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2015:groups:sm:wmass

Theory uncertainties for W mass measurement

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

Presentation at Les Houches

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

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

Vidyo link to connect from outside Les Houches: http://vidyoportal.cern.ch/flex.html?roomdirect.html&key=v5QzoUCLTk5TMhuubxqNMEQe7j0

PDF uncertainties

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

EWK uncertainties

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)

Polarization

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.

Boson pT

QCD non perturbative scale choice at Tevatron driven by fit on Z data.

QCD perturbative scale variation not taken into account at Tevatron. Fully uncorrelated scale variation would lead to several tens of MeV uncertainty. Is it possible to use Z data to (at least partially) constraint the W pT?

Summary of the discussion

Apart from NLO+PS combinations like POWHEG+Pythia, how to take into account higher order corrections from codes like the NNLO+NNLL DYRES? Reweighting? Tuning?

Do we need to consider the propagation of UE uncertainties?

Correlations

PDF, Underlying event, QCD soft scale resummation and perturbative scales, polarization uncertainties are correlated.

How to handle them properly?

Would it be possible to remove datasets from PDF “on demand”? (for instance, no W charge asymmetry)

2015/groups/sm/wmass.txt · Last modified: 2015/07/14 08:28 by philippe.gras