[Rivet] Born and dressed level in Rivet

[Andy Buckley]

Hi Ulla, all,

I've discussed this a bit with Daniel Froidevaux and think that it would
make sense for us to at least add a flag to the ClusteredPhotons tool in
Rivet to exclude photons which come from hadron decays. Taus are a bit
of a borderline case, but that does not affect (current) EW measurements.

This is not *exactly* the same definition, but I think that "only
photons from W/Z" is hard to implement in a generator-unspecific way.

Maybe Frank Siegert wants to comment more on this proposal to use the
fromDecay() function in ClusteredPhotons, since he did most of the
detailed work to put these W/ZFinders and related classes together.

Re. the Born comparisons, I believe that the ATLAS W/Z analyses written
so far *don't* compare to the Born-level results, since there *isn't* a
generator-portable way to write them. I remember removing a
generator-specific code along those lines in a previously submitted
analysis for that reason: it's fine for ATLAS-internal versions of
analyses but won't go into the public Rivet library.

Hope that helps,
Andy

PS. For those who care, if we agree that that is a reasonable route, I
propose that the exclude-decay-photons functionality would go into Rivet
2.0.1 or 2.0.2. The exact version depends on the extent to which we want
to separate different types of change -- 2.0.1 might just be adding some
"queued" analysis codes, or it could be a combination of that and some
definition changes. The numbering does not really reflect anything about
the timescales! But note that we'll only be making this change in the
Rivet 2 series -- 1.x is in "maintenance mode".


On 03/10/13 14:51, Roman Lysak wrote:
> 
>  Hi Ulla,
> 
> I think the Rivet authors are better to replay to your questions so I'm
> cc-ing this to them.
> Could anyone address Ulla's questions?
> 
> Cheers,
>   Roman
> 
> On 10/03/2013 12:25 PM, Ulla Blumenschein wrote:
>> Hi Roman,
>>
>> we have currently a discussion in SM about how to synchronize  the
>> Atlas internal definition of dressed leptons with the Rivet
>> implementation.
>> Currently in SM, we sum all photons emitted from the W/Z decay
>> products whereas Rivet sums all photons.
>> With the extreme phase spaces which we access with 8TeV there are
>> differences up to percentage level between these definitions due to
>> pi0 decays from hadronic activity close to leptons.
>>
>> Is it possible to  implemet an alternate Z finder which can
>> discriminate photon sources? I understand that this might be against
>> the philosophy of Rivet (MC independence). Or are there other
>> problems?
>>
>> Also the born level Z finder is not completely clear to me. I assumed
>> so far that the born level is defined by different status codes in
>> different MC generator, so how does Rivet handle this issue?
>>
>>
>> Many thanks in advance,
>> Ulla
>>
>>
>>
>>
>>
>> On Sun, Sep 15, 2013 at 7:46 PM, Roman Lysak <lysak at fzu.cz> wrote:
>>>   Hi Ulla,
>>>
>>>
>>>
>>> On 09/12/2013 06:51 PM, Ulla Blumenschein wrote:
>>>> Hi Roman,
>>>>
>>>> Could you explain how we define Born and dressed in a generator
>>>> independent way in Rivet?
>>>
>>> it depends on the object type.
>>> For example, for Z boson (similarly for W boson), you can specify
>>> whether to
>>> add photons (next to last one parameter in the constructor below) in
>>> a given
>>> radius (2nd next to last one parameter) around the leptons from Z
>>> decay to
>>> the Z boson 4-momentum.
>>>
>>>        //fiducial phase space + born level
>>>        ZFinder zfinder_mu(-2.4, 2.4, 20, MUON, 66.0*GeV, 116.0*GeV, 0.1,
>>> false, false);
>>>        addProjection(zfinder_mu, "ZFinder_mu");
>>>
>>>        //for combined cross-sections (combined phase space + dressed
>>> level)
>>>        ZFinder zfinder_comb_mu(-2.5, 2.5, 20, MUON, 66.0*GeV,
>>> 116.0*GeV, 0.1,
>>> true, false);
>>>
>>>
>>> Sorry for late response.
>>>
>>> Cheers,
>>>    Roman
>>>
>>>
>>>
>>>> Cheers, Ulla
>>>>
>>>> /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
>>>>       Ulla Blumenschein
>>>>       II Physik, Uni Goettingen
>>>>       Friedrich-Hund-Platz 1, D01.110
>>>>       phone: 0049-551-397645
>>>> /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
>>>
>>
>>
> 
> _______________________________________________
> Rivet mailing list
> Rivet at projects.hepforge.org
> http://www.hepforge.org/lists/listinfo/rivet


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