My inspection of the qweak euclid file and the associated ntuple
proved by Julliete in row 20 of
the table on the live collimator page suggests that a Region
1 chamber 10cm x 20cm in area should cover the elastic
scattering envelope which passes through the first collimator in
the experiment centered at Z=-575.79 cm (distance upstream of
QTOR magnet center). At Z=-568.17, the inner radius of the
collimator is given as 6.2 cm and the outer radius is at 19.3cm.
A graph of elastic scattered electrons as a function of vertx_in
and verty_in at that position confirms this observation.
The profile
of the electrons about 23 cm downstream of that location
appear to start at an inner radius of about 8 cm and extend to an
outer radius of 27 cm.
Based on the above images, I would conclude that a GEM ionization
chamber with a 12 cm x 23 cm active area would encompass the
elastic scattered electron profile in Qweak no matter where it is
placed within the 20 cm wide Region 1 area. Since this size is
not readily available, the GEM foils and readout board will need
to be designed. Furthermore, since effort will be made to
design this size one need only invest a minimal amount of further
effort to make the shape more
trapezoidal than square to
facilitate the possibility of constructing a detector which will
not intrude into nearby octants.
Another improvement to the previous Qweak design would be to
construct a charge collector using lines of "r" and "phi" (polar
coordinates) instead of the "x" and "y" (Cartesian) design. One
would be able to ideally align a given "phi" charge collector
strip to allow a direct measurement of a given scattering angle.
Rui at CERN has stated that the above special design GEM foils
and readout board could be supplied within 1 year.
The VFAT board is schedule for Beam tests at CERN in October. My plan is to participate in those tests.
A loan agreement form has been submitted which will allow us to borrow the spare BoNuS RPC electronics and should be enough to instrument a 10 cm x 10cm GEM detector. The BoNuS input connector to the pre-amplifer needs to be changed so it is compatible with the protoype chamber connectors. The alterations to the preamp board have been made, I am waiting for the electronics to arrive from JLAB so I can confirm all connectors before getting a board made. I hope this can be put in place by July.
