Charged Hadron pT Spectra from Au Au at sNN 62'4 GeV

1
Charged Hadron pT Spectra from AuAu at ?sNN
62.4 GeV

• Conor Henderson, MIT
• For the collaboration
• Division of Nuclear Physics, Chicago
• 29 October 2004

2
Collaboration (October 2004)
Burak Alver, Birger Back, Mark Baker, Maarten
Ballintijn, Donald Barton, Russell Betts, Abigail
Bickley, Richard Bindel, Wit Busza
(Spokesperson), Alan Carroll, Zhengwei Chai,
Vasundhara Chetluru, Patrick Decowski, Edmundo
García, Tomasz Gburek, Nigel George, Kristjan
Gulbrandsen, Clive Halliwell, Joshua Hamblen,
Ian Harnarine, Conor Henderson, David Hofman,
Richard Hollis, Roman Holynski, Burt Holzman,
Aneta Iordanova, Jay Kane, Nazim Khan, Piotr
Kulinich, Chia Ming Kuo, Wei Li, Willis Lin,
Steven Manly, Alice Mignerey, Gerrit van
Nieuwenhuizen, Rachid Nouicer, Andrzej
Olszewski, Robert Pak, Heinz Pernegger, Corey
Reed, Christof Roland, Gunther Roland, Joe
Sagerer, Iouri Sedykh, Wojtek Skulski, Chadd
Smith, 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 INSTITU
TE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS
INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL
UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT
CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF
ROCHESTER
3
PHOBOS Detector 2004
T0 counter
137000 Silicon Pad Channels
Paddle Trigger Counter
Spectrometer
NIM A 499, 603-623 (2003)
4
Centrality Range Studied at 62.4 GeV
5
Charged Hadron pT Spectra

• Corrected for
• Acceptance
• Efficiency
• Feed-down
• Secondaries
• Momentum resolution
• Ghosts
• Bin width
• Dead channels

nucl-ex/0405003
6
RAA for AuAu at ?sNN 62.4 GeV

• RAA significantly higher at 62.4 GeV than at 200
  GeV

7
RAA at 62.4 GeV from Theory (I)

• From parton energy loss calculations

Adil, Gyulassy nucl-th/0405036
Vitev nucl-th/0404052
XN Wang nucl-th/0405029
8
RAA at 62.4 GeV from Theory (II)
Eskola, Honkanen, Salgado, Wiedemann
hep-ph/0406319
Gallmeister, Cassing hep-ph/0408223
9
Factorization of Energy and Centrality Dependence

• Centrality dependence of
• vs. pT is the same at both energies
• Challenge to collision models to reproduce this

10
Factorization for Particle Multiplicity
PHOBOS, Phys. Rev. C70, 021902(R) (2004)

• Factorization also seen for mid-rapidity
  multiplicity, from 19.6 to 200 GeV

11
PHOBOS PID Capabilities at 62.4 GeV
dE/dx in Silicon
Time-of-flight
12
Conclusions

• PHOBOS has measured h? pT spectra up to 4 GeV in
  AuAu collisions at ?sNN 62.4 GeV
• RAA significantly higher at 62.4 GeV than at 200
  GeV
• But the centrality dependence of the pT yields
  found to be remarkably similar at the two
  energies - this factorization also seen in
  mid-rapidity particle yields from 19.6 to 200 GeV
• Appears to be a key feature of heavy-ion
  collisions which remains to be understood

13
Back-up Slides
14
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
15
Definitions
16
Centrality Range at 200 GeV
17
Centrality Range at 62.4 200 GeV
18
Npart and Ncoll vs. ?sNN

• Nucleon-nucleon inelastic cross-section grows
  with collision energy
• So Ncoll/Npart increases with ?sNN

19
RAANpart and RPCNpart
20
RPCNpart vs. Npart in pT bins for 200GeV
21
pp Reference Spectrum at 62.4 200 GeV
SFM _at_ISR
Z Phys. C 69, 55 (1995)
Nucl. Phys. B 207, 1 (1982)
Phys. Lett. B 83, 257 (1979)
Nucl. Phys. B 335, 261 (1990)
22
PHOBOS and STAR at 200 GeV
PLB 578297, 2004 PRL 91, 172302, 2003
23
PHENIX pT Spectra at ?sNN 200 GeV
Insert PHENIX reference
24
RAA at 62.4 GeV from Theory (IV)
Adil, Gyulassy nucl-th/0405036
25
RAA at 62.4 GeV from Theory (II)

• pQCD collinearly factorized formalism with
  radiative parton energy loss

Eskola, Honkanen, Salgado, Wiedemann
hep-ph/0406319
26
RAA at 62.4 GeV from Theory (III)
Gallmeister, Cassing hep-ph/0408223

• Hadron string dynamical transport model
• Hadron attenuation attributed to inelastic
  collisions of leading pre-hadron with dense
  hadronic medium