[G12] My multiple beam photon study

[Lei Guo]

Hi, MK and Michael,

In general I agree with Michael what you are showing is reasonable. The 1-photon-only probability plot shows basically the percentage (for Egamma > 3.6GeV) is about 86.6%+-1% (eyeballing). What Will showed from his ppbar channel is about 87%+-1% (also eyeballing, and he starts from 3.9GeV). There is no difference here. The two plots (you and will) looks dramatically different because of the energy range (x-axis), and because of will shows on the Y-axis from 0 to 100%, and you zoomed in from 80% to 90%. It tells exactly the same story.

For the low energy part (Egamma <3.6 GeV), I think Michael’s explanation is probably right — although I won’t call it trigger efficiency or inefficiency. It’s only inefficient when a event that should have triggered and been recorded did not get registered.
But even if you compare these two ranges, it’s really a only 1.5% difference. Do you think our systematic uncertainty on the normalization is less than 1.5%? I think in the big picture, we are fine.

But I do agree with MK that his picture is different from FSU, particularly in the low energy part, since it showed opposite trend. 

How does Rafael’s results compare with you, particularly for the low energy part?

Is it possible that again this is due to you and FSU are not showing the data from exactly the same set of runs?





Lei Guo
Assistant Professor
Physics Department
Florida International University
Miami, FL

email: leguo at fiu.edu <mailto:leguo at fiu.edu> or lguo at jlab.org
Office:305-348-0234

> On Mar 31, 2015, at 2:31 PM, Michael Paolone <mpaolone at jlab.org> wrote:
> 
> Hi MK, All,
> 
> This looks reasonable, and I think I can explain the energy dependence. 
> The key is that all events have to fire a trigger whose efficiency is
> dependent on the momentum and angle of the tracks created from the
> reaction which itself IS photon energy dependent.
> 
> Look at the 1 photon probability plot and ask how likely is it that that
> photon is the one that created the trigger.  For very low energy photons
> the overall trigger efficiency drops, and since we see an event at all, it
> becomes more likely that another higher energy photon in the same beam
> bucket generated the reaction that triggered the event.
> 
> The sharp jump at 3.6 GeV shows that the event is now more likely to
> trigger with just that photon (since that's where the primary trigger
> starts).
> 
> The downward slope after 3.6 GeV might again be a trigger efficiency
> effect, where it becomes more likely that we lose small angle tracks down
> the beam hole which could have fired the trigger.
> 
> -Michael
> 
>> Greetings,
>> 
>> I did not want to show this last night because I thought there was a bug
>> in my code. But I do not think I have a bug in my code, so I want to
>> show you what I concluded.
>> 
>> First of all, my result does not agree with the values found by FSU or
>> FIU. I actually see a strange dependence on energy. What I am depicting
>> are plots of the probability of multiple photons within the same bucket
>> as clasEvent choose ±1.002 ns, meaning the photon energy on the X-axis
>> of the plots are of clasEvent chosen, which was the best timed beam
>> photon compared to the average _of_ start times.
>> 
>> The data used for this is only the 566* runs, which is approximately 7%
>> of the data.
>> Please see:
>> https://clasweb.jlab.org/rungroups/g12/wiki/index.php/TAGR_code#March_31
>> 
>> --
>> BR
>> MK
>> ----------------------------------------
>> Michael C. Kunkel, PhD
>> Forschungszentrum Jülich
>> Nuclear Physics Institute and Juelich Center for Hadron Physics
>> Experimental Hadron Structure (IKP-1)
>> www.fz-juelich.de/ikp
>> 
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> 
> 
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