Monte Carlo Tuning for Hadronic States in e+e- Collisions

We perform two tunes of the SHERPA Monte Carlo generator for the simulation of
annihilation of e+e- to hadrons using the publicly-available LEP analyses in
Rivet.  In each of these tunes, we generate events at a center-of-mass energy
of 91.25 GeV with matrix elements for final states containing up to six
partons.  In the first, ``LO'' tune, all final states are generated using
leading-order matrix elements; in the second, ``NLO'' tune, states with up to
four partons are generated with next-to-leading order matrix elements using
BlackHat, while states with five and six partons are generated at leading
order.  The tunes are accomplished using Professor, and comparisons with
unfolded LEP1 and LEP2 data are produced with Rivet.  We also compare the data
with events generated with KK2f interfaced to PYTHIA using a LEP-era tune.  We
find that both SHERPA samples show improvement relative to KK2f for
observables related to multi-jet final states, which are of interest for
analyses at future lepton colliders.  At the same time, all three samples
produce comparable results for event-shape variables.