[Halld-offline] Beam Polarization

[Dominik Werthmueller]

I'm not sure we should rely on stable polarization within a run given the CEBAF beam stability and the extreme GlueX beam optics, surely Ken could comment on that in more detail. As single GlueX runs are rather long, I would definitely favor a finer granularity (ranges of events, for example). I think that a simple LUT with polarization values for all tagger counters is more flexible than storing parameters for a certain polarization parametrization that might change in the future.

Cheers,
Dominik


> Am 23.02.2016 um 02:53 schrieb Justin Stevens <jrsteven at jlab.org>:
> 
> It seems the simplest place to include this in our current framework is the CCDB, assuming the polarization is not varying much within a single run or range of runs.  For the energy dependence of the polarization, we could store
> 
> 1) a table with polarization values for individual energy bins (eg. tagger counters/columns) or
> 2) some parameters for a function which describes the polarization shape with energy
> 
> The polarization direction for a run should already be in RCDB, but probably should be mirrored in CCDB for simplicity.
> 
> -Justin
> 
> On Feb 22, 2016, at 8:50 PM, Paul Mattione wrote:
> 
>> Well, if we were to fit the polarization many different times within a run, we would need a mechanism for storing, and then looking up, the fit results relevant for each given range of events.  Do we have a mechanism that can do this yet?  Or am I thinking about this wrong? 
>> 
>> - Paul
>> 
>> On Feb 22, 2016, at 8:30 PM, Curtis A. Meyer <cmeyer at cmu.edu> wrote:
>> 
>>> Yes, but it does depend on the photon energy. E.g. how far away from the coherent edge are you?
>>> Events near the edge will have the highest degree of linear polarization, while those far away will
>>> have less. If the edge is stable, the function is pretty simple., but we still need to be able to assign
>>> both a polarization and a polarization direction to our photons on an event-by -event basis.
>>> 
>>> Curtis
>>> ---------
>>> Curtis A. Meyer			MCS Associate Dean for Faculty and Graduate Affairs
>>> Wean:    (412) 268-2745	Professor of Physics
>>> Doherty: (412) 268-3090	Carnegie Mellon University
>>> Fax:         (412) 681-0648	Pittsburgh, PA 15213
>>> curtis.meyer at cmu.edu	http://www.curtismeyer.com/
>>> 
>>> 
>>> 
>>>> On Feb 22, 2016, at 8:25 PM, Paul Mattione <pmatt at jlab.org> wrote:
>>>> 
>>>> I was under the impression that, for a given beam energy, the polarization would be relatively constant over the course of a run.  
>>>> 
>>>> - Paul
>>>> 
>>>> On Feb 22, 2016, at 8:22 PM, Curtis A. Meyer <cmeyer at cmu.edu> wrote:
>>>> 
>>>>> Hi Everyone,
>>>>> 
>>>>>  I am not sure if we have this capability yet, but as we move forward we are going to
>>>>> want the REST files to contain the photon polarization. This is likely a function that
>>>>> we have to call when we have decided what the correct photon is, but we should have
>>>>> the hooks in place to do this on an event-by-event basis.
>>>>> 
>>>>> Curtis
>>>>> ---------
>>>>> Curtis A. Meyer			MCS Associate Dean for Faculty and Graduate Affairs
>>>>> Wean:    (412) 268-2745	Professor of Physics
>>>>> Doherty: (412) 268-3090	Carnegie Mellon University
>>>>> Fax:         (412) 681-0648	Pittsburgh, PA 15213
>>>>> curtis.meyer at cmu.edu	http://www.curtismeyer.com/
>>>>> 
>>>>> 
>>>>> 
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