[Rivet] New LHCB analysis --- definition of z_0

[Andy Buckley]

On 03/11/15 21:49, David Grellscheid wrote:
> Hi all,
>
>> I can't see an immediate problem with Vector3 Particle::prodPos(). What
>> do you think?
>
> How about Particle::origin(). "production position" is such a clumsy
> HepMC-ism. Also, it really is a 4-vector. Not all of the hadrons are
> produced at the same lab time.

I'm down with that :-)

Any gotchas we've not anticipated? I feel like there's a reason that I 
didn't do this already, but maybe it was just a mix of unease at the 
broken symmetry with decay, and uncertainty about whether we'd need a 
more "connected" vertex object than just a 3- or 4-vector (and again re. 
decays, there's no obvious "null" invalid value of Vector3/4).

> The calculation of z0 should certainly not be a member function, but I
> don't think that's what Holger suggested.

Holger suggested Particle::z0 ;-)

> If you have the collision
> point, a particle's origin, and its momentum, you can work out most of
> these offset calculation tasks (except for the ones that experimentally
> trace back along curved tracks).

Yep, that should be fine and is what I had in mind. But I don't 
guarantee that the experimentalists' version is entirely constructed 
from such sensible things!

Andy

-- 
Dr Andy Buckley, Lecturer / Royal Society University Research Fellow
Particle Physics Expt Group, University of Glasgow