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Jet quenching and energy loss in CMS

Jet quenching and energy loss in CMS. Christof Roland for the CMS Collaboration. CMS Detector. Muon Detectors |  | < 2.5. Pixel and Silicon-Strip Tracker Excellent momentum resolution Large acceptance |  | < 2.5 3.8 T Solenoid. Hermetic calorimeter coverage

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Jet quenching and energy loss in CMS

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  1. Jet quenching and energy loss in CMS Christof Roland for the CMS Collaboration

  2. CMS Detector Muon Detectors || < 2.5 Pixel and Silicon-Strip Tracker Excellent momentum resolution Large acceptance || < 2.5 3.8 T Solenoid Hermetic calorimeter coverage ECAL + HCAL || < 3.0 Forward HCAL 3.0 || < 5.0 DAQ+Trigger: Dedicated triggers for Jets, Photons, Muon, high pT charged particles, etc.

  3. Single particles in the CMS Detector + 4T

  4. The “Particle Flow” algorithm to form Jets Underlying event is subtracted using the iterative pile-up subtraction method Jets from Anti-kT, R = 0.3

  5. Isolated Photons Photon candidate from jet Isolated photon Two independent handles to measure isolated photons: isolation and shower shape Jet, pT: 99.7 GeV/c Shower Shape Photon, pT: 142.1 GeV

  6. Motivation Ein-ΔΕ θ Ein Δx muon “Bethe-Bloch curve” Energy loss of a charged particle in matter (QED) Bethe equation Goal: achieve the same level of understanding for partons traversing strongly interacting matter (QCD)

  7. Parton Energy Loss in PbPb Collisions • Angular deflection () • Study angular correlation dijet and gamma jet correlations • Constrains the scattering mechanisms • Study the “lost” energy (Medium Ionization) • Missing pT studies • Energy loss (E) • Study dijet and gamma jet momentum balance • Direct observation of parton energy loss • The Bethe Curve • Study the momentum dependence • Dijet balance vs. pT • Different projectiles • Dijet and gamma-jet momentum balance • Gluon vs quark dominated processes

  8. Initial State Non Interacting Probes: Photon, Z0, W • No strong modification of the initial state observed • Use PYTHIA and Ncoll scaling for unquenched reference • Embed in HYDJET (underlying event) QED: QCD: PbPb 0-10% Central

  9. Dijet Measurements E-ΔΕ1 E-ΔΕ2 From QM2011: Parton Energy Loss observed as Dijet Momentum Imbalance QED: Ein- ΔΕ Ein QCD:

  10. Jet Fragmentation • Select dijets with • pTJet1>100GeV/c • pTJet2>40GeV/c • 12>2/3 • Correlate reco. Jet pT with track pT • Tracks in R=0.3 cone • pT> 4 GeV/c • z = p ||Track/pJet,  = log (1/z) • Compare Leading and Subleading Jet in pp and PbPb Pb Pb Pb Pb  = log (1/z) dN/dpTJet Yetkin Yilmaz, Parallel IVB, Thursday 14:00

  11. Jet Fragmentation in pp and PbPb Leading and subleading jet in PbPb fragment like jets of corresponding energy in pp collisions Pb Pb Pb Pb  = log (1/z) Yetkin Yilmaz, Parallel IVB, Thursday 14:00

  12. Fragmentation of jets PbPb results in AJ bins

  13. Fragmentation of jets PbPb results in AJ bins At the same reconstructed jet energy, jets in PbPb fragment like jets in pp • We can reliably reconstruct jets • We can safely use PYTHIA derived jet energy scale corrections in PbPb • Calibrate to final state particle level

  14. Where does the “lost” energy go? Medium ionization 0-30% Central PbPb E? arXiv:1102.1957 [nucl-ex] unbalanced jets balanced jets

  15. Missing-pT|| Missing pT||: Calculate projection of pT on leading jet axis and average over selected tracks with pT > 0.5 GeV/c and |η| < 2.4 0-30% Central PbPb arXiv:1102.1957 [nucl-ex] unbalanced jets balanced jets Leading jet defines direction Sum all tracks in the event

