[Halld-physics] Polarization values

[Alexander Somov]

Hello Richard,

A couple of things:

1. Based on Mike's tool, for the full run set
of 2017 (if I use the tool correctly, v2),
error bars don't allow to conclude much about the
edge of the coherent peak. Shapes look  identical
for 0, 45, 90 and 135 deg. within error bars. The
energy resolution of even 100 MeV will not impact
the shapes much.

2. The energy spread, which Mike presented seems
to be relatively large (I have to check my Geant
simulations). For the typical electron angle of
about 0.1-0.2 mrad, the energy spread (sigma) in
the horizontal plane should be better than
25-30 MeV  for the near converter (station 1).

For the far converter, the flight distance is
larger, resulting in the (slightly) worse energy
resolution due to the intrinsic PS angle. Originally
we wanted to place the TPOL to the station 1. I think
that we have to move it (at some point); the PS magnet
fringe field should be Ok.

3. A concern of using the tagger spectrum for
high-statistic polarization measurements (without
TPOL) is non-uniform and poorly known efficiencies
(especially in TAGM), which we don't need for
the tagged flux calculation but have to use
to correct the shape.

Cheers,
       Sasha



On Tue, 19 Sep 2017, Richard Jones wrote:

> Hello Mike,
>
> It might be better to plot the same quantity on the x axis across the
> entire plot, even if the statistical errors turn out to be somewhat larger.
> Whatever the acceptance of the TAGH might be, it IS what defines the tagged
> beam at energies above the TAGM. Unless someone has a physics channel for
> which they do not need to know the energy of the beam photon, it is only
> the tagged flux that is of any interest to GlueX analyses.
>
> in response to Sascha,
>
> The PS energy contains a polarization bias. If one is in a flat part of the
> spectrum then this will average out, as you say. But if you are sitting in
> a steep location, say just above the coherent edge then the PS has a
> different energy resolution depending on the polarization of the photon. If
> the pair comes out in the horizontal plane then it has an energy spread on
> the order of 100 MeV, as Mike showed. The resolution for vertical-plane
> pairs is much better. This would be expected to produce a different
> steepness of the coherent edge in PARA and PERP runs. This is what I mean
> by artifacts. But Mike is using the TAGM energy in the region of the
> coherent edge, so that is good.
>
> -Richard Jones
>
>
> On Tue, Sep 19, 2017 at 12:04 PM, Michael Dugger <dugger at jlab.org> wrote:
>
>>
>> Richard,
>>
>> In the coherent peak I use the tagger energy. For energies outside the
>> coherent peak, I use the PS. I use the PS outside the coherent peak because
>> of statistics.
>>
>> For the Spring 16 priority set, I use the tagger energy for energies
>> bewteen 8.4 and 9.4.
>>
>> For the Spring 17 runs, I use the tagger energy for energies between 8.2
>> and 9.3.
>>
>> As long as people are within the energy ranges given above, the tagger
>> energy is being used to bin the data.
>>
>> If you don't like the mixing of PS and tagger for the energy binning, I
>> can easily modify the code so that only tagger information is used. For the
>> most part, it will just pump up the error bars for the energy regions
>> outside the coherent peak.
>>
>> Take care,
>> Michael
>>
>>
>> On Tue, 19 Sep 2017, Richard Jones wrote:
>>
>> Mike,
>>>
>>> These are very nice results, good to see that the spread between the
>>> different polarization orientations is now much less than we were seeing
>>> before, esp. 2017.
>>>
>>> One question about the energy scale. Are you using the tagger energy to
>>> decide which bin each event should go into? Now that we know the PS energy
>>> is entangled with the polarization, to produce a spectrum free of
>>> artifacts
>>> we should only be using the tagger energy to make this spectrum.
>>>
>>> -Richard
>>>
>>> On Tue, Sep 19, 2017 at 10:08 AM, Michael Dugger <dugger at jlab.org> wrote:
>>>
>>>
>>>> Hi,
>>>>
>>>> I have code that creates the polarizations for
>>>> Spring 16 (priority set 1) and Spring 17 data
>>>> at
>>>>
>>>> https://userweb.jlab.org/~dugger/triPol/makePolValsV2.tar
>>>>
>>>> Once you have un-tarred the file, go through the steps in
>>>> the README file to generate the polarizations.
>>>>
>>>> Take care,
>>>> Michael
>>>>
>>>> _______________________________________________
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>>>>
>>>>
>>>
>