Physical Results by means of CompHEP

AbstractThe CompHEP package was developed for calculations of decay and high energy collision processeswith, correspondingly, up to 5 and 4 final particles in the lowest order (tree) approximation. The mainidea put into CompHEP was to make available passing from the Lagrangian to final distributionsefficiently with high level automation what is extremely needed in collider physics.The present talk describes a general structure of the CompHEP facilities and reports some physicalresults obtained with its help. The main purpose of the talk is to attract the attention of high energyphysicists to this user-friendly package which is completely aimed at making easier their routine andtedious calculations in the TeV region. 1. IntroductionCompHEP project was started in 1989 by group of physicists and programmers from the Institute ofNuclear Physics, Moscow State University. The first versions of the CompHEP package were written inTurbo Pascal for IBM compatible PC. In 1992 this package was rewritten in the C programming languageand now the installation on UNIX workstations is available. At present time there are some versions fordifferent platforms: HP Apollo 9000, IBM RS 6000, DECstation 3000, Sparc station, Silicon Graphics.CompHEP is a menu-driven system with the mixed text/graphical output of information and thecontext HELP facility. The notations used in CompHEP are very similar to those used in particlephysics. It contains several buit-in theoretical models of particle interactions including the StandardModel in the unitary and ’tHooft-Feynman gauges. A creation of a new particle interaction model by theuser is available. The user can change interaction vertices and model parameters. In the present versionpolarizations are not taken into account. Averaging over initial and summing over final polarizations areperformed automatically.The general structure of the CompHEP package is represented in Fig. 1. It consists of the symbolicpart and the numerical one. The main facilities of the symbolical part allow the user to• select process by specifying in- and out- particles for decays of 1 → 2,...,1 → 5 types and collisionsof 2 → 2,...,2 → 4 types;• generate and display tree-like Feynman diagrams in the lowest order;• eliminate some number of diagrams from the further consideration;• generate and display squared Feynman diagrams (corresponding to squared S-matrix elements);• derive analytical expressions corresponding to squared diagrams with the help of the fast built-insymbolic calculator;• carry out numerical calculations for 1 → 2, 1 → 3 and 2 → 2 processes and show plots of variousdistributions on the screen;• generate LATEX files for graphical outputs;• save analytical results in the REDUCE and MATHEMATICA codes for further symbolical manip-ulations;• generate the optimized FORTRAN codes for the squared matrix elements in order to make furthernumerical calculations.The numerical part of the CompHEP package is written in FORTRAN. It uses the CompHEP FOR-TRAN output and the BASES&SPRING package [2] for Monte-Carlo integration and event generation.By means of the CompHEP numerical part the user is able to1