[Rivet] Rivet and covariance matrices etc

[Andy Buckley]

Hi Hannes,

This is something we're very interested in, and I would be happy to
participate in general although am indisposed at the critical time tomorrow
(maybe someone else from the "team" can join?) We're also following this up
in the context of other measurements and searches.

But I think there's a misunderstanding in saying that Rivet uses
uncorrelated data uncertainties. Other than for plotting cosmetics, Rivet
doesn't use data uncertainties at all: they only come in downstream when
computing goodness of fit or other likelihood measures. Do you mean that
the reference data files in Rivet do not separate error classes or encode
correlations?: this is true, but not fundamental. What's needed is parallel
development for a) HepData to output the correlation breakdown in a
standardised way which can be automatically identified with the relevant
histograms, and b) for YODA's Scatter types to support multiple error bars:
the latter work is underway.

Happy to discuss this more, because it's really become critical for a lot
of physics exploitation.

Andy


On 3 May 2018 at 07:14, Hannes Jung <hannes.jung at desy.de> wrote:

> Dear Rivet developers, Andy et al
>
> in the LHC EW working group on jets and vector-bosons we are starting
> to compare measurements from the different LHC experiments to see,
> whether the measurements are consistent.
> We start just doing a comparison using the Rivet plugins with one or two
> well defined theory calculation.
>
> At the moment, the experimental uncertainties (stat and syst) in Rivet are
> treated as uncorrelated uncertainties, while for a detailed comparison
> with theory
> also the correlations and the different correlated systematic uncertainties
> should be treated.
>
> Is there already some discussion under the Rivet developers, to include
> those
> uncertainties, or if not, would you be interested to join the discussion
> in our
> working group on how to consistently define the correlation matrices
> between the
> experiments, such that they can be used also within Rivet ?
>
> We will have a first meeting of the Jets + Bosons WG on Friday, tomorrow:
>
> https://indico.cern.ch/event/721044/
>
> Your participation would be very welcome
>
>
> Best
>
> Hannes
>
> ***********************************************************************
> Hannes Jung
> Email: Hannes.Jung at desy.de
> mobile :+49 40 8998 93741
> http://www.desy.de/~jung
> Tel: +49 (0) 40 8998 3741
> Fax: +49 (0) 40 8994 3741
> DESY, CMS 01B/02.213
> Notkestr.85 <https://maps.google.com/?q=Notkestr.85&entry=gmail&source=g>,
> 22603 Hamburg, FRG
> ***********************************************************************
>
>
>
>
>
>


-- 
Dr Andy Buckley, Lecturer / Royal Society University Research Fellow
Particle Physics Expt Group, University of Glasgow
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