# Presentation: 620683

##  Jet Studies at RHIC via 2+1 correlations

- Olga Barannikova
*for the STAR Collaboration*

## Outline

- Motivation for di-jet studies
- Evolution of jet-type correlation analyses
- Theoretical interpretation of data
- Data Analysis
- Results
- Energy loss in di-jet events
- Summary

## Signature two-particle correlation result:
Disappearance of the away side jet in central Au+Au collisions
Evidence for strongly interacting medium
Effect vanishes in peripheral/d+Au collisions

- Signature two-particle correlation result:
- Disappearance of the away side jet in central Au+Au collisions
- Evidence for strongly interacting medium
- Effect vanishes in peripheral/d+Au collisions

***4<p******T****** ******trig******<6 GeV/c        2<p******T****** ******assoc******<p******T****** ******trig***

**PRL 91 (2003) **
**072304**

- Motivation

## Energy loss in the hot QCD medium
Mach cone  (Stoecker, Casalderrey-Solana, Shuryak, Teaney, Ruppert, Muller, Renk)  
Cherenkov gluon radiation (Dremin, Koch, Majumder, Wang)	
Large angle gluon radiation (Vitev, Salgado)
Parton multiple scattering (Chiu, Hwa)
Flow-induced deflection (Armesto, Salgado, Wiedemann)
....

- Mach cone  (Stoecker, Casalderrey-Solana, Shuryak, Teaney, Ruppert, Muller, Renk)
- Cherenkov gluon radiation (Dremin, Koch, Majumder, Wang)
- Large angle gluon radiation (Vitev, Salgado)
- Parton multiple scattering (Chiu, Hwa)
- Flow-induced deflection (Armesto, Salgado, Wiedemann)
- ....

***4<p******T****** ******trig******<6 GeV/c        2<p******T****** ******assoc******<p******T****** ******trig***

**PRL 91 (2003) 072304**

**Phys.Lett. B639 (2006) 38 **

- Energy Loss in QCD Medium

- Use di-jets to explore the mechanisms of energy loss

- Jet Quenching
- Dissipation jet energy propagating through the medium

- Mach-Cone
- Double-hump structure on away-side?

- Mono-jet
- Single jet on near-side
- Excess on away side due to momentum conservation

## Two high-pT triggers
Reappearance of the away-side jet
For central Au+Au collisions
First observation of di-jets

New analysis exploits this observation

- Reappearance of the away-side jet
- For central Au+Au collisions
- First observation of di-jets
- New analysis exploits this observation

**PRL 97 (2006) 162301**

**8<p****T****(trig)<15 GeV/c**

- First Di-Jet Observation

## Aim of this analysis is to “pin” the jet axis
Assuming di-jets
Only select events with high-pT particles back-to-back in 

Correlate all particles with this axis

- Assuming di-jets
- Only select events with high-pT particles back-to-back in 
- Correlate ***all*** particles with this axis

**associates**

**associates**

**primary**
**trigger (T1)**

**“****jet-axis”**
**trigger (T2)**

- Signal sit atop of a largely
- uncorrelated background

- Data Analysis - Technique

**Courtesy of R .Hollis**

## Simulation of one scenario, mach-cone

New method should be sensitive to this and other effects

- New method should be sensitive to this and other effects

***by M. Andrews (UIC)**

- Monte-Carlo Shape Examples

## Require that the 2 highest pT particles are back-to-back in 

Assume this defines the jet-axis, look in 2D-space about the second trigger

- Require that the 2 highest pT particles are back-to-back in 
*Assume *this defines the jet-axis, look in 2D-space about the second trigger

- T1: pT>5GeV/*c*
- T2: pT>4GeV/*c*
- A:   pT>1.5GeV/*c*

**T1T2**

- Correlation primary trigger (T1) and “jet-axis trigger” (T2)

- Data Analysis – Di-Jet Selection

*****±** **0.2*

## Mixed Events Background:

***a.u.***

- Accounts for:
- pair acceptance
- triangular shape in 
- uncorrelated background
- particles not related to initial jet

## Need to account for  elliptic flow

- Need to account for  elliptic flow

**Phys. Rev. C72 (2005) 014904**

***Note: this is the correction function for T1A1***

-  Dynamic weighting in analysis

- V2  Removal:

## Normalization:

**T1T2**

- T1: pT>5GeV/*c*
- T2: pT>4GeV/*c*
- A:   pT>1.5GeV/*c*

**STAR Preliminary**

## Normalization:

**T1A1**

- T1: pT>5GeV/*c*
- T2: pT>4GeV/*c*
- A:   pT>1.5GeV/*c*

**STAR Preliminary**

## 2+1 Signal Construction:

- 

- 

**Raw Correlation**

**Background**

**Signal**

**Flow**

- T1: pT>5GeV/*c*
- T2: pT>4GeV/*c*
- A:   pT>1.5GeV/*c*

**STAR Preliminary**

## Correlated Background:

- T2: pT>4GeV/*c*
- A:   pT>1.5GeV/*c*

- Accounting for correlated background on T1 and T2 side
- Correlated background approximated by di-hadron correlations
-  **T2A1**, 	**T1A1**

## One high-pT trigger (only)
Away-side modification
Mono-jets?
Energy loss for away-side jet?

Di-jet trigger
No modification on away-side
Surface dominated?
No energy loss for di-jets?

- Away-side modification
- Mono-jets?
- Energy loss for away-side jet?
- Di-jet trigger
- No modification on away-side
- Surface dominated?
- No energy loss for di-jets?

- Preliminary Results:

- T1: pT>5GeV/*c*
- T2: pT>4GeV/*c*
- A:   pT>1.5GeV/*c*

##   Di-jets in d+Au
  200 GeV Minimum bias data

Slight narrowing of the same-side, big effect for away-side
Difference in yields
Di-triggers sample higher energy jets

*  **200 GeV Minimum bias data*
- Slight narrowing of the same-side, big effect for away-side
- Difference in yields
- Di-triggers sample higher energy jets

- Preliminary Results:

- T1: pT>5GeV/*c*
- T2: pT>4GeV/*c*
- A:   pT>1.5GeV/*c*

- vs.

## Di-Jets in Au+Au Collisions

- T1: pT>5GeV/*c*
- T2: pT>4GeV/*c*
- A:   pT>1.5GeV/*c*

*200 GeV Au+Au, 12% central*

- No away-side suppression
- Shapes of near- and away-sides are similar
- Central Au+Au ~ d+Au

***No energy loss for triggered di-jets?***

## Shape Modifications

**Centrality dependence**
**** projection:**  **no significant shape/yield modifications
**** projection:**   **no apparent ridge

- T1: pT>5GeV/*c*
- T2: pT>4GeV/*c*
- A:   pT>1.5GeV/*c*

_*ZYAM normalization*_

## Surface Effects

**STAR Preliminary ****

- T1: pT>5GeV/*c*
- T2: pT>4GeV/*c*
- A:   pT>1.5GeV/*c*

- If the triggers have tangential bias: expect a term related to the surface
- Surface ~ R2 ~ Npart2/3

*** **Shown are statistical errors only*

- Number of triggers per event
- 		(per number of binary collisions)
- Single triggers and (all qualified) pairs behave similar to inclusives

## Summary:

- New analysis of 2+1 correlations
- Events triggered with 2 high-pT particles
- Preliminary results show a di-jet structure with this technique, with no modification
- New technique allows further exploration of the “surface bias” apparent in triggered di-hadron studies.

- Many thanks to A. Iordanova, R. Hollis, M. Andrews