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Missing E T Reconstruction in ATLAS

Missing E T Reconstruction in ATLAS. X.Chen, L.Flores, B.Mellado, S.Padhi and Sau Lan Wu University of Wisconsin-Madison ATLAS Analysis Tutorial, TAU 11/02/07. Outline. Introduction Status of Cell-Based MET package in Athena Status of Object-Based MET package in Athena

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Missing E T Reconstruction in ATLAS

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  1. Missing ET Reconstruction in ATLAS X.Chen, L.Flores, B.Mellado, S.Padhi and Sau Lan Wu University of Wisconsin-Madison ATLAS Analysis Tutorial, TAU 11/02/07

  2. Outline • Introduction • Status of Cell-Based MET package in Athena • Status of Object-Based MET package in Athena • MET Tails and Fake MET studies • MET checks with (first) data Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  3. Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  4. The LAr Calorimeter Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  5. Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  6. 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, ATLAS Analysis Tutorial, TAU 11/02/06

  7. Object-Based Calibration Cell-Based Calibration Missing ET Reconstruction Missing ET Reconstruction Cell-based Refined Method (TP 1994 and TDR 1999) Object-Based Method (inspired by D0) Final State Final State Classification Classification E/M Hadronic Other High ET Objects Low ET Objects Un-clustered depositions   0  e/ jets ATLAS and CMS are moving towards the object-based method Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  8. Topological Clustering(Sven Menke) • Cell clusterization is a crucial tool • Define thresholds on the seed and the neighboring cells • Cuts on seed, neighbor and rest of clustered cells • Cut on rest of cells is as low as 0 • We do not observe bias on physics Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  9. Cell-Based Approach D. Cavalli, S.Resconi (INFN/Milan) Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  10. 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, ATLAS Analysis Tutorial, TAU 11/02/06

  11. Montecarlo comparison s(Ex(y)miss) vs SumET in CSC Jets data (Pythia andHerwig) Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  12. 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, ATLAS Analysis Tutorial, TAU 11/02/06

  13. Linearity vs EtMiss_Truth Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  14. ATHENA MissingET: First look at LocalHadronCalibration • looked at some CSC samples (low statistics!) using cell weights from LocalHadronCalibrationimplemented in 12.0.1 (including Dead Material corrections up to || < 3) • W e, Z sample,minimum bias events: EtMiss resolution and linearity comparable to the ones from default H1-like calibration • in QDCJ5 (280<pT<560GeV) sample, EtMiss resolution is worse respect to H1-like calib and there are larger tails to be understood • New simulation/weights determination with 12.0.1 hopefully more significant results for Barcelona Calorimeter Calibration workshop EtMiss resolution in W e Ex(y)Miss resolution in QCD J5 MET from TopoCells LocalHadronCalibration MET from TopoCells Default H1-Calib MET from TopoCells LocalHadronCalibration MET from TopoCells Default H1-Calib  ~ 14.6 <> ~0.4 • ~ 18.5 <> ~-0.5  ~ 5.7 <> ~-2.4  ~ 6.0 <> ~-0.3 Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  15. 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, ATLAS Analysis Tutorial, TAU 11/02/06

  16. 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, ATLAS Analysis Tutorial, TAU 11/02/06

  17. 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, ATLAS Analysis Tutorial, TAU 11/02/06

  18. 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 cuts in page 9 (except for mass window) with Hll ATLFAST Summer 2005 =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, ATLAS Analysis Tutorial, TAU 11/02/06

  19. Summer 2005 • Performance comparison with default method at the time (first half of 2005) • That method is no more default in ATLAS =9.8 GeV RMS 19.6 GeV M=129.1 GeV M Tails were significantly improved later on Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  20. 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, ATLAS Analysis Tutorial, TAU 11/02/06

