[Sbs_gems] [EXTERNAL] UV Latency Analysis Results

[Sean Jeffas]

Hi All,

I have finished analyzing the spatial distribution of the peak time
samples. I have attached the results below for two runs.

*Run 13240: *Taken January 11th with all four UV layers and 2 uA on LH2 at
the SBS-14 kinematic.
*Run 12423:* Taken December 1st with J0 still in the layer 1 position but
the UV layer was in layer 3 position. This was 2 uA on LD2 at SBS-11.

In the recent run (13240) you can clearly see the peak time sample is
uniform over the hit map for every layer except for layer 1 and layer 3.
Similarly if you look at the December run (12423) the same issue was
present in layer 3, but we never noticed it because we were always the
first and last bin out of the analysis. John and I measured the resistors
on the GEMs today and did not find a resistance that would suggest that the
gas window has collapsed onto the cathode. Unfortunately the shielding
blocks us from seeing the gas window, otherwise it would be very easy to
tell.

Therefore our current conclusion is that since the GEM layers 1 and 3 both
have a non uniform gas flow, this is probably causing some bend in the
readout board, which causes this issue. To fix this we can turn down the
gas flow rate and see how everything is affected. Since the experiment is
down for a few days it would be good to turn it down today and take some
cosmic data, if possible.

Best,
Sean
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