[Rivet] Partonic top support?

[Frank Siegert]

Hi all,

I am with Andy and Hannes here, in the sense that we are not a moral
instance but rather a tool. It is not about maximising the number of
analyses, but about letting the community decide on whether they want
to use partonic analyses in certain cases. I don't even see the need
to introduce any technical (compile flag) barriers, but would be
confident that the community of Rivet users will on its own decide to
not use such analyses as they will never really be able to know what
exactly has been "measured".

Cheers,
Frank

On 20 June 2016 at 22:23, Andy Buckley <andy.buckley at cern.ch> wrote:
> Hi all,
>
> As we all know, we *massively* favour writing Rivet analyses based on
> post-hadronisation particles. And that approach has had increasing purchase
> in the experiments, with the likes of fiducial "pseudo-top" measurements
> increasing.
>
> But for top analyses in particular, there are many useful analyses that rely
> on parton-level tops. For example, we were sent a CMS analysis a few months
> ago which included a parton-top finder digging around in HepMC... and I've
> not included it in the official analysis collection because it doesn't fit
> with our philosophy. I don't need to repeat the many reasons that this
> approach is suboptimal, but the measurements will continue to be made, there
> is still useful physics in them, and it seems unfortunate for Rivet to not
> be able to include them.
>
> I wonder if this situation is sufficiently nuanced that we should swallow
> our distaste and provide an official "DodgyPartonFinder" to avoid repetition
> of that fragile code? I'd want to make it print out some warning messages to
> flag up the dangerous unportability, and clearly mark as dangerous in the
> .info file of any analysis that uses it... but it's still better than
> needing to maintain n *different* implementations of dirty HepMC-walking
> parton finder algorithms.
>
> I'm convinceable either way, but (as having initiated this thread suggests)
> I'm leaning toward thinking that analysis coverage and pragmatism are
> sufficiently valuable to allow a compromise... in the case of top physics.
>
> Thoughts & feelings? I expect controversy -- please deliver ;-)
>
> Andy
>
> PS. As Rivet v3 approaches we also need to develop a plan for how future
> analysis distribution, separated from the core library, can work without
> destroying the quality control that we've made a key feature. Maybe we'll
> grasp that nettle in person in September, but I just note here that we could
> have several "grades" of approval, and hence put partonic top top analyses
> in a "use with caution" category.
>
> --
> Dr Andy Buckley, Lecturer / Royal Society University Research Fellow
> Particle Physics Expt Group, University of Glasgow
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