[Sbs_gems] [EXTERNAL] Question on pedestal plots

[Gnanvo, Kondo (kg6cq)]

Hi Andrew,
Thanks, This all make sense. I was also suspecting that sag will have to do with the negative pulses.
There are 3 different features that I can see here that might be worth investigating

1-) The sagging for Danning method is significantly larger than for the sorting algorithm, this should impact the occupancy calculation and ultimately performance. I am not sure I understand what you mean by “more downside bias for the Danning method” compared to the sorting algorithm

2-) Sagging is worse for the U/V layers than for the X/Y layers ==> is it just because of the background rate, I guess we can study this by looking at the low beam currents GEM studies runs. I can’t think of anything intrinsic to the U/V layers that would explain that.

3-) We can also look at the negative pulse rate as a function of the beam current and consequently look at te correlation between  the common mode sagging amplitude and the  negative pulse rate

Best regards
Kondo

From: Andrew Puckett <puckett at jlab.org>
Sent: Saturday, January 22, 2022 7:28 PM
To: Gnanvo, Kondo (kg6cq) <kg6cq at virginia.edu>
Cc: Sbs_gems at jlab.org
Subject: Re: [EXTERNAL] Question on pedestal plots

Hi Kondo, We’ve seen this phenomenon since the beginning of the experiment, it was worse for high Q2 kinematics. The negative sag of the common mode for either method  is attributable to the wrong polarity fluctuations. The difference between Danning and sorting method calculations is something we’ve also seen from the beginning. The Danning method as implemented offline is subject to more downside bias as a result of this compared to the sorting method. I suppose if we see a larger difference in some modules it could affect the efficiency, but is hopefully correctable in software.

Andrew
puckett.physics.uconn.edu


On Jan 22, 2022, at 6:58 PM, Gnanvo, Kondo (kg6cq) <kg6cq at virginia.edu<mailto:kg6cq at virginia.edu>> wrote:

Hi Andrew,
I was looking at some pedestal plots and I noticed two things,

1-) The difference between sorting and Danning method has this curve-like shape for the U-V strip layer that is not seen for the X-Y layers and the difference is quite significant compare to the common mode fluctuation itself. I looked at some earlier plots (run 13394) when we had all 4 U-V layers as well as the most recent one and it seems quite consistent.

https://logbooks.jlab.org/files/2022/01/3975625/summaryPlots_13455_BBGEM_ped_and_commonmode_50k_printme.pdf

https://logbooks.jlab.org/files/2022/01/3974078/summaryPlots_13394_BBGEM_ped_and_commonmode_50k_printme.pdf

2-) I also see for the V stripe of layer#1, the difference is more pronounced and I am thinking this might partly explain the lower efficiency we are seeing with this layer

I was wondering if there is any explanation for the discrepancy. Maybe there is something here that we can learn something from

Best regards
Kondo
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