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Search for anomalous tau production in b-tagged top quark events |
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We present a search for the anomalous production of high transverse momentum taus in the decay products of pair produced top quarks using 335 pb-1 of data taken with the CDF detector in Run II at the Tevatron. We select events with a tau, an electron or muon, large missing transverse energy, and jets, in which at least one b-quark is identifed using a secondary vertex tagging algorithm. We find good agreement between the number of events predicted by the Standard Model and the number observed. In the context of the Minimal Supersymmetric Model, we place an upper limit on the top quark branching fraction to a charged Higgs boson (H+) and b-quark. We expect to exclude B(t → H + b)> 0.34 at 95% confidence level for a charged Higgs' mass of 120 GeV/c².
We developed a likelihood discriminant to select hadronically decaying taus (τH) based on the number of reconstructed tracks and pi0s associated with the tau candidate. The types of tau candidates we select are listed in the following table:
and the shapes of the likelihood for taus (signal) and jets (background) are shown in the following plot:
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Likelihood shape for signal and background for
each tau type. EPS or GIF |
The following table shows the expected and observed events with an electron or muon, tau, missing Et, and (at least one) b-tag in the two or more jet bin:
The last row represents the probability to observe greater than or equal to the number of events found in the data given the expected number of events and their uncertainty. The probability that the Standard Model prediction agrees with the data is 20%. The errors include statistical and systematic uncertainties.
The systematic uncertainties are summarized in the following table:
We employ a Bayesian method
to set upper limits on the branching
fraction of the top quark to a charged Higgs boson and b-quark as a
function of the charged Higgs' mass. We assume
the cross section for top quark pair production at the
Tevatron is 7.0 pb.
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Limits on the branching fraction of top → H+
b as a function of H+ mass. EPS or GIF |
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Projected limits as a function of luminosity. With 1 fb-1
of data we expect to exclude a branching fraction greater than 0.1. EPS or GIF |
We show here the event display of an event with an (electron, tau) final state where the tau decays to a track and pi0. This is the only event (out of the six) with two jets that are b-tagged.
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Inner layer of the silicon detector with the two
b-tagged jets shown as red stars. The tau decays to a track
and pi0 with a reconstructed mass of 1.78 GeV/c^2. EPS or GIF |
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We have performed a search for anomalous tau production in b-tagged top quark events using 335 pb-1 of data from CDF's Run II. We expect 3.9 ± 0.5 events from Standard Model sources and observe 6 events, which has 20% probability. We set an upper limit on the top quark branching fraction to a charged Higgs boson and b-quark as a function of the charged Higgs' mass.