Proposed updates for HepMC event record

GenRun

There is a need to store the names and version numbers of all generators used in producing an event. Propose to define a GenRun object to contain cross section (GenCrossSection) and other run-level quantities discussed below. Each GenEvent should link to the GenRun.

Generator names and versions

Add string array to Genrun with pairs of strings:

“generator name” “generator version”

All generators used in the production should be listed, with full version numbers.

Vertex ID

The GenVertex.id() is not currently used/specified. We propose to define six codes:

• 0 – undefined (no information)
• 1 – Matrix Element vertex (i.e. the hard process which defines the PDF arguments). (Same as signal vertex)
• 2 – secondary partonic scatters (useful for studies of MPI jet production, e.g. for suppressing jets from MPI while retaining the low pT tail of the underlying event, as in this paper.
• 3 – Hard decay (prehadronisation) e.g. of W, H, Z, t. Useful e.g. for optimisation studies of mass resolution
• 4 – parton shower (including QED radiation) Useful for e.g. identifying g→bb splitting probability; ME/PS matching studies; identifying photons for dressing leptons. NB any parton shower after a hadronisation is ignored, and the hadrons from it

are flagged as being produced in a hadron decay.

• 5 – primary hadron formation Useful for e.g redoing hadroisation, applying BEC corrections, studying/tracking decay chains.
• 6 – hadron, tau and muon decays

We propose that 10-99 be reserved for generator-specific types.

Weight names

Some standardisation of weight names is desirable:

“MUF* MUR* PDF10801 PDF20123” (last numbers are the LHAPDF/PDFLIB unique PDF member IDs)

names for each weight, to go in the GenRun, linked to GenWeightContainer?