[Rivet] Neutrino question - once again

[David Grellscheid]

Hi all,

what's our justification again for being allowed to use two 
distinguishable truth neutrinos in ATLAS_2012_I1203852 == 
http://arxiv.org/pdf/1211.6096.pdf ?

I'll need to rewrite that section along the lines of the W-Finder fixes, 
to assume generic invisibles rather than standard model neutrinos. Can 
someone on ATLAS please help me to interpret this statement from the 
paper in terms of measurables?

   "dineutrino invariant mass close to the Z boson mass"

The event selection section is very brief on how I get to the Z-nunu 
candidate in the first place.

Thanks,

   David