We explore the prospect of charged Higgs boson search in top quark decay at the Tevatron collider upgrade, taking advantage of the opposite states of $\tau$ polarization resulting from the $H^\pm$ and $W^\pm$ decays. Methods of distinguishing the two contr
1INTRODUCTION
There is indirect evidence for the existence of top quark in the mass region of
m t?175GeV(1) from the precision measurements of electro-weak parameters,particularly at LEP[1].Moreover,a promising top quark signal in this mass range has been recently observed by the CDF and D0/collaborations[2]at the Tevatron¯p p col-lider.The ongoing Tevatron collider experiments by the CDF and D0/collabo-rations are accumulating a luminosity of～100pb?1each,which is expected to yield a few tens of top quark events for the mass range of(1).Thus one expects to see a more de?nitive signal of top quark production from these experiments at the end of this run.The upgradation of the Tevatron collider luminosity via the installation of the main injector following this run is scheduled to give a typical accumulated luminosity of
L dt～2fb?1,(2) which corresponds to several hundred top quark events for the above mentioned mass range(1).This will enable us to search for new particles in top quark decay;the large top quark mass o?ers the possibility of carrying on this search to a hitherto unexplored mass range for these particles.There has been a good deal of recent interest in the search for one such new particle,for which the top quark decay provides by far the best discovery limit[3,4].This is the charged Higgs boson of the two-Higgs doublet models and in particular the minimal supersymmetric standard model(MSSM).
Generally the charged Higgs signature in top quark decay is based on its preferential coupling to theτchannel vis-`a-vis e andµ,in contrast to the universal W coupling to all the three channels.Thus a departure from the universality prediction between these decay channels can be used to separate the charged Higgs signal from the W boson background in
t→bH(W)→bτν.(3)
Moreover the charged Higgs and the W boson decays lead to opposite states of τpolarization,i.e.
H?→τ?R¯νR,H+→τ+LνL(4) and
W?→τ?L¯νR,W+→τ+RνL(5)
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