[Halld-offline] Beam Polarization

[Sean Dobbs]

It should be easy enough to add polarization parameters to DBeamPhoton
(which I think is what Curtis was advocating).

Supporting beam polarization parameters that vary over the run is more
complicated.  The CCDB doesn't currently handle conditions that vary over
less than the run.  A potential solution could be to write out coherent
peak fit parameters in EPICS variables in the data stream, such that a LUT
for the tagger counters could be regenerated over the run.  Parameters for
the derivation could be stored in the CCDB.  Hopefully all the hard work on
the accelerator side will results in a stable enough beam that we won't
need this level of detail for real production runs.

Cheers,
Sean

On Tue, Feb 23, 2016 at 2:50 AM Dominik Werthmueller <werthm at jlab.org>
wrote:

> 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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