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

[silvia at jlab.org]

Dear Sebastian,
I think we should discuss all this tomorrow.

In any case, quick replies:

- if the target polarization (or its knowledge) doesn't improve, as you
fear, this would affect in the same way the FTon or FToff data.

- the factor 2.5 of increase of luminosity you mention is new to me: I
thought FToff would allow a factor of 2 more luminosity, at most. Aside
from DC occupancies (which must be verified experimentally with ELMO +
raster) I understand that the target can work with twice the present
current by doubling the rastered area (as will happen moving from 1.5 to
2cm diameter). But if the current increases further we'll have to anneal
more often, thus increasing the loss of beam time.

- I could reverse your second argument by asking: how will the physics
conclusions you'll draw from your DIS data change by going from 33 to 43
days on each target type? (and you're still not counting the data taken
until now, in your estimates for DIS).

Anyway, let's talk about this tomorrow as planned, please.

Best regards,
Silvia


> Dear all (especially all RG-C spokespersons),
>
> Silvia’s proposal would leave 107 calendar days for FTout and 60 days at
> 40% luminosity in the FTon configuration - in other words, about 131/2 =
> 66 PAC days of data for DIS/SIDIS, or 33 each for NH3 and ND3. IF instead
> we stay with the present schedule, with a switchover beginning next
> weekend, we would get 43 days each, close to the amount originally planned
> for FTout. So any Physics arguments to STAY with the present run plan
> should be based on a comparison between these 2 scenarios.
>
> Meanwhile, any Physics argument in favor of Silvia’s proposal should
> assume that, out of the 60 days, about 30% or 18 days would go to the
> various background targets necessary for DIS/SIDIS analysis, and the
> remaining 42 days would be split between NH3 and ND3 (21 each). Assuming a
> 50% efficiency (which we haven’t reached yet), the argument should then
> show that WITH those extra 10.5 PAC days (4 mC = roughly what we have so
> far if things go REALLY well) for each target, the data collected with
> FTon would go from “marginal” or “useless” to “enough for a
> publication” for the two DVCS channels, in spite of having maybe 18%
> fewer statistics overall (outside of FT) and most likely still less and
> less well-known target polarization.
>
> - Sebastian
>
>
> On Aug 21, 2022, at 1:23 PM, silvia at jlab.org<mailto:silvia at jlab.org>
> wrote:
>
> Dear Sebastian,
> both your points are fair, and well taken.
> Here are my replies, which can of course be discussed and modified
> according to the opinion of all other spokespersons.
>
> 1) if we agree on an extension of FTon, we will of course agree also on a
> run plan suiting all experiments. We (DVCS people) have put a veto on
> changing solenoid polarity during FTon assuming it was our only shot to
> take data, but if we extend we can agree to compromises. Same holds for
> the background targets runs (by the way, we took 10% of our data with
> carbon so far, so we did not skip background targets altogether).
>
> 2) How about October 31?
>
> Best regards,
> Silvia
>
>