[Rivet] MissingMomentum and WFinder problem & plans for 2.4.0

[Chris Pollard]

The validation is running now. Will let you know the outcome when it
finishes (~hours).

Chris

On Tue, Sep 15, 2015 at 5:14 PM, Andy Buckley <andy.buckley at cern.ch> wrote:

> Done, and pushed. I added an optional "mass" arg to the
> MissingMomentum::visibleMom and ::missingMom methods, and fixed up WFinder
> to use the zero-mass target rather than subtracting the visible momentum
> from (sqrtS,0,0,0) -- cunning, but I think it meant that the vector still
> had the mass of what went down the beampipe, i.e. high!
>
> This definitely needs a validation run. Maybe we could even try running a
> few WFinder analyses in the system ~now, Chris, to make sure I didn't
> completely balls it up?
>
> Andy
>
>
>
> On 15/09/15 15:17, David Grellscheid wrote:
>
>> 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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>>>> Rivet at projects.hepforge.org
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>>>>
>>>>
>>>
>>>
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>
>
> --
> Dr Andy Buckley, Lecturer / Royal Society University Research Fellow
> Particle Physics Expt Group, University of Glasgow
> _______________________________________________
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> Rivet at projects.hepforge.org
> https://www.hepforge.org/lists/listinfo/rivet
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