Let me add a note about the target polarization since there seems
to be some confusion about the expectations. We run the hydrogen
target in single state mode mainly because the polarization in this
mode is high and not affected by the target field. This target was
designed to produce a high polarization even at a 5 Gauss holding
field.
The concerns in the past were based on little understood measurements
of P=0.35 that might have been caused by surface effects -recombination
and possibly relaxation- on the surface that vanished after we arrived
at a all-Drifilm target cell (after removal of the teflon injection
tube) that is protected by a collimator.
In the past week we measured target polarization values between
0.65 and 0.75 dependent on the analysis you look at and person you
talk to, which shows that we are almost in the high polarization
limit near 0.75 that we aimed for. At these polarizations values
there is little room for a significant field dependence and one
expects the same target polarization at a spin angle of 60 deg.
Hauke
On Tue, 2004-11-02 at 15:48, John Calarco wrote:
>
> Since it seems that people are lobbying by making "public" statements
> about their choice of target spin angle, I seem to have no choice but
> to reply.
>
> Facts:
>
> (1) It is not true that Ge/Gm is insensitive to the choice of spin
> angle. Chris' analysis of the recent 32 and 45 deg data shows that
> the properly normalized errors are reduced by a factor of about 0.7
> in going from 32 to 45 deg. This is equivalent to a factor of 2 in
> beam time. MC shows even further improvement if we get the equivalent
> target polarization at a spin angle of 60 deg.
>
> (2) Ge/Gm is the PAC approved experiment and the one we have promised
> to the DOE review committee to complete by the end of 2004.
>
> (3) The parasitic experiments are NOT the PAC approved physics.
>
> It is very clear that the studies in the Delta would prefer the smaller
> spin angle, but they are not what is driving the choice. If the upcoming
> test at a spin angle of 60 deg (after the 40 kC at 32) shows that the
> target polarization is still high, the spokespersons of the approved
> program will request to run at that angle. It does not seem reasonable
> to compromise the results of an approved program in order to try to
> extract physics which we may or may not be able to.
>
>
> --
> John R. Calarco
> Dept. of Physics
> Univ. of New Hampshire
> Durham, NH 03824
> phone: (603)862-2088
> FAX: (603)862-2998
> email: calarco@unh.edu
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