  16. Missing-pT|| Missing pT||: 0-30% Central PbPb excess away from leading jet excess towards leading jet arXiv:1102.1957 [nucl-ex] balanced jets unbalanced jets Integrating over the whole event final state the momentum balance is restored

  17. Missing-pT|| Missing pT||: The momentum difference in the dijet is balanced by low pT particles 0-30% Central PbPb Calculate missing pT in ranges of track pT: excess away from leading jet excess towards leading jet arXiv:1102.1957 [nucl-ex] Phys. Rev. C84 (2011) 024906 balanced jets unbalanced jets

  18. Missing-pT|| in-cone out-of-cone 0-30% Central PbPb In-Cone R<0.8 Out-of-Cone R<0.8 Phys. Rev. C84 (2011) 024906 balanced jets unbalanced jets The momentum difference in the dijet is balanced by low pT particles at large angles relative to the away side jet axis

  19. Dijet Angular Correlations pT1 pT2 Dijet Angular Correlations PLB 712 (2012) 176 QED:  ) pT,2> 30GeV/c QCD: Correlation peak is the same in data and Pythia across all values of pT Yetkin Yilmaz, Parallel IVB, Thursday 14:00

  20. pT-dependence of the dijet imbalance PLB 712 (2012) 176 pT,2> 30GeV/c 12 > 2/3 pT,2/pT,1 Unbalanced Balanced Energy loss apparent in all bins of leading jet pT Yetkin Yilmaz, Parallel IVB, Thursday 14:00

  21. pT-dependence of the dijet imbalance pT-dependence of the dijet imbalance PLB 712 (2012) 176 No significant dependence on jet pT Yetkin Yilmaz, Parallel IVB, Thursday 14:00

  22. -Jet Correlations Jet  • Correlate Isolated Photons with Jets • Photons do not interact with the medium • Tag initial parton energy and direction • -Jet channel selects predominantly quark jets  ) Ein Ein-ΔΕ

  23. -Jet Angular Correlations Submitted to PLB, arXiv:1205.0206 pT> 60 GeV/c || < 1.44 pTJet> 30 GeV/c || < 1.6 Subtract background from • Multiple hard scatterings • fragmentation/decay photons Yue Shi Lai, Parallel VB, Thursday 16:30

  24. -Jet Angular Correlations Submitted to PLB, arXiv:1205.0206 No significant angular decorrelation is observed for -jet pairs pT> 60 GeV/c || < 1.44 pTJet> 30 GeV/c || < 1.6 Yue Shi Lai, Parallel VB, Thursday 16:30

  25. -Jet Momentum Balance Submitted to PLB, arXiv:1205.0206 • Momentum ratio shifts/decreases with centrality • jets shifting below the 30 GeV pT threshold not included pT> 60 GeV/c || < 1.44 pTJet> 30 GeV/c || < 1.6 Yue Shi Lai, Parallel VB, Thursday 16:30

  26. -Jet Momentum Balance vs. Centrality CMS Mean xJ -Fraction without jet: RJ • 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 Yue Shi Lai, Parallel VB, Thursday 16:30

  27. Summary • Many different aspects of parton energy loss have been studied • Angular correlation of partons not affected by the medium • Measured in dijets and in photon-jet correlations • Over a wide range in pT • Constrains the scattering mechanisms • Energy redistribution in the medium • Momentum difference in the dijet balanced by low pT particles at large angles relative to the away side jet • Large dijet momentum imbalance observed • Momentum imbalance persists out to the highest pT • First measurement of gamma jet correlations in PbPb • Direct observation of energy loss with respect to the initial parton energy • Probes quark energy loss vs. gluon energy loss in dijets • The Challenge: • Develop a description of the energy loss mechanism that consistently describes all aspects of parton energy loss

