[Rivet] Z projection on Rivet

[Andy Buckley]

Thanks Gavin,

Since your talk in Edinburgh last term I've had "check the Rivet Z -> mu
mu implementation" on my TODO list! We'll get it fixed asap...
fortunately the one place it's been used in tuning is already excluding
that low-pT region.

Frank, is there a neater way to say to not do any photon clustering than
setting the cone radius == 0? Perhaps the W and Z finders can be
improved further based on your experience of the ATLAS clustering approach?

Cheers,
Andy


On 31/01/11 12:37, Gavin Hesketh wrote:
> 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
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-- 
Dr Andy Buckley
SUPA Advanced Research Fellow
Particle Physics Experiment Group, University of Edinburgh

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