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H  ZZ (*)  4e

H  ZZ (*)  4e. S. Baffioni 1 , C. Charlot 1 , F. Ferri 1 , 2 , N. Godinovi c 3 , P. Meridiani 4 , I. Puljak 3 , R. Salerno 1, 2 , Y. Sirois 1. 1 LLR Ecole Polytechnique, Palaiseau , France

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H  ZZ (*)  4e

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  1. H  ZZ(*) 4e S. Baffioni1, C. Charlot1, F. Ferri1,2,N. Godinovic3, P. Meridiani4, I. Puljak3, R. Salerno1,2, Y. Sirois1 1 LLR Ecole Polytechnique, Palaiseau, France 2 University of Milano Bicocca and INFN, Milano, Italy 3Technical University of Split - FESB, Split, Croatia 4 University of Roma I and INFN, Rome, Italy CMS - France, Mont St Odile, 30 Mars 2006

  2. Outline • Signal and backgrounds • Trigger efficiencies • Electron reconstruction and preselection • Offline analysis • Impact parameter • Track isolation • Hadronic isolation • Electron ID • Missing ET • Kinematic cuts • Significances • Mass and width measurements • Detector systematics • Conclusions S.Baffioni2Réunion CMS-France, 30/03 /06

  3. Signal • Generator preselection:  2e+ & 2e- with pT > 5 GeV in || < 2.7 • Combinatorial enhancement: 2(ZZ4e)/(ZZ2e2) > 1 S.Baffioni3Réunion CMS-France, 30/03 /06

  4. Backgrounds Generator preselection:  2e+ & 2e-, pT > 5 GeV in || < 2.7 Zbb in addition: mee > 5 GeV &  2 e+e- pairs with mass between 5 and 400 GeV • ZZ  4e (Z means Z*/*) • qq inital state • t channel only • KNLO mZZ dependant (in progress) • gg initial state • 20% additional LO contribution • NLO unknown • Zbb(eebb) 4e • generated with CompHEP + PYTHIA • no b decay forcing • KNLO = 2.4 ± 0.3 • tt  4e • W leptons, no b decay forcing S.Baffioni4Réunion CMS-France, 30/03 /06

  5. Trigger • L1 and HLT electron trigger = single or double or double relaxed All numbers are relative to generation preselection S.Baffioni5Réunion CMS-France, 30/03 /06

  6. Golden electron Big-brem electron Electron reconstruction – global view • Electron: an object consisting of ECAL SuperCluster + Track • Offline reconstruction different from HLT one • Important effects: • Bremsstrahlung in the tracker material • Incomplete containment in ECAL • Energy lost in the tracker material • Cracks • ECAL superclustering • SuperCluster threshold: ET > 1 GeV •  road extended for better bremsstrahlung collection al low pT • GSF tracking algorithm • SuperCluster driven pixel match seeding • With relaxed parameters for offline electrons • Track followed to the outermost layer • Usefull estimate of the bremsstrahlung loss • SuperCluster – Track matching and combinations • Classification for better corrections • E-p combination for better momentum estimation • Many usefull variables for better identification S.Baffioni6Réunion CMS-France, 30/03 /06

  7. Electron reconstruction and preselection HZZ* 4e 150 GeV HZZ*4e 150 GeV • Electron = GSF track + Sc with: • E/p< 3 • || <0.02 and ||<0.1 • H/E <0.2 • Pt > 5 GeV • Loose iso: Pttracks,R=0.2/Pt < 0.5 •  = fraction of elgen having a matching elrec (R<0.07 and same charge) HZZ*4e 150 GeV S.Baffioni7Réunion CMS-France, 30/03 /06

  8. Offline analysis - global view Starting with: • Impact parameter • Transverse IP significance • To supress electrons from displaced vertices in tt and Zbb • Isolation • Track isolation • Hadronic isolation • Electron identification • Refining further selection using characteristic variables • Missing ET • Suppresing mainly tt • Kinematical cuts • Electron pT • On and off-shell Z mass windows S.Baffioni8Réunion CMS-France, 30/03 /06

  9. Impact parameter cut • tt and Zbb: important fraction of electrons from displaced vertices • Significance of transverse IP (STIP) • STIPe1 + STIPe2 • Separately for electrons from Z and Z* wrt to preselection acceptance S.Baffioni9Réunion CMS-France, 30/03 /06