  28. More news from CMS • Plenary Presentations: • Jet quenching and energy loss in CMS, • Christof Roland (Massachusetts Inst. of Tech.) Plenary 1b, Monday 28.05 • Hadron correlations in CMS • Charles Felix Maguire (Vanderbilt University) , Plenary 2B, Tuesday 10:55 • Quarkonia and heavy flavor production in CMS • Torsten Dahms (LLR, Ecole Polytech., IN2P3-CNRS) , Plenary 3A, Wednesday 09:30 • W,Z and photon production in CMS • Begona De La Cruz (CIEMAT), Plenary 4A, Thursday 09:30 • Parallel Presentations: • Measurement of charged hadron R_AA at high pT in PbPb collisions at sqrt(s)=2.76TeV with CMS • Krisztian Krajczar (KFKI Research Inst. for Part. & Nucl. Phys.) , Parallel IIC, Monday 17:30 • Measurement of dN/deta and dET/deta in PbPb collisions at sqrt(s)=2.76TeV with CMS • Michael Murray (The Univ. of Kansas) , Parallel IIC, Monday 16:30 • Measurement of charged hadron v_2 at high pT in PbPb collisions at sqrt(s)=2.76TeV with CMS • Victoria Zhukova (The Univ. of Kansas) , Parallel IC: Correlations, Monday 14:00 • Measurement of Fourier components of two-particle correlations in PbPb collisions at sqrt(s)=2.76TeV with CMS • Rylan Towne Conway (UC Davis) , Parallel IC: Correlations, Monday 14:40 • Dijet transverse momentum imbalance, fragmentation functions and jet-track correlations in PbPb collisions at sqrt(s)=2.76TeV with CMS • Yetkin Yilmaz (Massachusetts Inst. of Tech.) , Parallel IVB, Thursday 14:00 • Measurement of isolated photon R_AA at high pT in PbPb collisions at 2.76TeV with CMS • Yen-Jie Lee (CERN) , Parallel IIIC: Tuesday 14:35 • Measurement of isolated photon-jet correlations in PbPb collisions at sqrt(s)=2.76TeV with CMS • Yue Shi Lai (Massachusetts Inst. of Tech.) , Parallel VB, Thursday 16:30 • Measurement of charmonium production in PbPb collisions at 2.76TeV with CMS, • Dong Ho Moon (Korea University) , Parallel IA: Quarkonia, Monday 14:00 • Measurement of bottomonium production in PbPb collisions at 2.76TeV with CMS • Camelia Mironov (LLR, Ecole Polytech., IN2P3-CNRS) , Parallel VA, Thursday16:30 • Measurement of electroweak boson production in PbPb collisions at 2.76TeV with CMS • Lamia Benhabib (LLR, Ecole Polytech., IN2P3-CNRS) , Parallel IIIC: Tuesday14:55 • Quarkonium production in pp collisions with CMS • Carlos Lourenco (CERN), Parallel IIIA, Tuesday 14:15

  29. Backup Slides

  30. Fragmentation Functions

  31. pp results and reference for PbPb Soft fragments Hard fragments Reference for PbPb data by reweighting pp data

  32. Data sample of 2011 Dijet Momentum Balance PLB 712 (2012) 176 AJ = (pT,1 - pT,2) / (pT,1 + pT,2) Yetkin Yilmaz, Parallel IVB, Thursday 14:00

  33. Dijet Correlation and Background Dijet correlation and background At high pT, only very few jets get completely lost on the away side: A less biased quantification of energy loss arXiv:1202.5022 33 Yetkin Yilmaz (MIT) Dijets in CMS

  34. Track-Jet Correlations Dijet Partner η-reflected Background Cone Signal Jet Cone • Study charged particle distributions within jet cones • Use  reflected ( -> -) reference cones for jet-by-jet subtraction of Pb+Pb underlying event • This avoids  dependent variations due to elliptic flow • Exclude |Jet| < 0.8 and |Jet| > 1.6 • Study associated track distributions versus pT and ΔR • Uncertainties in background subtraction limit this method to pT > 1 GeV/c and ΔR < 0.8

