# Presentation: 835962

## System Size and Energy Dependence of Jet-Induced Hadron-Hadron Angular Correlations in Heavy Ion Collisions at PHENIX

**System Size and Energy Dependence of Jet-Induced Hadron-Hadron Angular Correlations in Heavy Ion Collisions at PHENIX**

- Michael P. McCumber for the PHENIX Collaboration
- April 2007 APS Meeting
- Jacksonville, Florida

## Heavy Ion Collisions

_**Jet Suppression:**_
- Fast partons lose energy in the medium
- Lost energy should be deposited locally in the medium

- Where does the energy go?
- Does anything of the jets remain?
- Does the lost jet energy elicit a response from the medium?

- ?

## PHENIX Detector

**Central Arms**

-  |η| < 0.35

- Charged tracking from DC, PC1, and PC3 at mid rapidity, η.
- Centrality and Reaction-plane from BBC and ZDC at large |η|.

## Charged Hadron Correlations

**p+p**

- PRC 73, 054903 (2006)

- nucl-ex/0611019

- _p-p collisions:_
- ● Pair yield near Δφ=0 and Δφ=π
- ● Back-to-back jet scenario

- _Central Heavy Ion Collisions:_
- ● Requires significant subtraction of combinatoric event correlations (elliptic flow)
- ● Pair yield near Δφ=0 and Δφ≈2
- ● Several qualitatively consistent scenarios

## System and Energy Scan

- nucl-ex/0611019

- Away-side structure vs. beam species, beam energies, and centrality
- _All cases:_
- ● Peripheral similar to p-p
- ● Central shows development of “lobe”-like structure

## Npart Shape Scaling

- nucl-ex/0611019

**J(****Δφ****)**

- ● Shape saturates above 100 Npart

## Testing Thickness Scaling

*peripheral*

- thicker via centrality
- selection

- thicker via trigger to reaction plane selection

*central*

*in*

*out*

*mid*

- Cu+Cu                             Au+Au

## Correlation & Jet Functions

***Correlation & Jet Functions***

_**Jet Functions:**_
- ● Large dependence with centrality

- ● No observed dependence in jet functions with reaction-plane

## Geometrical Thickness

- Overlapping Wood-Saxon Distributions

- Distant Observer

- 0

- freq.

- R-<R>

- trms = 2 Rrms

- trms is a typical radial thickness along lines of sight from within a reaction-plane bin
- Includes reaction-plane resolution

## Shape Metrics

- Little sensitivity with reaction plane binning

## Away-side Jet-Induced Structure

- 	Systematic and detailed study of away-side shape
- 	Observe that the away-side shape scales with Npart
- 	No observed reaction-plane shape dependence
- 	Unable to differentiate:
- 		no thickness scaling
- 		expected thickness scaling from centrality variation
- 	New Reaction-Plane Detector
- 		Better resolution
- 		Better flow systematic errors

## Backup Slides

## Au+Au 200 GeV – Cent 30-40%

- (QM 2005)

- The inclusive distributions vary greatly with Ψ-φ bin due to large changes in the flow contribution.

- The in-plane & out-plane JFs show no rxpn-dependence within the reported errors.

## Angle Definitions

- Beam View

- “reaction plane”

- “trigger hadron” (2.5-4.0 GeV/c)

- “partner hadron”
- (1.0-2.5 GeV/c)

## Acceptance Correction

- 0

- π

- Acc(Δφ)

- ΔΦAB

- The two-arm acceptance effects are removed by building a correction from event mixing.

**A**

**B**

**A**

**B**

**A**

**B**

**A**

**B**

**A**

**B**

- Event N

- Event N-1

- Event N-2

- Event N-3

- Event N-4

- Rolling buffer mixing technique
- Pooled by Event type:
- 5cm zvertex
- 5% centrality

## Correlation Functions

- _Correlation Decomposition:_

- Bielcikova, Esumi, Filimonov, Voloshin,& Wurm
- PRC69 (2004) 0211901

- Where we have both sufficient rx-pn resolution and sufficient event contribution, there exist large differences in the elliptic flow contribution.
- This can be seen here in central collisions as differences between in-plane and out-plane as C(Δφ) is dominated by the elliptic flow.

## Correlation Functions

## Flow Functions

## Jet Contribution Errors

## Why Cu+Cu?

- nucl-ex/0611019

- Increasing Thickness?

- If the Npart scaling is in fact related to the geometrical thickness through the medium, we should also see a dependence on line-of-sight through the medium.
- Need a small system to probe transition region, Cu+Cu is ideal in this regard.

**Cu+Cu**

## Shape Metrics by Npart

- Same Npart trend as previously measured.
- No observed difference between reaction plane bins

## Shape Metrics by trms

- Overall trend as expected from Npart dependence.
- The current poor reaction-plane resolution does not give sufficient thickness sensitivity to distinguish between no reaction-plane dependence and the expectation from the centrality dependence.

## Measuring Reaction-Plane Resolution

- _Two Methods:_
- Ollitrault-Voloshin
- Mean Projection Method

## Reaction-Plane Detector

- Now fully installed