[Olympus] OLYMPUS main tracker upgrade

[frullani@iss.infn.it]

Dear All,
following Alexander mail, as far as the cost of the electronic readout for
GEM I do not see a big problem in doubling the channels of the GEM
tracker, if we have two planes in each arm (of course if the electronics
we are developing in Rome will be used).
The Jlab project on which we are working (both for chambers and
electronics production) and that it is already funded by INFN foresees
about 50.000 channels (+ spare) for electronics. If we double the number
of GEM tracker channels (1300 -> 2600) and we add the GEM luminosity
channels (2000) we are at 1/10 of the channels of the JLAB's SBS (Super
Bite Spectrometer) request (in a 10**38 cm-2s-1 luminosity environment).
This is a reasonable number for a test experiment as OLYMPUS could be
presented respect to INFN as far as regard the money contribution of INFN.
If needed, more information when I will be back in Rome next week.
Regards. Salvatore
>   Dear colleagues,
>
>   Doug pointed out to me yesterday (I admit I overlooked
> this issue in the TRD draft) that main tracker upgrade will
> consist of a *single* 2D XY-plane GEM in each arm, meaning 0
> redundancy design. Also, if I get it right, foils will be
> patchy, meaning some (small?) dead zones.
>
>   Such low-redundancy setups may become problematic in many
> respects (although perhaps not all of them apply to GEM/APV
> configuration, I have no experience with this hardware):
>
>   - track finding and ghost track rejection is very sensitive to
>     background hits; in case of noisy/dead channels/planes it
>     needs to fall back to less efficient "low-resolution" mode
>     provided by other detectors (existing wire chambers in our case);
>
>   - tracking resolutions for cases when GEM detectors have no hits
>     in X-layers will be as bad as before, so data analysis will have
>     to combine both low- and high-resolution tracks, which is a pain;
>
>   In my view, if we really tend to use this upgrade to reduce operating
> costs (obtain much better resolution --> suppress background --> lower
> down magnet current at least for the last 2 months of operation), we
> should better take care that there are usable hits in GEM tracker for
> ~all tracks under any conditions.
>
>   Ideally we would probably need to at least double number of
> registering planes within the existing design. If this is excluded
> for financial reasons, perhaps consider to install say 2x2D planes in
> each arm, but with bigger strip spacing (thus maintain comparable number
> of channels). Or at the very least to install suggested single 2D layers
> at +/-45 degrees instead of XY-orientation, so that each side (being
> combined with the beam line constraint) delivers a measurement in
> horizontal plane, where exactly we have a problem.
>
>   Regards,
>     Alexander.
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