Glossary

BR
Beam Remnants; not much used since it may be confused with Branching Ratio
BSM
Beyond-the-Standard-Model physics, as a generic term for anything not contained within the SM
FSR
Final-State Radiation, implemented in terms of timelike showers
LHA
Les Houches Accord for user processes, describing which process-level information should be stored to allow further showering and hadronization of "skeleton" hard processes
LHAPDF
Les Houches Accord Parton Distribution Functions, originally a standard format for defining PDF's and later a library with such PDF's
LHEF
Les Houches Event File(s), a file format for storing LHA process and event information
ISR
Initial-State Radiation, implemented in terms of spacelike showers
MPI
Multiparton Interactions, i.e. several (more or less) independent parton-parton subcollisions as part of a hadron-hadron event (previously called MI for multiple interactions)
MSSM
Minimal Supersymmetric extension of the Standard Model
PDF
Parton Distribution Function (alternatively Parton Density Function)
PDG code
a scheme for assigning unique integers, particle identity codes, to known and hypothetical particles; code rules and tables are published in the RPP (see below).
pileup
several hadron-hadron collisions in a bunch crossing; not to be confused with MPI
RPP
Review of Particle Physics, the biannual review by the ParticleData Group (PDG) from which many Standard-Model parameter values and much particle data has been taken (but, given the poor data on many hadron resonances, a lot of extra (guess)work is needed)
setting
collectively used to denote all the boolean flag, integer mode, double-precision parm and string word variables that can be set by the user to steer the behaviour of a run; normally particle data are considered separately but clearly are closely related
SLHA
SUSY Les Houches Accord for interchange of mass and coupling information in SUSY scenarios, via a well-defined file format
SM
the Standard Model of particle physics
SUSY
SUperSYmmetry
units
Normal PYTHIA input, internal operations and output is based on a set of standard units, such as:
GeV for all energies, momenta and masses, always with c = 1;
mm for all distances and mm/c for all times, so that again they match for c = 1;
mb for all cross sections (but input or output via the Les Houches Accord takes into account that the unit there is pb)