Charged Higgs Boson Search at the Tevatron Upgrade Using Tau(14)

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

These plots are well suited for comparing the relative merits of the three meth-ods in extracting the signal from the background.For this purpose the cuto?values are to be so chosen that one gets a viable

H±signal/W±background≥1.(58)

The resulting signal size is a reasonable criterion for the merit of the method. Comparing the signal and background cross-sections for m H=140GeV,we see that this condition is achieved at a far greater sacri?ce to the signal size in Fig.3a than in b and c.The size of the resulting signals,as given by the corresponding cross-over points,are～1/2fb,3fb and7fb respectively.Making a similar comparison of the signal and background cross-sections for m H=100 GeV,one sees that the ratio1is reached in3a with a signal size of～2fb, which is larger than that in3b and comparable to the one in3c.However, the ratio increases more rapidly with cuto?in the latter two cases compared to the?rst.Since this increase is required to o?set the rapid fall of the signal to background ratio with increasing tanβ(see eqs.9,10),the latter methods give more favourable signal size at tanβ>1.4as shown in Fig.4.

Fig.4a,b,c show the size of the signals from the three methods satisfying a viable signal to background ratio>1.The signal cross-sections are shown as functions of tanβfor m H=80,100,120and140GeV.One clearly sees that the use ofτpolarization e?ect via the isolation cut(Fig.4b)or the?E T distribution(Fig.4c)will give a viable charged Higgs signal over a wider range of the charged Higgs mass and tanβparameters.

It is reasonable to consider a signal size of10fb,satisfying a signal to background ratio≥1,to constitute a viable charged Higgs signal.With the expected integrated luminosity of～2fb?1,this will correspond to20signal events over a W boson background of similar size.Since the number of back-ground events can be predicted from the number of dilepton(?+??)events in t¯t decay using W universality,this will correspond to a4.5σsignal for the charged Higgs boson.Thus one can get the discovery limit of charged Higgs boson at the Tevatron upgrade by demanding a signal size of10fb in Fig.4.Evidently the best limits come from Fig.4c.For m H=100(120)GeV one expects a viable signal except for the region tanβ=2?15(1.5?20).The gap in the tanβspace is due to the dip in the t→bH coupling at tanβ～6,as remarked before.It may be mentioned here that there is a current suggestion of further upgradation of Tevatron luminosity by another order of magnitude—i.e.the Tevatron?.The corresponding discovery limit of charged Higgs boson can be obtained by demanding a signal size of1fb in Fig.4c.In this case the gap

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