Charged Higgs Boson Search at the Tevatron Upgrade Using Tau Polarization

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

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TIFR/TH/95-08CHARGED HIGGS BOSON SEARCH AT THE TEV ATRON UPGRADE USING TAU POLARIZATION Sreerup Raychaudhuri and D.P.Roy 1Theoretical Physics Group Tata Institute of Fundamental Research Homi Bhabha Road,Bombay 400005,India ABSTRACT 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 τpolarization resulting from the H ±and W ±decays.Methods of distinguishing the two contributions in the inclusive 1-prong hadronic decay channel of τare suggested.The resulting signature and discovery limit of H ±are presented for

the Tevatron upgrade as well as the Tevatron ?and the Ditevatron options.March 1995

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)

1

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

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

Γt→bW=

g2

2 1,m2b m2t

m2W(m2t+m2b)+(m2t?m2b)2?2m4W (9)

Γt→bH=

g2

2 1,m2b m2t

(m2t cot2β+m2b tan2β)(m2t+m2b?m2H)?4m2t m2b (10)

ΓH→τν=

g2m H

32πm2W m2c cot2β+m2s tan2β .(12) From these one can construct the relevant branching fractions

B t→bH=Γt→bH/(Γt→bH+Γt→bW)(13)

B H→τν=ΓH→τν/(ΓH→τν+ΓH→c¯s).(14) It is the product of these two branching fractions that controls the size of the observable charged Higgs signal.The t→bH branching fraction has a pronounced dip at

tanβ=(m t/m b)1

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

events.Moreover,since the hadronicτand QCD jet events dominantly populate the1-prong and multi-prong channels respectively,the prong distribution of the narrow jets can be used to distinguish the two.This way the CDF experiment [11]has been able to identify the W→τνevents and test W universality as well as put modest constraints on t and H±masses from(3)using a data sample of integrated luminosity～4pb?1.In the present case,however,one would be looking for a few tens of hadronicτevents in a data sample of～500 times larger integrated luminosity,for which the QCD jet background cannot be controlled by the above method.Therefore one cannot use the singleτchannel for the charged Higgs search and even theττchannel may be at best marginal.The best charged Higgs signature is provided by the?τchannel. The largest background comes from W→?νaccompanied by QCD jets,which can be easily suppressed by the above mentioned jet angle and multiplicity cuts.Besides the hard isolated lepton?provides a more robust trigger than the missing-E T.Therefore in this work we shall concentrate mainly on the?τchannel;but similar analysis can be carried over in theττchannel as well.

The?τandττchannels correspond to the leptonic decay of both the charged bosons in(16),i.e.

H+H?,H+W?,H?W+,W+W?

↓↓↓↓↓↓↓↓

τ+Lτ?Rτ+Lτ?L,??τ?Rτ+R,?+τ+R,?+τ?L,??(17)

By convention,

Pτ≡Pτ?=?Pτ+,Pτ±=σ

τ±

R?

στ±L

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

Nonetheless the method of enhancing the signal to background ratio by theτpolarization e?ect discussed below can be extended to this channel,provided one can identify theττevents from the QCD background.

3TAU POLARIZATION EFFECT

We shall concentrate on the1-prong hadronic decay channel ofτ,which is best suited forτidenti?cation.It accounts for80%of hadronicτdecays and50% of overallτdecays.The main contributors to the1-prong hadronicτdecay are [1]

τ±→π±ντ(12.5%)(20)

τ±→ρ±ντ→π±π0ντ(24%)(21)

τ±→a±1ν→π±π0π0ντ(7.5%)(22) where the branching fractions for theπandρchannels include the small con-tributions from the K and K?channels respectively,since they have identical polarization e?ects.Note that only half the a1decay channel contributes to the 1-prong con?guration.The masses and widths ofρand a1are[1]

mρ(Γρ)=770(150)MeV,m a

1(Γa

1

)=1260(400)MeV.(23)

One sees that the three decay processes(20,21,22)account for about90%of the1-prong hadronic decay ofτ.Thus the inclusion ofτpolarization e?ect in these processes will account for its e?ect in the inclusive1-prong hadronic decay channel to a good approximation.

The formalism relatingτpolarization to the momentum distribution of its decay particles in(20,21,22)has been widely discussed in the literature[5,6, 12,13].We shall only discuss the main formulae relevant for our analysis.A more detailed account can be found in a recent paper by Bullock,Hagiwara and Martin[6],which we shall closely follow.Forτdecay intoπor a vector meson (ρ,a1),one has

1

d cosθ=

1

Γv

dΓvL2m2τ

Γv dΓvT

m2τ+2m2v

(1?Pτcosθ)(26)

5

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

where v stands for the vector meson and L,T denote its longitudinal and trans-verse polarization states.The angleθmeasures the direction of the meson in theτrest frame relative to theτline of?ight,which de?nes its polarization axis.It is related to the fraction x of theτenergy-momentum carried by the meson in the laboratory frame,i.e.

