Hephy-pub 754/02

For energies relevant to future linear colliders, √ s & 500 GeV, the WW fusion channel dominates the Higgs boson production cross section e+e− → ν̄νh0. We have calculated the one-loop corrections to this process due to fermion and sfermion loops in the context of the MSSM. As a special case, the contribution of the fermion loops in the SM has also been studied. In general, the correction is negative and sizeable of the order of 10%, the bulk of it being due to fermion loops. As no Higgs boson could be detected so far, the search for the Higgs boson as the primary goal of high energy physics will continue. The four LEP experiments delivered a lower bound for the Standard Model (SM) Higgs mass, mh & 114 GeV [1]. In e e collisions, for energies & 200 GeV, the production of a single Higgs boson plus missing energy starts to be dominated byWW fusion [2, 3, 4], that is ee → ν̄eνe WW → ν̄eνe h, whereas the Higgsstrahlung process [5] ee → Zh → ν̄ν h becomes less important. h denotes the SM Higgs boson or the light Higgs boson of the Minimal Supersymmetric Standard Model (MSSM), while H is the heavy CP -even Higgs boson in the MSSM. The rates for the ZZ fusion are generally one order of magnitude smaller than those of the WW channel. At LHC, in p p collisions, the gluon-gluon fusion mechanism provides the dominant contribution to Higgs production. The next important Higgs production channel is vectorboson fusion V V → h/H. In particular, it provides an additional event signature due to the two energetic forward jets. Recently, it has been argued that the channels WW → h/H → τ τ̄ and WW , can serve as suitable search channels at LHC even for a Higgs boson mass of mh ∼ 120 GeV [6]. At Tevatron, with p p̄ collisions at 2 TeV, the WW fusion process plays a less important rôle. The g g fusion is the dominant process for Higgs production there, but the Higgsstrahlung q q̄ → W → Wh is larger than the WW fusion for mh . 180 GeV [7]. It is worth mentioning that WW (and ZZ) fusion is also the most important Higgs boson production mechanism in e p collisions. Actually, it was shown [8] that the e poption at LHC would offer the best opportunity to search for a Higgs boson in the mass range mh < 140 GeV. In this paper, we have calculated the leading one-loop corrections to the WWh vertex in the MSSM by taking into account fermion/sfermion loops. They are supposed to be the dominant corrections due to the Yukawa couplings. We have applied them to the Higgs boson production in ee annihilation in the energy range √ s = 0.4− 3 TeV, i. e. ee → ν̄eνe WW → ν̄eνe h. We included the Higgsstrahlung process ee → Zh → ν̄ν h and the interference between these two mechanisms. Because the Higgsstrahlung process is much smaller in this range, we have neglected its radiative corrections. We have also discussed the SM case where we have studied the dependence on the Higgs boson mass. As to the one-loop corrections to the WWh vertex in the SM we quite generally refer to the review article [9]. For this coupling also QCD corrections were included, the O(αsGF mt ) in [10] and O(α2 s GF mt ) in [11]. As for energies √ s > 400 GeV the dominant channel ee → ν̄νh is by far the WW