[Sbs_gems] [EXTERNAL] Re: Non-uniform GEM signal timing in BigBite during GMN/GEN

[Sean Jeffas]

Hi Andrew,

This is due to improper gas flow in layers 1 & 3 because they were
manufactured and sent to us with a defect. Therefore they do not have
uniform gas flow and the GEM foils bulge slightly inside. We have reduced
gas flow in these layers to mitigate the effect. In the pdf attached below
I have the plots showing this during GMn running. The color scale shows the
average time sample peak. Clearly the layers except for 1 & 3 are uniform.
Interestingly, in layer 1 & 3 you can clearly see the spacers on the GEMs.
If you look at the picture I have attached of the GEM foil with the spacer
it perfectly matches up with the timing hit map.

Best,
Sean

On Thu, Apr 27, 2023 at 4:49 PM Andrew Puckett via Sbs_gems <
sbs_gems at jlab.org> wrote:

> Hello all,
>
>
>
> As you may remember, we saw that GEM layers 1 and 3 in BigBite exhibited
> significantly wider timing distributions during GMN (and GEN), even for the
> good signals. Recently, for the first time, I tried to get a closer look at
> the uniformity (or lack thereof) of the signal timing for the GEMs, with
> some interesting findings. I wanted to solicit the opinions of the GEM
> hardware experts to see if this is something that has been seen before, and
> if the pattern has a simple explanation, what the physical mechanism might
> be, and whether it could be mitigated in the future.
>
>
>
> The first picture shows the average signal timing (U+V)/2 on the x axis
> for the five BigBite GEM layers versus global “x” position of the hit on
> the y axis. As we can see, in UV layers 0 and 2, the timing is relatively
> uniform as a function of vertical hit position, whereas for layers 1 and 3,
> there is a significant correlation that follows a similar x dependence.
> Layer 4 also exhibits an x dependence qualitatively similar to layers 1 and
> 3 but the magnitude is smaller compared to the resolution. Also, in all
> cases the width of the good timing peak for layers 1 and 3 is wider (~10
> ns) compared to layers 0, 2, and 4 (~6-7 ns), even after accounting for the
> non-uniformity versus position. The second attachment shows the correlation
> with the y-coordinate. Here layers 1 and 3 still show a fairly significant
> correlation while layers 0, 2, and 4 show almost no correlation.
>
>
>
> While this is something we can in principle measure and correct for if we
> want to apply tighter timing cuts in the analysis, I would love to hear
> people’s ideas for what is happening here. Thoughts?
>
>
>
> Best regards,
>
> Andrew
>
>
>
>
>
>
>
> Andrew Puckett
> Associate Professor, Physics Department
> University of Connecticut
> 196 Auditorium Road, Unit 3046
> Storrs, CT 06269-3046
> Office phone: (860) 486-7137
> https://urldefense.proofpoint.com/v2/url?u=https-3A__puckett.physics.uconn.edu&d=DwIFaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=IY9rjQPVeUBORHn2z0jGy7U2Cc-U0-dYM3Rqg9Kcgwk&m=mqnr-u03fz88sFWzNehQ_K9gIZ354OKqu8BXbauy_ozF8ZM098hMov7wraXZim1F&s=PWgMf4P2IDtkIF4iMhHRA-8Ko-zkQSdC33M2uBySJBo&e= 
> puckett at jlab.org <andrew.puckett at uconn.edu>
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