[Rivet] MissingMomentum and WFinder problem & plans for 2.4.0

[David Grellscheid]

Hi all,

I agree with zero mass as the default. Maybe we can introduce a target 
mass in the MissingMomentum projection, to give theory input in the 
analyses that may need it. But in the absence of any other information 
the m=0 assumption is certainly a good one.

   David

On 15/09/2015 10:09, Chris Pollard wrote:
> 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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