Spin-Spin Asymmetries in Large Transverse Momentum Higgs Bos

a r X i v :h e p -p h /9208250v 1 26 A u g 1992PSU/TH/113MAD/PH/709August 1992Spin-Spin Asymmetries in Large Transverse Momentum Higgs Boson Production M.A.Doncheski Department of Physics University of Wisconsin Madison,WI 53706and R.W.Robinett and L.Weinkauf Department of Physics The Pennsylvania State University University Park,PA 16802Abstract We examine the spin-dependence of standard model Higgs boson production at large transverse momentum via the processes gg →gH 0,qg →qH 0,and q

The prospects for probing the spin-dependence of the standard model of particle physics at collider and supercollider energies have recently received renewed attention

[1],partly because of the successful experimental tests of the Siberian snake concept

[2].Polarization options at collider energies[3,4]and supercollider energies[5,6]and the physics programs possible at such facilities have been discussed extensively.

Predictions for the longitudinal spin structure of hard scattering events at such en-ergies require two ingredients:a knowledge of the helicity structure of the contributing matrix elements and parameterizations of the spin-dependent parton distributions of the proton.Lowest order predictions for the spin structure of many standard collider processes now exist,often quoted as partonic level asymmetries,

?a LL≡?σ(++)??σ(+?)

of Ref.[6]have focused on low transverse momentum H0production via gluon fusion (gg→H0)and weak gauge boson fusion(qqqq→W+W?→H0)and the partonic level asymmetries in these cases are known to be quite large,e.g.?a LL(gg→H0)=+1.

Higgs boson production at large transverse momentum,via the processes gg→gH0,qg→qH0,and q

q→H0g(and the crossed process qg→qH0)depend only on a single heavy quark triangle graph and the resulting ggH0form factor appears as a simple multiplicative factor in the amplitude.While this factor changes the total cross-section,it as no e?ect on the helicity structure of the matrix elements so the

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partonic level spin-spin asymmetries for these two processes are independent of M t and are given by

?a LL(qg→qH0)=

?s2??u2

q→gH0)=?1.(2) These asymmetries were plotted for several values of

√

d?t =

1

4·64

spins,colors

|M|2(3)

where the spin and color summed invariant matrix elements are given by

|M|2=αwα3

S 96

M2W

(|A2(?s,?t,?u)|2+|A2(?u,?s,?t)|2

+|A2(?t,?u,?s)|2+|A4(?s,?t,?u)|2).(4)

The dimensionless functions A2and A4are given in terms of standard loop integrals and thus depend on the quark loop mass and are actually proportional to the gluon helicity amplitudes which we require for the partonic level spin-spin asymmetry.In fact,we?nd

?a LL(gg→gH0)=|A4(?s,?t,?u)|2+|A2(?s,?t,?u)|2?|A2(?u,?s,?t)|2?|A2(?t,?u,?s)|2

3,A2(?s,?t,?u)→?

?s2

so that the partonic level asymmetry is simply

M8H+?s4??t4??u4

?a LL(gg→gH0)=

ij dx a dx b f i(x a,Q2)f j(x b,Q2)d?σij(8) where f i(x,Q2)are the appropriate parton distributions.We use EHLQ2distributions [14]for consistency with Ref.[12]as well as the choice of momentum scale Q2=

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M2H+p2T,and include all three relevant subprocesses.We see that the average partonic level asymmetries are quite reasonable in all of the kinematic regimes relevant for high p T Higgs production.Finally,we can include the e?ects of the polarized parton distributions by calculating values of the observable spin-spin asymmetry,

ij dx a dx b?f i(x a,Q2)?f j(x b,Q2)d?σij·?a ij LL

A LL≡

National Science Foundation under grant PHY–9001744(R.R.),by the Texas National Research Laboratory Commission under an SSC Junior Faculty Fellowship(R.R.), by the University of Wisconsin Alumni Research Foundation(M.D.),by the U.S. Department of Energy under contract DE-AC02-76ER00881(M.D.),and by the Texas National Research Laboratory Commission under grant No.RGFY9173(M.D.).

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References

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Figure Captions

Fig.1.Partonic level asymmetries?a LL for gg→gH0versus cos(θ?)(whereθ?is the center-of-mass scattering angle)in the M t→∞limit.?s/M2H=2(20,200)is shown in the solid(dashed,dotdashed)curve.

Fig.2.Ratio of‘exact’partonic level asymmetry?a LL to that in the M t→∞limit (?a LL(∞))versus cos(θ?)for two values of M t/M H(M t/M H=0.2(0.8)on the left(right)respectively).Three values of?s/M2H are shown as in Fig.1.We use the fact that the angular distribution is symmetric around y=cos(θ?)=0.

Fig.3.Di?erential cross-section,dσ/dp T(nb/GeV)versus p T(GeV)for Higgs boson

√

production for M H=100GeV,(200GeV)for

s=17T eV solid(dotted)curve.The parton distributions of Ref.[14]are used(EHLQ2)with the scale choice Q2=M2H+p2T.

Fig.4.The average partonic level asymmetry(as de?ned in Eqn.8)in the quantity dσ/dp T versus p T(GeV).Curves are labelled as in Fig.3.

Fig.5.The observable spin-spin asymmetry,A LL(de?ned in Eqn.9)in the quantity

√

dσ/dp T versus p T(GeV).Asymmetries for

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