# Presentation: 733930

## STAR’s measurement of correlation and fluctuations between photons and charged particles at forward rapidity at RHIC

- University of Jammu, India
*(For the STAR collaboration)**‏*

- Outline
- 	Motivation
- 	STAR Experiment
- 	Analysis Method
- 	Results
- 	Summary

## Inclusive photons provide the information of production of  

- Inclusive photons provide the information of production of  ****
-  Chiral symmetry restoration could be reflected via study of Photon-Charged particles Fluctuations.
- Formation of Disoriented Chiral Condensates (DCC) generate fluctuations between photons and charged particles.
-  **DCC formation** is expected to provide information on the vacuum structure of strong interaction and chiral phase transition.

***Anti-CENTAURO event of JACEE***
***36 photons, 1 charged particle***

## STAR Experiment

- Nucl.Instrum.Meth.A499:624-632,2003

**Coverage: |******** < 1.5 **

- Nucl.Instrum.Meth A 499, 713 (2003)

## Photon Multiplicity Detector

- Two planes CPV+Preshower
-  Gas detector of hexagonal cells
-  Cell cross section : 1.0 cm2
-  Cell depth : 0.8 cm
-  Gas used: Ar+CO2 in 70:30
-  Total number of cells : 82,944
-  Area of the detector : 4.2 m2
-  Distance from vertex : 540 cm
-  Coverage: -2.3 to -3.8 in  with full 

## Principle of Photon Multiplicity detector

- Photons passing through the converter initiate an electro-magnetic shower and produce large signal on several cells of the sensitive volume of the detector.
- Hadrons normally affect only one cell and produce a signal representing minimum ionizing particles.

## Efficiency and Purity of Photon sample

-  clusters with *N**cells* > 1 & Cluster ADC > 5*MIP
-            *(Purity ~ 67%)**‏*

- Charged hadrons are
- rejected by using
- thresholds on **strengths**
**and number of cells**
- on PMD clusters.
- Raising thresholds on
- cluster ADC increases
-  purity of photon samples.

## Data Samples

- AuAu (200GeV) : 1.8 M events
- CuCu (200 GeV) : 320 K
-  Event cuts:
-  Zvertex <30 cm

**Photon samples (PMD):**
- cluster ADC > 5 MIP
- No of cells > 1
**Charged tracks (FTPC):**
- dca < 2 cm,
- nHits > 5,
- 0.1< *p**T *<3.0 GeV/c

## Photon and Charged Particle Multiplicities(Uncorrected)‏

- Au+Au 200 GeV

**Photon and Charged Particle Multiplicities****(Uncorrected)****‏**

##   /Mean of ratio (measuring the width)‏

** ****(Methods)****‏**

-   /*Mean* of ratio (measuring the width)‏
- *dynamics*(measure of total correlated fluctuations)‏

## Fluctuations in N / Nch

- 2 /*Mean) scaled by N**part** : almost constant with N**part** **     *
*                       **(approximate 1/N**part  **scaling )**‏*

**Error bars are Statistical**

***part****** ***

**Measure of Fluctuations = ********2**** /*****Mean ***** **

**Error bars are Statistical**

## Photon – Charged Particle Fluctuations by dynamics 

- *dynamics * =

***Charge fluctuations ***

***Photon fluctuations***

***Correlated fluctuations***

**C. Pruneau et al. Phys. Rev. C 66, 044904(2004)****‏**
**Nystrand et at.  Phys. Rev. C 68, 034902(2003) **

**Notes:**
1/<N

## Three Terms in dynamics 

- Three Terms in ***dynamics*

*Individual fluctuations are larger than correlation making  ****dynamics  **positive*

## Effect of purity and efficiency variation

***Different cuts on photon samples:***
*3 MIP*
*4 MIP*
*5 MIP*
*6 MIP*

*Independent of MIP cuts*

## dynamics  :Dependence of  Coverage

*********dynamics ****** ****similar at different ** coverage*
*(upstream material effect is small)**‏*

***dynamics*  :Dependence of  Coverage

## Scaling of dynamics with Npart 

***Observation:***
***dynamics **scaled by N**part**  : almost constant at lower N**part** and  increases at higher N**part*

***Scaling of ************dynamics ******with N******part****** ***

##   pT dependence of fluctuations

- χ

- DCC particles are soft
- Signals expected to
-  increase for lower pt
- First time access to *p**T *
-  dependence of charged
-  particles (absent in WA98)‏

**Notes:**
If nu is sentive to the DCC, we would expect ..... Especially at low pt region.

## dynamics  with pT cut of Charged Particles

***Small or No DCC signal?***

***dynamics*  *with p**T **cut of Charged Particles*

- ....a+1/Npart

**Error bars are Statistical**

## Summary

** ****Photon and Charged particle multiplicity correlations are studied for AuAu &  CuCu at 200 GeV Collisions at forward rapidities.**
-   **Two Method  used: ************ /*****Mean***** and ********dynamics**** **
********** ****/*****Mean of ******N******************/N******ch******  shows approximate 1/N******part****** scaling***
*********dynamics****** is positive ****** ******(individual fluctuations >  than correlated term)******‏***
*********part  *************************dynamics****** almost constant at lower N******part****** and increase for higher N******part***
***No pt dependence -> No abnormal correlations, induced by DCC***
***An analysis to determine sensitivity  of ************dynamics******  for  DCC  is  ongoing***