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

[silvia at jlab.org]

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




> Hi again,
>
> 2 quick points:
>
> 1) The way we have been running so far has been much less suitable for
> DIS/SIDIS than the factor 2.5 in luminosity. For one, the suboptimal
> target polarization is not only affecting DVCS (and I don’t see a good
> argument how it will become much better in the future). But even more
> importantly, you yourself used the argument that “FTon is anyway mostly
> for DVCS” to argue against background runs (including outbending torus)
> and other systematic checks that would be required for DIS/SIDIS to make
> full use of the data we are presently collecting.
>
> 2) Instead of doing the math for us, just tell us: How many additional
> days of running FTOn are you proposing, and at what point in time do you
> propose to start the 1-week configuration change? Then everyone can work
> off the same numbers. In light of 1), also state whether you agree to
> accept the needs of DIS/SIDIS to decide which targets to run how long, and
> how much outbending torus polarity to include, starting now.
>
> - Sebastian
>
>> On Aug 21, 2022, at 11:53 AM, silvia at jlab.org wrote:
>>
>> 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 â?otwo LESS monthsâ? as you are the one
>>> proposing a change from the agreed-upon run plan.
>>>
>>> Just to be entirely clear: Originally, the FTout (â?oELMOâ?)
>>> 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. â?o2 less monthsâ?
>>> 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.
>>>
>>>
>>
>>
>
>