# Presentation: 318156

## -jet Measurements

**Quark Matter 2008, February 4-10, Jaipur, India**

_**The STAR experiment**_

_**A. Hamed for the STAR Collaboration**_

**Jaipur 02-08-08**

**Texas A&M group**

_**Table of Contents:**_

- Introduction

- Data and Analysis Method

- Results and Interpretation

- Experimental setup

- Summary

## Introduction

_**Introduction**_

**X.N.Wang, Z. Huang, and I. Sarcevic. PRL 77(1996) 231-234 **

- In the central AA collisions at mid-rapidity the 0 –spectra are suppressed by
- a factor of ~5 relative to the incoherent superposition of pp collisions.

_**Theory**_

_**Experiment**_

- In vacuum frag.

- In medium frag.

_**Motivation**_

- The comparison between the extracted Fragmentation Function in AA and pp collisions
- can be used to determine the jet E and mean-free-path in the dense matter produced in
- high-energy heavy-ion collisions.

**vac**

**med**

## Experimental setup

_**Experimental setup**_

_**STAR BEMC**_

- 0.1

## Correlate photon candidates “triggers” with associated tracks 

- Correlate photon candidates “triggers” with associated tracks

- Beam axis

**BEMC**

**TPC**

_**Data and Analysis Method **_

- Level-2 trigger: L~600ub-1 Run 2007

## Need /0 discrimination.

**Combined (********0****+********)- hadrons correlations**

**Need ********/********0**** discrimination.**

**30ub****-1**

**600ub****-1**

_**Results and interpretation**_

**Near side is suppressed with centrality due to the increase of ********/********0**** ratio .**

**AuAu**

## Shower Shape Analysis

**Shower Shape Analysis**

_**Results and interpretation**_

**In this analysis the ********0**** cuts are chosen to provide high purity. **

**Wide shower**

**Narrow shower**

**AuAu2007**

## Results and interpretation

_**Results and interpretation**_

******-rich sample versus ********0****-rich sample**

**The ********-rich sample has lower near-side yield than ********0****.**

## Results and interpretation

_**Results and interpretation**_

**(********0****-charge****) versus (****charge-charge-****PRL 97(2006)162301****) correlations **
**in pp,dAu, and AuAu**

**The momentum dependence of the yields in near- and away-**
**sides of  the associated particles per  trigger of jet-like correlations **
**in ********0****-charge and charge-charge correlations are similar.  **

**,assoc**

**Similar **
**near-side**
** ****yield **
**for pp,dAu, **
**and AuAu.**

## Results and interpretation

_**Results and interpretation**_

**(********0****-charge****) versus (****charge-charge-PRL 97(2006)162301****) correlations**
** ****in pp,dAu, and AuAu**

**The medium effect on the yields of away-side of **
**the associated particles per trigger of jet-like correlations in **
******0****-charge and charge-charge correlations are similar.  **

## Results and interpretation

_**Results and interpretation**_

**I****AA**** of ********0**

**I****AA**** of the away-side in ********0****-trigger shows similar suppression **
**for all p****t**** associated bins (3-8GeV/c).**

## Results and interpretation

_**Results and interpretation**_

**Extraction of direct******** away-side yields**

**Assume no near-side yield **
**for direct ******** **** ****then the away-side yields per **
**trigger obey **

## Results and interpretation

_**Results and interpretation**_

**Direct******** away-side yields**

**The away-side yield of the associated particle per trigger in ********-jet **
**is suppressed.  **

## Results and interpretation

_**Results and interpretation**_

**I****AA**** of direct******** **

**Within the current uncertainty in the scaling the I****AA**** of direct ******** and ********0**** **
**are similar.**

## Results and interpretation

**I****cp**** of ********-jet exhibits same suppression on the **
**away-side yield per trigger of the associated particles (3-8GeV/c).  **

_**Results and interpretation**_

**I****cp**** of direct******** **

## First result of -jet azimuthal correlations in AuAu at STAR 

**First result of ********-jet azimuthal correlations in AuAu at STAR **
**experiment is reported.**

**All results of  ********0****’s near and away-side of associated **
**particles yield shows consistency with that of charged hadrons. **

**Shower shape analysis is effective for ********/********0**** discrimination.**

_**Summary**_

**The I****AA**** of ********-jet agrees with the theoretical predictions.**

******’****s I****AA**** is close to R****AA**** of inclusive hadrons and similar to ********0****’s I****AA**** .**

## Thank you

**Thank you**

## Backup Slides

**Backup Slides**

## Slide 18

## Results and interpretation

***Assume no near-side yield for direct *********

- -

_**Results and interpretation**_

**Extraction of direct******** away-side yields**

**In the yield of the associated particles per trigger the away-side yield of **
******-jet is given by the yield subtraction of ********-rich and pure proper normalized ********0**** .**

## Data and Analysis Method

**Data and Analysis Method**

**Data in Run2007**

**L2 Trigger on cluster of one or two neighboring towers with Et>7.54GeV**

**Offline:**

**Trigger particle as of Et>8GeV in one or two adjacent towers.**

**Charged particles veto as of:**

**p>3GeV**

******<0.025 ********<0.025**

**Run2007**

**Online:**

**Number of fit points >20.**

- _Photon candidates “trigger particles”_

**Trigger particle as of E>0.5GeV in one of BSMD strips.**

- _Tracks “associated particles”_

**Pt>3GeV/c**

- ( ~590 ub-1 )

**Basic QA**

**Basic QA**

- 1.Et1+Eti>=7.54GeV

- 2.Et1>=5.75GeV

**L2 trigger conditions**

- i=0,1,..,8

## Slide 21