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Missing E T in ATLAS (Emphasis of Object-Based MET)

Missing E T in ATLAS (Emphasis of Object-Based MET). X.Chen, L.Flores, B.Mellado, S.Padhi and Sau Lan Wu University of Wisconsin-Madison West Coast Physics Forum 08/22/06. Outline. Introduction Status of Cell-Based MET package (default) in Athena MET Tails and Fake MET studies

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Missing E T in ATLAS (Emphasis of Object-Based MET)

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  1. Missing ET in ATLAS(Emphasis of Object-Based MET) X.Chen, L.Flores, B.Mellado, S.Padhi and Sau Lan Wu University of Wisconsin-Madison West Coast Physics Forum 08/22/06

  2. Outline • Introduction • Status of Cell-Based MET package (default) in Athena • MET Tails and Fake MET studies • Status of Object-Based MET package in Athena • Looking at resolution of various objects • Towards the development of MET significance for ATLAS Bruce Mellado, West Coast Physics Forum, 08/22/06

  3. Loop over cells (cell-based) High PT Particle escaping detection Low PT particles • ATLAS is developing a robust effort to understand MET issues produced in physics events Jets, ’s Muons Loop over objects (object-based) Electrons, Photons Bruce Mellado, West Coast Physics Forum, 08/22/06

  4. Cell-Based Approach (default in ATHENA) D. Cavalli, S.Resconi (INFN/Milan) Bruce Mellado, West Coast Physics Forum, 08/22/06

  5. ATHENA MissingET : EtMiss Reconstruction and Calibration All Calorimeter cells in ||<5 |Ecell | > 2(noise) H1-like weights from jets OR OR OR Estimated energy loss in cryostat between LAr and Tile from reco jets (cone07) w*sqrt(EM3*TILE1) from MOORE mu ||<2.7 pT from external Spectrometer BestMatch /good quality MET_Final = MET_Calib + MET_Cryo + MET_ Muon Calorimeter cells in Topoclusters 4/2/0 H1-like weights from jets from MuonBoy muons in || < 2.7 from reco jets (kT) Calorimeter cells in Topoclusters 4/2/0 LocalHadronCalibration (under test) Topoclusters 4/2/0 LocalHadronCalibration (under test) Refinement of Calibration for cells in different objects (e/g, t, m ,jets...) a la TDR (implementation in 12.0.2) Bruce Mellado, West Coast Physics Forum, 08/22/06

  6. ATHENA MissingET: Performance Good EtMiss measurement crucial for mass reco in Z   and H   • Performance depends on: • Noise suppression, Calibration, Dead material correction … • Physics channel topology: presence of leptons, Eleptons, Njets, Ejets, energy outside phys objects, activity out of coverage... • No dependence on Montecarlo observed (Pythia QCD jets very similar to Herwig jets) EtMiss resolution vs SumET CSC MC CSC MC For CSC linearity within 5%, resolution slightly worse respect to TDR parametrisation (s(EtMiss)=0.46*sqrt(SumET)) Bruce Mellado, West Coast Physics Forum, 08/22/06

  7. Linearity vs EtMiss_Truth Bruce Mellado, West Coast Physics Forum, 08/22/06

  8. MET Tails and Fake MET studies Bruce Mellado, West Coast Physics Forum, 08/22/06

  9. ATHENA MissingET: detailed study of events in EtMiss tails CSC QCD J6 (560<pT<1120GeV), 50Kevts (129pb-1) reconstructed with 11.041 EtMiss_rec-EtMiss_true tipically < 100GeV, look at events with DEtMiss>250GeV F. Paige, Spephane Willoq EtMiss_rec-EtMiss_true (GeV) Shower leakage both from punchtrough and cracks important. Veto on muons chamber activity seems effective Fake muons also important: can reduce with more severe muon quality cuts For DEtMiss>100GeV less muon activity, cracks do not seem dominant Bruce Mellado, West Coast Physics Forum, 08/22/06

