THE REACTION E(-)-]NU(NU)OVER-BAR-B(B)OVER-BAR AND THE HIGGS SIGNAL AT LEP200 AND NLC()E()

A complete tree-level calculation of the reaction e(+)e(-) --> vvbb in the electroweak standard theory for the energy range of LEP200 and th e Next Linear Collider is presented. The matrix elements were calculat ed by means of the package CompHEP, and phase space integration and ev ent generation were carried out with the computer programs BASES/SPRIN G. Cross sections for the vvbb final state, the rate for Higgs product ion and for different background contributions are studied as a functi on of the ems energy and the Higgs mass in the range from 80 to 140 Ge V. At LEP200 energies, the Higgs bremsstrahlung reaction and the two-b ody process e(+)e(-) --> ZZ are dominant while near 500 GeV the Higgs fusion and two-to-three body background processes govern the vvbb fina l state. Interference patterns were searched for and found to be negli gible except for root s < M(H) + M(Z), where interferences are found t o be of comparable strength with the Higgs signal diagrams. Some cance llations between different background diagrams are observed which are expected within the Standard Model. Missing transverse momentum and vi sible energy distributions for the vvbbfinal state indicate some furth er possibilities of removing background for Higgs searches. A suggesti on for an approximate treatment of the reaction e(+)e(-) --> vvbb, is presented so that much computer time can be saved in Monte Carlo simul ations.