[Rgc] RGC weekly meetings back on Tuesdays (this time focused on FTon extension)

[silvia at jlab.org]

Hello Sebastian,
as I said in my email a few days ago, my proposition came after I closely
looked at the data currently collected and realized that the situation is
quite dire for my experiment - and not looking great for pDVCS as well.
Therefore I think it would be fair, for the discussion planned for
Tuesday, to understand what all parties have to lose with the various
scenarios.
My understanding - but maybe I am missing something - is that all that DIS
loses running with FTon compared to FTout is a factor of 2 in count rates,
due to the lower beam current. So I wouldn't say the current running we
had with FTon means 50 days lost for DIS, but 25 days of running instead
of 50.
Likewise, two more months of FTon would mean 30 days of high-lumi data
instead of 60. So DIS would still get the equivalent of 170-25-30 = 115
days at the highest luminosity. I would like to see the impact of this
reduction on the projected observables, to understand what is at stake.
Some time ago, during the toughest first days of the experiment, in
particular when the issues with the ND3 target started, in our RC meetings
it came up the possibility, if things continued being bad, to bring back
the FTon configuration during the Christmas break. This option, that can
be in principle OK with me (we'd get even more beam time than with my
current proposition), has potential risks from the technical point of you,
as Raffaella mentioned in our RC meeting of Friday. Remaining in FTon
right now seemed to me the safest option. But we can discuss this, of
course.
As far as fixing the ND3 NMR as soon as possible, yes, that seems to me an
unavoidable condition to proceed, whether or not we decide change FT
configuration now. The target group won't be available in part of
September, so this work cannot be delayed much further.
Best regards,
Silvia


> Hi Silvia,
>
> You probably meant to say “two LESS months” as you are the one
> proposing a change from the agreed-upon run plan.
>
> Just to be entirely clear: Originally, the FTout (“ELMO”)
> configuration with full luminosity and raster was scheduled to run for 180
> calendar days. Right now, we have anyway only 170 days left since we
> postponed the changeover by 2 weeks already. “2 less months” relative
> to what the original, agreed-upon run plan (and official schedule) showed
> would correspond to 120 days for FTOut, which means 50 additional days
> lost. In that case, the absolute latest to switch over to FTOut would be
> the 2nd week of October if we want to preserve at least those 120 days. IF
> you also insist on spending a week NOW on fixing the deuteron NMR (without
> synergy with the configuration change), this would give FTOn at most 5-6
> more weeks. Switching over at the end of October (even if we begin the
> switch October 24) would reduce the FTOut part to 3 1/2 months or roughly
> 100 out of originally 180 days. If you ask everyone to prepare a case for
> why we should NOT overturn an agreed-upon run plan in the middle of the
> run, at least be clear what you are requesting.
>
> - Sebastian
>
> On Aug 21, 2022, at 5:45 AM, silvia at jlab.org<mailto:silvia at jlab.org>
> wrote:
>
> it would be great if the DIS and SIDIS representatives can
> provide motivations of how two more months of FTon will affect their
> results and physics conclusions.
>
>