[Halld-tagger] Photon flux calibration

[Michael Dugger]

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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