Charged Higgs Boson Search at the Tevatron Upgrade Using Tau(13)

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

the signal to background ratio is enhanced by a factor of～2;but the signal

size goes down by a factor of～2.5.Of course the enhancement of the signal

to background ratio increases further with increasing E T cut as we shall see

below.Moreover the isolation cut has the advantage of suppressing the QCD

jet background.Nonetheless the factor of2.5drop in the signal size is a high

price to pay,particularly at the Tevatron collider[18].The reason for this big

drop in the signal size is of course that the isolation cut removes not only the

ρT and a1T contributions but also large parts of theρL and a1L contributions

corresponding to their x′?0peaks.The second strategy discussed below aims at retaining these latter contributions.

Here one plots the rate ofτ-jet events,satisfying(54),as a function of

?E T=|E ch T?E0T|=|E ch T?E ac T|;(56)

i.e.the di?erence between the E T of the charged track and the accompanying

neutral E T.The hardτ-jet events from the H±signal and W±background

are expected to be dominated by theπ,ρL,a1L and theρT,a1T contributions

respectively.The latter contributions favour comparable values of E ch T and

E0T and hence relatively small?E T,while the former favour large values of

?E T.Thus the signal events are expected to show signi?cantly harder?E T

distribution compared to the background.

Fig.2shows theτ-jet cross-sections from the H±signal and the W±back-

ground for tanβ=1.4and two values of H±mass,viz.100and140GeV.

Fig.2a and b show the E T distributions of the inclusive1-prongτjet

events from(20,21,22)before and after the isolation cut(55).The isolation cut

is clearly seen to enhance the signal to background ratio,but at the cost of a

drop in the signal size.The signal to background ratio improves by a factor

of1.5—3over the E T range shown,while the signal size drops by a factor of

2-3.Fig.2c shows these inclusive1-prongτ-jet events as a function of?E T.

Evidently the signal events have a much harder?E T distribution than the

background,which is far more striking than the di?erence in the corresponding

E T distributions shown in Fig.1a.Thus the?E T distribution provides a much

clearer separation between the signal and the background than the simple E T

distribution.It helps to improve the signal to background ratio signi?cantly

without sacri?cing the signal size.

Fig.3shows the corresponding integrated cross-sections against the cuto?

value of the E T(?E T),i.e.

σ(E T)= E T∞dσ

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