Tagger calibration

 Tagger Momentum resolution

The tagger calibration runs have been taken with the beam passing though the four chambers.

For each run the reconstucted electron momentum (4 cluster algorithm) has been fitted with a gaussian function after requiring no energy in the CU: the fit gives the offset in momentum reconstruction and the resolution.

For the same runs the  clusters position in the vertical (non bent) plane have been used to calculate the angle difference between the incoming and outcoming direction of the beam and therefore the multiple scattering

The picture below showes an example of this analysis with the 1.5 GeV beam. 

All the result from the calibration runs have been summarized in the following picture. 

The tagger energy linearity plot has a slop of 1.004 +- 0.005

The multiple scattering plot fit gives: x/x0 = 2.94 +- 0.03

Notice that some of the runs have a different magnet current (this is necessary if we don't change the geometry), so a rescaling to the same bending power is needed.

The (rescaled) momentum resolution fit gives a constant value: c = (1.395 +- 0.007)%
 

 The momentum resolution, at different bending power, can be evalueted with:

dp/p(%) = c*BL_max/BL = 1.395*0.7089/BL

Here is a table of calculated tagger resolution for particular current settings:

 Calibration of the bending magnet

 The bending magnet data have been fitted with a quadratic polinomial:

B*L (T*m) = 0.0012271*I(A) - 7.60132e-08*I^2(A^2)

 Angular reconstruction

Few screenshots from the tagger calibration runs.