# Presentation: 422155

## Non identical particle correlation

- LBL soft hadron meeting
- February 26th, 2001

## Non identical particle correlation @ STAR

- What?
- --+
- K--K+
- K--+, K+--, K+-+, K---
- 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

## Sequence of emission

**Kinematics selection**

- 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

## Detector issues

- Uncorrelated pairs
*Lower the whole correlation function*
- Combination of pions misidentified kaons and electrons
-  Aihong’s pid probability
- Pions from strange hyperon and K0s decays
- Hijing + scaling on global DCA?
- Or, Al Saulys’s probability?

- Correlated pairs
_*Unpredictable effect*_
- e--e+ from  conversion
- Hijing for shape + scale from Aihong’s probability
- Momentum resolution
*Lower the “sharp” part of the correlation function*
- Single particle resolution from embedding
- Convolution into CF

## --+

- Detector issues
- Uncorrelated pairs
- Combination of pions misidentified kaons and electrons
- Pions from strange hyperon and K0s decays
- Correlated pairs
- e--e+ from  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!

## K--K+

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

- 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 @ RHIC
- Status of the analysis
- Correlation function
- Effect of the e--e+ pairs
- Sequence of emission

## K--K+ correlation function

- K--K+ correlation function

- Loose cuts :
- |Y|<1. and pT<1. GeV/c
- Nhits >15
- Loose dEdx pid
- 2 tight cuts :
- Momentum > 0.25 GeV/c
- Tight e-/e+ removal
- Shape
- Coulomb
- Strong interaction, resonances a0 and f0

- 

## Detector issues 1Purity and momentum resolution

- 78% Pair purity
- when k*<0.2 GeV/c

- K- momentum resolution
- from embedding.
- Need to fold it in CF

## Detector issues 2Effect of the e--e+ pairs

## Detector issues 2Effect of the e--e+ pairs

- No correlation
- expected

- Correlation from
-   -> e+e-

## Sequence of emission

- Low statistics

## K--+, K+--, K+-+, K---

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

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

## K--+, K+--, K+-+, K--- correlation functions

## Correlation under control

## Sequence of emissionKaon first?

## 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 K and K+K- seem to be understood.
- How to parameterize the sequence of emission (3D?)
- Model comparison
- Time scale
- Before next beam time : doable?