[Rivet] Partonic top support?

[Andy Buckley]

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