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2015:groups:sm:wmass [2015/06/04 14:24]
luca.perrozzi [Theory uncertainties for W mass measurement]
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 ======
  
-Workshops ​are being organized ​to discuss ​these items+//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   * 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   * CERN, Oct 2014 https://​indico.cern.ch/​event/​367442/​other-view?​view=standard#​all
-==== PDF uncertainties ==== 
  
 +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 ==== ==== 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)
2015/groups/sm/wmass.1433420699.txt.gz · Last modified: 2015/06/04 14:24 by luca.perrozzi