HBT Radii and Space-Momentum Correlation at RHIC

Jingbo Zhang

Department of Physics, Harbin Institute of Technology

July 11, 2008 @ Hefei

July 11, 2008

HBT effect uses to find the size of the fireball from a measurement of two particle correlation function.

Two particle correlation function

)(1 kk

)(2 lk

ondistributi particle single :)( on,distributi particle two:),( 11212

2111

21221

)()(

),(),(

kPkkP

kPkP

kkPkkC

source theofdensity Wigner particle single :),(

,2 2121

2224

1114

24

),(),(

)2,(1),(

kxS

kkqkkK

kxSxdkxSxd

eKxxSdqKC

xiq

July 11, 2008

Transverse mass dependence: Au+AuTransverse mass dependence: Au+Au

LPSW(05) - DATA in color-- experimentalist’s plot

July 11, 2008

Transverse mass dependence:Transverse mass dependence: elementary collisions elementary collisions

mT dependence in elementary collisions (e.g. OPAL, DELPHI, E735) usually attributed to

• String fragmentation

• Resonance contribution

• Heisenberg uncertainty

G. Alexander, hep-ph/0302130

DELPHI - e+e- annihilation

July 11, 2008

Transverse mass dependence: pTransverse mass dependence: p++pp

p+p: HBT radii decrease with increase of mTSTAR data

flow not expected in such a small system as p+p

Shuryak: hep-ph/0405066

mT dependence of HBT radii in pp is not generated by the transverse flow, but by the transverse temperature inhomegeneities of hadron-hadron collisions due to the freezing scale – Csorgo et al.: hep-ph/0406042

July 11, 2008

Surprising Surprising SScalingcaling

All pT(mT) dependences of HBT radii observed by STAR scale with pp although it’s expected that different origins drive these dependences

July 11, 2008

RQMD + Correlation after a burner

222222

1)( llssoo RqRqRqeqC

mt-dependence due tocollective flow?or space-momentumcorrelation?

July 11, 2008

Single-particle mt-spectra

July 11, 2008

Slope Parameter

July 11, 2008

Radial Expansion Velocity

outp

TTout pRp

outp

Tp

outR

0outv

0outv

x

y

July 11, 2008

Single-particle mt-spectra II

July 11, 2008

HBT Radii without SMC

July 11, 2008

Summary

• The mt-dependence of HBT appears in both heavy-ion and elementary collisions

• The different mechanism may drive such a dependence.

• However, it can be considered as a universal reason: space-momentum correlation.

• The “surprising scaling” of HBT radii suggests that the SMC should be studied in detailed.