[Rivet] our use of fastjet

[Hendrik Hoeth]

Hi,

I've seen that in the transition to fastjet 2.4 we changed the overlap
threshold in the CDF cone algorithms from 0.5 to 0.75. The svn log says
"Using overlap_threshold for midpoint and jetclu, as advised by the
FastJet authors.", so I guess the reasoning behind this change is the
following comment in the fastjet code:

  /// NB: as of version 2.4, the default value for the
  /// overlap_threshold threshold has been removed, to avoid
  /// misleading people into using the value of 0.5 without thinking,
  /// which is known to have adverse effects in high-noise
  /// environments. A recommended value is 0.75.

But we shouldn't use the recommended value without thinking, in the same
way nobody should use the old 0.5 without thinking. Most CDF analyses
are using 0.5 and our aim is not to do a new analysis, but to reproduce
whatever the experiments have done. So I think we should stick to the 0.5.

Opinions?

    Hendrik

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