# Presentation: 709616

## Charged Hadron pT Spectra from Au+Au at sNN = 62.4 GeV

- C_o_nor Henderson, MIT
- For the                     collaboration
- Division of Nuclear Physics, Chicago
- 29 October 2004

##                     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 Hołyński, 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 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

## PHOBOS Detector 2004

**Spectrometer**

**Paddle Trigger Counter**

**137000 Silicon Pad Channels**

**T0 counter**

**NIM A 499, 603-623 (2003)**

## Centrality Range Studied at 62.4 GeV 

| Centrality | <Npart> | <Ncoll> |
| --- | --- | --- |
| 45-50% | 61  7 | 85  14 |
| 35-45% | 86  9 | 136  22 |
| 25-35% | 130  10 | 240  30 |
| 15-25% | 189  9 | 402  36 |
| 6-15% | 266  9 | 643  48 |
| 0-6% | 335  11 | 883  65 |

## Charged Hadron pT Spectra

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

- nucl-ex/0405003

## RAA for Au+Au at sNN = 62.4 GeV

-  RAA significantly higher at 62.4 GeV than at 200 GeV

## RAA at 62.4 GeV from Theory (I)

- Vitev:
- nucl-th/0404052

- XN Wang:
- nucl-th/0405029

- Adil, Gyulassy:
- nucl-th/0405036

-  From parton energy loss calculations:

## RAA at 62.4 GeV from Theory (II)

- Eskola, Honkanen, Salgado,
- Wiedemann: hep-ph/0406319

- Gallmeister, Cassing: hep-ph/0408223

## Factorization of Energy and Centrality Dependence

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

## Factorization for Particle Multiplicity

- PHOBOS, Phys. Rev. C70, 021902(R) (2004)

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

## PHOBOS PID Capabilities at 62.4 GeV

- dE/dx in Silicon

- Time-of-flight

## Conclusions

- PHOBOS has measured h pT spectra up to 4 GeV in Au+Au 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

## Back-up Slides

## 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

## Definitions

## Centrality Range at 200 GeV

| Centrality | <Npart> | <Ncoll> |
| --- | --- | --- |
| 45-50% | 65  4 | 99  11 |
| 35-45% | 93  5 | 164  15 |
| 25-35% | 138  6 | 286  25 |
| 15-25% | 200  8 | 483  40 |
| 6-15% | 276  9 | 762  57 |
| 0-6% | 344  11 | 1040  77 |

## Centrality Range at 62.4 & 200 GeV

## Npart and Ncoll vs. sNN 

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

## RAANpart and RPCNpart

## RPCNpart vs. Npart in pT bins for 200GeV

## p+p Reference Spectrum at 62.4 & 200 GeV

**Z Phys. C 69, 55 (1995)**

**Nucl. Phys. B 207, 1 (1982)**

**Phys. Lett. B 83, 257 (1979)**

**Nucl. Phys. B 335, 261 (1990)**

- p+p Reference Spectrum at 62.4 & 200 GeV

**SFM @ISR**

## PHOBOS and STAR at 200 GeV

**PLB 578297, 2004**
**PRL 91, 172302, 2003**

## PHENIX pT Spectra at sNN = 200 GeV

- Insert PHENIX reference

## RAA at 62.4 GeV from Theory (IV)

- Adil, Gyulassy: nucl-th/0405036

## RAA at 62.4 GeV from Theory (II)

- Eskola, Honkanen, Salgado, Wiedemann: hep-ph/0406319

-  pQCD collinearly factorized formalism with radiative parton energy loss

## 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