Dear colleagues,
as we have discussed today in the meeting about the final positions for
LADS and NC, we agreed to favor version 2, with neutron acceptance up
to 90 degrees, and forward angle acceptance with LADS walls down to 28.3
degrees.
There were actually only arguments for and none against that choice.
1) We gain 10 degrees at backward angle while loosing only 1 degree at
forward angle as compared to version 1.
2) In order to explore the off-quasielastic peak region by a variation of
the neutron angle, doing that at on the backward side is favorable due
to less background.
3) In both versions the quasielastic angle even for the highest Q2 is well
within acceptance
4) Though there might be quite some material in front of the detector
between 80 and 90 degrees, it is better to have at least a possibility
to detect anything.
5) It is easier for Jim Kelsey to build a support and move the NC in when
it covers the 90 degrees.
Best regards,
Michael
On Mon, 2 Jun 2003, Michael Kohl wrote:
> Dear collaborators,
>
> Jim Kelsey has worked out detailed CAD layouts of the possible final
> positions for the neutron walls (existing NC and refurbished LADS).
>
> Taking into account that four LADS bars out of 28 per sector have to be
> excluded (due to lack of phototubes), there are now two approaches
> optimized for two separate requirements.
>
> The first approach optimizes the forward-angle acceptance, with two LADS
> bars behind each other, resulting in 35cm thickness. The most forward angle is
> thus 27.5 degrees. The two 15+20cm LADS walls overlap between 27.5
> and 42.7 degrees. The price for this is the reachable most backward angle
> for the NC, which is 80 degrees while providing still a small overlap with
> the LADS walls around 43 degrees.
>
> The second approach covers neutron angles with the NC up to 90 degrees.
> Thereby, the LADS acceptance to forward angles shrinks a little and the
> most forward angle which is covered is 28.3 degrees. The overlap
> with NC is at 46 degrees. The two 15+20cm LADS walls overlap between 28.3
> and 42 degrees. In a slightly modified version, the most forward angle
> would be 29.6 degrees, and the two LADS walls overlap between 29.6 and
> 43.3 degrees.
>
> The second approach is technically less difficult to handle for Jim, as
> the first approach needs an additional support for the NC.
>
> In the present layouts for the LADS positions, the lead glass detectors
> can't be in at the same time.
>
> As there might be different preferences from various experiments, it is
> suggested to have a meeting tomorrow (June 3) at 11am in the conference
> room) in order to discuss this and to come closer towards a decision
> which makes everybody happy.
>
>
> Regards,
>
> Michael
>
>
>
>
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