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Hi,<br>
<br>
Frank pointed out that there are crashes in LEP analyses, when <br>
running Sherpa in a configuration where Fragmentation is off.<br>
<br>
I found that the culprit are events with exactly two charged<br>
partons in the event with vertices as shown below.<br>
<br>
Due to the mass of the quarks being zero, and thrust being<br>
exactly 1 for this event, the calculation of e.g.<br>
<br>
<blockquote>const double rapidityT = 0.5 * std::log((energy + momT)
/ (energy - momT));<br>
</blockquote>
in ALEPH_1996_S3486095 leads to<br>
<ul>
<li>division by zero as energy == momT for the quarks (energy
being the energy of<br>
the particle and momT the projection of the momentum vector onto<br>
the thrust axis)</li>
<li>and subsequently to rapidityT being infinite (inf)<br>
</li>
</ul>
<p>The crash occurs when rapidityT is filled into a histogram:<br>
</p>
<ul>
<li>_histRapidityT->fill(fabs(rapidityT), weight);</li>
</ul>
<br>
So I wonder what to do in these pathological cases.<br>
<br>
I was using the head versions of yoda and rivet to reproduce this
problem.<br>
<br>
<br>
<br>
Cheers,<br>
Holger<br>
<br>
<br>
<tt>I: 4 10005 -11
-0.00e+00,-0.00e+00,-4.56e+01,+4.56e+01 11 -6<br>
10007 11 -0.00e+00,-0.00e+00,+4.56e+01,+4.56e+01
11 -6<br>
10011 3 -3.22e+01,-4.78e+00,+3.20e+01,+4.56e+01
3 -6<br>
10012 -3 +3.22e+01,+4.78e+00,-3.20e+01,+4.56e+01
3 -6<br>
O: 7 10009 11 +0.00e+00,+0.00e+00,+4.56e+01,+4.56e+01
3 -5<br>
10010 -11 +0.00e+00,+0.00e+00,-4.56e+01,+4.56e+01
3 -5<br>
10013 3 -2.66e+01,-3.96e+00,+2.65e+01,+3.77e+01
1<br>
10014 -3 +1.80e+01,+8.08e+00,-1.87e+01,+2.72e+01
1<br>
10015 21 +1.19e+01,-1.85e+00,-1.34e+01,+1.80e+01
1<br>
10016 21 +1.90e-01,-1.28e+00,+4.15e+00,+4.35e+00
1<br>
10017 21 -3.47e+00,-9.85e-01,+1.51e+00,+3.91e+00
1</tt><br>
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