# Presentation: 008377

## High pT Hadron Correlation

- Rudolph C. Hwa
- University of Oregon

- Hard Probes 2006
- Asilomar, CA, June 10, 2006

- and No Correlation

## Hard scattering  high pT jet

- Hard scattering  high pT jet
- 		       hadron correlation

- (usual conductor has resistance)

- (superconductor has no resistance)

## Slide 3

## same side

- STAR

## Associated particle pT distribution

- p1 -- trigger

- p2 -- associated

## Associated particle distribution in the recombination model      	-- for  only 

- Associated particle distribution in the recombination model      	-- for  only
-  Hwa & Tan, PRC 72, 057902 (2005)

## Medium modified dihadron fragmentation function  -- more relevant at higher pT.

- Medium modified dihadron fragmentation function  -- more relevant at higher pT.

- Majumder, Wang, Wang nucl-th/0412061

## Slide 8

## Away side

## Slide 10

##  production in AuAu central collision at 200 GeV

- Hwa & CB Yang, PRC_70_, 024905 (2004)

- fragmentation

- recombination

## pT(assoc)

- 4

- 8

- 12

- 16

- 4

- 8

- 12

- 0

- pT(assoc)

- pT(trig)

## Trigger-normalized fragmentation function

- Trigger-normalized momentum fraction

## STAR, nucl-ex/0604018

## pT(assoc)

- 4

- 8

- 12

- 16

- 4

- 8

- 12

- 0

- pT(assoc)

- pT(trig)

## Slide 16

## Slide 17

## Correlation on the near side

-  and  distributions

- STAR, PRL **95**, 152301 (2005)

## Chiu & Hwa, PRC 72, 034903 (2005)

- Chiu & Hwa, PRC **72**, 034903 (2005)

- At low trigger momentum, hard partons can originate farther in.

## Slide 20

## Away-side distribution

- Dremin					Cherenkov gluons
- Ruppert, Muller 				color wake
- Koch, Majumder, Wang                        Cherenkov radiation
- Vitev					jet quenching+fragm
- .
- .
- Chiu, Hwa				parton multiple 						scattering

## Parton multiple-scattering model

- Sample trajectories for 2.5<p(trig)<4, 1<p(assoc)<2.5

- exit tracks

- absorbed (thermalized) 		tracks

## Away-side  distribution

- Event averaged, background subtracted.

- Cannot distinguish between 1-jet and 2-jet contributions    	  (e.g., Mach cone)

- Chiu’s talk in parallel session on Monday

## Slide 24

## Autocorrelation

## Correlation function

- Treat 1,2 on equal footing --- no trigger

- No ambiguous subtraction procedure; only do as defined.

## Slide 27

## STAR data on Autocorrelation for central Au+Au at 130 GeV for ||1.3, 0.15<pT<2 GeV/c

- nucl-ex/0605021

- NO trigger, no subtraction

## Slide 29

##  and  production at intermediate pT

- strange-quark shower is very suppressed.

## If they are produced by hard scattering followed by fragmentation, one expects jets of particles.

- Hwa & CB Yang, nucl-th/0602024

## We claim that no shower partons are involved in  production,    so no jets are involved.

- Select events with  or  in the 3<pT<6 region, 	and treat them as trigger particles.

- We claim that no shower partons are involved in  production,    so _no jets are involved_.

## charged hadrons

## Slide 34

## Forward production of hadrons

- Without knowing pT, it is not possible to determine xF

## Theoretically, can hadrons be produced at xF > 1?

- It seems to violate momentum conservation, pL >  √s/2.

- (TFR)

- In the recombination model the produced p and  can have smooth distributions across the xF = 1 boundary.

## proton

- pion

- Hwa & Yang, PRC 73,044913 (2006)

- : momentum   degradation    factor

## BRAHMS, nucl-ex/0602018

## Slide 39

## pT distribution fitted well by recombination of thermal partons

- Hwa & Yang (2006)

- pT distribution fitted well by recombination of thermal partons

## Slide 41

##  and p production at high pT at LHC

- New feature at LHC: density of hard partons is high.

- High pT jets may be so dense that neighboring jet cones may overlap.

- If so, then the shower partons in _**two nearby jets**_ may recombine.

## The particle detected has some associated partners.

- There should be no observable jet structure 		_distinguishable from the  background_.

## Proton-to-pion ratio at LHC

-  -- probability of overlap of 2 jet cones

- Hwa & Yang 	nucl-th/0603053

## We predict for 10<pT<20 Gev/c at LHC

-   Large p/ ratio

-   NO associated particles 		above the background

## Summary