lhe

Lhe refers to the Les Houches Event format, a standard for representing simulated particle collision events. It is commonly implemented as the Les Houches Event File (LHEF) and is used to exchange event data between Monte Carlo generators and downstream tools such as parton showering, hadronization, and detector simulation. The format was developed as part of the Les Houches Accords (LHA) to promote interoperability among different software components in high-energy physics.

The LHE format is a plain-text, structured file that typically begins with a header describing the generator, center-of-mass energy, parton distribution functions, and scale choices. This is followed by a series of event blocks. Each event block lists all particles in the event with attributes such as PDG ID, status code, mother indices, color flow tags, and four-momenta (and sometimes mass). The information enables a complete reconstruction of the event kinematics and the relationships between particles.

LHE files are widely produced by matrix-element generators such as MadGraph, POWHEG, aMC@NLO, and Sherpa, and are then passed to showering and hadronization programs like Pythia and Herwig, or to analysis frameworks such as Rivet. The format is valued for its generator-agnostic structure, facilitating end-to-end simulation pipelines from event generation to detector-level analysis.

Limitations include its emphasis on leading-order event information in many setups and the potential for large file sizes for extensive samples. Extensions and conventions exist for including multiple weights, scale variations, or parton-shet information, but users should consult specific tool documentation to ensure compatibility.