Taus in OL MEs (width=0) + hadron decays

[Frank Siegert]

It is currently not possible to use WIDTH[15]=0 with the tau decays in HADRONS++. This is due to the line hdc->SetWidth(BR*Flav().Width()); in Hadron_Decay_Table.C.

Since at the same time the OL interface will complain about width>0.0 external particles, it's currently not possible to use ME taus with the hadronic decays.

[Frank Siegert]

A workaround is to remove the corresponding warning lines in OpenLoops_Interface::MapFlavours. Since the OL interface is completely plugin-based, this is even possible without modifying the Sherpa installation by creating a new plugin library. The corresponding source code (taken from Sherpa 2.1.1) is attached and can then be compiled via

g++ -shared $(/your/path/to/bin/Sherpa-config --cppflags) -O2 -fPIC -DPIC $CXXFLAGS -o libSherpaOpenLoopsReplace.so OpenLoopsReplace_Interface.C

and used in a run card by specifying

SHERPA_LDADD=SherpaOpenLoopsReplace
ME_SIGNAL_GENERATOR=Amegic OpenLoopsReplace
...

Loop_Generator OpenLoopsReplace  # (in processes)