BigCal Calibrations

Update from last meeting

Last meeting I showed that using calibration coefficients obtained from perpendicular pi0 events did not work (see plot below). Interestingly the protvino (bottom) coefficients appear to be independent of the target field orientation, while the RCS (top) clearly are differ with the field orientation.

The causes are unknown and could be a number of things :

• Magnetic field effects on RCS PMTs
• Just a time dependent effect (HV changed, block transparency changed, ...)
• something else?

Parallel Calibration

It becomes apparent that the top blocks need attention due to their difference with perp and looking at the plots below which show Hovannes's "parallel" calibration.

Note that the mass has a Y dependence that is not obvious when looking at just the mass (which is centered on the correct value).

Calibration iteration plots when focusing on the upper part of bigcal are shown below. There is a clear improvement in the Y position vs mass, which is again, not obvious when looking at the whole detector.
The first column of plots show:

• histogram of reconstructed mass and a simple fit
• 2d histogram of 2-photon opening angle vs reconstructed mass.

• Y position of photon 1 VS mass
• Y position of photon 2 VS mass
• X position (vertical axis) of photon 1 VS mass
• X position (vertical axis) of photon 2 VS mass

Before:

After:

Before:

After:

Looking at the plots above you can see that the Y dependence is entirely isolated to the RCS part of bigcal.

Improvements

The most improvement will likely come from the middle region where the bottom has been contaminated by the top.
Need to go back and look for the eta which is most sensitive to the energy reconstruction, which was poor before because the opening angle is much larger thus requiring both section of bigcal to be calibrated.

Moving Forward

I have two new sets of calibrations and the data is being replayed as we speak. However, I am sure that I could further improve these calibrations but would like to see their effect first.

Not sure what to expect in terms of how the results will change but we will see...

	Name	Last modified	Size	Description
	Parent Directory		-
	pi0Calibration_para_..>	2015-01-09 17:56	37K
	pi0Calibration_para_..>	2015-01-09 17:56	37K
	pi0CalibrationCompar..>	2015-01-09 17:56	38K
	pi0Calib_para_2.png	2015-01-09 17:56	42K
	pi0Calib_para_1.png	2015-01-09 17:56	44K
	pi0Calib_para_0.png	2015-01-09 17:56	43K
	para_init.png	2015-01-09 17:56	29K