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

A complete tree-level calculation of the reaction e(+)e(-) --> vvbb in the electroweak standard theory for the energy range of LEP200 and the Next Linear Collider is presented. The matrix elements were calculated by means of the package CompHEP, and phase space integration and event generation were carried out with the computer programs BASES/SPRING. Cross sections for the vvbb final state, the rate for Higgs production and for different background contributions are studied as a function of the ems energy and the Higgs mass in the range from 80 to 140 GeV. At LEP200 energies, the Higgs bremsstrahlung reaction and the two-body process e(+)e(-) --> ZZ are dominant while near 500 GeV the Higgs fusion and two-to-three body background processes govern the vvbb final state. Interference patterns were searched for and found to be negligible except for root s < M(H) + M(Z), where interferences are found to be of comparable strength with the Higgs signal diagrams. Some cancellations between different background diagrams are observed which are expected within the Standard Model. Missing transverse momentum and visible energy distributions for the vvbbfinal state indicate some further possibilities of removing background for Higgs searches. A suggestion for an approximate treatment of the reaction e(+)e(-) --> vvbb, is presented so that much computer time can be saved in Monte Carlo simulations.