wiki:FAQ-Matching-2
Last modified 6 years ago Last modified on 04/06/12 16:33:02

Yes, you can, the shape of distributions are kept. However the normalization change. In the case you use scalefact and alpsfact in the run_card, this change of scales can be compensated by using the parameters $PARP(64)$ and $PARP(72)$. Let's see this in more details:

For ME, the parameters are as follows:

  • scalefact multiplies the (linear) factorization scale and
    • for non-matched production also the renormalization scale since those are set equal in this case
    • for matched production the renormalization scale of QCD vertices that are not considered "extra jet" vertices
  • alpsfact multiplies the renormalization scale for extra jets for matched production only.

For Pythia, the parameters are:

  • For spacelike showers: PARP(64) is factor of $K_{T}^{2}$ (note squared, so alpsfact=2 corresponds to PARP(64)=4)
  • For timelike showers: $\Lambda_{QCD}$ is given in PARP(72), so this value should be multiplied by 0.5 when alpsfact is 2, and by 2 when alpsfact is 0.5. The default value is 0.25 !GeV.

-- Main.SimonDeVisscher - 02 Mar 2009

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