[Halld-physics] Analysis Working Group Meeting: Tuesday August 9th @ 1:30pm

[Richard Jones]

Ok, will look into it.

Richard

On Aug 9, 2016 5:54 PM, "Paul Mattione" <pmatt at jlab.org> wrote:

> Richard, the shift corresponds to a change of 25 MeV in beam energy.  I
> have computed it from the data (g, p -> 4pi, p (nothing missing)) and have
> plotted it at:
>
> https://logbooks.jlab.org/entry/3416791
>
> So it’s about a whole counter.
>
>  - Paul
>
> On Aug 9, 2016, at 3:33 PM, Richard Jones <richard.t.jones at uconn.edu>
> wrote:
>
> Hello Paul and all, related to discussion at today's analysis meeting:
>
> Brendan and I did a quick estimate of the sensitivity of the
> missing-mass-squared to the tagger energy scale in the region of the step
> revealed in the plots you showed today, around 4 GeV photon energy. We
> conclude that an offset as small as 6-8 MeV in the mean tagged photon
> energy associated with a given tagger counter could explain this step. The
> tagging counters in this region subtend about 25 MeV. So the observed step
> could be generated by systematic shifts in the position of the tagger
> hodoscope counters by as little as 1/3 of their width. Their width in this
> region is only 3mm wide, so the required scale for the shift would be 1mm.
> We looked at the geometry of the tagger and we think there is a large
> physical path-length distance between sets of counters with a boundary
> close to the region where your step occurs. The fact that one data point
> seems to interpolate across the step is not surprising, given Dan Sober's
> observation that beam divergence and multiple scattering effects create
> significant cross-over of tagged electrons between neighboring tagger bins.
> This break appears because the counters are arranged in rows with different
> distances from the focal plane, and at the downstream end of the hodoscope
> the path length between rays that hit the front row blocks and the back row
> is large compared to their spacing within a row.
>
> All of this is to say that shifts of order 0.010 - 0.015 GeV^2 in
> missing-mass-squared are expected based on the present precision (~10MeV)
> of the calibration of the position of the boundaries of the tagger energy
> bins in this region. In the region of the microscope, I expect that the
> precision is better, of order 5MeV, but not by an order of magnitude.
>
> -Richard Jones
>
> On Mon, Aug 8, 2016 at 11:37 AM, Paul Mattione <pmatt at jlab.org> wrote:
>
>> The next analysis working group meeting will be tomorrow at 1:30pm in
>> room A110.  The agenda is posted at:
>>
>> https://halldweb.jlab.org/wiki/index.php/August_9,_2016,_
>> Analysis_Working_Group
>>
>>  - Paul
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>> Halld-physics mailing list
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>>
>
>
>
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