[Rivet] Born and dressed level in Rivet

[Tim Martin]

Hi Jon,

Yes for our tuning distributions we want to avoid this grey area.

However the issue here is that we have many measurement which did use
only identified FSR photons in their dressing cones. If it can be
shown that for our common generators, this is close enough to the
non-hadronic-decay-and-tau-photons definition as to be compatible over
all the Z phase space then we get a more accurate Rivet class for our
published data and a tighter definition of Dressed to use in the
future.

Cheers, Tim.



On 7 October 2013 10:45, Jon Butterworth <jmb at hep.ucl.ac.uk> wrote:
> Dear all,
>
> Happy this seems to be solved (or being solved). Since I've also been
> involved with some discussions with Daniel, Ulla, Tim & others on this, I
> just wanted to make one point here.
>
> It makes some physical sense to separate photons from hadronic decays (and
> e.g. tau decays) from "prompt" ISR/FSR photons. The latter are essentially
> emitted at the matrix element, whereas the timescales for hadronisation or
> tau decay are much longer. Whether it make sense to sum of all photons from
> pi0 or then becomes to some extent a matter of choice/taste and may depend
> on how the calibration etc is really done.
>
> However, try to get "FSR only" photons or "photons from the W or Z decay
> products only" is not physical. Photon emission via ISR or from the
> propagator happen on the same timescale as FSR and are in principle not
> separable (though in many generators they are separated as a decent
> numerical approximation in most of phase space).
>
> So a definition which excludes photons from hadrons & taus, as proposed by
> Andy I think, is good. A definition which only includes FSR photons is not.
> (For our current generators I expect little or no difference, but it is
> important that Rivet and ATLAS do it right and do it the same!)
>
> Cheers,
> Jon
>
>
> On 03/10/2013 17:39, Ulla Blumenschein wrote:
>>
>> Hello Oleg,
>>
>> would be great, if you could test the new proposed dressed-definition
>> vs the FSR-only option, just to make sure we don't miss anything
>> unexpected. But  I second Tim, currently I can also not think of any
>> further substacial contribution. (Have to cross check some slides
>> which Evelin had shown a year ago..)
>>
>> Cheers, Ulla
>>
>
> --
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Prof. Jonathan Butterworth,              http://www.hep.ucl.ac.uk/~jmb/
> Head, Physics and Astronomy Department            Tel: +44 20 7679 3444
> University College London                 Gower St, London WC1E 6BT, UK
> ATLAS, CERN                                       Tel: +41 22 76 72340
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



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