First tuning of HERWIG/JIMMY to ATLAS data

This note describes the first systematic tuning of the HERWIG generator to ATLAS data, with the JIMMY model for multiple parton interactions. We present a new set of HERWIG/JIMMY tunes for the MRST LO∗, CTEQ6L1 and CTEQ6.6 PDFs, collectively titled "AUET1". The MC09 HERWIG/JIMMY tuning was taken as a starting point for the AUET1 tunes, but important methodological modifications have been made, in particular use of more tuning parameters. In the tuning of the regularisation scale for multiple scattering, an energy-dependence ansatz similar to the one found in the PYTHIA 6 generator has been used. While CDF data has been included in the fits, the weighting is strongly biased towards ATLAS underlying event data, particularly at 7 TeV.