[Halld-tagger] rho beam asymmetry from 2018-01 ver15

[Alexander Austregesilo]

Dear colleagues,

I used the first offline monitoring launch over the full 2018-01 data to 
extract the rho beam asymmetry for beam energies between 8.2 and 8.8 GeV.

The PSigma values  extracted for 0/90 and 45/135 are consistent within 
0.3% (absolute). You can find the fits to the full data sample in the 
attachment (rho_fit.pdf).

I also looked at the individual orientations as a function of run number 
(rho_run_PSigma.pdf). No visible degradation of the polarization can be 
seen with the current precision. I will try to group several runs 
together and look at the polarization as a function of energy to obtain 
a better handle on this.

The third plot shows the extracted orientation angle as a function of 
run number (rho_run_psi0.pdf). The offsets from the nominal orientation 
are in the order of 5% and seem to be quite stable during the run. In 
addition, all assignments from RCDB (colors) look correct.

Best regards,

Alex

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