Title: Energy and Centrality Dependence of Charged Hadron pT Spectra from Au Au at sNN 62'4 and 200 GeV
1Energy and Centrality Dependence of Charged
Hadron pT Spectra from AuAu at ?sNN 62.4 and
200 GeV
- Edward Wenger, MIT
- For the Collaboration
- APS Meeting, Tampa
- 17 April 2005
2 Collaboration (April 2005)
Burak Alver, Birger Back, Mark Baker, Maarten
Ballintijn, Donald Barton, Russell Betts,
Richard Bindel, Wit Busza (Spokesperson),
Zhengwei Chai, Vasundhara Chetluru, Edmundo
García,Tomasz Gburek, 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, 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 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
3PHOBOS Detector (2005)
T0 counter
Time-of-Flight
Spectrometer Trigger
Calorimeter
Paddle Trigger Counter
Vertex Detector
Octagon
Spectrometer
NIM A 499, 603-623 (2003)
4The PHOBOS Spectrometer
- Corrected for
- Acceptance
- Efficiency
- Feed-down
- Secondaries
- Ghosts
- Momentum Resolution
- Bin width
- Dead channels
10 cm
70 cm
z
x
y
5Overview
- Look at centrality evolution of h? pT spectra in
AuAu collisions at ?sNN 62.4 GeV - Examine scaling behavior with binary collisions
and participant pairs over this range of
centrality - Compare factorization in centrality and collision
energy to other Phobos results
6Charged Hadron pT Spectra
- How do the spectra scale with centrality?
- And with collision energy?
- (How does one quantify centrality?)
62.4 GeV AuAu
PRL 94, 082304 (2005)
7Centrality measures
Participants
Npart/2 A (volume)
Collisions
Ncoll of NN collisions A4/3
Collisions
8Centrality measures
Participants
Glauber Model (AuAu)
Npart/2 A (volume)
Collisions
Ncoll of NN collisions A4/3
Collisions
9RAA at 200 and 62.4 GeV (AuAu)
pp reference data 62.4 GeV ISR SFM,
0.5lt?lt1 200 GeV UA1 -2.5lt?lt2.5 (acceptance
correction with PYTHIA)
Gradual suppression compared to Ncoll scaling
10 RAA
Npart
PERIPHERAL
CENTRAL
Yields normalized by Npart are less
centrality-dependent
11Factorization energy, centrality
PRL 94, 082304 (2005)
12Factorization energy, centrality (II)
- Particle production at pT gt 1 GeV/c is expected
to be influenced by many effects - Cronin effect
- Medium-induced energy loss of fast partons
- Collective transverse velocity fields
- Parton recombination
- All these effects are expected to exhibit
different dependences on collision energy,
centrality - Yet we see surprisingly clean factorization
13Factorization for Particle Multiplicity
PHOBOS, Phys. Rev. C70, 021902(R) (2004)
- Factorization also seen for mid-rapidity
multiplicity, from 19.6 to 200 GeV
14 Rapidity Distributions
PRL 91, 052303 (2003)
15Conclusions
- 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 and in pseudorapidity
distributions from 19.6 to 200 GeV - Appears to be a key feature of heavy-ion
collisions which remains to be understood
16Outlook
- How do the spectra depend on system size (nuclear
mass number)? - Centrality and A can be dialed separately
AuAu, peripheral
CuCu, central
similar Npart, different geometry
Half a BILLION CuCu events recorded recently
for this analysis (at 200, 62.4, and 22.5 GeV)!
17Back-up Slides
18Centrality Determination
DataMC
200 GeV
b (fm)
Npart
Paddle signal (a.u.)
62.4 GeV
Paddle signal (a.u.)
19Centrality Range at 62.4 200 GeV
20PHOBOS PID Capabilities at 62.4 GeV
dE/dx in Silicon
Time-of-flight
21RAA 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
22RAA at 62.4 GeV from Theory (II)
Eskola, Honkanen, Salgado, Wiedemann
hep-ph/0406319
Gallmeister, Cassing hep-ph/0408223
23RPCNpart vs. Npart in pT bins for 200GeV
24pp 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)
25Definitions
26PHOBOS and STAR at 200 GeV
PLB 578297, 2004 PRL 91, 172302, 2003
27PHENIX pT Spectra at ?sNN 200 GeV
Insert PHENIX reference
28Cronin Effect in dAu vs. Centrality
Phys.Rev.Lett. 91, 072302 (2003)
6 most central AuAu
29RAA at 62.4 GeV from Theory (II)
- pQCD collinearly factorized formalism with
radiative parton energy loss
Eskola, Honkanen, Salgado, Wiedemann
hep-ph/0406319
30RAA 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
31RAA at 62.4 GeV from Theory (IV)
Adil, Gyulassy nucl-th/0405036