# Presentation: 794338

## What is the connection between away-side cone and near-side ridge? 

- John Chin-Hao Chen
- (for PHENIX collaboration)
- Department of Physics and Astronomy
- Stony Brook University
- CATHIE-RIKEN Workshop: Critical Assessment of Theory and Experiment on Correlations at RHIC
- 02/25/2009

- CATHIE-RIKEN Workshop

- 02/25/2009

## Outline

- What do we learn from two particle  correlation
- What do we learn from two particle correlation?

- CATHIE-RIKEN Workshop

- 02/25/2009

## Study the Medium with Two Particle Correlation

- Select a high pT particle as the trigger particle.
- Select another lower pT particle, calculate the angular  distribution.
- Use ZYAM (Zero Yield At Minimum) method to remove the flow background.
- use p+p two particle correlation as a baseline, to compare with same measurement in Au+Au

- CATHIE-RIKEN Workshop

- 02/25/2009

## Two particle  correlation

- The shape of awayside varies with partner pT!

- Phys. Rev. C **78** 014901 (2008)

- CATHIE-RIKEN Workshop

- 02/25/2009

## The awayside jet is modified!

- Phys. Rev. Lett. **98**, 232302 (2007)

- The awayside peak moved to ~  +/- 1.1 in central collisions!
- Independent of colliding system and energy!

- CATHIE-RIKEN Workshop

- 02/25/2009

## The nearside is also modified!

- The nearside width is wider than pp
- The yield at low partner pT is also larger than pp

- Phys. Rev. C **78** 014901 (2008)

- CATHIE-RIKEN Workshop

- 02/25/2009

## Ridge is everywhere!

- Happened in central collisions
- Extend to large  range
- Ridge yield independent of trigger pT
- Baryon/meson ratio similar to bulk

- CATHIE-RIKEN Workshop

- 02/25/2009

## 2-D  correlations

- shoulder  ridge

****

****

******rad**

****

- Peripheral Au+Au

- Central Au+Au

*Both near and away side*
*are modified!*

- CATHIE-RIKEN Workshop

- 02/25/2009

## Yield in  slices: peripheral

- Yield in  slices: peripheral

**Au+Au ~  p+p **

**0<|********|<0.1**

**0.1<|********|<0.3**

**0.3<|********|<0.5**

**0.5<|********|<0.7**

- CATHIE-RIKEN Workshop

- 02/25/2009

## Yield in  slices: 0-20% central

**0<|********|<0.1**

**0.1<|********|<0.3**

**0.3<|********|<0.5**

**0.5<|********|<0.7**

- CATHIE-RIKEN Workshop

- 02/25/2009

## When jet interacts with medium

- Nearside: jet + ridge
- Awayside: punch through jet (head) + shoulder
- How does ridge compare with shoulder?

- Peripheral Au+Au

- Central Au+Au

- CATHIE-RIKEN Workshop

- 02/25/2009

## Decomposition method

- Fit away side jet with sum of three Gaussians to decompose components:
- Head: punch through jet
- Shoulder: new peak at either side of (medium response ?!?!)
- Treat all components as Gaussian in shape
- Use ZYAM method to fix background level

- CATHIE-RIKEN Workshop

- 02/25/2009

## Nearside Yield vs Centrality

**Enhancement!**

- pp

- CATHIE-RIKEN Workshop

- 02/25/2009

## Ridge & shoulder both increase with centrality

**Yields are very similar!**

- RidgeShoulder

- CATHIE-RIKEN Workshop

- 02/25/2009

## Inverse slope of ridge & shoulder pT spectra vs. p+p

- Inverse slope of ridge & shoulder pT spectra vs. p+p

- Both ridge and shoulder are softer than hard scattering.
- Ridge harder than shoulder?
- Shoulder not quite as soft as inclusive hadrons

- CATHIE-RIKEN Workshop

- 02/25/2009

## How do theorists think?

- Ridge :
- Longitudinal flow?
- Radial flow?
- Back splash?
- Momentum kick?
- Recombination?

- Shoulder:
- Mach cone?
- Recombination?
- Radial flow?

- CATHIE-RIKEN Workshop

- 02/25/2009

## What do we learn from two particle correlation?

- In central collision:
- At low partner pT, both nearside and awayside yield are enhanced
- At high partner pT, awayside is suppressed

- Do we have other approach?

- CATHIE-RIKEN Workshop

- 02/25/2009

## Conservation of transverse momentum

- If we can collect all particle after collision, the total transverse momentum between the back to back jets should be conserved
- Weighted the per trigger yield of each component with transverse momentum (relative to the direction of the trigger particle), and normalized the pT weighted yield in awayside by the pT weighted nearside yield
- Use p+p as base line, see how the momentum ratio scales with Npart

- CATHIE-RIKEN Workshop

- 02/25/2009

## Near & away increase with centrality

**Number of particles**

**p****T**** Weighted yield**

- CATHIE-RIKEN Workshop

- 02/25/2009

## How does the transverse momentum redistribute?

**p****T **** is transferred from  head ******** shoulder**

**shoulder to ridge ratio is roughly constant**

**0 < |******** < 0.1**

- CATHIE-RIKEN Workshop

- 02/25/2009

## summary

- In heavy ion collisions, both nearside jet and awayside jet are modified
-  Ridge in nearside and shoulder in awayside
- Ridge and shoulder have similar yields
- The inverse slope of ridge and shoulder
- Both harder then inclusive spectra
- Both softer then hard scattering
- Ridge carries about twice of the momentum then shoulder

- CATHIE-RIKEN Workshop

- 02/25/2009