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Dijet Imbalance in 2.76 TeV PbPb Collisions in CMS

Dijet Imbalance in 2.76 TeV PbPb Collisions in CMS. David Krofcheck on behalf of the CMS Collaboration ICHEP 2012, Melbourne, July 6 th. Jet production in pp collisions. j et-jet correlation in QCD “ vaccuum ” . Jet production in PbPb collisions.

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Dijet Imbalance in 2.76 TeV PbPb Collisions in CMS

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  1. Dijet Imbalance in 2.76 TeVPbPb Collisions in CMS David Krofcheck on behalf of the CMS Collaboration ICHEP 2012, Melbourne, July 6th

  2. Jet production in pp collisions jet-jet correlation in QCD “vaccuum” Dijet Imbalance in 2.76 TeVPbPb Collisions

  3. Jet production in PbPbcollisions • jet-jet correlation in QCD “medium” γ – jet correlation to probe the medium? Dijet Imbalance in 2.76 TeVPbPb Collisions

  4. E-ΔΕ1 E-ΔΕ2 • Dijet imbalance in PbPbcollisions Δφ Phys. Rev. C 84, 024906 (2011) Dijet Imbalance in 2.76 TeVPbPb Collisions

  5. The CMS Detector Muon Detectors || < 2.5 Beam Scintillators Pixel and Silicon-Strip Tracker Excellent momentum resolution Large acceptance || < 2.5 3.8 T Solenoid Hermetic calorimeter coverage ECAL + HCAL || < 3.0 Forward HCAL3.0 || < 5.0 DAQ+Trigger: Dedicated triggers for Jets, Photons, Muon, high pT charged particles, etc. Dijet Imbalance in 2.76 TeVPbPb Collisions

  6. Selecting jets in PbPb collisions Phys. Rev. C 84, 024906 (2011) “peripheral” • “central” Dijet Imbalance in 2.76 TeVPbPb Collisions

  7. Observed angular correlation between the PbPbdijets Dijet Imbalance in 2.76 TeVPbPb Collisions

  8. Dijets in PbPb are more imbalanced than PYTHIA+HYDJET Dijet Imbalance in 2.76 TeVPbPb Collisions

  9. Dijets in PbPb- asymmetry in central collisions PLB 712 (2012) 176 Dijet Imbalance in 2.76 TeVPbPb Collisions

  10. Observed angular correlation between γ– jet in PbPb collisions γ– jet Correlation across PbPb overlap Dijet Imbalance in 2.76 TeVPbPb Collisions

  11. Observed momentum imbalance in γ– jet correlation Submitted to PLB, arXiv:1205.0206 • Momentum ratio shifts/decreases with centrality • jets shifting below the 30 GeV pT threshold not included Dijet Imbalance in 2.76 TeVPbPb Collisions

  12. CMS Observed deviation between γ– jet from PbPb collisions Mean xJ -Fraction without jet: RJ Submitted to PLB, arXiv:1205.0206 • Significant deviation of〈xJ〉in PbPb compared to PYTHIA + HYDJET • The centrality dependence is mostly visible in RJ • jet pT shifting below the 30 GeV threshold Dijet Imbalance in 2.76 TeVPbPb Collisions

  13. Summary • We used dijets to compare PbPbcollisions 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 γ– jet correlations Measuring the γand jet energies may tell us about the energy loss mechanism of in-medium partons. Dijet Imbalance in 2.76 TeVPbPb Collisions

  14. Backup slides

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