# Andrei's recipe for BCAL Timing Calibration

From GlueXWiki

Here is an e-mail that Andrei Semenov sent around to a select group on Mar. 18, 2013 describing a plan for timing calibration of the BCAL.

Will: The following is the time-walk correction procedure that I prefer. You have the times (TDC values) from upstream and downstream (t_up, t_do) as well as correspondent amplitudes (ADC values) a_up and a_do. 1. On event-by-event basis, you form the difference dt0=(t_up-t_do), fill 1-dim histograms with dt0 for the slices (intervals) on a_up, calculate mean values (with uncertainties) for these histograms, plot these mean values as a function of a_up, and fit the data points with the function f1(a_up). 2. On event-by-event basis, you form the corrected difference dt1 = (t_up-t_do) - f1(a_up), fill 1-dim histograms with dt1 for the slices (intervals) on a_do, calculate mean values (with uncertainties) for these histograms, plot these mean values as a function of a_do, and fit the data points with the function f2(a_do). 3. (Optional step but it helps sometimes.) On event-by-event basis, you form the corrected difference dt2 = (t_up-t_do)-f1(a_up)-f2(a_do), fill 1-dim histograms with dt2 for the slices (intervals) on r=(a_up/a_do), calculate mean values (with uncertainties) for these histograms, plot these mean values as a function of r, and fit the data points with the function f3(r). 4. The corrected difference dt3=(t_up-t_do)-f1(a_up)-f2(a_do)-f3(r) is the corrected time difference you want for the z-position calculation (surely, you should add to this value the "correct" constant time shift for the position in the calorimeter you working with). To improve the result, I would suggest to process the corrected dt3 through the steps 1-3 again (so in the end you'll have dt6=(t_up-t_do)-f1-f2-f3-f4-f5-f6). I would strongly recommend to work directly with the value of interest (viz., dt=t_up-t_do) instead of correcting the artificial difference of the "registered signal" and the "first energy deposition time" because the later will be not available in the real data. (Surely, the smaller range of time-walk correction required for the difference will also help.) David: Can we put into our simulation data the real coordinates of the shower from the simulation (to be able to compare the positions reconstructed from the time with the "real" values that will be an estimation of our position resolution). For the mean time (viz., (t_up+t_do)/2 ), I would propose to perform indipendent correction. Some information on this time-walk procedure can be found in the report GlueX-doc-1221-v4 and in my talk https://halldweb.jlab.org/wiki/images/a/a5/Meet121113.pdf Hope it will help, Andrei