[G14_run] From Dao Ho: question about electron beam polarization with negative sign

[Franz Klein]

Dao,

most of your observed sign changes can easily be extracted from the 
given information (polarization of Fe foil, half-wave plate, spin 
rotator "Phi_FG"). I explained that twice at a g14 meeting.
Besides, the signs are not in bold, only the degree of polarization 
(which reflects the injector settings for the given run range).

Nonetheless, thanks for bringing up the issue!!!
There is some additional influence from the horizontal Wien (Hwien). 
Based on the 12/7/2011 measurements I only considered Hwien=+-90deg: 
Hwien=-90deg the helicity is flipped (rows 5,6). Qweak had also Moeller 
measurements with Hwien=+90deg (and helicity is flipped too). There is 
no helicity change if the magnitude of the angle is less then 90deg.

BUT:  January/February data have opposite sign: Despite a 
Hwien=-60.85deg the helicity is flipped.
And I checked the Qweak measurements for spin dance on 1/19/2012, which 
show a helicity flip as well!
Do not ask me why the helicity is flipped for Hwien=-60deg but not for 
Hwien=-70deg or -50deg ....

I added a summary of the Qweak Moeller measurements to the webpage ( 
https://clasweb.jlab.org/rungroups/g14/wiki/index.php/Beam_Polarization_%28Circ.%29 
). The summary is incomplete because the injector settings for other 
measurements were missing in the Hall-C logbook.

Again, thanks for pointing this out!
I think that I see it correctly now (but please check it yourself!!!): 
The reversed sign for the helicity in the January data is consistent 
with the Moeller measurements and Qweak data. Sorry that I did not 
realize this earlier!

Franz


On 12/13/2013 12:42 PM, daoh at andrew.cmu.edu wrote:
> Dear all,
>
> In the
> https://clasweb.jlab.org/rungroups/g14/wiki/index.php/Beam_Polarization_%28Circ.%29
> page, the Beam polarization measurements table (this is an updated one)
> shows negative beam polarization as well as positive one (the ones in
> bold). I discovered that silver 3,4 and gold2 both have negative sign
> (-76.2% and -83.4% respectively), while silver 5a and 5b both have
> positive sign (+88.8%). My question is whether we have taken into account
> of this difference in sign when computing the beam helicity (i.e, during
> cooking or analysis). For my case, I always used positive 88% for the beam
> polarization regardless of whatever run periods.
>
> Another observation shows that silver 1 and 2 have opposite sign comparing
> to silver 3, but I don't remember me comparing the E asymmetry between the
> two periods with either silver3 or gold2 (Tsuneo might have done that).
>
> Anyway, I hope this is the sign problem in silver 5 period that we have
> been chasing after.
> Let me know what you think.
> Sincerely,
> Dao Ho
>
>
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                   Franz J. Klein, Associate Professor
                   CUA, Department of Physics
                   Washington, DC 20064
   office: Hannan Hall 206          phone: 202-319-6190
   or: Jefferson Lab,CC F-243       phone: 757-269-6672
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