  10. Jet leakage from Tile/ExtTile crack, shower in muon system Bruce Mellado, West Coast Physics Forum, 08/22/06

  11. Fake EtMiss study A bad EtMiss mesurement could fake a non-zero reconstructed EtMiss in events with no true EtMiss dedicated meetings each 1-2 months • Event production (S.Asai, A. Gupta) • QCD jets (background for SUSY) - and • Z(ll)+jets events (background for Hllnn) • Filters • Events with true EtMiss>threshold (study true EtMiss distribution) • Events with a jet pointing to a crack (study fake EtMiss) (R. Pradhu) • Definition of crack regions • Dead material hits information • Contribution to EtMiss from DM regions will be calculated in MissingET • Study Instrumental effects: problems in electronic channels, crates, HV sectors… give fake EtMiss. Can correct and recover EtMiss? (R. McPherson et al) • Define Event quality variables: out-of-time cells, hot cells, number of muon segments… (D. Tovey et al) 100GeV  1TeV N. Kanaya Bruce Mellado, West Coast Physics Forum, 08/22/06

  12. Object-Based Approach (In Athena since 12.1.0/12.0.2) X.Cueh, L.Flores, B.Mellado, S.Padhi, Sau Lan Wu (Wisconsin) Bruce Mellado, West Coast Physics Forum, 08/22/06

  13. Object-Based Calibration Missing ET Reconstruction Object-Based Missing ET Final State Classification High ET Objects Low ET Objects Un-clustered depositions   0  e/ jets Bruce Mellado, West Coast Physics Forum, 08/22/06

  14. Object Based Calibration • The Object-Based approach is very FLEXIBLE. It accommodates any calibration strategy Use local hadronic calibration or in-situ calibration or a combination of both In-situ calibration Bruce Mellado, West Coast Physics Forum, 08/22/06

  15. OBMET in 12.0.2 • The following features are now available in 12.0.2 Bruce Mellado, West Coast Physics Forum, 08/22/06

  16. OBMET solved long standing shifts and degraded resolution in H, so important for low mass Higgs searches • Higgs mass reconstruction after the application of all analysis cuts with Hll ATLFAST Rome MC Samples =10.5 GeV FULLSIM RMS 19.8 GeV M=131.5 GeV =9.8 GeV Assumed in VBF SC Note RMS 19.6 GeV M=129.1 GeV M M Bruce Mellado, West Coast Physics Forum, 08/22/06

  17. Missing ET resolution after the VBF analysis cuts • Table with Gaussian mean, width and RMS before and after the implementation of low ET objects (in GeV) Bruce Mellado, West Coast Physics Forum, 08/22/06

  18. Resolution reported in TDR with A Bruce Mellado, West Coast Physics Forum, 08/22/06

  19. Resolution reported in TDR with A is 0.46ET Bruce Mellado, West Coast Physics Forum, 08/22/06

  20. Achieve ~1% linearity with W’ Bruce Mellado, West Coast Physics Forum, 08/22/06

  21. Achieve ~2% linearity with SUSY MET in SU2 is under study Bruce Mellado, West Coast Physics Forum, 08/22/06

  22. SUSY events with high PT leptons (e,) (OBMET) PT>20 GeV PTe>20 GeV Bruce Mellado, West Coast Physics Forum, 08/22/06

  23. Towards the Development of MET Significance in ATLAS Bruce Mellado, West Coast Physics Forum, 08/22/06

  24. There are a number of cases when the simple expression, EXYmissSumEt, breaks down • We cannot use Missing ET significance as • The Object-Based method offers the advantage of calculating the expected missing ET resolution based on the resolution of each of the objects. This also solves the issue of the event topology • Then Calculate missing ET significance (D0 experience) Bruce Mellado, West Coast Physics Forum, 08/22/06

  25. Towards MET Significance • For definition of MET significance see Ariel’s talk • It is crucial to understand the resolution of different objects as a function of || and Energy • ATLAS has cracks and significant amount of inactive material in front of the calorimeter Jet Linearity (EM scale) Bruce Mellado, West Coast Physics Forum, 08/22/06

  26. Shown are fractional deviation from the true energy for single pions with energy 100 GeV (hadronic scale) in “critical” regions Bruce Mellado, West Coast Physics Forum, 08/22/06

