Main facilities.

CalcHEP  is a package for automatic calculations of elementary particle decay and collision properties in the lowest order of perturbation theory (the tree approximation). The main idea prescribed into the CalcHEP  is to make available passing on from the Lagrangian to the final distributions effectively with a high level of automation. Other packages created to solve a similar problem are FeynArts/FeynCalc[1], GRACE[2], HELAS[3], MADGRAPH[4]. See also the review [5].

CalcHEP  is a menu-driven system with the context help. The notations used in CalcHEP  are very similar to those used in particle physics.

The present version contains the Standard Model (SU(3)xSU(2)xU(1)) and its Minimal Sypersymmetry extension (MSSM). The user can change particle interaction and model parameters. It is also possible to create new models of particle interaction.

In the present version polarizations are not taken into account. Averaging over initial and summing over final polarizations are performed automatically.

The CalcHEP  package consists of two parts: symbolic and numerical ones. The symbolic part generats codes for a squared matrix element which are used in the numerical calculations.

The symbolic part of CalcHEP  lets the user:

• select a model of particle interaction and implement some changes in the model. In paricular one can choose the package for solution of RGE equations in case of SUGRA models;
• coose a gauge. Physical gauge and t'Hooft-Feynman one are available.
• select a process by specifying incoming and outgoing particles for the decays of 1->2, ..., 1->5 types and the collisions of 2->2, ..., 2->4 types;

• generate Feynman diagrams, display them, and create the corresponding L^ATEX  output;

• exclude some diagrams;

• generate and display squared Feynman diagrams;

• calculate analytical expressions corresponding to squared diagrams by using the fast built-in symbolic calculator;

• save symbolic results corresponding to the squared diagrams calculated in the Reduce  and Mathematica  codes for further symbolic manipulations;

• generate the optimized C  codes for the squared matrix elements for further numerical calculations;

• launch the compilation of the generated codes and start the corresponding numerical session;

• generates libraries of matrix elements for other packages.

The numerical part of CalcHEP  offers to:

• convolute the squared matrix element with structure functions and beam spectra. CTEQ  PDFLIB, CTEQ, MRST parton distribution functions, the ISR and Beamstrahlung spectra of electrons, the laser photon spectrum, and the Weizsaecker-Williams photon structure functions are available;

• modify physical parameters ( incoming momenta, couplings, masses etc.) involved in the process;

• select the scale parameter for evaluation of the QCD coupling constant and parton structure functions;

• calculate Higgses widths and decay rates taking into account hight order QCD loop corrections.

• apply LEP mass limits on MSSM spectrum, as well as calculate b -> s gamma, B_s -> mu-mu , and (g-2) constraints.

• apply various kinematic cuts.

• define the kinematic scheme (phase space parameterization) for effective Monte Carlo integration;

• introduce a phase space mapping in order to smooth sharp peaks of a squared matrix element and structure functions;

• perform a Monte Carlo phase space integration by Vegas;

• generate partonic level events and direct them to PYTHIA;

• display distributions in various kinematic variables;

• create the graphical and L^ATEX  outputs for histograms.

The current version is accompanied with different {\it batch} programs which allows to performs all calculations in non-interactive regime.