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
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