  27. Fractional deviation from the true energy for single electrons with different energies in bins of 0.625<||<1.25 in steps of 0.025 Bruce Mellado, West Coast Physics Forum, 08/22/06

  28. Fractional deviation from the true energy for single electrons with different energies in bins of 1.25<||<1.875 in steps of 0.025 Bruce Mellado, West Coast Physics Forum, 08/22/06

  29. Outlook and Conclusions • ATLAS has embarked in a vigorous collective effort to develop robust algorithms for Missing ET reconstruction • Cell-Based and Object-Based algorithms available in ATHENA releases • MET performance is being evaluated and studies in a large variety of final states • Shifts in the module of MET are now significantly reduced. Efforts made to improve resolution • Study of various sources of tails and fake MET underway • Regular meetings set up and new tools are being developed • Moving towards development of MET significance • At present compiling resolution of different objects as a function of Energy and || Bruce Mellado, West Coast Physics Forum, 08/22/06

  30. Additional Slides Bruce Mellado, West Coast Physics Forum, 08/22/06

  31. All Calorimeter Cells with |Ecell | > 2 ( noise ) SumET EtMiss Resol -- Rec -- Truth <> = 528.2 <> =560.1 <> ~ 3.1  ~ 16.0 Calorimeter Cells in TopoClusters (4/2/0) EtMiss Resol SumET -- Rec -- Truth <> = 538.3 <> =560.1 <> ~ 1.5  ~ 15.2 • Figure shows A   sample with mass of A = 800 GeV • Resolution and scale improves with the use of noise suppression using CaloTopoCluster Bruce Mellado, West Coast Physics Forum, 08/22/06

  32. EtMiss with early data:resolution with minimum bias and Wjets Minimum bias: Possible to test EtMiss resolution up to SumET=300GeV N. Kanaya Can use W+njets to evaluate EtMiss resolution up to SumET ~ 1TeV. • Need a way to distinguish effect of resolution and offset. Bruce Mellado, West Coast Physics Forum, 08/22/06

  33. Montecarlo comparison s(Ex(y)miss) vs SumET in CSC Jets data (Pythia andHerwig) Bruce Mellado, West Coast Physics Forum, 08/22/06

  34. EtMiss with early data: in situ scale determination with Z   Rec  mass Signal Z   Inclusive W e Inclusive W  top Rome data. Applied cuts : pt(lep) > 15 GeV, ||<2.5 pt(jet) > 15 GeV, ||<2.5 isEM & 0x7FF) ==0 , lep isolation: Etcone30<5GeV 1.< < 2.7 or 3.6< <5.3 mT(lept-EtMiss)<50GeV -likelihood > 8 (-eff ~ 30%) 66<rec mtt<116 GeV Expected in 100pb-1 ~ 300 evts with ~ 20% backgd Possible to loosen cuts to increase statistics? Or more severe cuts necessary to reduce bb backgd? In TDR :EtMiss>20 GeV mT(lept-EtMiss)<25GeV D. Cavalli <> ~ 90  ~ 16 Rec  mass vs EtMiss scale +3% -3% - 10 % +10 % Results still preliminary due to low statistics Need to have also a bb sample Trigger-aware analysis and Cuts tuning Bruce Mellado, West Coast Physics Forum, 08/22/06

  35. Expect O(10K) per 1pb-1 • With 100 pb-1 of data can check EtMiss in most of useful range for low mass Higgs physics and with different jet topologies • The ratio pT(n)/pT(lep) can be calculated with MC. It depends on experimental cuts 100pb-1 R calculated using truth +3% +2% No cuts X.Cueh, L.Flores, B.Mellado, S.Padhi, Sau Lan Wu (Wisconsin) PTL>20 GeV, |l|<2.5 Method is sensitive to EtMiss scale. Less sensitive to EtMiss resolution (use di-jets). Addressing systematic errors and combination with Zll events Bruce Mellado, West Coast Physics Forum, 08/22/06

  36. PTL>20 GeV, |l|<2.5 ATLFAST +5% shift 1pb-1 +3% shift Nominal Bruce Mellado, West Coast Physics Forum, 08/22/06

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