[Halld-tagger] [EXTERNAL] Re: DBeamPhoton tests

[Richard Jones]

Alexander, my response to your questions. -Richard

Comparing the two versions with and without the requirement of ADC/TDC
> matching for the hodoscope, I only see a loss of events below 1% in
> almost the full energy range. There is only one 100MeV-wide bin near
> 9.1GeV, where the loss is about 15%. Could this be a sign of a broken or
> miscalibrated TDC?


No, the DAQ was working ok in that sector. The loss of 15% is pretty much
uniform across the entire TAGM. The reason the ratio looks like 1 in the
low-energy end is because the missed tags are missing from both the
numerator (tdc*adc) and denominator (adc) in that region, so the ratio
looks close to 1. I will present my analysis of these data at the beamline
meeting next Tuesday.

 Once the thresholds were fixed in run 71724, the loss goes down to 10%
> in the higher-energy part of the microscope, while it completely
> recovers for the low-energy part. What is the reason for this
> discrepancy? New vs old fibers?


Basically the ratio is close to 1 in the low-energy end of the TAGM because
the low-amplitude pulses are missed by both the adc and tdc. What really
surprised me is the additional tags that are recovered at the high-energy
end where the new fibers are: by lowering the adc threshold way down, we
are able to see an additional 15% of tags in the adc over what is seen by
the tdc which just counts on the primary MIP peak. I believe that this 15%
are coming from electrons that passed through the cladding of the fiber,
instead of the core. Originally I assumed that light produced in the
cladding would be totally lost because it is outside the
total-internal-reflection capture cone of the fiber. Now I see that this
assumption was wrong! Nevertheless, there is probably not enough light from
these pulses to make good tags.

Let's discuss the "15% problem" at the beamline meeting next week.

On Fri, Apr 24, 2020 at 11:46 AM Alexander Austregesilo <aaustreg at jlab.org>
wrote:

> *Message sent from a system outside of UConn.*
>
>
> Hi,
>
> I looked at the accidental corrected rho yields as a function of energy
> for the three test runs. You can see the plots on this wiki page:
>
>
> https://urldefense.proofpoint.com/v2/url?u=https-3A__nam10.safelinks.protection.outlook.com_-3Furl-3Dhttps-253A-252F-252Fhalldweb.jlab.org-252Fwiki-2Dprivate-252Findex.php-252F2020-5FTagM-5FThreshold-5FTest-26amp-3Bdata-3D02-257C01-257Crichard.t.jones-2540uconn.edu-257Ca352d79c11974c79fea808d7e866a12e-257C17f1a87e2a254eaab9df9d439034b080-257C0-257C0-257C637233399810094785-26amp-3Bsdata-3D4zYaxV2ZzXphRsiaR5eFzgX3ebxm-252BHN7owoyTIl-252F1lA-253D-26amp-3Breserved-3D0&d=DwIFaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=-MwMW0sKroUIjy-Lh9rb3KzmWIgdcbbr9_jez8RLmto&m=iX1lXNpi6V_q0QPmEr59lqvAzNjcGLwUObwfy25WB3c&s=ANiDrG8v8JeYgM7CpEonES5NeseIQAkdvo2A7xZJYdU&e= 
>
> Comparing the two versions with and without the requirement of ADC/TDC
> matching for the hodoscope, I only see a loss of events below 1% in
> almost the full energy range. There is only one 100MeV-wide bin near
> 9.1GeV, where the loss is about 15%. Could this be a sign of a broken or
> miscalibrated TDC?
>
> For the 2 runs before the adjustment of the microscope thresholds, the
> loss of rho events with tagged beam photons is close to 30% as expected.
> Once the thresholds were fixed in run 71724, the loss goes down to 10%
> in the higher-energy part of the microscope, while it completely
> recovers for the low-energy part. What is the reason for this
> discrepancy? New vs old fibers?
>
> Best regards,
>
> Alex
>
>
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