[Rivet] electroweak results used to tune/validate theory

[Gavin Hesketh]

Hi Heidi,
the effect was really just on differential distributions like the Z pT, 
and then only Z pT < 5-10 GeV.

We don't need to regenerate MC, just use a modified definition of what a 
"Z" is, constructed just from the stable final state particles. eg for 
Z->ee, take opposite charge electrons, add on any EM object within 0.2, 
then apply the mass cut. For muons, just take the stable muons (no cone 
addition). This introduces a little difficulty in combining e and mu, 
but almost entirely removes the model dependence. I could show this in 
an upcoming EW meeting, but am about to leave town for two weeks...

Then, for publications, results can be included for the "particle level" 
Z *and* the generated Z.

cheers,
	Gavin



Heidi Schellman wrote:
> Yes, but taking PHOTOS out means regenerating millions of full MC 
> events... and making certain that one's colleagues don't get the wrong 
> set...
> 
> Andy Buckley wrote:
>> Heidi Schellman wrote:
>>  
>>> One issue here - we do use photos in our MC, but that is partially 
>>> because, we also have real photon radiation from the detector - which 
>>> is almost certainly a larger effect.  At least for the total Z cross 
>>> section, we found that if we use a .2 cone for electrons in D0, 
>>> photos or not photos made very little effect in our results.
>>>     
>>
>> Gavin did the detailed study, so he can probably comment more
>> knowledgeably than I, but the effect was around 5% for for Z pT peak
>> position, which is sensitive to low pT effects like QED resummation. I
>> would expect that inclusive quantities like total cross-section are
>> relatively unaffected, but for Monte Carlo tuning the differential ones
>> are essential.
>>
>>  
>>> And we are going to quote for our fiductial PT, eta range, as well as 
>>> for the full extrapolated range.
>>>     
>>
>> Excellent! I hope it's clear that what we're advocating is publishing
>> purely detector-corrected data "as well as" any extrapolations or theory
>> unfoldings... rather than "instead of"!
>>
>> Andy
>>
>>