CompHEP-PYTHIA interface: integrated package for the collision events generation based on exact matrix elements

CompHEP, as a partonic event generator, and PYTHIA, as a generator of final states of detectable objects, are interfaced. Thus, integrated tool is proposed for simulation of (almost) arbitrary collision processes at the level of detectable particles. Exact (multiparticle) matrix elements, convolution with structure functions, decays, partons hadronization and (optionally) parton shower evolution are basic stages of calculations. The PEVLIB library of event generators for LHC processes is described.Comment: Standard LaTeX, 4 pages. To appear in the proceedings of the Seventh International Workshop on Advanced Computing and Analysis Technics in Physics Research (ACAT2000, Fermilab, October 16-20, 2000

Event Generators for WW Physics

The report summarizes the results of the activities of the Working Group on Event Generators for WW Physics at CERN during 1995.Comment: 99 Latex, including 30 figures, 24 tables. The report is part of: G.Altarelli,T.Sjostrand and F.Zwirner (eds), Physics at LEP2 CERN 96-0

Higgs Physics at LEP2

In this report we review the prospects for Higgs physics at LEP2. The theoretical aspects and the phenomenology of Higgs particles are discussed within the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM). The experimental search techniques are described and the discovery limits for Higgs bosons in the LEP2 energy range are summarized. In addition, opportunities of detecting Higgs particles in non-minimal extensions of the SM and the MSSM are investigated.Comment: 112 pages, latex file + figures (some bitmapped), to appear in Vol. 1, Report of the Workshop on Physics at LEP2, G. Altarelli, T. Sjostrand and F.Zwirner (eds), CERN 96-01. (Full postscript and uuencoded files, including full resolution figures are available at the www address http://surya11.cern.ch/surya_info/users/mcarena in finrep.ps, finrep.uu

Complete tree-level calculation of the reaction e+e−→μ+μ−bbˉe^ + e^ - \to \mu ^ + \mu ^ - b\bar b and the Higgs boson signal at LEP200 and NLC energies

A complete tree-level calculation of the reaction$e^ +e^ -\to \mu ^ +\mu ^ -b\bar b$ in the electroweak standard theory for the energy range of LEP200 and the next linear collider is presented. The matrix elements have been calculated by employing the computer program CompHEP, the phase space integrals by the Monte Carlo integrator and event generator BASES/SPRING. The dependence of the 4-fermion cross section on energy and the Higgs boson mass is studied in detail. Interference contributions between the various diagrams are found not to alter significantly the production and decay properties of the Higgs boson. It is shown that already the counting rate of the reaction$e^ +e^ -\to \mu ^ +\mu ^ -b\bar b$ at LEP200 can provide evidence for the existence of the Higgs boson

The reaction e+e−→ννˉbbˉe^+ e^- \to \nu\bar{\nu}b \bar{b} and the higgs signal at LEP200 and NLC

A complete tree-level calculation of the reaction 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 final state, the rate for Higgs production and for different background contributions are studied as a function of the cms 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 final state. Interference patterns were searched for and found to be negligible except for , 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 final state indicate some further possibilities of removing background for Higgs searches. A suggestion for an approximate treatment of the reaction is presented so that much computer time can be saved in Monte Carlo simulations