# Presentation: 529552

## Rapidity and kT dependence of HBT correlations in Au+Au collisions at 200 GeV

- Burt Holzman
- Brookhaven National Laboratory
- for
- the PHOBOS Collaboration:

- Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley, Richard Bindel, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski, Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Stephen Gushue, Clive Halliwell, Joshua Hamblen, Adam Harrington, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Erik Johnson, Jay Kane, Nazim Khan, Piotr Kulinich, _**Chia Ming Kuo**_, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Michael Ricci, 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, Siarhei Vaurynovich, Robin Verdier, Gábor Veres, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Alan Wuosmaa, Bolek Wysłouch, Jinlong Zhang

- ARGONNE NATIONAL LABORATORY, BROOKHAVEN NATIONAL LABORATORY, INSTITUTE OF NUCLEAR PHYSICS, KRAKOW, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, NATIONAL CENTRAL UNIVERSITY, TAIWAN, UNIVERSITY OF ILLINOIS AT CHICAGO, UNIVERSITY OF MARYLAND, UNIVERSITY OF ROCHESTER

## PHOBOS Schematic

- 200 GeV Au+Au dataset after HBT cuts:
- 1 million events7 million pairs

## PHOBOS Spectrometer

-  Reversible 2T field
-  Two symmetric arms
-  Fine pixel granularity    gives small two- particle inefficiency   region (25x50 mrad)
-  p/p < 1.5%
-  Pairs with small q also have small separation   at detector: small detectors  are good for HBT!

## HBT @ RHIC: Challenge for Theory

- 	Newer models include opacity but still don’t fit data, i.e. Hirano & Tsuda [NPA 715, 815 (2002)]

- I will not be solving the HBT puzzle; but I will dump more pieces into the mix!

- PHOBOS 200 prelim. -- [NPA 715, 611 (2002)]
- STAR 130 [PRL 87, 082301 (2001)]
- PHENIX 130 [PRL 88, 192302 (2002)]
- Theory: Soff, Bass, Dumitru [PRL 86, 3981 (2001)]

- Huge (15 fm) source doesn’t exist at RHIC
- Ro/Rs ~ 1

- PHOBOS Preliminary

## Some HBT definitions

- kT: pair transverse momentum
- Bertsch-Pratt (BP) parameterization
- Yano-Koonin-Podgoretsky (YKP) parameterization

## MC studies

|   |  | Rout (fm) | Rside (fm) | Rlong (fm) | Rol  (fm) |
| --- | --- | --- | --- | --- | --- |
| MC | .48.02 | 3.2  .14 | 18.0 .9 | 5.8  .2 | 1.2  .4 |
| Recon | .43.02 | 3.1  .15 | 16.1  .9 | 5.8  .3 | 1.5  .3 |

- First principles HBT generator [Kadija & Seyboth, PLB 287, 63, (1992)] - we can do 15 fm!

- That was our first naive attempt -- let’s try something else

## MC studies

|   |  | Rout (fm) | Rside (fm) | Rlong (fm) | Rol (fm) |
| --- | --- | --- | --- | --- | --- |
| MC | .5 | 4.0 | 4.0 | 4.0 | 2.0 |
| Recon | .52  .02 | 4.1  .13 | 4.2  .4 | 4.2  .2 | 1.6   .7 |

- HIJING (weight “actual” pairs), simulate detector with GEANT, real reconstruction

- We can reproducecorrelation functions quite well

## PHOBOS Coulomb Correction

- Usual plot

**Gamow****λ = 1     R****inv**** =  5 fm**
**λ = 0.5  R****inv**** =  5 fm****λ = 0.1  R****inv**** =  5 fm**

**Coulomb Correction**

**Qinv (GeV/c)**

**PHOBOS Coulomb Correction: Used from Day 1**

- 
- Rout
- Rside
- Rlong
- Rol

- 0.57  .05 4.7  .3 fm4.3  .4 fm 5.1  .3 fm1.2  1.9 fm2

- PHOBOS
- CoulCorr

- Ceres02
- CoulCorr

- 2

- PHOBOS data corrected with

- 0.57  0.04
- 4.8  0.3 fm
- 4.4  0.4 fm
- 5.0  0.3 fm
- 1.6  1.8 fm2

## Coulomb Correction II

- Bowler(‘91)/Sinyukov(‘98)/CERES(‘02)/STAR(‘03)/PHENIX(‘03)

- PHOBOS(‘02)

## Particle Identification

- K-

- 

- Contamination from K, pp, pK < 10%
- Contamination from KK, pp < 1%

## Bertsch-Pratt vs. kT

- Au+Au -- 0-15% central

## Bertsch-Pratt vs. kT: RHIC data

- Bertsch-Pratt vs. kT: RHIC data

- PHOBOS 200 GeV prelim.
- STAR QM2002 [NPA 715, 623 (2002)]
- PHENIX PRL (sub.) [nucl-ex/0401003]

- Au+Au -- central

- PHOBOS Preliminary

- PHOBOS Preliminary

- PHOBOS Preliminary

- PHOBOS Preliminary

## Bertsch-Pratt vs. Y

- Within errors, no BP Y-dependence in our acceptance

- PHOBOS Preliminary

- PHOBOS Preliminary

- PHOBOS Preliminary

## Why YYKP ?

- YYKP

- Y

- Exploding source in zstrong p-z correlations

- Y scales with YYKP

- Slowly expanding source in zweak p-z correlations

- Y slowly varies

- z

- z

## Yano-Koonin-Podgoretsky vs. Y

- Pair rapidity scales with source rapidity

- Fit in LCMS frame

- PHOBOS Preliminary
- 0-15 % Central

- Fit in Lab frame

- PHOBOS Preliminary0-15% Central

- All results presented in lab frame

## Comparison to NA49

- SPS (sNN = 17.2 GeV) RHIC (sNN = 200 GeV) both exhibit similar scaling behavior

- Fit in LCMS frame

- PHOBOS Preliminary
- NA49 [EPJ c2, 661 (1998)]

## Conclusions & Outlook

- More pieces added to the puzzle
- PHOBOS nicely complements the current RHIC HBT dataset in kT and Y
- Rout, Rside, Rlong: consistent with weak or no rapidity dependence from .4 < Y < 1.3
- Pair rapidity scales with source rapidity
- High statistics from current RHIC run will decrease errors and increase kT reach
**See C. Ming Kuo’s poster at 5 pm**