Les Houches

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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:

parton shower –> hadronisation –> pre-hadronisation W decay –> mass optimisation post-hadronisation particle decay –> vertexing etc

genvertex.ID()

• 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 lepton.
• 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.

NB any shower after a hadronisation is ignored, and the hadrons from it are flagged as being produced in a hadron decay.

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“MUF* MUR* 10801 20123” (last number is the PDF ID)

names for each weight.