Re: Tagger energy resolution? (fwd from David)

[Alexander Somov <somov@jlab.org>]

Hi David,

Here are a few tiny remarks:
Be sure that you use the right microscope range of 0.8 GeV
in your slide, rather than 0.6 GeV which you have mentioned
in your mail. As Richard has explained, the microscope
counter resolution should be less than 6 MeV:
~ 8 MeV / Sqrt(12) (counter size)  +  2% from 12 GeV (magnet optics)
+ multiple scattering. Counters granularity is driven by the rate.

The fixed-array counters are ( most likely ) useless for high-lumi
runs even for the endpoint energy region. The singke counter rate
in this region is about 5 MHz. As an example, for 20 counters the
rate is ~ 100 MHz (on average 1 hit every 10 ns). There will be  a
lot of multiple hits in any reasonble electronics time integration
window. I doubt that it will be possible to resolve multiple hits
even in the offline analyses with our detector resolution.

Cheers,
        Sascha




On Wed, 20 May 2009, Elton Smith wrote:

>
>
> ---------- Forwarded message ----------
> Date: Wed, 20 May 2009 17:09:35 -0400
> From: David Lawrence <davidl@jlab.org>
> To: halld-tagger@jlab.org
> Subject: Tagger energy resolution?
>
> Hi Photon-ists,
>
>    I'm getting my talk put together for CIPANP next week and I'm a bit
> confused about the tagger energy resolution numbers I'm seeing. I've
> spoken with Eugene and Elton and I think I understand them better now,
> but I would like to get confirmation from the group.
>
>    I've seen a couple of places (GlueX-doc-1167, GlueX-doc-1127) where
> the microscope resolution is quoted as 0.5% of the electron beam energy
> or 60MeV. However, the microscope has 100 detectors covering a 600MeV
> range so the tagger itself is capable of something closer to 6MeV
> resolution. As I understand it, the 60MeV comes from the uncertainty in
> the electron beam energy and not due to any limitation of the tagger
> design itself. The "over-design" of the resolution is due to rate
> considerations.
>
>    What raised a flag for me was the fixed array which seems to always
> be quoted as having detectors spanning a 30MeV bite which is half as big
> as the quoted microscope resolution. Though I don't actually see it
> anywhere, I'm assuming that the fixed array also has an energy
> resolution of 60MeV limited by the electron beam energy resolution.
>
>    Can someone confirm that all of this is correct?
>
>    If this all is correct and the fixed array and the microscope both
> have the same energy resolution and they both can handle the rate at
> full luminosity and they both fully cover the same energy range (8.4-9.0
> GeV) then why do we need both?
>
>    Sorry if this is a stupid question, but I've always assumed that the
> purpose of the microscope was to give much finer energy resolution.
>
> Regards,
> -David
>
> -- 
>
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