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<p>Hi,</p>
<p>the WFinder or more precisely the MissingMomentum it is based on<br>
has a problem when running on purely partonic events:</p>
<p><br>
<tt>EventScale -1 [energy] alphaQCD=0.120687
alphaQED=0.00776384
</tt><br>
<tt>PdfInfo: id1=2 id2=-1 x1=0.000319351 x2=0.303109 q=78.7088
xpdf1=2.25358 xpdf2=0.00657298
</tt><br>
<tt> </tt><br>
<tt> GenParticle Legend
</tt><br>
<tt> Barcode PDG ID Name Stat ProdVtx
DecayVtx ( Px, Py, Pz, E , m)
</tt><br>
<tt> 10001 2 u 3 -2 -1
( +0, +0, +1.28, +1.28,-6.12e-07)
</tt><br>
<tt> 10002 -1 d~ 3 -2 -1
( +0, +0,-1.21e+03,+1.21e+03, 0)
</tt><br>
<tt> 10003 -11 e+ 3 -1 -2
( +19.7, -19.1, -171, +173,-1.91e-06)
</tt><br>
<tt> 10004 12 nu_e 3 -1 -2
( -19.7, +19.1,-1.04e+03,+1.04e+03,-1.53e-05)
</tt><br>
<tt> 10005 2 u 11 0 -2
( +0, +0, +1.28, +1.28,-6.12e-07)
</tt><br>
<tt> 10006 -1 d~ 11 0 -2
( +0, +0,-1.21e+03,+1.21e+03, 0)
</tt><br>
<tt> 10007 -11 e+ 1 -2 0
( <b> +19.7, -19.1, -171, +173,-1.91e-06</b>)
</tt><br>
<tt> 10008 12 nu_e 1 -2 0
( <b> -19.7, +19.1,-1.04e+03,+1.04e+03,-1.53e-05</b>)</tt><br>
</p>
<p><tt>Rivet.Projection.WFinder: TRACE MET = 27.452 GeV vs.
required = 25 GeV
</tt><tt><br>
</tt><tt>Rivet.Projection.WFinder: DEBUG Found at least one
dressed lepton: <b>(172.942; 19.6765,-19.1428, -170.749)
</b></tt><tt><br>
</tt><tt>Rivet.Projection.WFinder: DEBUG Found missing
4-momentum: <b>(172.942; -19.6765, 19.1428, 170.749)</b></tt><br>
</p>
<p>This is the 'culprit' if you want to call it a culprit:</p>
<blockquote>
<p><tt>const FourMomentum missingMomentum(double mass=0*GeV) const
{ return visibleMomentum(mass).reverse(); }</tt><br>
</p>
</blockquote>
<p>That's probably not the best choice for partonic events.<br>
<br>
I would suggest we check in the WFinder is the beams<br>
are defined. If they aren't we can probably safely assume that<br>
this is a partonic event where you would reconstruct the <br>
W from the neutrino anyways and hence use the old method<br>
of reconstructing the W from the neutrino.</p>
<p>Here is a plot (thanks Marek) that illustrates the current
situation:<br>
</p>
<blockquote>
<p><a class="moz-txt-link-freetext" href="http://www.physik.uzh.ch/~marek/plots/YFS/Wtest/MC_WINC/W_mass.pdf">http://www.physik.uzh.ch/~marek/plots/YFS/Wtest/MC_WINC/W_mass.pdf</a></p>
</blockquote>
<p>red is purely partonic<br>
blue is with parton shower<br>
green is with parton shower and beams<br>
</p>
<p>I.e. the WFinder result depends on whether you have particles<br>
travelling down the beam pipe or not.</p>
<p>Not sure whether this is related to the problem Raghav reported.<br>
</p>
<p>Cheers,<br>
Holger<br>
</p>
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