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2015:groups:sm:wmass [2015/06/04 14:27] 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 ====== | ||
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+ | //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.// | ||
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Andre David, Fulvio Piccinini, Luca Perrozzi, Mariarosaria D'Alfonso, Gigi Rolandi, Josh Bendavid, | Andre David, Fulvio Piccinini, Luca Perrozzi, Mariarosaria D'Alfonso, Gigi Rolandi, Josh Bendavid, | ||
Alessandro Vicini, Carlo Oleari, ... | Alessandro Vicini, Carlo Oleari, ... | ||
- | Workshops are being organized to discuss these items | + | [[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]] |
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+ | 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 | ||
Starting point: theory uncertainties as defined in Tevatron analyses likely to be very aggressive | Starting point: theory uncertainties as defined in Tevatron analyses likely to be very aggressive | ||
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+ | 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? | ||
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+ | Summary of the discussion | ||
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+ | {{:2015:groups:sm:wmass_les_hoches.jpg?300|}} | ||
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+ | 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? | ||
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+ | Do we need to consider the propagation of UE uncertainties? | ||
==== Correlations ==== | ==== Correlations ==== | ||
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+ | PDF, Underlying event, QCD soft scale resummation and perturbative scales, polarization uncertainties are correlated. | ||
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+ | How to handle them properly? | ||
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+ | Would it be possible to remove datasets from PDF "on demand"? | ||
+ | (for instance, no W charge asymmetry) |