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2017:groups:tools:lhe

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LHE v3 (and MC technicalities) sub working group

Scales

It has been claimed that the shower starting/veto scales need to be more flexible. Something like that is already included in the Pythia8 which interprets eg. an attribute pt_start_3=“42” in a <scales> tag as the starting scale of particle 3. These attributes are in addition to the mups defined in the current version together with mur and muf.

After the discussions on Saturday it was agreed that much of the complications of scale settings for individual particles must in any case be handled through specialized hooks into the parton shower, the interface of which is determined by the individual parton shower, with different implementations done by the respective matrix element providers. For this to work smoothly there is nevertheless a need to formalise the information that goes into the event file.

The suggestion is to allow subtags named <scale> with the content specifying a special scale in GeV. This tag can have a number of attributes:

  • stype (mandatory) specifies the type of scale intended. The allowed values are currently “veto” for a veto scale for a parton shower emission, and “start” for the starting scale of the parton shower.
  • p specifies for which particle the scale applies, given by an integer where '1 is the first particle in the HEPEUP block. If two integers are given it should be interpreted as the emission from the first in a “dipole” connecting to the second. If not specified this scale applies to all particles that do not have a specific <scale> tag.
  • etype specifies the emission type for which the scale should be applied. This should be a list of integers corresponding to the PDG code of the emitted particle. Short-hands allowed are “QCD” corresponding to any quark or a gluon, and “EW” corresponding to any lepton or electro-weak gauge boson. If not supplied, the scale applies to any emission.
2017/groups/tools/lhe.1497097563.txt.gz · Last modified: 2017/06/10 14:26 by leif.lnnblad