[Frost] Target polarization questions

[Eugene Pasyuk]

Yes, this is true, downstream end of the target get more heat from the 
e+e- than upstream. A also was thinking about cross checking 
iterpolation with exponential decay from HF data and LF measuremnts

-Eugene

Christopher D. Keith wrote, On 03/17/11 22:09:
> Michael,
> It's important to remember that different coils were used for the high
> field and low field NMR systems, and it is unlikely that they sampled the
> equal parts of the target with equal weight.  The LF system was intended
> to only be a monitor of the polarization during the beam-on, frozen spin
> runs.  Unlike the HF system it was never accurately calibrated in a
> dedicated set of polarization measurements.  Instead, it was cross
> calibrated against the HF measurements prior to, and following each frozen
> spin run.  These are the type 2 and 3 measurements you describe.
>
> Ideally these cross-calibrations should have been consistent, ie
> c_{LF1}/c_{LF2} = 1.  This is the same as saying A(1)/A(4)=A(2)/A(3).
> Why aren't they more consistent?  It's my belief that forward-going
> charged particles produced by the photon beam depolarized the downstream
> part of the target faster than the upstream.  The geometry of the LF coil
> was such that it sampled the downstream part of the target a little more
> heavily than the upstream.  So it "registered" more polarization loss
> following a frozen spin run (type 3 measurement) than did the HF coil
> (type 4).
>
> Does this make sense?
>
> Chris
>
>
>>
>> Hi,
>>
>> I'm trying to understand the target polarization and have a couple of
>> questions.
>>
>> Here is what I understand. Please correct me if I am wrong:
>>
>> > From what I can tell by looking at the "Target Polarization" web page at
>> http://clasweb.jlab.org/rungroups/g9/wiki/index.php/Target_Polarization
>> To find the calibration constants for the polarization by cutting the
>> data up into 4 types:
>>
>> 1) High B-field after polarization and just before going to low B-field
>>
>> 2) Low B-field right after the switch between low and high B-field
>>
>> 3) Low B-field right before the switch between low and high B-field
>>
>> 4) High B-field just after switch from low B-field and just before
>> repolarization
>>
>> We assume that the polarization can be calculated in the form p = c*A,
>> where p is the polarization, c is a calibration constant, and A is the
>> area under the peak of a frequency deviation plot. The c calibration
>> constant is determined using only high B-field data. For low field data,
>> the equation is p = c_{LF1}*A, where the c_{LF1} calibration constant is
>> determined by using the c calibration constant and comparing the area A
>> between the type 1 and type 2 data (i.e. c_{LF1} = c*A1/A2).
>>
>> There is a calculation made for c_{LF2}, where c_{LF2} = c*A4/A3. There
>> are some measurement where c_{LF2} are deemed as "anomalous", but even
>> where the anomalous distinction is not made, there are fairly large and
>> systematic differences between c_{LF1} and c_{LF2}. The values of the
>> ratio between c_{LF1} and c_{LF2} (for non-anomalous measurements) are
>> given as:
>> 1.025
>> 1.036
>> 1.093
>> 1.080
>> 1.037
>> 1.171
>> 1.030
>> 1.074
>> 1.049
>> 1.013
>>
>> These value of c_{LF1}/c_{LF2} are systematically high and have an average
>> value of 1.061.
>>
>> Question: We are using c_{LF1} and the area A throughout the low B-field
>> data to determine the polarization, so I must assume that the High-B field
>> type 4 determination of P is not as accurate as type 1. Am I looking at
>> this wrong?
>>
>> Question: Do we use both high B-field types (types 1 and 4) to determine
>> c? If so, how is it possible to have a systematic uncertainty in c be only
>> 1.6% when the c_{LF1}/c_{LF2} ratio is systematically high by 6.1% ?
>>
>> Thanks for your time.
>>
>> -Michael
>>
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>
>
> ______________________________________________________________________
> Christopher D. Keith
> Jefferson Lab, MS 12H                        email: ckeith at jlab.org
> 12000 Jefferson Ave.                         ph: 757-269-5878
> Newport News VA 23606                        fax: 757-269-5235
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