# Presentation: 028970

## Near-side

**Near-side**
- ** ****correlations of high-p****t**** **
**hadrons from STAR**
- Jörn Putschke for the STAR collaboration
*Lawrence Berkeley National Laboratory *

## “Ridge” observation

## Outline

_**2-particle **____** correlations:**_
**How to extract the “ridge” yield ? ****(additional near-side long ****range corrl. in ********)**** **
**Quantify ridge properties ****in Au+Au (Cu+Cu)****200 GeV collisions**** **
**Summary & discussion**

- 3<pt,trigger<4 GeV
- pt,assoc.>2 GeV

## Components of  correlations

**Near-side jet-like corrl.****+ ridge-like corrl. ****+ v****2 ****modulated bkg.**** **
**Ridge-like corrl. ****+ v****2 ****modulated bkg.**** **
**Away-side corrl.****+  v****2 ****modulated bkg.**

- _Strategy:_ Subtract  from  projection to isolate the ridge-like correlation

## Extracting near-side “jet-like” yields

**Extracting near-side “jet-like” yields**

- Au+Au 20-30%

## Jet and Jet+Ridge yields & widths

- pt,assoc. > 2 GeV

- preliminary

- Jet+Ridge yield ()

- Jet yield ()

**Jet and Jet+Ridge yields & widths**

-  Jet+Ridge yield increasing with centrality
- Jet+Ridge shape asymmetric in _and_

- preliminary

- pt,assoc. > 2 GeV

- Jet+Ridge width ()

- central

- Correlate Jet ((J)) and Jet+Ridge ((J+R)) widths & yields via centrality

- Jet width ()

- preliminary

- periph.

**Yield**

**Width**

## Jet yields & widths:  vs. 

- Correlate Jet ((J)) and Jet ((J)) widths and yields via centrality

- pt,assoc. > 2 GeV

- pt,assoc. > 2 GeV

- Jet yield ~ symmetric in 
-  Jet shape ~ symmetric in  for pt,trig > 4 GeV (asymmetric in  for pt,trig < 4 GeV)

- preliminary

- preliminary

- Jet yield ()

- Jet yield ()

- Jet width ()

- Jet width ()

**Yield**

**Width**

## Extracting the ridge yield

-  _Definition of “ridge yield”:_
-     i)  ridge yield := Jet+Ridge(  Jet()
-     ii) relative ridge yield := ridge yield / Jet()

- preliminary

**Jet+Ridge (********) ****Jet (********)**
**Jet********)**

- yield,)

- Npart

- 3 < pt,trigger < 4 GeV and pt,assoc. > 2 GeV

## Ridge shape measurement in central Au+Au 

-  ridge yield as function of  saturates at high 
-  non-uniform ridge shape in 
-  ridge more collimated in  for higher trigger pt

## Ridge yield in Au+Au

**Ridge yield in Au+Au**

- pt,assoc. > 2 GeV

- preliminary

- Ridge yield slightly decreasing (~ constant) as function of trigger pt

## “Jet yield” vs. pt,assoc. in central Au+Au

**“****Jet yield” vs. p****t,assoc.**** in central Au+Au**

- “Jet spectrum” much harder than inclusive h and increasing with pt,trigger

- preliminary

**Jet yield**

- inclusive

## Ridge yield vs. pt,assoc. in central Au+Au

**Ridge yield vs. p****t,assoc.**** in central Au+Au**

- preliminary

- “Ridge spectrum” slightly harder than inclusive h and ~ independent of pt,trigger

- inclusive

## “Jet”/ridge yield vs. pt,assoc. in central Au+Au

- preliminary

- Au+Au 0-10%

- preliminary

**Ridge / Jet yield**

- preliminary

## Pion vs. Proton ridge yield

- Proton content of ridge larger than of jet part
- (more from strange assoc. particles in Janas talk)

**Assoc. Protons**
**Assoc. Pions**
**Assoc. h******

## Ridge yield in Au+Au and Cu+Cu

- Relative ridge yield comparable at same Npart  in Au+Au and Cu+Cu

## Scenarios

- i) Parton radiates energy before fragmenting    and couples to the longitidunal flow
-  Gluon bremmstrahlung of hard-scattered parton
-  Parton shifted to lower pt
-  Radiated gluon contributes to broadening
-  _contradicts surface bias emission picture !_
- ii) Parton recombination (Chiu & Hwa Phys. Rev. C72:034903,2005)
-  Recombination of thermal partons only indirectly affected    by hard scattering  not part of the jet
- iii) Radial flow + jet-queching (Voloshin nucl-th/0312065)

## Discussion

-  ridge spectrum harder than inclusive h+,- (~ 40-50 MeV in slope parameter)  consistent with parton recombination (T~15 MeV) ?
-  agreement with radial flow + jet quenching ?
-  ridge spectrum qualitatively in agreement with parton energy loss and coupling to longitudinal flow
-  quantitative calculation for comparison needed

## Outlook

-  Study geometry effects in more detail:   Look at near-side modifications in Au+Au with respect to the reaction plane
-  PID ridge yield study with pions, protons and strange particles (see Janas talk)
-  3-particle  near-side correlations

## Backup slides

## Analysis methods cont.

**Use event-mixing to account for pair acceptance & use eff. correction for ass. particles**
**Background:**
- Subtract constant backgroundfor (J) method
- Subtract v2 modulated background for (J+R) method
**Assume Gaussian correlation shape:****yield(********) = gaus integral / bin counting******** (********) = gaus width**

## Au+Au near-side (J)(J+R) yields & widths II

- Correlate (J) and (J+R) widths & yields via centrality

- (J) yield ~ J+R)yield _x0010_
-  J) and J+R)widths ~ constant

## Relative ridge yield in Au+Au 

- Relative ridge yield strong increasing with centrality for lower trigger pt

- relative ridge yield

## Summary

**Ridge shape non-uniform in ******** in central Au+Au**** ****collisions**** **
**Ridge yield slightly decreasing (~ constant) as function of p****t,trigger**
**Ridge spectrum independent of p****t,trigger ****and slightly harder than ****inclusive charged hadron spectrum (~40-50 MeV in slope parameter)**** **
**Relative ridge yield for identified assoc. pions suppressed with respect****to charged hadrons (identified assoc. protons enhanced)  **** **
**At the same N****part**** the relative ridge yield seems to be comparable in periph. Au+Au (30-40%) and in central Cu+Cu (0-10%) collisions**