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
which can be used to augment the above signature(or even as an independent signature)[5,6].The present work is devoted to a quantitative analysis of the signature and discovery limit of the charged Higgs boson at the Tevatron upgrade based on the above ideas.In particular it shows how theτpolarization e?ect can be exploited to improve the signature and the discovery limit of the charged Higgs boson even without identifying the mesonic states inτdecay, which will be the case at a hadron collider.
2CHARGED HIGGS SIGNAL IN TOP QUARK DECAY
We shall concentrate on the charged Higgs boson of the MSSM.Its couplings to fermions are given by
H+ cotβV ij m u i¯u i d jL+tanβV ij m d j¯u i d jR L=g2m
W
¯νj?jR +H.c.(6)
+tanβm?
j
where V ij are the Kobayashi-Maskawa(KM)matrix elements and tanβis the ratio of the vacuum expectation values of the two Higgs doublets.The QCD corrections are taken into account in the leading log approximation by substi-tuting the quark mass parameters by their running masses evaluated at the H±mass scale[4].Perturbative limits on the tbH Yukawa couplings of Eq.
(6),along with the constraints from the low energy processes like b→sγand
B d?¯B d mixing,imply the limits[7]
0.4<tanβ<120.(7) In the most predictive form of MSSM,characterised by a common SUSY break-ing mass term at the grand uni?cation point,one gets stronger limits[8]
1<tanβ<m t/m b.(8) Such a lower bound also follows from requiring the perturbative limit on the tbH Yukawa coupling to hold upto the uni?cation point[9].
In the diagonal KM matrix approximation,one gets the decay widths
2