Jet-Hadron Correlations in Pb-Pb Collisions with ALICE
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Transcript of Jet-Hadron Correlations in Pb-Pb Collisions with ALICE
Megan Connors
MEGAN CONNORS YALE UNIVERSITY
FOR THE ALICE COLLABORATION
Jet-Hadron Correlations in Pb-Pb Collisions with ALICE
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Outline
Why Jet-Hadron correlations are interestingHow do we measure Jet-Hadron correlationsΔϕ correlations in ppFirst look at Pb-Pb
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Jet Probes in Heavy Ion Collisions
Hard Scattering is early in the collisionResulting partons lose energy in the mediumPathlength dependenceCorrelations with the resulting particlesBias the nearside correlation but not the awayside
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Studying Energy Loss with Correlations
Hadron-hadron
-Surface bias the trigger-Tangential jets or maximized modification- Broad parton energy distribution
Jet-hadron
-Some surface bias-Several parameters to vary pathlength-narrower parton energy
Direct photon-hadron
-No surface bias due to trigger-p≈pjet
-Measure D(z)
Complimentary observablesRequire Energy loss models to explain all observables
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What we learned at RHIC
Suppression of high momentum particles is balanced by an enhancement of low momentum particles
Widths show no significant broadening when accounting for higher order harmonics
Need to measure jet vn
LHC can study effect at higher sNN and access higher parton energies
Note the cuts applied: 2 GeV/c constituents & a EMCal Tower Trigger of 6 GeV
Jet pT is not unfolded (trigger jet uncertainty)
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STAR Preliminary
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How to bias Jets at the LHC
Density of vertices for 30-60 GeV JetsTrack cuts enhance surface biasSurface biased jets should be comparable to pp jets
YaJEM at LHC T. Renk
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Jet
S=LHS/RHS Constituent cut Plus leading track requirement
arXiv:1210.1330v1
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ALICE Detector7
Tracking:|η|<0.9, 0<φ<360° TPC: gas detectorITS: silicon detector
• EMCal is a Pb-scintillator sampling calorimeter which covers: |η|<0.7, 80°<φ<180°
• Towers Δη~0.014, Δφ ~0.014°
JETAssociated
Tracks
Δϕ
Anti-kT R=0.4Constituents >3GeV/cLeading particle > 6GeV/c
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20-60GeV/c
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How to Measure Correlations
CF=same-event-pairs/mixed-event-pairs
CF=Jet+Underlying eventUnderlying event
Flat pedestal in pp Flow modulated (initial collision
geometry) in Heavy Ion
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What is Jet vn?
Phys.Lett. B708 (2012) 249-264
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Jet-Hadron Correlations in pp: Measurement
For 20-60 GeV Jets with 3 GeV/c constituent cut and 6 GeV/c particle bias
Associated tracks are below constituent cut and don’t affect the Jet finder
Pedestal subtraction gives uncertainty band about zero
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Jet-Hadron Correlations in pp: Observations
Note: 3 GeV/c constituent cut and 6 GeV/c particle bias do not bias the fragmentation of awayside jet
Clear observation of near and away-side jet peaksGoal is to extract widths and yields from these
correlations for comparison to Pb-Pb
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Jet-hadron in Pb-Pb
Jet-Hadron correlations observed in Pb-Pb
Underlying event subtraction in Pb-Pb complicated by Flow
Must understand UE and vn before we can subtract it from the jet correlations
Nearside Jet Peak
Awayside Jet Peak?
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Status of Jet-Hadron Correlations in ALICE
Measured Jet-hadron correlations at ALICE in pp
Observed Jet-H Correlation in Pb-PbWorking toward a comparison of these
measurementsMore results soon!
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Backup Slides
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Jet-h vs h-h at RHIC
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Parton distribution for hadron triggers is broader than for Jet triggers
T. Renk arXiv:1210.1330v1
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Surface Bias Follow up
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~ No surface bias for 100 GeV jets with constituents down to 1 GeV
T. Renk, arXiv:1202.4579v2