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--- 2015:groups:sm:wmass [2015/06/04 14:13]
luca.perrozzi created
+++ 2015:groups:sm:wmass [2015/07/14 08:28] (current)
philippe.gras Added instructions for CERN account
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-Theory uncertainties for W mass measurement
+====== Theory uncertainties for W mass measurement ======
+//If you are interested in contributing please subscribe to the [[https://e-groups.cern.ch/e-groups/EgroupsSearch.do?searchValue=houches-2015-topics-sm-wmass|mailing list]]. You will be asked to log in with your CERN account. If you don't have a CERN account, please fill [[https://account.cern.ch/account/Externals/RegisterAccount.aspx|this form]] to create a lightweight account.//
+Andre David, Fulvio Piccinini, Luca Perrozzi, Mariarosaria D'Alfonso, Gigi Rolandi, Josh Bendavid,
+Alessandro Vicini, Carlo Oleari, ...
+[[http://phystev.cnrs.fr/wiki/?ns=2015%3Agroups%3Asm%3A&image=2015%3Agroups%3Asm%3Aw_mass_at_les_houches.pdf&do=media|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
+  * 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 ====
+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
+{{: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 ====
+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)

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