PPR PWG 6 Work Plan - Correlations Working document… C. Pruneau July 23, 2008.

PPR PWG 6

Work Plan - CorrelationsWorking document…

C. Pruneau

July 23, 2008

Introduction

• Physics of Interest– Impact of Jets on the Medium– Impact of the Medium on Jets (our focus)

• Some key questions– Parton interaction with medium

• Transport, energy loss, q-hat?

• “Flow Effects on Jets”, early transverse fields

– Hadronization: A+A vs p+p• Fragmentation function: one or multi-particle

• Jet heating (away-side)

• Jet flavor composition (away-side)

JT

Measurements (Jet-Jet Correlations)

• Change of Di-jet Cross Section– A.k.a number of associate jets/per trigger jet

• Change of Di-jet Invariant mass spectrum

• Energy (pt) Loss: pt1 vs pt2, pt1-pt2

• Acoplanarity , pt,out

• Away-side jet modification– Fragmentation function– Jet Transverse Momentum – Particle composition (ratio).

A+A vs p+p

JT

kT

Di-jet Acoplanarity

Measurements: distribution• kTx,kTy distribution• Above with selection of |pt1-pt2|

From Isabel Dominguez

Not yet the right model !

Cuts to be tuned !

From Isabel Dominguez

From Isabel Dominguez

To be tested with improved model using final state kT !

From Isabel Dominguez

Di-jets Di-jet angle

√s=5.5 TeV√s=200 GeV

• Reconstructing dijets is ‘easy’!• Use background level to monitor/subtract combinatorics in A+A• Widening of at LHC energies: increase of initial state radiation, 3-jet

events• Background effects in A+A ?

Marco

Di-jets (pt1 vs pt2)

√s=5.5 TeV√s=200 GeV

Marco

•Di-jets balance in energy Handle on initial parton energy•Correlation widens at LHC: radiation + 3-jet events•Difference between A+A and p+p?

• Background effects ? • Jet Modification Sensitivity?

Di-jet energy balance

pT for balancing di-jets• Irreducible effects: kT, mult-jet events: ~ 5-10 GeV• Still works for charged-only jets (deteriorates quickly beyond)• Direct measure of energy loss fluctuations (E) in Heavy Ion Collisions• Sensitivity (E) ~ few GeV, can we be more precise?• To do: Assessment of Emcal resolution (common to pp & AA), bulk+flow

background effects in A+A•Background cancels in pt2-pt1 measurements. How bad are finite stat effects.•Energy loss phenomenology (out-of cone radiation)

√s = 5.5 TeV

Away-side Fragmentation Fct.

• Select “geometry”:

• Select high-pt jet (EMCal), Study away-side jet (TPC)– Measure Fragmentation P(z)– Measure – Requires EMCal trigger, Best Jet Energy (trigger)

determination.– Simulation (To do): Precision of P(z), measurements

relative to medium modification.

JT

JT

Summary

• Acoplanarity: kTx,kTy,Dj– Can be done – Multi-jet effects important– How large are medium effects?

• Pt vs Pt– Can be done– Background effects? Jet splitting?– How large are medium effects?

• Away Side Jet – Enrich sample of modified jet. Bias of reconstruction?