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W,Z precision measurement October WS preparation
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Europe/Zurich
31/S-027 (CERN)
W,Z precision measurement October WS preparation (12 Sep 2012)
- The topic of how theoretical predictions are computed was discussed and it was agreed this is an important item we should discuss in the working group (EWK parameters and scheme, program versions, ecc.). It was decided that at next meeting each experiment should report the details about its own calculations so that a careful comparison can be done.
- In view of the LPCC October workshop.
- It was agreed that we are going to have a monthly meeting, and the next one is tentatively scheduled for the
- People: Max, Alberto, Jan, Adrian, Maarten (ATLAS), Simone, Katarina (LHCb).
- The scope of the documentation was discussed. It has been agreed that an internal note shared among the three collaborations is required to keep track of all the details for extrapolation/correction factors and related uncertainties which are useful to compare as an internal cross-check before releasing overlay-plots. A public note will then be made out of the internal one, containing only the information we want to be public.
This is going to be only overlay-plots and not the extrapolation factors to avoid others to use them to manipulate our measurements: the originally published results are those and only those to be used to improve theory. Corrections factors for different lepton definitions could be part of this document if not already published along with original data.
- The possibility of sharing preliminary results on MC corrections factors, to be shown and discussed in the informal meetings of this working group was discussed and recognised as a valuable option. Need to verify if this is fine with respect to the internal approval procedures of each collaboration (should be).
- The comparisons of measurements in different fiducial volumes was discussed.
--- Integrated cross-sections compared in the same fiducial volume. Could be interesting only for ATLAS-CMS given the large eta-extrapolation that would be required for LHCb results. To be discussed further with CMS colleagues (not present at the meeting).
--- Overlay of differential results for Ws (W charge asymmetry, W+ and W- absolute cross-sections). ATLAS already provided extrapolated measurement for W charge asymmetry in overlay with CMS and LHCb results. LHCb is preparing the correspondent overlay adding the mT and MET cuts. Status of CMS activity to be verified. Same exercise to be worked out for W+ and W- cross-sections.
--- Overlay of the Z rapidity measurements. It was agreed that LHCb will get the corrections to extrapolated to full eta in order to overlay with ATLAS (corrections expected to be mainly for |yZ|<3). CMS measurement is normalised so another iteration is required with CMS colleagues to see if an absolute version can be provided.
- It has been agreed that all the extrapolation factors need to be provided with an estimation of the theoretical uncertainties. The strategy adopted is the one proposed at last LPCC meeting, namely 3 sources: PDFs, PS-hadronisation and ME uncertainties. MCs to be used are: Powheg-Pythia (central value), Powheg-Herwig and MC@NLO for systematics (all based on CT10 PDFs). The availability of these MC samples in each collaboration was not discussed, this is a potential issue that need to be verified asap.
- Lepton definitions: Born, Bare, Dressed. Some correction factors are already published (references to be circulated). Numbers to be compared. References from each collaboration to be shared so that numbers that are already public can be compared and eventually be material for October LPCC status report.
- The topic of how theoretical predictions are computed was discussed and it was agreed this is an important item we should discuss in the working group (EWK parameters and scheme, program versions, ecc.). It was decided that at next meeting each experiment should report the details about its own calculations so that a careful comparison can be done.
- In view of the LPCC October workshop.
The status report should then focus on available results (W charge asymmetry and published corrections for different lepton definitions) since it was agreed that due to lack of manpower it's quite hard that new results will be available in time. Of course new/refined items for discussion (e.g. theoretical predictions) will be reported too.
- Longer time-scale activities were discussed. Overlay of boson pT measurements (ATLAS and CMS) and
of DY mass spectrum measurements. To be discussed further at next meeting with also CMS colleagues.
- It was agreed that we are going to have a monthly meeting, and the next one is tentatively scheduled for the
week after LPCC meeting, Wednesday Oct. 17th. 11-13. It's now CMS turn to organize that meeting.
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