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Higgs  4 leptons

Higgs  4 leptons. Stathes Paganis ATLAS UK meeting Durham, 18 - Sep -2006. UK contribution. e/ g calibration (long weights) in ATLAS e/ g data analysis (CTB04 papers) Vertexing in ATLAS offline (Kirill Prokovief) H  4l CSC note coordination (SP) Artemis EU Network:

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Higgs  4 leptons

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  1. Higgs  4 leptons Stathes Paganis ATLAS UK meeting Durham, 18-Sep-2006

  2. UK contribution • e/g calibration (long weights) in ATLAS • e/g data analysis (CTB04 papers) • Vertexing in ATLAS offline (Kirill Prokovief) • H  4l CSC note coordination (SP) • Artemis EU Network: • Durham, Sheffield, UCL, Saclay, Pisa, MPI, Aristotle University

  3. Signal and Backgrounds Irred R~250 R~1000

  4. Definitions (this analysis) • Electron • An egamma cluster (98%) • SW 3x7, 3GeV Energy Threshold, Cluster Corrections • (TDR: optimum is 5x5 in the EndCap) • A cluster/track match (92%) • An isolated cluster (Recon. flag eg_ISEM=0) • Track Quality: at least 9 Silicon hits, E/p<2.3 • Muon • A combined (muon-Spec)+(ID) “cb” muon • Refitting Quality: fitcodecb=0.

  5. Apply EM corrections to ‘electrons’ Use Et from LAr, h, f from tracks Combine Et from ID and Et from LAr (TDR) Apply TDR-like cuts 4 leptons with pt(1,2)>20, pt(3,4)>7GeV with |h|<2.5 EM isolation cuts (eg_ISEM=0) Only for electrons ID isolation cuts Electrons Spt(0.01 < dR < 0.2) < 10 GeV Muons Spt(0.01 < dR < 0.2) < 5 GeV Impact Parameter cut Electrons a0vert/s < 10 (for 4e), 5 (for 2e2m) Muons a0vert/s < 3.5 Z, Z* mass cuts M12, M34 and Higgs mass window as in TDR H->4l analysis cuts For high masses: isolation and impact parameter cuts are relaxed for the 4e and 2e2m case.

  6. Comparison with TDR (30fb-1 low lumi) Bill Quayle The increase of the background at 180GeV has been previously noted: it is driven by the ZZ background which rises fast at the M(ZZ)=180GeV region (not included in TDR analysis)

  7. EventView and HiggsToFourLeptons (12.0.x) AOD ElectronInserter MuonInserter TruthParticleAssociator EventViewInserters TruthParticleInserter EVUDAssociators TrackParticleAssociator GenParticleInserter EV_H4lPreselector ClusterAssociator PassedIsEM PassedEgamma PassedTrkIso Electron AANtuple Muon Local Analysis GenParticle TrueE, TrueMu

  8. Critical Issues

  9. Background Extraction in (cand) Signal Region • From “theory”: • PDF error 4-5% • Renorm/Factor. Scales error 3-5% • Efficiency error ?% • Luminosity error (5-10% ?) • How about the Zbb (low mass 20-50% error but only a fraction of ZZ)? • From Normalization • Lumi/Efficiency errors reduced • Ratio less sensitive to scale/PDF uncertainties • How about the Zbb (low mass)? • From Sidebands • Limited statistics at low masses • Difficult below 130GeV due to kinematic turnover • But, error well defined using a profile likelihood (i.e. use MINOS errors of multiple fits with different background parameterization assumptions). Abdulin et al, hep-ph/0604120 (pg 113) Jan Conrad et al

  10. ZZ background Pt lepton > 5 GeV. No Z mass cuts. Notice the turn-over at 120GeV. Notice the turn-on of ZZ at 180GeV.

  11. Sideband fitting: 30fb-1 background only Assume a test for Higgs(130GeV). We ran 1M experiments. 3sigma test finds: 1712 events passing out of 1350 expected from fluctuations

  12. Sidebands: 30fb-1 130GeV Signal+Bgnd <B>=5, <S>=12 events Fit may exclude/include “signal region” (here the fit excludes the sr) For every experiment we know the true Signal and Background, so we can check how well a fitting method does in extracting the signal significance (coverage study).

  13. Sidebands: S+B relaxing Z mass cuts <B>=15, <S>=12 events

  14. Accuracy of Background prediction Background extraction using an unbinned extended likelihood fit <B> unbiased 15 Background events in signal region: RMS of prediction: 3.5 events 5 Background events in signal region: RMS of prediction: 2 events 3sigma test finds: 1712/1M events passing out of 1350 expected from fluctuations: This undercoverage can be corrected analytically (in the large statistics limit): K.Cranmer, S.Paganis ATL-COM-PHYS-2005

  15. Softest lepton Pt and electron efficiency 12.0.x Generated softest lepton pt H120 H150 H180 IsEM only Most of the soft electrons (and so the light Higgs events) are lost due to non optimized isolation cuts below 15GeV. Reminder (at NLO): H(120GeV): xsection*BR*Acceptance ~ 2events/fb-1. Similar problem in SUSY analyses. We will address the problem in coordination with the egamma group. Also 9GeV electron CTB data are available to study shower shapes. Extraction of efficiency at low pt using data is also an issue.

