[Rivet] Born and dressed level in Rivet

[Ulla Blumenschein]

Hi Tim,

I still think it would be useful to have a comparative study by that
time.  I am without real internet connection this week and can not
help with this.  I really like the new method but without input data I
fear it won't be useful to discuss the proposal.
I personally don't know anyone who is using the dressed-all
definition, so it might be useful to have a list of analyses, since
you state it is commonly used.

Best,
Ulla

On Wed, Oct 9, 2013 at 3:51 PM, Tim Martin <tim.martin at cern.ch> wrote:
> Hi all,
>
> I have tried to summarise this discussion for next weeks ATLAS
> Higgs+Top+SM unfolding meeting.
>
> Try and make everyone aware of the little problem and how we're
> proposing to fix it.
>
> For ATLAS people, the slides are on
> https://indico.cern.ch/conferenceDisplay.py?confId=273212
>
> Cheers, Tim.
>
> On 9 October 2013 07:34, Ulla Blumenschein <ublumenschein at googlemail.com> wrote:
>> Hi Andy,
>>
>>
>> On Tuesday, October 8, 2013, Andy Buckley wrote:
>>>
>>> On 08/10/13 15:52, Ulla Blumenschein wrote:
>>> > Hi David,
>>> >
>>> >
>>> > On Tuesday, October 8, 2013, David Grellscheid wrote:
>>> >
>>> >     Hi Ulla,
>>> >
>>> >         We didn't identify the FSR photons experimentally but we
>>> >         unfolded to a
>>> >         reference where a  lepton was dressed with the respective
>>> > technical
>>> >         FSR implementation.
>>> >
>>> >
>>> >     I'm sorry, I don't understand fully what you did there. The
>>> >     "reference" you refer to is a certain MC run with a certain setup?
>>> >     In that case isn't your unfolding dependent on that MC author's
>>> >     choice of where to put photon emissions in that specific version of
>>> >     the code?
>>> >
>>> >
>>> > we depend on at least three authors of three generators' choices.
>>> >
>>> >
>>> >         We checked that we get a similar correction in the
>>> >         standard generators, (pythia, herwig, sherpa..).
>>> >
>>> >
>>> >     That doesn't mean it makes physical sense to split FSR from ISR
>>> > photons.
>>> >
>>> >
>>> > No of course not. We are talking here merely in terms of dominating and
>>> > negligible contributions to the collinear photon radiation.
>>>
>>> Recent QED modelling studies by Steve Muanza showed that there is a
>>> substantial "ISR" QED structure in Z->l+l- events only in Pythia8 (with
>>> or without Photos++ to produce the QED FSR). We didn't see the same
>>> structure in invariant masses for Sherpa or Herwig++. Was Py8 included
>>> in the three models used to derive the dressing correction?
>>>
>>
>> No, only Pythia6 so far.
>>
>>>
>>> In Steve's study there was still relatively little difference between
>>> that and other models once observables were constructed from IR-safe
>>> clustering (and there we/he explicitly excluded photons from hadron
>>> decays as discussed here), so I suspect that as suggested the FSR will
>>> turn out to be dominant.
>>>
>>> If there is no significant distinction between the two approaches, then
>>> this sort of separation of photon origins is, I think, preferable to the
>>> dependence so far on particular generators' schemes for representing QED
>>> FSR. It's a lot more portable (unless a generator standard
>>> representation is agreed upon -- good luck!) and I think physically less
>>> contentious.
>>>
>>
>> I personally agree.
>>
>> Cheers, Ulla
>>
>>>
>>> Cheers,
>>> Andy
>>>
>>> --
>>> Dr Andy Buckley, Royal Society University Research Fellow
>>> Particle Physics Expt Group, University of Glasgow / PH Dept, CERN
>>
>>
>>
>> --
>> /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
>>     Ulla Blumenschein
>>     II Physik, Uni Goettingen
>>     Friedrich-Hund-Platz 1, D01.110
>>     phone: 0049-551-397645
>> /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
>
>
>
> --
> -+-+-+-+ Tim Martin +-+ ATLAS +-+-+-+-
> Room 448A, University of Warwick, CV47AL
> Tel: (+44) 0-24761-51769
> Web: http://Tim-Martin.co.uk



-- 
/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
    Ulla Blumenschein
    II Physik, Uni Goettingen
    Friedrich-Hund-Platz 1, D01.110
    phone: 0049-551-397645
/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/