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2015:groups:sm:wmass [2015/06/04 14:19] luca.perrozzi |
2015:groups:sm:wmass [2015/06/05 17:52] luca.perrozzi |
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====== Theory uncertainties for W mass measurement ====== | ====== Theory uncertainties for W mass measurement ====== | ||
+ | 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 | ||
+ | |||
+ | Vidyo link to connect from outside Les Houches: http://vidyoportal.cern.ch/flex.html?roomdirect.html&key=v5QzoUCLTk5TMhuubxqNMEQe7j0 | ||
==== PDF uncertainties ==== | ==== 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 ==== | ==== 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 ==== | ==== 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 ==== | ==== 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 | ||
+ | |||
+ | {{:2015:groups:sm:wmass_les_hoches.jpg?300|}} | ||
+ | |||
+ | 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 ==== | ==== 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) |