[G12] resolution of tagger in kinematic fitter

[Lei Guo]

> 
> The uncertainty in the energy of the photon is 0.001* E_beam (per NIM and Eugene P.)


I copy and pasted from the 2007 tagger energy calibration NIM paper ():

"In this report, we present the energy calibration of the Hall B bremsstrahlung tagging system at the Thomas Jefferson National Accelerator Facility. The calibration was performed using a magnetic pair spectrometer. The tagged photon energy spectrum was measured in coincidence with e+e- pairs as a function of the pair spectrometer magnetic field. Taking  advantage of the internal linearity of the pair spectrometer, the energy of the tagging system was calibrated at the level of ±0.1%Eγ . The absolute energy scale was determined using the e+e-
e
e
 rate measurements close to the end-point of the photon spectrum. The energy variations across the full tagging range were found to be < 3MeV”




> The hodos were built such that this is true (different widths)
> 
> Then consider a counter of width (energy) "a"  where the (assume) energy distribution is flat: then Variance = sigma^2 = 1/a* int^a_0 E^2 dE = a^2/3
> 
> Therefore if we distribute the uncertainty over a counter (energy bin) the variance is : sigma^2 = (0.001*E_beam)**2/3
> 
> =Carlos
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