[Rivet] Jets in DIS

[Jonathan Butterworth]

Hmmm.

Except that in principle a "scattered" lepton is only identifiable as 
such via its final state characteristics. In a multilepton final state 
no one tells us which it is by any other means. That's quantum mechanics.

The "generator independent" way Hannes mentions was, I think, just a 
bunch of if/then statements looking at the MC matrix element: not really 
allowed.

TBH this is something that has worried me on HERA results since I 
started worrying about such things (about halfway through being ZEUS 
photoproduction convener I think).

In practice I think choosing the highest energy lepton with
4 > eta > -2.5 or something is what the experiments did (though at 
detector level) and should work for rivet. An isolation requirement 
might also be relevant I guess. I believe for nearly all analyses any 
misID is a tiny effect, and since the experiments generally didn't 
measure the scattered lepton unambiguously via a final state definition, 
it's probably the best we can do.

I'll have a read of some old papers and try and check this.

Cheers,
Jon



On 19/10/2011 18:01, Hannes Jung wrote:
> Hi Leif, Andy et al
>
> the measurements are in terms of Q2,y,x, so the definiton of the
> scattered electron does no longer enter here. In hztool we had a
> definiton of the scattered electron idependent on the generator,
> and it stored the scattered electron.
> Now since the effect of misidentification of the scattered electron is
> already included in the correction of the data, one needs a defintion,
> which really identifies the scattered electron.
> There should be not different ways to identify the electron, there is
> only ONE scattered electron in DIS.
>
> Cheers
>
> Hannes
>
> On 19 Oct 2011, at 17:40, Andy Buckley wrote:
>
>> On 19/10/11 12:24, Leif Lönnblad wrote:
>>> On 2011-10-19 10:04, Hannes Jung wrote:
>>>> hm, taking just the frist electron might be tricky, as it is not based
>>>> on physics.
>>>
>>> I'm a bit surprised about this discussion. The whole point with rivet is
>>> to do what the experiments do. H1 had one (or maybe several) very
>>> specific way of finding the scattered electron. For an H1 analysis, this
>>> should be reproduced in Rivet. The modular structure of Rivet means that
>>> we can implement several electron finders (subclasses of DISLepton). A
>>> given rivet analysis should use the one which corresponds to the one
>>> used in the experimental analysis. And if the ones included in the rivet
>>> distribution does not fit a specific analysis, one would have to
>>> implement a new one. Or am I misunderstanding the discussion?
>>
>> I don't think you're misunderstanding the discussion, no! So if the
>> HERA people on this email can point us to the scattered lepton
>> experimental definitions for the few HERA papers implemented in Rivet,
>> we'll happily implement them as appropriate.
>>
>> Cheers,
>> Andy
>>
>> --
>> Dr Andy Buckley
>> SUPA Advanced Research Fellow
>> Particle Physics Experiment Group, University of Edinburgh
>>
>> The University of Edinburgh is a charitable body, registered in
>> Scotland, with registration number SC005336.
>>
>
>
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-- 
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Prof. Jonathan Butterworth,              http://www.hep.ucl.ac.uk/~jmb/
Physics and Astronomy Department                  Tel: +44 20 7679 3444
ATLAS, CERN                                       Tel: +41 22 76  72340
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