Non identical particle correlation

1
Non identical particle correlation

• LBL soft hadron meeting
• February 26th, 2001

2
Non identical particle correlation _at_ STAR

• What?
• p--p
• K--K
• K--p, K-p-, K-p, K--p-
• What physics?
• Source size parameters
• Additional constraints especially to kaons
• Sequence of emission
• Different emission space/time for different
  particles?

• How?
• Correlation function calculation
• Coulomb interaction
• Strong interaction (resonances contribution)
• Detector issues
• Non correlated pairs lower correlation
• Correlated pairs Bad!!!
• Momentum resolution

3
Sequence of emission

• Catching up
• long interaction time
• large correlation function
• Moving away
• short interaction time
• small correlation function
• Ratio of both scenarios allow quantitative study
  of the emission asymmetry

Kinematics selection
4
Detector issues

• Correlated pairs
• Unpredictable effect
• e--e from g conversion
• Hijing for shape scale from Aihongs
  probability
• Momentum resolution
• Lower the sharp part of the correlation
  function
• Single particle resolution from embedding
• Convolution into CF

• Uncorrelated pairs
• Lower the whole correlation function
• Combination of pions misidentified kaons and
  electrons
• Aihongs pid probability
• Pions from strange hyperon and K0s decays
• Hijing scaling on global DCA?
• Or, Al Saulyss probability?

5
p--p

• Detector issues
• Uncorrelated pairs
• Combination of pions misidentified kaons and
  electrons
• Pions from strange hyperon and K0s decays
• Correlated pairs
• e--e from g conversion
• Momentum resolution

• What physics?
• Source size crosscheck coulomb correction
  applied to HBT
• Sequence of emission
• Would be a huge surprise if something seen
• Status of the analysis
• Not far!

6
K--K

• What physics?
• Source size understand coulomb correction for
  KK HBT
• Sequence of emission
• Would be a rather big surprise if something seen
  given the low baryon density _at_ RHIC
• Status of the analysis
• Correlation function
• Effect of the e--e pairs
• Sequence of emission

• Detector issues
• Uncorrelated pairs
• Combination of pions misidentified kaons and
  electrons
• Correlated pairs
• e--e from g conversion may be important
• Momentum resolution

7
K--K correlation function

• Loose cuts
• Ylt1. and pTlt1. GeV/c
• Nhits gt15
• Loose dEdx pid
• 2 tight cuts
• Momentum gt 0.25 GeV/c
• Tight e-/e removal
• Shape
• Coulomb
• Strong interaction, resonances a0 and f0

f
8
Detector issues 1Purity and momentum resolution
78 Pair purity when klt0.2 GeV/c
K- momentum resolution from embedding. Need to
fold it in CF
9
Detector issues 2Effect of the e--e pairs
10
Detector issues 2Effect of the e--e pairs
No correlation expected
Correlation from g -gt ee-
11
Sequence of emission
Low statistics
12
K--p, K-p-, K-p, K--p-

• What physics?
• Source size how does it compare to pp and KK?
• Sequence of emission
• Sudden freeze out of every particles?
• Flow effect?
• Status of the analysis
• Correlation function
• Sequence of emission

• Detector issues
• Uncorrelated pairs
• Combination of pions misidentified kaons and
  electrons
• Pions from strange hyperon and K0s decays
• Correlated pairs
• None ?
• Momentum resolution

13
K--p, K-p-, K-p, K--p- correlation functions
14
Correlation under control
15
Sequence of emissionKaon first?
16
Conclusions

• Experimental signal
• Clean correlation functions
• Evidence of emission asymmetry between Kaon and
  pions
• Purity and momentum resolution being studied
• However, unexpected detector issues
• Correlated pairs
• Others?

• Physics
• Correlations Kp and KK- seem to be understood.
• How to parameterize the sequence of emission
  (3D?)
• Model comparison
• Time scale
• Before next beam time doable?