[Rivet] Check CMS double parton scattering and 4 jet correlations codes

[Andy Buckley]

Hi Lars and Albert,

I've integrated the CMS double parton scattering and 4 jet correlations
analysis codes that you supplied into the Rivet trunk, aiming for a new
release next week, but there were several opportunities for code tidying
and minor fixes along the way which I took since it'll make maintenance
easier for us in the long run.

I don't have easy access to an MC setup that could be used to revalidate
the analysis codes, but the changes were made carefully and the logic
agrees with the papers as far as I can see. In particular the 4 jet
correlation analysis reduced in size by almost a factor of 2, but most
of that came from just using vector methods rather than getting all the
px,py components and doing it by hand! But while I'm reasonably
confident, I thought it would be best for you (and the original authors)
to cast an eye over the updated code and check that it still looks ok to
you:

https://rivet.hepforge.org/trac/browser/src/Analyses/CMS_2013_I1272853.cc

https://rivet.hepforge.org/trac/browser/src/Analyses/CMS_2013_I1273574.cc

Please let us know if you see anything concerning. Otherwise I think we
are on target to release Rivet 2.1.1 early next week. We *might* just
have time to integrate one more analysis in time for that, if you happen
to have any which are nearly ready!

Best wishes,
Andy & the Rivet team

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