The LHE file format has been around since 2006 and has been very successful. At the Les Houches workshop in 2009 an update was suggested, mainly to improve the handling of NLO and matching/merging. The proposal was published in the proceedings (arXiv:1003.1643), but have never really been properly used. Nevertheless, some shortcomings has been noticed and some superflous features have been identified.

In the discussions at this years workshop some ideas on how to better specify weights were suggested, and also some other new features were suggested and old features were suggested to be dropped. Here is a summary of what was discussed.

Here is a list of XML-tags that were introduced in 2009 with comments on what should be with them, and also some suggested new tags.

• <generator> There should be more than one generator tag with a version attribute allowed in the <init> section.
• <xsecinfo> Unchanged
• <cutsinfo> Unchanged
• <procinfo> Unchanged
• <mergeinfo> Should be removed
• <weightinfo> New tag added to define which weights are given the <weights> tag (see below) in each event. The attributes are (also other attributes are allowed, but they do not have a standardized meaning):
  • name Should follow the convention proposed for HepMC
  • muf The factor multiplying the nominal factorization scale for the event for the given weight
  • mur The factor multiplying the nominal renormalization scale for the event for the given weight
  • pdf The LHAPDF code corresponding to the given weight

• <weightgroup> Can be used to group together <weightinfo> tags. The only attribute is
• name A string which will be combined with the name attribute of the included <weightinfo> tags to give the HepMC weight names.