[b1_ana] draft proposal

[J. P. Chen]

Oscar,

The BCM/BPM for low current readout was re-designed for g2p
(and also used for QWeak, so it is available in Hall C).
The signal (with noise ratio suppression) was designed to reach
1% in significantly less than 1s (we wanted to each helicity at 1KHz).
If you want, I can ask our student, Pengjia Zhu and/or Hall A staff
Alexandre Camsonne to give you results.
The absolute calibration is done with the Tungsten calorimeter, which
was designed for 1% precision. We achieved probably slightly worse,
at 1-2% level.

Cheers.

Jian-ping


On 5/3/2013 1:54 PM, O. A. Rondon wrote:
> Hi JP,
>
> J. P. Chen wrote:
>> 2) For charge determination, it is confusing. Should not say 5%. With the
>> calibration of Tungsten calorimeter, the BCM will have an absolute
>> uncertainty
>> at the level of 1-2%, and relative uncertainty (from one target
>> polarization period
>> to next period) should be better than 1%, depending on the linearity of the
>> BCM response.
>>
> We need to be careful here. Since this is a Hall C proposal, Dave Mack
> will tell you that he cannot calibrate the low current BCM's to better
> than 5% (5 nA at 100 nA). See this hclog entry
> https://hallcweb.jlab.org/hclog/0902_archive/090211140308.html
>
> I think the 1% estimate is reasonable, but it involves integrating over
> time. I believe the charge monitors read every 2s in Hall C. So we'll
> have to accumulate about 25 readings, or one minute, for a 1% delta Q/Q.
>
> I'm sure the Hall A calorimeter will help, but how long does it need to
> integrate at 100 nA for a 1% error?
>
> In any case, we need to be precise about this for the TAC.
>
> Cheers,
>
> Oscar
>
>
>