  10. Track Isolation • Track based electron isolation • Sum tracks within an isolation cone around each electron direction in () planeR = ()1/2 = 0.2 cut: (pT)/pT < 0.1 • A veto cone R = 0.015 is defined around the electron track • Consider only tracks coming from the electron primary vertex |Lip| < 0.1, with pT > 1.5 GeV • If another electron in the isolation cone: not considered if mee >10 GeV • All 4 electrons required isolated Total (loose included) isolation Signal (150 GeV) efficiency Background(tt) rejection power wrt to IP acceptance S.Baffioni10Réunion CMS-France, 30/03 /06

  11. Hadronic Isolation Worst isolated electron • Sum Hadronic Et within R = 0.2 • Consider only HCAL towers with ET > 0.5 GeV • Require for 3 stringent : (ET HAD)/pTe< 0.05+ 1 relaxed : (ET HAD)/pTe < 0.2 2nd worst isolated electron wrt to track iso acceptance S.Baffioni11Réunion CMS-France, 30/03 /06

  12. Electron ID • Variables used • Hadronic over EM energy: H/E • Angular dist. SC-track at vertex: ,  • Sum of central crystals in SC: 9/25 • Matching at ECAL entrance: Eseed/pout • Class dependant cuts • To better control fake electrons rate • See CMS Note/2006-040 wrt to isolation acceptance S.Baffioni12Réunion CMS-France, 30/03 /06

  13. Check point Impact parameter Preselection Iso(track +hadro) Electron ID S.Baffioni13Réunion CMS-France, 30/03 /06

  14. Missing ET • Use of Missing ET against tt ET < 70 GeV wrt to electronID acceptance S.Baffioni14Réunion CMS-France, 30/03 /06

  15. Electron Pt cuts • Motivation: • Backgrounds have important fraction of low pT electrons • But low mass Higgs has them too need balancing • Impose cuts for pT sorted electrons After electron Pt cuts wrt to missing Et acceptance S.Baffioni15Réunion CMS-France, 30/03 /06

  16. Z and Z* mass cuts • “ Z ” mass cut (Z could be a Z*)  After electron Z and Z* mass cuts ABSOLUTE EFFICIENCY S.Baffioni16Réunion CMS-France, 30/03 /06

  17. Mass distributions 120 GeV 150 GeV 300 GeV 200 GeV S.Baffioni17Réunion CMS-France, 30/03 /06

  18. Events counting for 30 fb-1 • Higgs window size for event counting depending on Higgs mass S.Baffioni18Réunion CMS-France, 30/03 /06

  19. Significances S.Baffioni19Réunion CMS-France, 30/03 /06

  20. Mass and width measurements Label = NG Bb N barrel + 10  NC + 100  NG Bb N endcap + 1000  Ns barrel +10 000  Ns endcap • Electron energy errors parameterizedper class + electron per electron track momentum error error on final electron momentum (E-p combination)  • Rescaled to take into account non-gaussian tails: constant rescaling factor per class, smaller for golden, larger for showering •  computed errors event by event on the 4e mass G = golden Bb = big brem N = narrow S = showering C = cracks • 3 Showering 36.7% of events 4 Golden 0.37%of events G - Bb - N barrel C G - Bb - N endcap S barrel S endcapv S.Baffioni20Réunion CMS-France, 30/03 /06

  21. Detector systematics • L1/HLT Trigger efficiency: ±1% (+) • Four main sources of detector systematics for electrons: • Material budget • Affecting both efficiency and precision • Reconstruction efficiencies • Energy/momentum scales and resolutions • Both for tracker and ECAL • Selection efficiencies • Identification • Isolation • Kinematical cuts • Global strategy for estimating/controling systematics • Use electrons from We and Zee decays where possible • Extrapolate to other regions using MC simulations • Estimation: • 1% uncertainty on efficiency • 0.5% on energy scale S.Baffioni21Réunion CMS-France, 30/03 /06

  22. Conclusions • Full Analysis : • Cut strategy • Complete results • Now included: • Full consistency with latest electron reconstruction results • Hadronic isolation • Missing Et cut • Electron Errors propagated on Higgs mass event by event • To do: • Significance with errors weighted events • Full systematics to be applied S.Baffioni22Réunion CMS-France, 30/03 /06

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