[Rivet] Validation & tuning phone meeting, Monday 29th Sept, 4pm (UK)

[Andy Buckley]

Lars Sonnenschein wrote:
> Just a short heads up:
> 
> I have put two new plots at:
> 
> http://www-d0.fnal.gov/~sonne/D0_2001_S4674421/

> Concerning the plots: The Pythia simulation is scaled to the data.
> The ratio is obtained by the scaled histo's, using ROOT's 
> histogram division function. Without scaling to data the ratio
> is by about 20% lower.

> I checked with the very first bin value in the histo's to be divided that 
> ROOT is doing the right thing. The ratio histo from Rivet is about a 
> factor of two lower than the Rivet answer.

Hi Lars,

What do you mean here: which of these "Rivet"s should have been "ROOT"? ;)

We need to be really careful with these divisions: by default ROOT's
histograms don't take any account of bin width, i.e. the BinContent(i)
function returns the sum of weights in bin i, rather than
sumW(i)/binWidth(i), which is the proper bin-measure invariant shape of
the histogram. This should drop out in taking the ratio, but don't the
bins end up not have matching edges in the W and scaled-Z histos
[because of the mW/mZ factor in d(sigma)/d(pT(Z)*mW/mZ)]? If this is the
case, then I have no idea how ROOT's division function attempts to match
up the bins and handle the width-factors. Yuck.

> The other thing is that when I run HerwigJimmy from the cern afs 
> cluster it's trying events but I never see the Rivet 100 events control 
> message, then after about 20 minutes my interactive job gets killed from 
> a daemon. So there are no accepted events.

I just tried running the AGILe HEAD with HerwigJimmy and LHC mode MPI
and found the same problem. I tracked it to the checking of the Herwig
error flag at the end of the event loop, which meant that the event was
never accepted. It's fixed in the AGILe head now. This might mandate an
AGILe patch release soon; silly error :(

Andy

-- 
Dr Andy Buckley
Institute for Particle Physics Phenomenology
Durham University
0191 3343798 | 0191 3732613 | www.insectnation.org