[Clascomment] OPT-IN: Demonstration of a novel technique to measure two-photon exchange effects in elastic e(+/-)p scattering

[Stepan Stepanyan]

Dear Larry,

Thanks, it is clear.

Regards, Stepan

On 6/3/13 4:55 PM, Larry Weinstein wrote:
> Dear Stepan,
>
> That is exactly what the code did.  We checked to see that the beta 
> values were consistent with the particle assignment (positron/proton 
> vs proton/positron).
>
> - Larry
>
> Stepan Stepanyan wrote:
>> Brian,
>>
>> Thanks for the respond. Of course what I was thinking, two magnets 
>> should have
>> the same polarity. Still I am not sure why you need +/- for polarity. 
>> In any case
>> it is up to you.
>>
>> Question of the beta is not clear for me. I am not suggesting to put 
>> that detail in the
>> paper, but just wanted to understand how it was done. In order to get 
>> the start
>> time, you need to make assumption on the particle type for one of 
>> tracks and
>> assign the mass and calculate the beta. For electron runs electron 
>> beta is always =1.
>> You cannot measure beta of both tracks in two track event. Anyway, I 
>> do not know
>> for sure, but it looks like cooking code takes one f tracks that has 
>> smallest time
>> and assigns beta=1, as electron, and calculates the start time from it.
>>
>> Regards, Stepan
>>
>> On 6/3/13 11:32 AM, Brian A Raue wrote:
>>> Stepan,
>>> Thanks for your comments.  Responses below.
>>>
>>> Brian
>>>
>>> Stepan Stepanyan wrote:
>>>> Dear Larry et al.,
>>>>
>>>> Few minor questions and comments:
>>>> - page 5, left column, last paragraph, I understand notation 
>>>> B=+/-0.4T for Italian magnets, since the had different
>>>> polarity, but why B=+/-0.38T for pair spectrometer magnet. As you 
>>>> point in the text, chicane polarity was not changed, and therefore 
>>>> pair spectrometer was run at one polarity, is not it?
>>> Actually, the two ID magnets had the same polarity in a given 
>>> chicane setting.  The PS then had the opposite polarity. During the 
>>> test run we did indeed swap polarities for the purpose of beam 
>>> diagnostics (Fig. 4).  You are correct, we did not take data with 
>>> both chicane polarities. An oversight that cost us about 4% on our 
>>> systematic uncertainty.
>>>> - how start time was determined for event, like for ++ case
>>> I don't think this is something we need to go into in the paper but 
>>> event reconstruction simply took the first particle (in time) in the 
>>> event to be the start-time particle.  As we explained in the paper, 
>>> if we checked to see which of the two particles had beta>0.9 and 
>>> checked to see if this particle assignment gave us an elastic 
>>> event.  I'm sure you are thinking back to last year when you helped 
>>> Robert with this issue for the full-run data analysis.  Between the 
>>> time the test run data were cooked and analyzed and when the full 
>>> run data were cooked, there were significant changes to the cooking 
>>> codes that caused the problems we saw with the full run cooking.
>>>> - page 9, right column, first paragraph of subsection B, line 3, 
>>>> better to sat "on lepton charge" instead of "on lepton polarity"
>>> Yes.
>>>> - page 11, left column, second paragraph, line 2, "this narrow a 
>>>> range of", should it be "this narrow range of"
>>> Okay.
>>>>
>>>> Stepan
>>>>
>>>
>>>
>>
>