[Rivet] DISLepton Class fails to find outgoing lepton

[Andrii Verbytskyi]

Dear Leif,

On Fri, 2017-11-17 at 11:10 +0100, Leif Lönnblad wrote:
> On 2017-11-16 12:26, David Grellscheid wrote:
> > please accept my apologies on behalf of the Rivet authors for this
> > email. This is not an appropriate response to your question
> 
> I certainly agree with this! The tone in that letter was completely out 
> of line.

It is sad you think so. I've offered help to Marion to solve the problem
but it was *explicitly* rejected. It does not look productive to me to
invest my time in collaboration in this case. I will get more work and
nobody will even say thanks.



> On 2017-11-16 16:23, Andy Buckley wrote:
> > My reading of the Rivet 2.5.3 code (copied below) is that it selects
> > the highest-|pz| final-state lepton. Looking back through my emails I
> > see that Andrii's concern about a final-state definition was actually
> > about using highest-pT, i.e. not the same thing. DIS experts, is
> > max-|pz| a reasonable heuristic?
> 
> Reading old H1 papers it seems their definition of the DIS kinematics is 
> based on their BEMC detector, which covers polar angles between 151 and 
> 177 degrees (wrt. the proton direction), and the scattered electron is 
> taken "as the most energetic BEMC cluster" with energy larger than 14 
> GeV. A rather simple experimental definition.

That is measurement technique and works well for low Q2. Not the case
for high Q2 or charged current. Or even simpler  -- what about
central/back region?


> However, looking at the old HZtool routines, they always use the 
> generator definition.

Exactly. And data was unfolded to it.

>  It's not clear to me if they generally correct for 
> this in any way. I saw one statement where they have studied QED 
> corrections and get effects of order 5% which they then include in the 
> systematic uncertainties, but do not correct for.

QED corrections is completely other thing. These are not included in
Rivet anyway. This means generators should be used w/o FSR.

> My guess is that any reasonable definition would do, and that the 
> original maximum-pz was reasonable, as is the generator definition. I 
> would, of course, prefer the the experimental definition, but it should 
> be easy to see what the differences are.

"Experimental definition" was quite complicated, i.e. in ZEUS it
involved probabilities derived with neural network, isolation of
electron, tracking and calorimeter information. 


Also, the whole discussion is going in circles (already 5 or more
years). It is up to developers to decide and understand what they want,
not up to me.


Best regards,
Andrii

> /Leif
> 
>