[Olympus] Slides for presentation on Monday

[Axel Schmidt]

Dear colleagues,
	I realize that I forgot to click reply-all, and just responded to Stan. Here's what I wrote back on Friday:

Dear Stan,
I'll try to answer your questions in advance of any discussion on Monday. 

1) Yes, the generator does take into account the range of possible photon kinematics. The generator produces a cross section that is differential in 5 variables:

theta_lepton, phi_lepton, theta_photon, phi_photon, delta_E

The asymmetry does have a single value for a given delta_E cut. The bands are not showing the range of photon kinematics. I am integrating over the photon angles. The bands are showing the statistical precision of the study. By simulating more events and accumulating more statistics in this study, the bands will shrink in size. 

2) The problem of divergences at delta_E -> 0 is a tricky one for generators. Both the MIT and Novosibirsk generators have to use some tricks to avoid problems for very small values of delta_E. Novosibirsk uses a cut around small delta_E, like you describe. The MIT Generator cancels the divergence in the cross section against the sampling distribution for the Maximon+Tjon tail. These are two different approaches, and we are in the process of studying them to confirm that their predictions agree. We also expect both approaches to match M+T at low delta_E, where M+T's soft-photon-approximation is valid. 

All the best,
Axel


On Dec 6, 2013, at 6:25 AM, Belostotski, Stanislav wrote:

> Dear Axel,
> This is really very well done and clear presentation.
> Unfortunately, I'll not be able to participate next Monday meeting,
> yet I have a couple of questions.
> 1.At slide 1, you state that the events are generated at a given lab. 
> theta angle. So  I am assuming  that the integration over emitted photon 
> kinematics is automatically done, and  therefore  at a fixed theta you 
> must have dSigma/dE_e as a function of one E_e variable (as it is in 
> your previous talk), same for Delta_E cut, i.e. the e+/e- ratio must be 
> a single value for each E_e but not a band.
> I presume that   shown is  the range of  dSigma/dE_e related to 
> variation of the photon kinematics. If yes, I would suggest to add this 
> such a note  at your slide. In any case it would also  be   interesting 
> to see  an integrated result  to be compared to the M+T line.
> 2.What happens if \Delta_E-> zero? Is there any cut applied on minimum 
> emitted photon energy to avoid divergence? this might be more 
> theoretical matter but seems  to be interesting and might be even 
> important for further analysis.
> With best regards StanB
> 
> On 05.12.2013 22:45, Axel Schmidt wrote:
>> Hi everyone,
>> 	I have posted slides on the wiki:
>> 
>> https://olympus-docu.hiskp.uni-bonn.de/dokuwiki/doku.php?id=meeting_20131209
>> 
>> for my talk on Monday. I will talk about the positron-electron asymmetry of the radiative corrections. I may modify the plots before Monday, but only to increase the sample size and improve statistics.
>> 
>> Best regards,
>> Axel
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