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First look at gg->tth with invisible higgs

First look at gg->tth with invisible higgs. Need lepton to trigger event Invisible Higgs AND neutrino contribute to missing pT. Used: Atlfast 7.0.2 (local) + Pythia 6.203 Pythia options as Elena Brambilla (m h = 121 GeV) Higgs forced to decay to neutralinos

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First look at gg->tth with invisible higgs

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  1. First look at gg->tth with invisible higgs Need lepton to trigger event Invisible Higgs AND neutrino contribute to missing pT • Used: • Atlfast 7.0.2 (local) + Pythia 6.203 • Pythia options as Elena Brambilla (mh = 121 GeV) • Higgs forced to decay to neutralinos • W, t: all decay channels open • Simulated: 5k events tth + 5k tt • Looked mainly at truth information

  2. The TRUTH! In general, smallish (Dq < 30deg) separation in polar angle between tops and Higgs => particles emitted in cone around beam direction Larger separation between 2 tops than betweeen top and Higgs Same applies to background Polar angles mainly forward due to boost from beam pZtot = (x1-x2)pbeam

  3. Separation in azimutal angle shows similar behaviour in signal and background ttBackground Df much narrower Ordering tops by pT, Higgs closer to lower pT top…nothing strange here. Has been used to discriminate against background (Dieter Schroff talk, Higgs group meeting December 2003)

  4. Just trying to get an idea of magnitudes of variables: Energy of tops generally above that of Higgs…must be mh dependant… Tails above 1TeV! pT of b jets reasonably above 10 GeV, but low-pTlight jets may be missed by jet finder (?) Tops decay mainly to b+W as expected Light jets spread reasonably evenly between u d s and c

  5. W+ b In CM of top: n Polar angles of leptons and neutrinos more central than tops and higgs Average energy of neutrino above that of lepton: W polarisation? If mb=0, W would be fully polarised Decay rate to W with P=0 ~ 4x P=-1 ~ 1000x P=1 (R.H.Dalitz and G.R.Goldstein, Phys.Rev.D, 45,5,1992) Paper also provides kinematic constraints which may be useful for event-by-event fit. lepton

  6. Some correlation between angle of lepton and of top: a better constraint may be found fromDalitz & Goldstein paper, looking into it Only broad correlation between lepton and neutrino azimuthal angle or between neutrino and missing pT Higgs seems much more correlated to missing pT, with the neutrino pT as a smearing effect. Can this be used to improve selection?

  7. Reconstructed quantities Missing pT and its reconstruction: Used value from event header (Atlfast). Also calculated using cells and the list of final state particles (except neutrinos and neutralinos) Polar angle hopelessly wrong due to unreconstructed particles Magnitude and azimuthal angle seem to agree between methods…

  8. Only brief comparison between MC truth and Atlfast reconstructed quantities so far. More reconstructed electrons than muons ~3% energy resolution No angle smearing was found (dq/q<10-6) Still a lot to be done!... Still a lot to be done!...

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