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 menudriven 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'HooftFeynman 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^{A}TEX output;
 exclude some diagrams;
 generate and display squared Feynman diagrams;
 calculate analytical expressions corresponding to squared diagrams
by using the fast builtin 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 WeizsaeckerWilliams 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 > mumu , and (g2) 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^{A}TEX outputs for histograms.
The current version is accompanied with different {\it batch}
programs which allows to performs all calculations in noninteractive
regime.