Jet-Hadron Correlations in Pb-Pb Collisions with ALICE

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MEGAN CONNORS YALE UNIVERSITY FOR THE ALICE COLLABORATION Jet-Hadron Correlations in Pb-Pb Collisions with ALICE Megan Connors 1 Hot Quarks 10/14/12

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Jet-Hadron Correlations in Pb-Pb Collisions with ALICE . Megan Connors Yale University For the ALICE Collaboration. Outline. Why Jet-Hadron correlations are interesting How do we measure Jet-Hadron correlations Δϕ correlations in p p First look at Pb-Pb. - PowerPoint PPT Presentation

Transcript of Jet-Hadron Correlations in Pb-Pb Collisions with ALICE

Page 1: 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