[Rivet] lifetimes in rivet

[Frank Siegert]

Andy Buckley, Saturday 03 April 2010:
> On 01/04/10 09:43, Alexander Richards wrote:
> > Was wondering if there was a nice Rivety was of cutting of particle
> > lifetimes such as a lifetime projection or something? I think I can
> > directly get the lifetime of the particles from the GenParticle but
> > was wondering if there was an easier way?
> 
> (Copying to Rivet list: please send to the list if possible!)
> 
> I don't *think* there is a way to get the generator's take on the
> lifetime from the GenParticle: at least, I don't see anything in the
> GenParticle interface that does this. HepPDT could probably be used to
> get this info from the PID, but there's no guarantee that the number
> matches that used by the generator.
> 
> If there is such a mechanism in HepMC (and it's used, including in the
> translation from the Fortran HEPEVT event record), then I'd be very
> happy: we could move a lot of restrictions on particle lifetime cuts
> from how the generator has to be configured into the Rivet analysis
> code, and a lifetime-sensitive projection of some sort would indeed be
> useful. But I don't know of such a mechanism: maybe someone can correct
>  me?

It should be relatively easy (and proper) to do this from the vertex 
offset in combination with the incoming momentum. At least that must be 
how the experiments do it when they run a Monte-Carlo, since there is no 
separate (duplicate) storage of "generated life time".

Frank