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University of Iowa

qqH qq ZZ qq e + e -  e  e A.Mestvirishvili , U.Akgun, A.S.Ayan, F.Duru E.Norbeck,Y.Onel,S.Wahg AN2005/14 March 2006 Physics meeting. University of Iowa. Higgs production and decay. H Z Z e + e -  e  e. t t. N . Of Events. CS(pb). CS(fb). 44257. 840. 9600.

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University of Iowa

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  1. qqHqq ZZ qq e+e-ee A.Mestvirishvili, U.Akgun, A.S.Ayan, F.Duru E.Norbeck,Y.Onel,S.Wahg AN2005/14 March 2006 Physics meeting University of Iowa Slide N

  2. Higgs production and decay Slide N

  3. H Z Z e+e-ee t t N. Of Events CS(pb) CS(fb) 44257 840 9600 Event generation and reconstruction PYTHIA 6.2, CMSIM , ORCA version 7.6.0, Pileup Signal events - qqH 300,350 and 500 GeV mass Higgs were generated. No tracker was simulated, e+ e- were selected from generator particle information Higgs and Z decay (forced)modes WW fusion ZZ fusion WBF total Background considered in this analysis Slide N

  4. Pre selection cuts • At least two “tracks” with opposite charge, • which then can be Identified as electron/positron • 2) L1 MET > 10 GeV ( missing Et from L1CaloTrigger) • 3) Either 2 L1 forward jet or 2 L1 central jet or 1 L1 • forward and L1 central jet Accepting all possible combinations of L1 jets are handy For forward jet tagging procedure. Forward “tag jets” are Searched over full pseudorapidity range Slide N

  5. Electron identificationissues No tracker was simulated and since electron identification equally relays on ECAL as well as tracker, it was not possible to perform such identification. Rate of Z ee after L1 and HLT and for low luminosity 1Hz Derived efficiency – 0.26 Correction factor for background using L1 and HLT efficiencies for W e 0.42 Reference: DAQ TDR – page 298 Slide N

  6. Missing Et distribution for signal • And background events • H(M=300GeV) • H(M=350GeV) • H(M=500GeV) • t t a) b) c) d) Cuts for leptons and missing ET Leptons (e+ e- ) were selected from generator particles data. Lepton cuts: ET > 20GeV for background |M(e+ e-)-M(Z)|<15GeV, Leptons are between tag jets Cut for reconstructed missing ET > 50GeV Slide N

  7. Jets 1) Iterative cone algorithm Cone radius – 0.5 finder with Et > 20 GeV 2) Jets are well within CMS detector acceptance ||  5 3) No calibration Slide N

  8. H(M=300GeV) H(M=350GeV) H(M=500GeV) t t FORVARD JET TAGGING Jets selection Forward jets were searched using rapidity gap method Over all pseudo rapidity range. Jets ET 30GeV – reduces Pileup contamination Jet pairs per event Jet isolation criteria – nothing around the jet in cone 0.5 Jets must be in opposite hemisphere 1 . 2 < 0 Difference between jets Pseudorapidity more than 4.0 If more than one combination of such jets found, jets with largest rapidity difference were accepted as a tagged jets Majority of signal events has At lest one pair of tagged jets If no such combination was Found, event was dropped Slide N

  9. FORVARD JET TAGGING Jets and leptons  Slide N

  10. H M=300 – Green points, H M=350 – Red points H M=500 – Blue points, – Black points t t H(M=300Gev) H(M=300Gev) H(M=300Gev) t t FORVARD JET TAGGING Jets Et and di jet mass Di Jet mass distribution for Signal and background events E t of tagged jets Cut is applied at 500 GeV Slide N

  11. Central Jet veto Standard approach: first to find tag jets, then to veto events with additional central jets. tagging jet selection conditions may lead to case when one of the jet is in central region (1 = -1) another in forward region (2 = 3.5) and satisfies tagging jet selection criteria “anti” b-tagging is necessary to reject the background events Slide N

  12. Central Jet veto First veto events with central jets, than search for tag jest “Central region” definition Pseudo rapidity range -2.0 << 2.0 Events with central jets were vetoed before forward jet tagging No need to use b tagging at all Slide N

  13. Central Jet veto Central jet veto is very efficient tool to reduce the background since signal events in qqH processes tends to have either no or small central jet activity. Jets in the background events tends to be central. Fraction of events containing at least one jetin the  region covered by the tracker Background has mainly central jets Slide N

  14. Central Jet veto It was decided to sacrifice nearly 40% of signal events to have background rejected at the level of 65% If one would select the  region fully covered by tracker rejecting 82% background, signal events will be reduced substantially as well Fraction of the events with two tagged forward jets with at least one tag jet in the region covered by tracker Slide N

  15. Central Jet veto Acceptances Overall acceptances whenForward Jet were Tagged, then additional Central Jets were Vetoed (second row) and with this cuts reversed (third row) . More than factor 3 is achieved in background reduction by reversing of this cuts Not corrected for electron identification efficiencies Slide N

  16. Acceptance and significance Acceptance correct acceptances from previous slide for electron identification efficiencies – correction factor for signal events – 0.26 – correction factor for background events – 0.42 Number of events – calculated using formula N =   L    Br Significance – calculated using formula from reference Expected signal observability at future experiments V. Bartsch, G. Quast. CMS note 2005/004 For 60 fb–1 LHCintegrated luminosity Slide N

  17. MH=300GeV MH=350GeV MH=500GeV H Z Z e+e-ee Acceptance 3.2% 3.8% 4.3% 0.005% Number of observed events 4 4 2 27 Significance 0.75 0.75 0.38 Acceptance and significance For 60 fb–1 LHCintegrated luminosity Slide N

  18. Significance BUT SIGNAL SIGNIFICANCE IS STILL WELL BELLOW THE ACCEPTABLE 5 LEVEL Even the background events Are suppressed substantially, Small cross section for signal Events and huge cross section For background is main reason For such low significance. Significance is calculated For 60 fb–1 LHC integrated luminosity Slide N

  19. Results presented on previous slides are for the one particular decay channel H ZZe+e-ee. H and Z’s were forced to decay Through this channels. Taking into account Zboson other decay modes one can extrapolate obtained significance Significance extrapolation Z decay modes included in extrapolation In addition to studied decay. Z1e+e- , Z2,  Number of observed signal events tripled Number of background events stays same Slide N

  20. Significance extrapolation Significance is calculated For 60 fb–1 LHC integrated luminosity BUT… Still well below the 5 level for 60 fb–1 LHCintegrated luminosity Slide N

  21. 300,350 and 500GeV mass Higgs production via VBF with • subsequent decay to ZZ when one Z decays to electron - • positron pair and another to neutrinos, and the tt major • background for this channel were studied. • 2. No b - tagging is necessary, if central jet veto is used • before forward jets are searched and tagged. • 3. Significance for this particular decay channel assuming • 60 fb-1 LHC integrated luminosity is well below acceptable • 5 level. SUMMARY Slide N

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