FTCal timing calibration tutorial

This page provide instructions on how to perform timing calibration for the FT-Cal. This include time offsets and time walk corrections. These two calibrations are interconnected and have to be performed iteratively as follows:

1. Calibrate time offsets with no time-walk corrections;
2. Load time offsets from the previous step and perform time-walk calibrations;
3. Load time offsets and time walk corrections from step 2 and re-calibrate the time offsets;
4. Load time offsets and time walk corrections from step 3 as a final check.

The events used for these calibrations are events with an electron in the Forward Detector and a cluster, neutral or charged in the FT-Cal. Timing calibrations are performed for each calorimeter crystal using the event start-time determined from the FD electron as a reference.

Step 1: Calibrate time offsets with no time-walk corrections

Launch the calibration suite. The initialization window will be displayed. Don't load any file with previous calibrations and click on Finish. Click on the H4 button at the bottom-right of the suite and load the input data file. Click on the "play arrow" on the left of the bottom bar to start the file processing. Go to the TimeCalibration tab of the GUI: this should look like in the figure below. The 6 plots from top-left to bottom-right show:

1. The raw time offset of all the crystals; 2.The corrected time offset of all the crystals (will be shown only after Step 1); 3 The graph of the individual crystals time offsets;
2. The time offset of the selected crystal in a wide range;
3. The time offset of the selected crystal in a narrow range;
4. The corrected time offset of the selected crystal (will be shown only after Step 1). The most relevant plot is #5, which is the one that is fitted to derive the offset.

Check that all the fits have properly converged selecting "View All" from the Histogram drop-down menu. Save the constants by selecting the "Save" option from the Constants drop-down menu and quit the calibration suite.

Step 2: perform Time-Walk calibrations

Launch the calibration suite. Load the time calibration results from Step 1 in the corresponding section of the initialization window and click on the Finish button. Load the input file and start data processing. Go to the Time-Walk tab of the suite. At the end of the file processing this should look as in the figure below: Even if time-walk is extracted for individual crystals, we are currently using the "global" time-walk (integrated over all crystals) and the relevant graph is the second in the top raw. Check the fit and, if satisfactory, save the constants, quit the suite and proceed to the next step.

Step 3: recalibrate the Time Offsets with Time-Walk corrections

Launch the calibration suite and load the TimeCalibration and TimeWalk results from Step 2 in the corresponding section of the initialization window. Load the input file and start data processing. Go to the TimeCalibration tab of the suite. At the end of data processing, this should look as follows: Both the global and individual crystal histograms should be narrower than at Step 1 because time walk corrections were loaded. Since time offsets from the previous calibration steps were loaded, the "corrected" time offset histograms will be displayed. This should be close to zero, but not exactly because of the interplay between the time-offset and time-walk calibrations. Check the fits as at Step 1, save the constants and quit.

Step 4: final check

Launch the calibration suite and load the TimeCalibration and TimeWalk results from Step 3 in the corresponding section of the initialization window. Load the input file and start data processing. The TimeCalibration and TimeWalk tabs at the end of data processing should look as follows: Check that the "corrected" time offsets in the TimeCalibration tab are centered at zero. Check that the "corrected" time walk plots (3rd column) are reasonably centered at zero. Save snapshots of both tabs and quit the suite.

Go to the JLab electronic logbook and select the Hall B CLAS12Calib logbook: https://logbooks.jlab.org/book/CLAS12CALIB Make a new logbook entry including:

• The run number that was calibrated and any detail you have been given about the data file (version of the cooking, etc.);
• The snapshots of the final results;
• The text files with the time offsets and time walk constants from Step 3;
• Any relevant remark on problematic fits or issues encountered.

find the documentation from March 2019 here