PowerPoint Presentation

Dijet Imbalance in 2.76 TeV PbPb Collisions in CMS

David Krofcheck

on behalf of the CMS CollaborationICHEP 2012, Melbourne, July 6th

Jet production in pp collisionsjet-jet correlation in QCD vaccuum D. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions2

Jet production in PbPb collisionsjet-jet correlation in QCD medium jet correlation to probe the medium?D. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions3

E-1E-2Dijet imbalance in PbPb collisionsD. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions4Phys. Rev. C 84, 024906 (2011)

Pixel and Silicon-Strip TrackerExcellent momentum resolution Large acceptance || < 2.53.8 T Solenoid

Hermetic calorimeter coverageECAL + HCAL || < 3.0Forward HCAL 3.0 || < 5.0Muon Detectors|| < 2.5 DAQ+Trigger: Dedicated triggers for Jets, Photons, Muon, high pT charged particles, etc.Beam ScintillatorsThe CMS DetectorD. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions5

Selecting jets in PbPb collisions

peripheralcentralD. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions6Phys. Rev. C 84, 024906 (2011)

Observed angular correlation between the PbPb dijetsD. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions7

Dijets in PbPb are more imbalanced than PYTHIA+HYDJET

D. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions8Dijets in PbPb - asymmetry in central collisions

PLB 712 (2012) 176D. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions9

Observed angular correlation between jet in PbPb collisions

jet Correlation across PbPb overlap

D. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions10Momentum ratio shifts/decreases with centralityjets shifting below the 30 GeV pT threshold not included Submitted to PLB, arXiv:1205.0206Observed momentum imbalance in jet correlation

D. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions11

CMS

Significant deviation ofxJin PbPb compared to PYTHIA + HYDJETThe centrality dependence is mostly visible in RJ jet pT shifting below the 30 GeV threshold

Mean xJ-Fraction without jet: RJObserved deviation between jet from PbPb collisions D. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions12Submitted to PLB, arXiv:1205.0206

We used dijets to compare PbPb collisions to pp at different impact parameters and transverse momenta Dijets can be strongly imbalanced in momentum as a result of passing through the QCD medium We observe jet correlationsMeasuring the and jet energies may tell us about the energy loss mechanism of in-medium partons. SummaryD. Krofcheck ICHEP, MelbourneDijet Imbalance in 2.76 TeV PbPb Collisions13Backup slides