Ph.D. Thesis by Leslie Stevan Groer

Rutgers, the State University of New Jersy
New Brunswick, New Jersey

Title
-----
A Search for Charged Higgs Boson Decays of the Top Quark using 
Hadronic Decays of the Tau Lepton in Proton-Antiproton Collisions 
at sqrt(s) = 1.8 TeV at CDF

Thesis Advisor: Terence Watts

Defended: July 14, 1998
Submitted: October 1998

Abstract
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The Standard Model predicts the existence of one neutral scalar Higgs boson,
which is a remnant of the mechanism that breaks the SU(2)_L x U(1)_Y
electroweak symmetry and generates masses for the heavy vector bosons and
fermions.  Many extensions to the Standard Model predict two or more Higgs
doublets, resulting in a larger spectrum of Higgs bosons including a charged
Higgs boson (H^+/-).  For a light charged Higgs boson mass, the top quark
decay into a charged Higgs boson and bottom quark might occur. 

This thesis presents results of a direct search for this top quark decay mode
via the charged Higgs decay to a tau lepton and tau-neutrino,  using the
hadronic decays of the tau leptons. The search data consist of 100 pb^-1 of
Run 1 data collected between 1992-1995 at the CDF detector, from p-pbar
collisions at a center-of-mass energy of 1.8 TeV produced at Fermilab's
Tevatron accelerator.

A total of seven events are observed in two search channels with an expected
background contribution of 7.4 +/- 2.0 events coming from fake taus
(5.4 +/- 1.5), heavy vector boson decays with jets (1.9 +/- 1.3) and dibosons
(0.08 +/- 0.06).  Lacking evidence for a signal, we set limits on charged Higgs
production at the 95% confidence level in the charged Higgs mass plane versus
tan beta (a parameter of the theory) for a top quark mass of 175 GeV/c^2 and for
top production cross sections (sigma_tt) of 5.0 and 7.5 pb, assuming the
Type-II Two-Higgs-Doublet-Model.  For large tan beta, this analysis excludes a
charged Higgs boson of mass below 147 (158) GeV/c^2 for sigma_tt = 
5.0 (7.5) pb.  Using the Standard Model measured top quark cross section from 
CDF, this limit increases to 168 GeV/c^2 and we also exclude a branching
fraction of top decays via this charged Higgs mode of greater than 43% for
charged Higgs masses below 168 GeV/c^2.


Posted to /cdf/pub/thesis/cdf4740_groer_thesis.ps
    http://www-cdf.fnal.gov/thesis/cdf4740_groer_thesis.ps

Posted by groer@cdfsga