  21. OBMET in Athena Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  22. Current Classification • In 12.0.1 we read out to AAN the following objects • Leptons (electrons and muons) • Muons reconstructed with Likelihood are separated from muons reconstructed with other packages • Jets (ET>20 GeV): • Taus are still treated as jets. Will separate taus and jets in subsequent versions • Mini-Jets: • Depositions with 1<ET<20 GeV in Barrel and Endcap • Charges and neutral pions are treated separately, but the AAN does not have that information yet. Will do that soon • Rest (or “unclustered” energy) • Depositions with ET<1 GeV in Barrel and Endcap and ET<20 GeV in FCAL • Three components (Barrel/HEC/FCAL) are separated Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  23. Calibration of High ET objects in ATHENA: Electrons • Electron calibration performed with 6,3,0 topo-clusters using single electrons (see L.Flores talks)   Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  24. Calibration of High ET objects in ATHENA: Jets • Jet calibration using Pseudo-H1 weights obtained with di-jets (see S.Padhi’s talks). Work very well for -jets too -jets Jet Lineariy for di-jets ET (GeV) ETruth/EReco Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  25. Calibration of Low ET Objects: Single 0 • Calibration of single pions using sampling method with TDR functional form (see B.M. talks) 0 0   Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  26. Calibration of Low ET Objects: Single  • Calibration of single pions using different functional forms for different || (see B.M. talks)    Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  27. SumET (Truth vs. Rec.) • Truth and reconstructed SumET in GeV • Need to study in truth fraction of SumET from very low ET particles (with 11.0.42) Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  28. Ratio of SumEt of various components to the Total truth SumEt for different samples Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  29. Misssing ET in Zll Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  30. Misssing ET in We Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  31. Resolution reported in TDR with A Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  32. Achieve ~1% linearity with W’ Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  33. Achieve ~2% linearity with SUSY MET in SU2 is under study Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  34. SUSY events with high PT leptons (e,) (OBMET) PT>20 GeV PTe>20 GeV Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  35. MET Tails and Fake MET studies Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  36. 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, ATLAS Analysis Tutorial, TAU 11/02/06

  37. Jet leakage from Tile/ExtTile crack, shower in muon system Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  38. 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, ATLAS Analysis Tutorial, TAU 11/02/06

  39. MET with Data Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  40. W and Z decays are a copious source of ’s and Missing ET • Expect S/B worse at LHC w.r.t. Tevatron. Especially important for W W Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  41. W,Zleptons Rates at LHC • Effective cross-sections and rates with basic cuts Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  42. Z Mass Reconstruction • In order to reconstruct the Z mass need to use the collinear approximation Tau decay products are collinear to tau direction Fraction of  momentum carried by visible  decay  l Z h  • x1 and x2 can be calculated if the missing ET is known • Good missing ET reconstruction is essential Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  43. 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, ATLAS Analysis Tutorial, TAU 11/02/06

  44. Results still preliminary due to low statistics Need to have also a bb sample Trigger-aware analysis and Cuts tuning Rec  mass vs EtMiss scale +3% -3% No background subtraction - 10 % +10 % Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  45. Missing ET with Wl • One can use the sharp end of the transverse mass in different missing ET bins • Shape of transverse mass changes with Missing ET, due to acceptance • One can also use the fact that in the average the pt of the charged lepton and the pt of the neutrino are of the W decay are known function, which can be calculated with MC Function can be calculated with MC and depends on experimental cuts Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  46. R calculated using truth No cuts Systematic errors are being addressed PTL>20 GeV, |l|<2.5 Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  47. PTL>20 GeV, |l|<2.5 ATLFAST +5% shift 1pb-1 +3% shift Nominal Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  48. PTL>20 GeV, |l|<2.5 ATLFAST 100pb-1 +3% +2% Nominal Can cover almost all dynamic range in low mass Higgs physics with 100 pb-1 Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  49. l+ l- • Is the transverse momentum escaping calorimeter coverage due to particles escaping though the beam-pipe or partially depositing energy in the back of the FCAL? • Use Zll as a sensitive tool Especial thanks to M.Krasny Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

  50. Re-do older earlier studies with present-day MC • Use ALPGEN to generate Z+njets (Matrix Element and Parton Shower matching) with ||<100 (light flavor only) • Impact of ZQQbar will be addressed in the future ATLFAST • Apply a veto on events with at least one jet with PT>10 GeV in ||<5: Events with Z+nj n>0 have a jet(s) going down the beam-pipe • Effect of particles going down the beam-pipe is expected to be small • Work needs to be done to understand instrumental effects of jets with partial depositions in FCAL Mostly from jets going down the beam-pipe Z+1j Z+0j Bruce Mellado, ATLAS Analysis Tutorial, TAU 11/02/06

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