Jet-Hadron Correlations in Pb-Pb Collisions with ALICE

1. Jet-Hadron Correlations in Pb-Pb Collisions with ALICE Megan Connors Yale University For the ALICE Collaboration Megan Connors

2. Outline Why Jet-Hadron correlations are interesting How do we measure Jet-Hadron correlations Δϕ correlations in pp First look at Pb-Pb Megan Connors

3. Jet Probes in Heavy Ion Collisions Hard Scattering is early in the collision Resulting partons lose energy in the medium Pathlength dependence Correlations with the resulting particles Bias the nearside correlation but not the awayside Megan Connors

4. Studying Energy Loss with Correlations Jet-hadron -Some surface bias -Several parameters to vary pathlength -narrower parton energy Hadron-hadron -Surface bias the trigger -Tangential jets or maximized modification - Broad parton energy distribution Direct photon-hadron -No surface bias due to trigger -p≈pjet -Measure D(z) Complimentary observables Require Energy loss models to explain all observables Megan Connors

5. What we learned at RHIC Suppression of high momentum particlesis 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) STAR Preliminary Megan Connors

6. How to bias Jets at the LHC Density of vertices for 30-60 GeV Jets Track cuts enhance surface bias Surface biased jets should be comparable to pp jets S=LHS/RHS Constituent cut Plus leading track requirement Jet YaJEM at LHC T. Renk arXiv:1210.1330v1 Megan Connors

7. ALICE Detector • EMCal is a Pb-scintillator sampling calorimeter which covers: • |η|<0.7, 80°<φ<180° • Towers • Δη~0.014, Δφ ~0.014° Anti-kTR=0.4 Constituents >3GeV/c Leading particle > 6GeV/c JET Tracking:|η|<0.9, 0<φ<360° TPC: gas detector ITS: silicon detector 20-60GeV/c Δϕ Associated Tracks Megan Connors

8. How to Measure Correlations • CF=same-event-pairs/mixed-event-pairs • CF=Jet+Underlying event • Underlying event • Flat pedestal in pp • Flow modulated (initial collision geometry) in Heavy Ion What is Jet vn? Phys.Lett. B708 (2012) 249-264 Megan Connors

9. 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 Megan Connors

10. 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 peaks Goal is to extract widths and yields from these correlations for comparison to Pb-Pb Megan Connors

11. 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? Megan Connors

12. Status of Jet-Hadron Correlations in ALICE Measured Jet-hadron correlations at ALICE in pp Observed Jet-H Correlation in Pb-Pb Working toward a comparison of these measurements More results soon! Megan Connors

13. Backup Slides Megan Connors

14. Jet-h vs h-h at RHIC Parton distribution for hadron triggers is broader than for Jet triggers T. Renk arXiv:1210.1330v1 Megan Connors

15. Surface Bias Follow up ~ No surface bias for 100 GeV jets with constituents down to 1 GeV T. Renk, arXiv:1202.4579v2 Megan Connors