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

[Stepan Stepanyan]

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
>>
>
>