[b1_ana] draft proposal

[J. P. Chen]

Hi, Oscar and Karl,

I just saw Alexandre and asked him to take a look at our data
(Pengjia probably would be better, but he is in China and time
zone makes it difficult to get him now).

One more systematics: The acceptance will change slightly with
the target magnet field. Since the scatter electron path will be
not along the target field (longitudinal) direction, the spectrometer
will be the regular (S)HMS+ target field. The effect is small for
small angle (but probably not negligible) and increases for large
angle. This should be looked into.

Cheers.

Jian-ping


On 5/3/2013 2:49 PM, O. A. Rondon wrote:
> Hi JP,
>
> That is good news. I think we should put some kind of reference or quote
> some numbers in the proposal, so the TAC and PAC know about it, although
> the TAC may know already.
>
> Cheers,
>
> Oscar
>
> J. P. Chen wrote:
>> 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
>>>
>>>
>>>
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