[Halld-tagger] Pair Spectrometer microstrip note

[Alexander Somov]

Dear Hrachya,

Thanks a lot for your prompt and useful comments.

> 1. I didn't see an evaluation  of random coincidence rate, that is 
> important for such an extended and mono- layer detectors, having app.0.18MhZ
> single rate in each arm.

The random coincidence rate estimates are given in the "Background rate" 
section. The rate was estimated to be on the 1% level and originated from 
the interactions of low-energy leptons (mainly from a e+e- pairs) with the 
magnet aperture. One comment here:
  - Originally, I found a relatively large random coincidence rate (on the
    level  of 4%) for the scintillator hodoscope counters. However, I was able to
    reduce it  to less than 1% by inserting the tapered collimator to
    the magnet aperture. I believe that the coincidence rate can be further
    reduced for the microstrip detectors by optimizing the collimator shape.

2. There is one "confusing" moment in the note. I call the detectors as
'microstrips'. However it seems that GEM detectors might be an appropriate
option for us (there will be a lot of GEM detectors used in the Hall-A);
we are collecting information now.

We will also need to use scintillators after the 'microstrips' to generate
the trigger and reduce background rate.


We will need to discuss everything during the beamline meeting. I will try
to get more information by then.


Cheers,
        Sascha









On Thu, 22 Jul 2010, Hrachya.Hakobyan wrote:

> Dear Sascha,
>
> I've seen  the note n Si-pixel's registration system of PS. The first 
> impression is positive in the sense of the expected performance, although I 
> didn't analyze in  detail.
> At moment I have two comments:
>
> 1. I didn't see an evaluation  of random coincidence rate, that is important 
> for such an extended and mono- layer detectors, having app.0.18MhZ single 
> rate in each arm.
>
> 2. The Si-pixels are an analog devices with noise, that should be somehow 
> cutted, need in temperature stabilisation, control and calibration of gain, 
> so is not simple  in  use. If I remember in the referemce on Hall B PS 
> calibration, the part of the pixel layers wasn't alive. So the specific 
> conditions/difficulties  of the pixels' use shoould be also presented.
>
>
> 3. I believe that for  the task of end point energy mesurement requested by 
> Primakoff experiment it is also  worth to consider an option of  small 
> Si-pixel arrays to cover the spectrum end region only, working in coincidence 
> with scintillation telescopes,  as an intermidiate cost saving solution.
>
>
> Best Regards, Hrachya
>
>
> On Wed, 21 Jul 2010, Alexander Somov wrote:
>
>> 
>> Dear beamline friends,
>> 
>> The note describing instrumentation of the Pair
>> Spectrometer with the microstrip detectors is
>> ready for your perusal, GlueX-doc-1563-v1
>> 
>> Please take a look and send me your comments.
>> 
>> Cheers,
>>        Sascha
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>