[Rgc] The future of RGC

[Sebastian Kuhn]

Dear RG-C members and interested parties,

as you probably already heard, the outlook for RG-C at present is definitely a “glass-half-full” situation. On the positive side, we are now convinced that the solenoid has survived the power supply fault without damage, and we should be able to go back to data taking as soon as the power supply situation is resolved (this means also to modify BOTH solenoid and torus power supplies to prevent anything like this happening again). This is a huge relief, as any damage to the solenoid would have been very difficult to repair. The power supply repair is also off to a good start. On the other hand, we expect that even under an optimistic scenario, we won’t be able to get back to data taking until the beam returns after the holiday break (officially on January 16, but I just learned possibly already on 1/12). *)
This means that we will have lost at least 33 calendar days of scheduled running, or potentially more if we can’t get everything back up by the 12th. Our plan is still to return with the FTon configuration to collect more data for forward gamma angles (the conversion can now already begin next week). We will have 63-67 calendar days before the planned shutdown (SAD) on March 19, which nominally corresponds to 32 PAC days but, given past experience, probably is closer to 25 PAC days given the less-than-50% efficiency of beam delivery. I did talk with Doug Higinbotham, but there is zero chance that the run will be extended immediately following this date, as the SAD is too complex and work-intensive to move. This means that, realistically, we will end the present run at least 2 months (34 PAC days) short of the 120 approved PAC days of running time. 

With this background, we may want to think about the following two scenarios:
1) We could ask for a resumption of RG-C after the end of the 2023 SAD, which is July 17. This would of course have to be negotiated with Patrick Achenbach and other parties, as it would impact the presently scheduled experiments at that time (first RG-D, then RG-K, for 2 months + 3 months).  It also would place the configuration change in the middle of the planned accelerator run, where beam would be otherwise available for Physics. (I don’t know how long this would take, but probably it would require another 3-4 weeks or so - maybe Chris can comment).
2) We could postpone the remaining PAC days to a later date (sometime in 2024 - tbd). This would entail removing the polarized target during the 2023 SAD and then perhaps reinstalling it either at the beginning of 2024, or - more likely - during the 2024 SAD. Of course, this would also impact the foreseen Hall B schedule.

At this point, I am asking you to think about either of these two options, and state your preferences (with supporting reasons - this could include availability of work force, ease of path to publication, etc.) in either case, I would ALSO like to ask you to prepare a PHYSICS-based argument for the amount of remaining beam time that is absolutely needed to achieve the Physics goals of “your” channel of interest - of course, only within the envelope of 120 PAC days overall. (If we want to ask for significantly more time, we will have to return to the PAC). Of course there are no guarantees - ultimately, it will be a decision by the Hall Leader (Patrick) and the scheduling committee. 

I would like to propose that we plan to use some part of the remaining RG-C analysis meetings (Tuesdays at 9:30) to discuss the status of the data already collected (and their significance or lack thereof, assuming 25-30 more PAC days of FTon only running). At the same time, we could use one of our standard “RGC-RC” time slots (weekdays at 2:00 p.m.) for the more general discussion about possible schedules. I am thinking that maybe having one “RGC-RC” meeting per week is reasonable - let me know which day works best. (Obviously not THIS week, which is basically a long holiday from here on out).

Happy Thanksgiving to everyone - Sebastian

*) This means we most definitely will need an RC starting 1/11/23 - so far I have listed Francesco with Noëmie as support. It would also be good to have someone who could act as “part-time” RC the preceding week - at least as a conduit for information, and to go to the relevant MCC and Hall B meetings.