The Les Houches Accords are agreements between particle physicists to standardize the interface between the matrix element programs and the event generator

Event generator

Event generators are software libraries that generate simulated high-energy particle physics events.They randomly generate events as those produced in particle accelerators, collider experiments or during the initial phases of the Universe creation....

s used to calculate different quantities. The original accord was initially formed in 2001, at a conference in Les Houches

Les Houches

Les Houches is a commune in the Haute-Savoie department in the Rhône-Alpes region in south-eastern France.-Overview:It is a ski-resort, and is located 6 kilometres from Chamonix with a ski domain which extends from an altitude of 950 metres up to 1900 metres...

, France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

, and was subsequently expanded.

In experimental high energy physics, several levels of computing are used to simulate data runs, including programs that generate matrix elements and ones that generate events. However, there are several programs for each of these tasks, such as CompHEP

CompHEP

is a software package for automatic computations in High Energy Physics from Lagrangians to collision events or particle decays.CompHEP is based on quantum theory of gauge fields, namely it uses the technique of squared Feynman diagrams at the tree level approximation...

 and MadGraph to generate matrix elements, and PYTHIA

PYTHIA

PYTHIA is a computer simulation program for particle collisions at very high energies in particle accelerators.-External links:* *...

 and HERWIG for event generation. Depending on specific properties of the particle decay

Particle decay

Particle decay is the spontaneous process of one elementary particle transforming into other elementary particles. During this process, an elementary particle becomes a different particle with less mass and an intermediate particle such as W boson in muon decay. The intermediate particle then...

 that physicists are interested in, they may desire to use a certain program for these tasks, but before the Les Houches Accords, there was no general interface for communicating between the programs. This enables physicists to choose more freely between different programs. The Accords also make it easier to generate probability density function

Probability density function

In probability theory, a probability density function , or density of a continuous random variable is a function that describes the relative likelihood for this random variable to occur at a given point. The probability for the random variable to fall within a particular region is given by the...

 cross section

Cross section (physics)

A cross section is the effective area which governs the probability of some scattering or absorption event. Together with particle density and path length, it can be used to predict the total scattering probability via the Beer-Lambert law....

s for events

Event (particle physics)

An event in particle physics describes one set of particle interactions occurring in a brief span of time, typically recorded together. At modern particle accelerators this refers to the interactions that occur as a result of one beam crossing inside a detector....

.

Sources

• The original paper:
• General overview:
• General information: