Andre David, Fulvio Piccinini, Luca Perrozzi, Mariarosaria D'Alfonso, Gigi Rolandi, Josh Bendavid, Alessandro Vicini, Carlo Oleari, …

Goal: discuss the relevant theory uncertainties for W mass measurement, trying to come up with some operational definitions, along the lins of the workshops organized recently

• Florence, Oct 2014 https://indico.cern.ch/event/340393/other-view?view=standard#all
• CERN, Oct 2014 https://indico.cern.ch/event/367442/other-view?view=standard#all

Starting point: theory uncertainties as defined in Tevatron analyses likely to be very aggressive

Tevatron quotes a single set (CTEQ). Which dataset to use? So called MetaPDF? What about removing datasets from the PDF fits?

Thorough comparisons performed by the Pavia group, leading to the understanding of the differences between Pythia8 and PHOTOS (order of 10 MeV), and the effect of including or excluding NLO EWK contributions (also sizeable)

Drell Yan polarization has been measred both at Tevatron and LHC, see for instance the recent CMS paper at 8 TeV http://arxiv.org/abs/1504.03512 On one side one can “tune” some POWHEG parameters to match data on the Z case. On the other side is not clear how universal these parameters are from Z to W and which uncertainty should be assigned for this extrapolation.