  16. Very Preliminary CTB04 Electrons Fraction of energy outside a 3 strip core data vs MC 11.4.0 for 6 energies. Cut important for e-ID and g/p0 separation. Maybe due to the physics list used in 11.4.0, or/and due to cross-talk. Notice larger departure at higher energies.

  17. Very Preliminary Lateral Width

  18. Very Preliminary e1diff (2nd maximum minus the minimum between the 2 maxima)

  19. Electron Uniformity/Scale with pt>7GeV Higgs electrons with pt>7GeV, 5x5 clusters The gap region must be checked: New calibration in 12.0.x is fine

  20. Sample resolution/Escale eta bins (pt>7GeV) 1.05<eta<1.25 0.2<eta<0.4 1.25<eta<1.45 2.08<eta<2.29 New calibration in 12.0.x is fine

  21. Weights from minimization: performance Now into Athena • Linearity evaluated on H->4e events (no cracks) averaged on full eta range (0-2.5) with Athena 12.0.2 out of the box • Low energy bias could be reduced by improving the low energy statistics for weights extraction

  22. CTB04: Range of energies (periods 5,6) Runs: 1004160,1000952,1000947,1000942,1000999 Data/MC 9GeV 20GeV 50GeV 100GeV 180GeV E 0.993(0.002) 1.0 (0.001) 1.004(0.001) 1.003(0.001) 1.002(0.001) PS 1.08 (0.03 ) 0.99 (0.02 ) 1.00 (0.02 ) 1.05 (0.02 ) 1.04 (0.02 ) S1 0.98 (0.01 ) 0.992(0.007) 0.994(0.007) 1.022(0.009) 1.02 (0.01 ) S2 0.98 (0.01 ) 0.995(0.005) 1.002(0.003) 0.993(0.003) 0.995(0.003) S3 0.9 (0.1 ) 1.01 (0.03 ) 1.03 (0.01 ) 1.00 (0.01 ) 1.03 (0.02 ) S1/S2 1.01 (0.02 ) 1.00 (0.01 ) 1.00 (0.01 ) 1.03 (0.01 ) 1.03 (0.02 ) Data PS S1/S2 MC PS+S1+S2+S3 A 0.15X0 of far upstream material was added to simulate the beamline. LAr/ID discrepancy: the ID data indicate no need for this. Trigger efficiency?

  23. Data vs MC ONLY far material PS S1 Period 8 20GeV run 2397 RATIOS Data/MC S2 E=20GeV Run= 2397 ------------------------------- E 1.003 PS 1.007 (0.006) S1 1.002 (0.002) S2 0.999 (0.002) S3 1.021 (0.007) S1/S2 0.995 (0.003) ------------------------------- PS+S1+S2+S3 S1/S2 Per Johansson+SP

  24. CTB04: very low energy electrons Good agreement between data and various MC versions/setups

  25. CTB04: Linearity (TDR weights + offset) Default configuration (0mm Al) 75mm Aluminium in front of cryostat Data MC Linearity at the 0.2% level: very close to CTB beam-line systematic limit. Absolute Scale? For 180GeV the syst. error is about 0.25% (beam line). The TDR method is biasing at low Energies: the bias increases with the material (also seen in ATLAS, see L.Carminati’s talk).

  26. Comparison between CTB04 and TB02 SP: August 2006 physics/0608012 • Analyses agree in sampling and c-term. • CTB04 Analysis with TDR weights + offset (Energy independent). • TB02 Analysis with new E-dependent calibration hit – like parametrization.

  27. Summary • Significant efforts in muon/electron performance issues in progress (focus on electrons here). • CTB04 and commissioning data • Lepton efficiencies – Calibration – Linearity – Uniformity - Material effects – Misaligned detectors – HV problems – Xtalk – etc etc • Measurement of the Mzz background • Even with a few tens of events of statistics, an unbinned extended likelihood fit could do reasonably well. However the systematic due to the background shape must be investigated. • CSC note in progress • Its success will require a well coordinated effort by the (many!) authors.

  28. Backup

  29. Weights from minimization • Energies in the samplings are reconstructed with approximate sampling fraction at the cell level • Weights are extracted by a chi2 fit on a sample of single electrons in the [-2;+3] around the MPV (most prob. value) of the reconstructed energy distribution: • It’s a more refined version of the TDR/DC1 calibration: the introduction of the offset cures most of the low energy linearity problems (TB2002) • Only 4 energy independent parameters per cell!

  30. Weights from minimization: eta dependence Now into Athena • Weights extracted with E>20 GeV ‘official’ electrons samples (DC3-02 detector geometry) w0 offset  w3

  31. Higgs events: electron efficiencies vs eta Egamma cluster egamma+track_iso egamma+IsEM egamma+TrkIsEM

  32. Higgs events: electron efficiencies vs pt Egamma cluster egamma+track_iso The problem is in caloIsEM egamma+IsEM egamma+TrkIsEM

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