Les Houches

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.