[Rivet] Z projection on Rivet

[Gavin Hesketh]

Hello,
A couple of points for the Z projection. First, in the analysis 
D0_2010_S8671338.cc (inclusive Z pT), the setup needs to be adjusted. 
Currently:
ZFinder zfinder(-1.7, 1.7, 15.0*GeV, MUON, 65.0*GeV, 115.0*GeV, 0.2);

ie sum all photons in a cone of 0.2 around the muon. This does not 
correspond to the analysis, which did not sum any photons into the 
muons, so:
ZFinder zfinder(-1.7, 1.7, 15.0*GeV, MUON, 65.0*GeV, 115.0*GeV, 0.0);

This actually makes a significant difference in the first few Z pT bins. 
I realise ATLAS are handling this slightly differently...


Then some fine-tuning which is a much lower priority. At the moment, it 
looks like the Z projection calculated the invariant mass before adding 
on photons, then adds on photons to both electron and muon channels. So:
1) calculate the mass after adding the photons, if the photons are going 
to be added (probably a tiny effect)
2) for D0 Z->mm, don't add the photons; for ATLAS Z->mm and all Z->ee, 
add the photons. I'm sure there is an easy way to code a switch here. 
Note that for the D0 Z->mm, still need to select the photons in a 0.2 
cone and exclude them from the jet finder. The current analyses 
(D0_2009_S8349509.cc, D0_2008_S7863608.cc) instead apply a cut on 
jet-muon overlap, which which was not done in the data analysis. The two 
methods (excluding photons around the muon vs removing jet-muon overlap) 
probably has an almost identical effects in the end though.

cheers,
	Gavin