[Rivet] Rivet: Accessing intermediate particles

[David Hall]

Hi Hendrik,

When I look at the parents of the electrons, it just gives me the 
incoming protons. It does this for >=2 electrons, so not just for 
electrons from the hard scatter. So it seems I can't differentiate 
between electrons this way.

I agree that in an ideal world we can just treat everything exactly as 
we would in data. Unfortunately, due to time constraints and deadlines 
we often need a quick way to do things, so we need to be able to do 
truth-level studies like this relatively quickly.

Thanks,
David

On Sat 30 Jun 2012 19:25:52 CEST, Hendrik Hoeth wrote:
> Hi David,
>
> Thus spake David Hall (David.Hall at physics.ox.ac.uk):
>
>> Unfortunately, when I check the status of each parent of the electron
>> in an event, I find that they are _all_ status 2. This suggests that
>> all the electrons are from decays, but I know this shouldn't be the
>> case. Two should be from the hard scatter. Is it possible this is
>> specific to Sherpa?
>
> Well, technically even in the hard scatter the electrons are decay
> products of something. Though luck, eh? I mean ...
>
>>>> I understand the philosophy behind Rivet not providing access to the
>>>> intermediate particles, but I believe that looking for the particles
>>> >from the hard process in this way is not _so_ bad. :-)
>
> ... nature doesn't mark the particles from the hard process, either. So
> the best thing is to resort to physically meaningful observables,
> similar to what you do in the experiment.
>
> Cheers,
>
>      Hendrik
>
> PS: I assume you know you can walk through the whole HepMC tree in the
> same way you asked for the electrons' parents. That's all the generator
> supplies.
>