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Dijet Imbalance in 2.76 TeV PbPb Collisions in CMS
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Dijet Imbalance in 2.76 TeV PbPb Collisions in CMS David Krofcheck on behalf of the CMS Collaboration ICHEP 2012, Melbourne, July 6 th
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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. - PowerPoint PPT Presentation
Transcript of 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 CollaborationICHEP 2012, Melbourne, July 6th
Jet production in pp collisions
jet-jet correlation in QCD “vaccuum”
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 2
Jet production in PbPb collisionsjet-jet correlation in QCD “medium”
γ – jet correlation to probe the medium?
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 3
E-ΔΕ1
E-ΔΕ2
Dijet imbalance in PbPb collisionsΔφ
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 4
Phys. Rev. C 84, 024906 (2011)
Pixel and Silicon-Strip TrackerExcellent momentum resolution Large acceptance || < 2.53.8 T Solenoid
Hermetic calorimeter coverageECAL + HCAL || < 3.0
Forward HCAL 3.0 || < 5.0
Muon Detectors|| < 2.5
DAQ+Trigger: Dedicated triggers for Jets, Photons, Muon, high pT charged particles, etc.
Beam Scintillators
The CMS Detector
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 5
Selecting jets in PbPb collisions
“peripheral” “central”
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 6
Phys. Rev. C 84, 024906 (2011)
Observed angular correlation between the PbPb dijets
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 7
Dijets in PbPb are more imbalanced than PYTHIA+HYDJET
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 8
Dijets in PbPb - asymmetry in central collisions
PLB 712 (2012) 176
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 9
Observed angular correlation between γ – jet in PbPb collisions
γ – jet Correlation across PbPb overlap
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 10
• Momentum ratio shifts/decreases with centrality– jets shifting below the 30 GeV pT threshold not included
Submitted to PLB, arXiv:1205.0206
Observed momentum imbalance in γ – jet correlation
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 11
CMS
• Significant deviation of x⟨ J in PbPb compared to PYTHIA + HYDJET⟩• The centrality dependence is mostly visible in RJ
– jet pT shifting below the 30 GeV threshold
Mean xJ -Fraction without jet: RJ
Observed deviation between γ – jet from PbPb collisions
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 12
Submitted 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 γ – jet correlationsMeasuring the γ and jet energies may tell us about the energy loss mechanism of in-medium partons.
Summary
D. Krofcheck ICHEP, Melbourne Dijet Imbalance in 2.76 TeV PbPb Collisions 13
Backup slides
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