Higgs particle detection using jets.

We study the possibility of detecting the Higgs boson in the intermediate mass range via its two jet channel. We consider only Higgs bosons produced in association with a t ¯ t pair. Both t and ¯ t are required to decay semileptoni-cally to reduce the QCD background. The signal is compared with the main background, t ¯ t + 2 jets, after appropriate cuts. A sizable signal above background is seen in our simulation at the parton level. Use of the t ¯ tZ channel with Z decaying to l + l − is suggested for eliminating theoretical uncertainties in determining the t ¯ tH signal. INTRODUCTION The Standard Model Higgs with mass up to 85 GeV/c 2 could be discovered at the planned LEP 200 experiments. At the SSC or the LHC on the other hand it should not be difficult to find a Higgs boson with mass between 140–800 GeV/c 2 , which can decay to two Z bosons, one of which may be virtual. To cover the mass gap between 85 and 140 GeV/c 2 , the rare decay H → γγ was suggested [ 1–3 ], where the Higgs boson H is produced in association with either a W ± boson or a t ¯ t pair in pp scattering experiments. A charged hard lepton from W ± or one of the t quarks is required as a trigger in order to reduce the QCD background. However, since the 2γ mode is a rare decay, it may be difficult to extract this signal from the complicated background [ 4 ]. We study instead the possibility of searching for an intermediate Higgs boson in the two-jet channel by reconstructing its invariant mass. We consider Higgs bosons that are produced in association with t ¯ t pairs only. This allows both the t and ¯ t to be tagged using semileptonic decays to cut down on the QCD background. We are motivated by recent works on jet spectroscopy. The GEM Collaboration [ 5 ] has presented mass plots where W and t peaks were successfully reconstructed from two and three jets in computer generated multi-jet events. Similar method are proposed for charged Higgs searches at HERA [ 6 ] and for top searches at the TEVATRON [ 7 ]. For earlier studies of Higgs searches using jets see Ref. [ 8 ].