[Rivet] [Rivet-svn] r2720 - trunk/src/Projections

Frank Siegert frank.siegert at cern.ch
Tue Oct 19 11:59:57 BST 2010


2010/10/19 Andy Buckley <andy.buckley at ed.ac.uk>:
> On 19/10/10 10:23, blackhole at projects.hepforge.org wrote:
>> Author: richardn Date: Tue Oct 19 10:23:23 2010 New Revision: 2720
>>
>> Log: if more than one W candiate take the one nearest to mW rather
>> than throwing the event away. Brings Herwig++ NLO into agreement with
>> D0_2000_S4480767 rather than being a factor of two low.
>
> Interesting: I based the W finder on the Z finder, for which I thought
> that the rate of multiple candidates inside the mass window was
> extremely low. This suggests that ~half of the W events lead to multiple
> candidates: I'm surprised. And also the weight counting in that analysis
> can't have been spot-on if vetoing multi-candidate events was affecting
> the overall normalisation. Maybe worth changing ZFinder to have the same
> behaviour, i.e. choose closest-to-mZ. Frank?

D0_2000_S4480767 is one of the analyses which doesn't have a real mass
window, but is corrected to the fully inclusive phase space. So this
problem shouldn't be as critical for Z's (which will always have to
have at least some kind of mass window), but I agree that it might be
nicer to do it correctly. The question for me is just what to define
as correctly... unfortunately the papers aren't very clear on their
procedure and up to now I always thought that the difference is not
noticeable. If it is as pronounced as the factor of 2 that Peter
found, we should probably be careful simply switching all of them to
the "nearest mass" procedure, shouldn't we?

Frank


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