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

[Andy Buckley]

On 19/10/10 11:59, Frank Siegert wrote:
> 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?

Good point ;) I was again relying on the vague memory that you had done
some testing and the effect was very small. Probably because of the mas
windowing. I think that the Z and W finders should do the same thing --
or possibly have a re-settable config flag to choose the strategy. And
we should make sure that the final normalisation is not affected by
this: without a mass window I'm not surprised that there are
duplicates... probably *miles* away from the W mass! Any other W
analyses without a mass window, or is this an isolated incident? Peter
has already changed the WFinder default, as the commit message indicates.

Andy

-- 
Dr Andy Buckley
SUPA Advanced Research Fellow
Particle Physics Experiment Group, University of Edinburgh

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