2x?1?m2π,v/m2τ

cosθ=

.(29)

m2τ+2m2v

Consequently the e?ect ofτpolarization is reduced by a factor of～1/2in ρmomentum distribution and practically washed out in the case of a1.Thus the inclusive1-prongτjet resulting from(20-22)is expected to be harder for the H±signal compared to the W boson background;but the presence of the transverseρand a1contributions makes the size of this di?erence rather modest.We shall see below that it is possible to suppress the transverseρand a1contributions and enhance the di?erence between the signal and the background in the1-prong hadronicτchannel even without identifying the individual mesonic contributions to this channel.

The key feature of vector meson decay,relevant for the above purpose,is the correlation between its state of polarization and the energy sharing among

6

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 decay pions.In order to use this feature,one must ?rst transform the polarization states of the vector meson appearing in (25,26)from the τrest frame to the laboratory frame.This is done by a Wigner rotation of the vector meson spin quantization axis

[14],i.e.

M ′λτλ′v = λv d 1λ′v λv (ω)M λτλv (30)

where the decay helicity amplitudes on the left and right correspond to the laboratory and the τrest frames respectively;and

cos ω=(m 2τ?m 2v )+(m 2τ+m 2v )cos θ

Γv

d Γlab vL

2m 2v

m 2v

cos 2ω+P τcos θ m τm 2v

cos 2ω?sin 2ω (32)1

d cos θ=1m 2τ+2m 2v 1+cos 2ω+

m 2τm 2v sin 2ω?

m τ

m 2τ 2 1+2m 2

m 2?m 2v +im Γv (m 2)(35)is the vector meson propagator with invariant mass m 2and the running width

Γv (m 2)=Γv

m f v (m 2v ).(36)7

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

Theρmeson line shape factor is

fρ(m2)=(1?4m2π/m2)3/2(37)

which takes account of the P-wave threshold behavior forρ→ππdecay.For the line shape of the a1meson we shall use the phenomenological parametrisation of Kuhn and Santamaria[15]

f a(m2)=1.623+10.38

m4

+

0.65

ΓππdΓ(ρ±L→π±π0)

2

cos2θ′?3

ΓππdΓ(ρ±T→π±π0)

4

sin2θ′?3x′(1?x′)(40) x′= 1+

s

(45)

where we have dropped a constant multiplicative factor in(44),which will not be relevant for our analysis.It will be adequate for our purpose to evaluate the

8

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

decay amplitudes (43-45)neglecting the a 1and ρwidths.The resulting decay distributions for longitudinal and transverse a 1are given by

1

d cos θa d cos θρdφρ

= m 2a +m 2ρ8πm a m ρ 2+8 (46)

1

d cos θa d cos θρdφρ

= m 2a +m 2ρ16πm a m ρ

2+8 .(47)In the a ±1→ρ±π0decay θa is the angle of ρin the a 1rest frame measured relative to the a 1line of ?ight in the laboratory (z -axis),while the plane con-taining these two vectors de?nes the x ?z plane.Similarly in the ρ±→π0decay θρand φρare the polar and azimuthal angles of the charged pion in the ρrest frame,measured relative to the above ρline of ?ight (z ′-axis)and the above plane respectively.In terms of these angles,the fraction of a 1laboratory energy-momentum carried by the charged pion is given by

x ′=E π±

m a m ρ

2m a m ρ

+m ρ2m a m ρcos θa +q m 2a ?m 2ρ2m a m ρcos θρcos θa ?q sin θρcos φρsin θa ,

(48)q =1m 2ρ?4m 2π?1

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

there is a visible peak only at x′?0but not at x′?1.The reason is that the latter condition holds only for a tiny region of the phase space as we see from (50).The a1T decay distribution(47)vanishes near the collinear con?guration (52).It has maxima at

cosθa=0and cosθρ=±1or cosθρ=0,cosφρ=0(53) which correspond to the plane of the three decay pions in the a1rest frame being normal to its line of?ight.This results in an even sharing of the a1energy as in the case ofρT decay.In particular both the distributions vanish at the extrema x′=0and1and peak near the middle,although the a1T peak occurs a little below x′=0.5.Indeed the shapes of a1L and a1T decay distributions in x′are qualitatively similar to those ofρL andρT,except for the suppression of the x′?1peak for a1L.A comparison of these distributions can be found in[6]. There is reason to believe that the above features of longitudinal and transverse a1decay are insensitive to the assumed dynamical model[15].Indeed it follows from general considerations that the a1L(T)→3πdecay favours the plane of the3pions in the a1rest frame being coincident with(normal to)the a1line of ?ight[13].The role of the model is only to determine the distribution of energy among the3pions in this plane.Moreover as shown in[6],the alternative model of Isgur et al[16]gives very similar pion energy distributions as that of [15].

