[Rivet] PartonicTops with em shower

[Markus Seidel]

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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>
>