[Halld-offline] Beam Polarization
Curtis A. Meyer
cmeyer at cmu.edu
Mon Feb 29 21:23:11 EST 2016
I think that all of the methods we have provide an estimate for the polarization for a given photon
energy, and none of them are event-by-event. The knowledge that we gain from each of them
has to be built into a function, that given a photon energy and an “event time”, can give us our
best estimate of both P and the error in P.
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 29, 2016, at 9:16 PM, Nathan Sparks <nsparks at jlab.org> wrote:
>
> My understanding is that the triplet polarimeter measurement cannot give us a polarization number for each event.
> The procedure for extracting the polarization using the TPOL is similar to extracting the beam asymmetry (Sigma),
> except in this you know Sigma instead of P:
> 1. Make a clean selection of triplet events and fill a histogram of the azimuthal angle of the recoil electron for a E_gamma bin.
> 2. Fit the phi distribution with N(phi) = N_0(1+P*Sigma*cos(2*phi)), determining P*Sigma.
> 3. Divide by the calculated Sigma to obtain P.
> There are variations on this procedure, similar to what Justin has described for extracting Sigma, which utilize both orientations of the beam.
> My main point is that this procedure provides an average polarization for a given E_gamma bin; As long as statistics are sufficient,
> the energy binning can be chosen to match the one used in an observable extraction. Then at this level the average polarizations
> could be combined or used as input for systematic uncertainty.
>
> -Nathan
>
>> On Feb 29, 2016, at 7:54 PM, Curtis A. Meyer <cmeyer at cmu.edu <mailto:cmeyer at cmu.edu>> wrote:
>>
>> Each will technically provide a P and an error. We should agree on how to combine them I guess.
>>
>>
>> ---------
>> 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 <mailto:curtis.meyer at cmu.edu> http://www.curtismeyer.com/ <http://www.curtismeyer.com/>
>>
>>
>>
>>> On Feb 29, 2016, at 7:51 PM, Paul Mattione <pmatt at jlab.org <mailto:pmatt at jlab.org>> wrote:
>>>
>>> Well, both could be useful: we could compare them for computing systematic uncertainties. But yes, having a standard source that everyone agrees on is ideal. But I don’t know how to make the determination of which to use, once both systems are up and running.
>>>
>>> - Paul
>>>
>>> On Feb 29, 2016, at 7:47 PM, Curtis A. Meyer <cmeyer at cmu.edu <mailto:cmeyer at cmu.edu>> wrote:
>>>
>>>> There should really only be a single number that is our best etimate from all data 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 <mailto:curtis.meyer at cmu.edu> http://www.curtismeyer.com/ <http://www.curtismeyer.com/>
>>>>
>>>>
>>>>
>>>>> On Feb 29, 2016, at 7:37 PM, Paul Mattione <pmatt at jlab.org <mailto:pmatt at jlab.org>> wrote:
>>>>>
>>>>> Do we want two beam polarization numbers in DBeamPhoton? One calculated via the fit to the tagger spectrum, and one via the triplet polarimeter measurements?
>>>>>
>>>>> - Paul
>>>>>
>>>>> On Feb 23, 2016, at 9:08 AM, Sean Dobbs <s-dobbs at northwestern.edu <mailto:s-dobbs at northwestern.edu>> wrote:
>>>>>
>>>>>> 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 <mailto: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 <mailto: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 <mailto: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 <mailto:curtis.meyer at cmu.edu> http://www.curtismeyer.com/ <http://www.curtismeyer.com/>
>>>>>> >>>
>>>>>> >>>
>>>>>> >>>
>>>>>> >>>> On Feb 22, 2016, at 8:25 PM, Paul Mattione <pmatt at jlab.org <mailto: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 <mailto: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 <mailto:curtis.meyer at cmu.edu> http://www.curtismeyer.com/ <http://www.curtismeyer.com/>
>>>>>> >>>>>
>>>>>> >>>>>
>>>>>> >>>>>
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