Thus the transverseρand a1decays favour even sharing of energy by the charged and neutral pions,while the longitudinalρand a1decays favour ex-treme con?gurations where the charged pion carries practically all or none of the vector meson energy.This can be exploited to suppress the former while retaining most of the latter contributions along with that of the pion(20).This will in turn enhance the H±signal to W±background ratio in the1-prong hadronic decay channel ofτas we shall see below.

4RESULTS AND DISCUSSION

We shall be interested in the inclusive1-prong hadronic decay ofτ,which is dominated by theπ±,ρ±and a±1contribution(20,21,22).It results in a thin 1-prong hadronic jet(τ-jet)consisting of a charged pion along with0,1or2π0s respectively.Since all the pions emerge in a collinear con?guration one can neither measure their invariant mass nor the number ofπ0s.Consequently it is not possible to identify the mesonic state.But it is possible to measure

10

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 energy of the charged track as well as the total neutral energy,either by measuring the momentum of the former in the central detector and the total energy deposit in the EM and hadron calorimeters or from the showering pro?les in the EM and hadron calorimeters.Thus one has to develop a strategy to suppress the transverse vector meson contributions using these two pieces of information.We shall consider two such strategies below.In either case a rapidity and transverse energy cut of

|η|<2and E T>20GeV(54) with be applied on theτ-jet,where E T includes the neutral contribution.We shall use the recent structure functions of[17]for calculating the t¯t cross-section.

Firstly,we consider the e?ect of an isolation cut requiring the neutral E T accompanying the charged track within a cone of?R=(?η2+?φ2)1/2=0.2 to be

E ac T≡E0T<5GeV.(55) Fig.1shows the E ac T distribution for aτ-jet satisfying(54).Theπ,ρand a1 contributions are shown separately for the H±signal and the W±background, where we have chosen m H=80GeV and tanβ=1for illustrative purpose. The¯p p CM energy is taken to be2TeV.Several points are worth noting in this ?gure.

i)The signal to background ratio forπ(～4.5)is twice as large asρand thrice as large as a1.This is a consequence of the E T>20GeV cut and theτpolarization e?ect(24-29).

ii)Theρand a1contributions to the signal(background)are dominated by the longitudinal(transverse)components.

iii)Theρ±L→π±π0peak at x′?1shows up in the signal at E ac T?0while the x′?0peak is smeared over the large E ac T tail.The absence of a E ac T?0 peak in the a+1L→π±π0π0contribution to the signal re?ects the absence of a corresponding peak at x′?1as remarked earlier,while the x′?0peak is smeared over the large E ac T tail.

iv)Theρ±T→π±π0peak at x′?0.5shows up in the background at E ac T?15 GeV.The peak in the a±1T→π±π0π0contribution to the background at a somewhat higher E ac T re?ects the corresponding peak at x′somewhat below0.5 as remarked earlier.

As one sees from Fig.1,the isolation cut(55)on the charged track will es-sentially remove all the contributions except forπ±and a part of theρ±L→π±π0 corresponding to its x′?1peak,where the decayπ0is very soft.Consequently

11

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

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

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

narrows down to tanβ=3?10(2.5?12)for m H=100(120)GeV.Moreover one can probe for m H=140GeV except for a gap in the region tanβ=2?15.

For the sake of completeness we have computed the signal and background

√

cross-sections for the suggested Ditevatron energy of

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

reduction in the signal size in the?rst case,while there is no such price to pay

in the second.Consequently the latter strategy o?ers the best discovery limit

for the charged Higgs boson.We have explored these discovery limits in the

parameter space of H±mass and tanβassuming an integrated luminosity of

～2fb?1for the Tevatron upgrade.For the sake of completeness we have also explored the signal and discovery limit for the suggested Tevatron?and Dite-

vatron options,corresponding to an order of magnitude increase of luminosity

and a doubling of the CM energy respectively.

Acknowledgements

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

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16

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

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(1993)and B309,492(1993).

[18]The isolation cut strategy may be more appropriate at the LHC,where

the signal size is very large.

17

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

Figure Captions

s=2TeV.The cross-sections are shown as functions of neutral pion E T accompanying

the charged track in theτ-jet.

Fig. 2.The1-prong hadronicτ-jet cross-sections are plotted against the jet E T in

(a)without and(b)with the isolation cut.They are plotted against the

?E T of the jet in(c).The H±signal(W±background)contributions are

shown as solid(dashed)lines for m H=100GeV and dot-dashed(dotted)

√

lines for m H=140GeV.We take

s=4TeV.The solid(dashed) and dot-dashed(dotted)lines correspond to the signal(background)for

m H=100and150GeV respectively.We take tanβ=1.4.

Fig. 6.The signal cross-sections of Fig.5(a,b,c),satisfying a signal to background ratio≥1,are shown as functions of tanβfor m H=80,100,120,140and

150GeV by solid,dashed,dot-dashed,double-dot-dashed and dotted lines

respectively.

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