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

[Richard Jones]

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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> https://mailman.jlab.org/mailman/listinfo/halld-physics
>
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