[Rivet] PartonicTops with em shower

[Andy Buckley]

Great. I think (should re-check) that we restrict the ancestry checks so 
particles with status 1 or 2, so 4 (beam particles) and 3, 11, etc. 
(hard process) should not accidentally trigger it.

Andy


On 09/05/17 10:25, Markus Seidel wrote:
> Hi Andy,
>
> thanks for the update!
>
> The `xor` in the hadronic would only be needed for the counting/modulo
> approach, to account for photon->(tau tau)->(e mu).
> So the !hasAncestor(PHOTON) should be fine, unless we go to e+e-
> collider studies... :s
>
> Cheers,
> Markus
>
>
> Am 08.05.2017 um 17:10 schrieb Andy Buckley:
>> Hi again Markus,
>>
>> I finally got time to think about this, and I think the
>> !p.hasAncestor(PHOTON) route is preferable to modulo-2 arithmetic.
>> Perhaps/probably in time we will come across another generator which
>> breaks this heuristic, but it seems pretty reasonable to me.
>>
>> I think with this, there is no need for the prompt_e && !prompt_mu type
>> of logic, but what do you mean by "for the hadronic part there needs to
>> be an `xor`"? I know what an xor is, of course, but am not sure which
>> line you're referring to, or whether it still applies in the
>> p.hasAncestor() approach. I think everything should be ok (fingers
>> crossed!) with just the hasAncestor(PHOTON) check, but please let me
>> know.
>>
>> Having just done this and a bunch of other fixes, I'm hoping that we can
>> get the backlog of analyses integrated and go for a Rivet 2.5.4 release
>> in the next week or so.
>>
>> Cheers,
>> Andy
>>
>>
>> On 20/04/17 10:04, Markus Seidel wrote:
>>> Dear Rivet authors,
>>>
>>> as you know PartonicTops projection is important for many CMS top
>>> analyses at 8 TeV :s
>>> People stumbled upon the following problem: If there is a photon->l+l-
>>> within the shower, the top mother is flagged as leptonic.
>>>
>>> Maybe we can replace
>>>> const bool prompt_e/mu = any(...);
>>> by
>>>> const bool prompt_e/mu = (count(...) % 2);
>>> and
>>>> if (prompt_e/mu && (...)) return true;
>>> by
>>>> if (prompt_e/mu && !prompt_mu/e && (...)) return true;
>>>
>>> For the hadronic part there needs to be an `xor` between `prompt_e` and
>>> `prompt_mu` at least...
>>>
>>> If you prefer to not mess around with the logic, we may just require
>>> that the lepton does not have any photon mother...
>>>> ... && !p.hasAncestor(PID::PHOTON)
>>>
>>> It seems to be hopeless to account for all possibilities of a full weak
>>> shower but at least the case of em shower is very common (at least in
>>> Pythia 8?).
>>>
>>> Cheers,
>>> Markus
>>> _______________________________________________
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>>> Rivet at projects.hepforge.org
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>>
>>


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