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The logic behind this new idea is as follows:</div>
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The brand new research by Gianni Benchvinni's group at Frascatti has shown that the improved uRwell could operate at hit rates upto 1 MHz/cm^2 (Gianni is physicist who invented uRwell concept; Huong has visited his lab and formed collaborative connections
with his group; Gianni has graciously agreed to collaborate with us on this new develpment aimed at SBS and SoLID.)</div>
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At these very high rates, to facilitate stable operation, uRwells need to operate at low gains, about 2000 as opposed to about 8000 for GEMs. These low gains are sufficient to support one readout direction, but not enought for charge to be divided between two
directions. As such one 1 detectors, for example U or V are the most optimum in these conditions.</div>
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Actually this is much better for us in SBS conditions: most of our random background, low energy photons, only give a random hit on a single layer, but not correlated hits on successive independent detectors. </div>
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In our UV or XW case, the total number of channels we have per chamber allows us to build a pixel detector with pixel sizes of 1 cm x 1 cm to have the same active area and the same total channels as a UV or a XW. </div>
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Having two pixel chambers seperated by some distance and requiring .AND. between hits on both can clean up most of the random hits and select mostly the high energy tracks. </div>
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Given the catchment area for these pixels, the occupancy level would be about 1/6<sup>th</sup> of that of any existing UV or XW chamber; so in the worst case the occupancy would be around 10%; and the .AND. condition would lower this by some factor (beween
1 and 10, and I think closer to 10)</div>
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Also we can place one pixel chamber at the front of the stack and one at the end of the stack; they will be built as independent detectors and can be seperated by any distance. </div>
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All this would ensure that we have a pretty narrow (about a factor of 100 smaller in area than right now) search area for hits on the strip chambers. </div>
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As for 1D strip chambers: in the current 2D strip chambers, since the same charge cloud gives both U and V hits, the random hits and hign energy track hits are indistinguishable: they would both give correlated and correct U/V combinations (as opposed to ghost
UV combinations which are filtered out in tracking), in the order of (occupancy); for example, at ~ 40% for GEp</div>
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On the other hand, when we have a 1D U chamber and a 1D V chamber (in this case not too far apart), we will only get correlated U/V hits, WITHIN THE NARROW SEARCH AREA POINTED TO BY THE PIXELS., only for the high energy tracks, and only trandom combinations,
in the oder of (occupancy^2) for the random hits; for example, ~ 16 % for GEp.</div>
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So, this is what makes the combination of two back to back pixel detectors, combined with a back to back 1D U and 1D V detectors so powerful in our situation.</div>
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<div id="divRplyFwdMsg" dir="ltr"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>From:</b> Sbs_gems <sbs_gems-bounces@jlab.org> on behalf of Liyanage, Nilanga K (nl8n) via Sbs_gems <sbs_gems@jlab.org><br>
<b>Sent:</b> Wednesday, May 15, 2024 12:33 PM<br>
<b>To:</b> Bogdan Wojtsekhowski <bogdanw@jlab.org>; Sbs_gems@jlab.org <Sbs_gems@jlab.org>; Mark Jones <jones@jlab.org><br>
<b>Subject:</b> [Sbs_gems] [EXTERNAL] Re: Test for GEp</span>
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Also, I am realizing that this information makes what I have been considering (outlined below) so much more important and urgent. :</div>
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I just got the quotes from Rui at CERN about the pixel uRwell chamber I have been talking about for GEp to make the tracking much easier than robust. The cost of material for a double chamber is about $ 30 k, and Huong and I would be happy to contribute person
power from our group to build two double chambers by late fall, hopefully in time for GEp installation; of course this will depend on when we can get the parts from CERN; Huong is traveling there in June and will try to convince Rui to get these foils to us
on time.</div>
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The ideal and the most powerful combination would be a double pixel chamber ( two back to back chambers with 1 cm x 1 cm pixels) and a double UV chamber (back to back strip chambers, same pitch as UV, one chamber with U readout and the second with V readout);
and we need to find $ 60 k for this set. Given the extremely high importance of this for GEp, and the urgency of the situation, I am happy to go ahead with the orders for the double pixel chamber using my grant funds at UVa. I plan to initiate these orders
today. </div>
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I will send in a request to Mark and Bogdan soon for the funds for the UV set, if you can find funds from either Jlab or from collaborators, we can place those orders very soon as well and build both double layer detectors at the same time.</div>
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Best</div>
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Nilanga</div>
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<div id="x_divRplyFwdMsg" dir="ltr"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>From:</b> Liyanage, Nilanga K (nl8n) <nl8n@virginia.edu><br>
<b>Sent:</b> Wednesday, May 15, 2024 12:20 PM<br>
<b>To:</b> Bogdan Wojtsekhowski <bogdanw@jlab.org>; Sbs_gems@jlab.org <Sbs_gems@jlab.org>; Mark Jones <jones@jlab.org><br>
<b>Subject:</b> Re: Test for GEp</span>
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Hi Bogdan</div>
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Yes, you are absolutely correct, it is a 30 cm target. I am sorry I missed that. So yes, it would be a factor of 6-7.</div>
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Yes, in that case it is good to push higher in the beam current for the test and also test the HV corrections on Sunday.</div>
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While I think that from the hardware perspective the GEMs would still be OK at that high luminosity, I think Andrew might have a really challenging problem with tracking with that factor of 6-7 increase: currently we are having raw occupancies of ~ 12.5 %
, so given the same gain etc. we will have about 80-90% level occupancies for GEp; I do not think we ever expected or prepared for those level of occupancies (Andrew, please correct me if I am mistaken here); in my opinion, it would be next to impossible to
