# Presentation: 004108

## Jet-Medium Interactionsfrom RHIC/STAR to LHC/ALICE

- Fuqiang Wang
- Purdue University
- What have been learnt at RHIC?
- What can be done at LHC?

## Jet-like angular correlations have provided valuable information at RHIC.

**Jet-like angular correlations have provided valuable information at RHIC.**

- At high pt
- away-side is
- suppressed.

- 4 < pTtrig < 6 GeV/c
- pTassoc > 2 GeV/c

- 8 < pTtrig < 15 GeV/c
- pTassoc > 2 GeV/c

- 4 < pTtrig < 6 GeV/c
- 0.15 < pTassoc < 4 GeV/c

- At low pt
- away-side is enhanced
- and broadened.

- At higher trigger pt
- away-side is
- reappearing.

## Associated pT spectra: experimental way to study thermalization processes.

- syst. error

- 4 < pTtrig < 6 GeV/c

- hard-soft parton interactions drive jet products and medium to equilibrate.

- PRL 95, 152301 (2005).

## Full reconstruction of “jet” energy

**Full reconstruction of “jet” energy**

- pp

- One may construct fragmentation functions for different centralities.

## <pt> can be studied in greater detail.

**<pt> can be studied in greater detail.**

- number
- correlation

- pT-weighted
- correlation

- pTtrig=4-6 GeV/c
- pTassoc=0.15-4 GeV/c

- path-length effect?  conical flow? deflected jets?

## centrality dependence of <pT> 

**centrality dependence of <p****T****> **

- <pT> from away jets

- <pT> from medium decay

- Away side <pT> (GeV/c)

## baryon/meson anomaly

- Coalescence/recombination models are very attractive.
- But baryon and meson trigger correlations are not much different.

## Away-side fragmentation patterns appear unchanged with centrality.

**With the emerged away-side jet, we can do tri- or quad-hadron correlations!**

- Are they the fraction of partons that escaped without interactions?
- Reconstruct the away-side jets including low pT.

- Dan Magestro

## All these studies can be carried out at LHC/ALICE, and better.

- ALICE best suited for “semi-hard” region: probably where most of the jet-quenching actions take place.
- Large pT coverage: full reconstruction of jets. Jet-fragmentation studies.

- background increase (x2) from RHIC to LHC. But huge increase in high-pT statistics.
- unique PID capabilities.
- larger statistics: multi-dimensional studies.

## And even better... with triggering!

-  (PHOS/EMC) + jet (TPC)  (EMC) + 0 (PHOS) (PHOS) + jet (EMC)
- both surface and volume emission.
- full reconstruction of away-side jets. energy balance? medium-energy pick-up?
- modified jet-fragmentation functions.
-  (PHOS/EMC) + e± (TPC) (PHOS) + e± (EMC)
- heavy-flavor energy loss

## Conical flow?

- PHENIX: ||<0.35

- STAR Preliminary

- trigger pt =2.5-4.0 GeV/c, associated pt =1.0-2.5 GeV/c

**Conical flow?**

- STAR: ||<0.35

- 60-80%

- 40-60%

- 20-40%

- 10-20%

- 0-5%

- 5-10%

- Jason Ulery
- Mark Horner

## Three-particle correlations?

**Three-particle correlations?**

## 3-particle correlation analysis

**3-particle correlation analysis**

- STAR Preliminary

- 3 < pTtrig < 4 GeV/c, 1 < pTassoc < 2 GeV/c, Au+Au 0-10%

- Raw signal: T(J+B)1(J+B)2

- Hard-Soft-bkgd: (TJ1)B2 + (TJ2)B1

- flow modulated background

- soft-soft correlation

- bkgd-bkgd: B1B2

## effect of v2 on 3-particle correlation

**effect of v****2**** on 3-particle correlation**

- correlation result is robust with v2.

- 4 particle cumulant v2

- 3 < pTtrig < 4 GeV/c, 1 < pTassoc < 2 GeV/c, Au+Au 0-10%

- reaction plane v2

- average of 4 particle cumulant v2 and reaction plane v2

- 1/Ntrig d2N/d(Δφ1)d(Δφ2)

- STAR Preliminary

##  pp and d+Au results

*** *****pp***** *****and d+Au results**

- 	Appears elongated along the diagonal axis in d+Au, possibly due to kT broadening

- Δφ

- Δφ

- Δφ

- 1/Ntrig d2N/d(Δφ1)d(Δφ2)

- 2 < pTtrig < 4 GeV/c, 1 < pTassoc < 2 GeV/c

- away	/2 = 0.89 ± 0.11
- 		   = 0.69 ± 0.05
- near	   = 0.66 ± 0.07

- pp

- d+Au

- 3 < pTtrig < 4 GeV/c, 1 < pTassoc < 2 GeV/c

- d+Au

- STAR Preliminary

## conical flow? 3-particle correlation

**conical flow? 3-particle correlation**

- d+Au and Au+Au elongated along diagonal:
- kT effect, and deflected jets?

- difference in Au+Au
- average signal per radian2:
- center – corner = 0.3 ± 0.3 (stat) ± 0.4 (syst)
- center – cone = 2.6 ± 0.3 (stat) ± 0.8 (syst)

- Three regions on away side:
- center =	(, ) ±0.4
- corner =	(+1,+1) ±0.4 	x2
- cone     =	(+1,-1) ±0.4 	x2

- Distinctive features of conical flow
- are not seen in present data with
- these pT windows.

## Three-particle correlations can be done at LHC, also much better.may have to be limited at low-modest pT (need 2 associated particles).