[Halld-tagger] Photon flux calibration

[Alexander Somov]

Hi Michael,

I hope that we'll be able to do this, i.e., to read out
the ps and the tagger ctates only using the special
trigger type generated by the ps (if needed, this
trigger can be prescaled).

Cheers,
       Sascha




On Wed, 11 Jul 2012, Michael Dugger wrote:

>
> If I understand correctly, we can do tagger reconstruction for each PS hit 
> during production running and not worry about the tagging efficiency. That 
> would be nice :)
>
> -Michael
>
> On Wed, 11 Jul 2012, Alexander Somov wrote:
>
>> 
>> Hi,
>> 
>> Here are some thoughts; most of them have already been
>> discussed.
>> 
>> It's important to check a PS acceptance sensitivity to
>> the beam profile at the converter (I guess/hope that the
>> effect is going to be relatively small).
>> 
>> Once the PS acceptance is determined we can use it for the
>> lumi determination and the tagger efficiency monitoring. The
>> PS acceptance can be calibrated in special runs.
>> 
>> One way to calibrate the PS acceptance is to use TAC counters
>> and the tagger energy. We can probably use a thin radiator and
>> large beam current; we don't care about tagging efficiency
>> at this point unless the beam profile remains the same. The
>> PS rate at small current is critical. If I remember correctly
>> (have to check), the PS coincidence rate is  about 40 kHz  for
>> the 10-3 converter for high-lumi runs ( 2.2 um current)
>> For 10^3 times smaller current the rate is going to be
>> about 40 Hz (we acquire ~24k events in 10 min of running,
>> ideally we have to bin events into a few energy bins).
>> 
>> Michael, regarding storing the PS/tagger info, we can have a
>> special trigger type and readout only the PS and Tagger crates
>> only. Reading out a few hits only is not an issue at 100 KHz rate
>> (these triggers can be prescaled as well).
>> 
>> Cheers,
>>        Sascha
>> 
>> 
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>