[Rivet] MissingMomentum and WFinder problem & plans for 2.4.0

[Chris Pollard]

I'm in favor of only exposing the MissingMomentum 3-momentum.

I also agree that setting the neutrino mass to zero when solving for the W
mass is the right way to go, although David G should comment on whether
this would break BSM reinterpretations.

Chris

On Tue, Sep 15, 2015 at 1:50 AM, Andy Buckley <andy.buckley at cern.ch> wrote:

> Hi all,
>
> A summer student working with Chris and I spotted last week that the W
> returned from WFinder is still nonsensical.
>
> The cuts are ok, and the lepton is also fine, but the use of the full 4D
> missing ET vector to make the "pseudo-neutrino" messes up because that
> vector has an energy component equal to the energy sum of all the
> in-acceptance particles used to calculated the *visible* momentum against
> which the missing one is balanced.
>
> One option would be to reduce the MissingMomentum to the transverse vector
> only, but that seems too far because it should also be usable in e+e-
> colliders. It also seems wrong to give the missing momentum vector a null
> mass, because while that's fine for neutrinos it's wrong for BSM invisibles.
>
> I suggest that we change the MissingMomentum interface (again... I already
> made some enhancements for 2.4.0) to only expose a 3-momentum. The E
> component is really a misleading accident. What do you think? Any
> objections or alternative suggestions? (A user-specified missing momentum
> mass target, maybe?)
>
> Similarly, we can't just restrict the WFinder to use transverse mass due
> to e+e- compatibility. But there we do have a definite hypothesis that the
> missing momentum vector should be a neutrino, so we could set the pseudo-nu
> mass to zero, and feed that into the pseudo-W mass in the case that full
> rather than transverse mass is used. Again, thoughts?
>
> Andy
>
> PS. Still waiting for analysis integration volunteers. I'll start forcibly
> assigning them if I don't hear soon (this is the procedure we agreed on!),
> so this is your chance to take a quick look at the tarballs and pick a
> couple of easy ones ;-)
>
> --
> Dr Andy Buckley, Lecturer / Royal Society University Research Fellow
> Particle Physics Expt Group, University of Glasgow
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