• Efficiency acceptance
• Momentum resolution
• Variable bin width
• Ghost tracks and secondaries

7
Centrality, Npart and Ncoll
3-6 uncertainty in ltNpartgt
Participant nucleons and number of binary
collisions related by Glauber calculation
8
Spectra Relative to pp

• Spectra divided by a fit to UA1 pp data at 200
  GeV
• Even most peripheral has large shape difference
  from pp

9
Spectra Relative to Most Peripheral

• Spectra divided by fit to most peripheral
• Shape changes less between peripheral and central
  AuAu, than between pp and peripheral AuAu

10
Slicing spectra in pT bins
We now study the evolution with centrality at a
given pT
11
Centrality-Scaling in pT Bins

• Relative to yield at ltNpartgt65 scaled by
  ltNpartgt
• Centrality evolution surprisingly similar at all
  pT

12
Observed Scaling at High pT
Ncoll-scaling
Normalized to yield at Npart 65
Npart-scaling
13
Summary

• PHOBOS has measured charged hadron pT
  spectra in AuAu collisions at ?SNN200 GeV, over
  the centrality range 65-344 participant nucleons,
  out to pT5 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