  35. Track-Jet Correlations Phys. Rev. C84 (2011) 024906 MC Pb Pb Data unbalanced jets balanced jets Increasing AJ

  36. Track-Jet Correlations MC MC Pb Pb Data Data unbalanced jets balanced jets Phys. Rev. C84 (2011) 024906 • In dijet events with a large imbalance, AJ>0.33, we find more energy in tracks below pT of 4GeV/c at large R • But, not nearly enough to restore the dijet balance • No indication of cone like structures around the jet up to a cone size of 0.8 • Not in the region currently accessible, to be extended later

  37. Jet Reconstruction Calorimeter based Jet Finder (IC5) • Iterative Cone Algorithm • R = 0.5 • arXiv:1102.1957 [nucl-ex] Particle Flow Jet Finder (PF) • Anti-kT Clustering Algorithm* • R = 0.3 • See Presentation by M. Nguyen Parallel Session, Friday Underlying event subtraction • Iterative PileUp subtraction** * M. Cacciari, G. P. Salam, and G. Soyez, JHEP 04 (2008) 063 ** O. Kodolova, I. Vardanian, A. Nikitenko et al., Eur. Phys. J. C50 (2007) 117

  38. Jet Reconstruction Jet Reconstruction fully efficient above: • 50 GeV/c, Calorimeter Jets • 40 GeV/c, Particle Flow Jets Calorimeter based Jet Finder (IC5) • Iterative Cone Algorithm • R = 0.5 Particle Flow Jet Finder (PF) • Anti-kT Clustering Algorithm • R = 0.3 Underlying event subtraction • Iterative PileUp subtraction

  39. Jet Reconstruction • Good Jet pT resolution • Jet pT corrected to generator final state particle level • Correction derived from PYTHIA Pb Pb Pb Pb Pb Pb Calorimeter based Jet Finder (IC5) • Iterative Cone Algorithm • R = 0.5 Particle Flow Jet Finder (PF) • Anti-kT Clustering Algorithm • R = 0.3 Underlying event subtraction • Iterative PileUp subtraction

  40. -Jet Signal Definition Leading order Higher orders γ γ γ Final state not differentiable ISOLATED ISOLATED NON-ISOLATED Isolated Isolated Non-isolated SumIso = uncorrected Track + ECAL + HCAL ET in R < 0.4 GenIso = generator level particle energy in R < 0.4 Isolated prompt (non-decay) photons with SumIso < 1 GeV Comparison to MC definition GenIso < 5 GeV SumIso ≠ GenIso due to PbPb underlying event fluctuation

  41. -Jet Statistical Background Subtraction Data, cf. Slide 13 Photon-Jet Background Photon–Jet Background Photon–UE Combinatorics Estimated from event mixingmethod using minimum-biasdata Photon–UE Combinatorics Δφ Signal region

  42. Fragmentation/decay photon subtraction Statistical Subtraction Photon-Jet Background Photon–Jet Estimated from shower shape sideband & purity Δφ Signal region

  43. Analysis Flow Chart Shower shape Signal like σηη<0.01 Z to ee Cross check the energy correction Super Clusters spike rejection Passing loose photon ID H/E<0.1 Photon isolation Energy correction Anti-kT 0.3 pile-up subtracted Jet candidates |η|<1.6 Electron rejectionRemaining contribution 1-3% Selected Jet candidates Leading Cluster Shower shape Background like 0.011<σηη<0.017 Shower shape Signal like σηη<0.01 Exclude photon candidate |ΔR| > 0.3 w/r to leading photon Background clusters (Fakes from jet) Photon Candidates Selected Jet Background template Photon Candidates- AllJet Event Mixing |Δφ| > 7π/8 Photon Candidates- All Jet Signal region Photon-Jet correlations in MIXED events Purity Determination Purity Determination Photon- All Jet Signal region Photon-Jet Final result Dijet Background subtraction

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