run with anything higher than ~ 50-60% occupancy and get useful tracking information.</div>
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In that case we will seriously have to think about the hadron filter you have been proposing; and this Sunday could be an idea opportunity to test something like that.</div>
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Best</div>
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Nilanga</div>
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<div id="x_x_divRplyFwdMsg" dir="ltr"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>From:</b> Bogdan Wojtsekhowski <bogdanw@jlab.org><br>
<b>Sent:</b> Wednesday, May 15, 2024 12:07 PM<br>
<b>To:</b> Liyanage, Nilanga K (nl8n) <nl8n@virginia.edu>; Sbs_gems@jlab.org <Sbs_gems@jlab.org>; Mark Jones <jones@jlab.org><br>
<b>Subject:</b> Re: Test for GEp</span>
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Hi Nilanga,</div>
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We can use BB tracker to monitor the beam stability and conformation from 50k analysis will good.</div>
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The difference between GEn-Rp and GEP operation is a bit larger: </div>
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GEP plans to use 50 uA on 30 cm long LH2 but GEn-RP used 15 uA on 15 cm LH2 => a factor of 6-7. </div>
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In addition, GEP will use SBS at 16 degree angle but now we have 23 degree.</div>
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So, it will be useful to see how GEM capable to operate with 30 uA on 15 cm long LH2.</div>
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Bogdan</div>
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<div id="x_x_x_divRplyFwdMsg" dir="ltr"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>From:</b> Liyanage, Nilanga K (nl8n) <nl8n@virginia.edu><br>
<b>Sent:</b> Wednesday, May 15, 2024 11:29 AM<br>
<b>To:</b> Sbs_gems@jlab.org <Sbs_gems@jlab.org>; Bogdan Wojtsekhowski <bogdanw@jlab.org>; Mark Kevin Jones <jones@jlab.org><br>
<b>Subject:</b> [EXTERNAL] Re: Test for GEp</span>
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Dear All</div>
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Looks like thanks to all the hard work put in by Holly, Vimukthi and the team, all GEM trackers are operating pretty well now, with efficiencies mostly around 75-80% per layer. </div>
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The current production running at 15 uA on LD2 is equivalent to about 25 uA on LH2; so about 50% of the GEp goal; this is consistent with the ~ 10-12% occupancies we are seeing in the SBS front tracker, I think Andrew was expecting about 25-30% for GEp.</div>
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Given this, the high efficiencies, good tracking etc. we are seeing now are great signs for GEp.</div>
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As I mentioned earlier, what we are doing now is much harder than the case for GEp: we are now requiring 3 hits out of 4 layers, while GEp will be asking for 4 hits out of 8 layers. This means that the layer efficiencies we are already getting are more than
enough for GEp. Given the combinatorials of C(8,4) we should be able to get a very high tracking efficiency with what we already have. In fact, we might be able to lower the gains a bit to achieve more stable performance under higher luminosity, and still
be able to get very good tracking efficiency in GEp.</div>
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We should be able to demonstrate this with the analyzer removed runs this Sunday</div>
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With the individual power supplies, is seems that the gains are pretty linear with beam current. So I think even at twice the current lumonosity we should be able to operate the power supplies like we are doing now, without any additional corrections to account
for protective resistor voltage drops. </div>
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As for the program on Sunday, I do not think we need to push too high on the beam current, if we can get something like 25 uA on LH2 and LD2, that would be sufficient; with LD2 that would be close to 42 uA on LH2. </div>
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One thing we MUST remember for the beam test on Sunday is that the GEM gains are going to go up for both FRONT AND BACK TRACKERS on SBS with beam current. This means that we may not be able to go to the same high voltage settings we are using for these chambers,
especially for the back tracker ones, for production right now. So, for the beam test, we should back down all the GEMs voltages to 3500 V and then carefully go up in voltage in 25 V steps while carefully monitoring the gains.</div>
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Also: if the beam is not stable and/or crappy, I think we should not turn on the GEMs on Sunday: given everything we have learned so far, there is nothing much left we must do to prepare for GEp. So if the beam quality is not good, I would rather not risk the
GEMs to take some data which is not a must. </div>
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I plan to be there on Sunday</div>
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Best</div>
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Nilanga</div>
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<div id="x_x_x_x_divRplyFwdMsg" dir="ltr"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>From:</b> Sbs_gems <sbs_gems-bounces@jlab.org> on behalf of Mark Kevin Jones via Sbs_gems <sbs_gems@jlab.org><br>
<b>Sent:</b> Thursday, May 9, 2024 5:15 PM<br>
<b>To:</b> Sbs_gems@jlab.org <Sbs_gems@jlab.org>; Bogdan Wojtsekhowski <bogdanw@jlab.org><br>
<b>Subject:</b> [Sbs_gems] Test for GEp</span>
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Hi all,</div>
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Everyone has been working hard to get the GEMs working at this setting. Thanks to everyone.</div>
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For the next experiment GEp, we need to verify that the GEMs can be run at that </div>
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the luminosity of 50uA on 30cm LH2 target. Nilanga seemed fairly confident </div>
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that we can run at the GEp luminosity after the current scan that was early in the experiment.</div>
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Do we need to do additional tests to show the expected performance for the GEp?</div>
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I am sure that we will get from Thia and Patrizia questions about the expected performance for GEp.</div>
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Cheers,</div>
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Mark</div>
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