Calibration on Cosmic Ray Data

After the assembly and preliminary test all the modules of the Preshower Detector were tested at TestLab with cosmic ray muons. Wherever it was possible the test were made to simulate closely the final experimental operating conditions, namely

• positions of the modules,
• the electronics and HV supplies,
• all the cables except the delay lines,
• data acquisition.

The test were performed 10 days with the objectives of:

• checking the operation of the modules;
• pulse height equalization from cosmic rays;
• checking the stability during the operation;
• determination of the pulse height resolution for cosmic rays and estimation of the expected energy resolution for electrons.

A system for the shower detector modules calibration on cosmic rays has been developed. This system is useful for preliminary equalization by the high voltage and tracing of amplitudes values from all of shower detector blocks using signals from cosmic rays.

All programs and data files, which are used during shower detector channels calibration on cosmic rays are in /work/halla/com97/armen/e91026/cosmic directory.

Cosmic data files e91026_1445.dat, e91026_1446.dat and e91026_1447.dat has been processed by the following.

First, by the ESPACE kumac program cosmic_cal.kumac distributions of $A$_i-P_i are created. Here, $i=1\; ÷144$ is a shower detector channel number, $P$_i -- pedestal value of the $i$-th channel and $A$_i -- amplitude of the cosmic ray signal on the $i$-th channel. Cosmic ray events are selected by condition of the unique fired block on the Preshower and the unique fired block on the Shower. Distributions of $A$_i-P_i are created through the ESPACE variable adc_c[[i];[i]] (see 2.1). For this it necessary to contain in the current directory a file shower_calib.dat, where calibration constants are equal to 1 for all of channels (see 2.2, 3.2).

Then, by the PAW kumac program cosmic_cal_paw.kumac the following is done.

• The mean values _i-P_i> for each of detector channel using the fit by Gauss are calculated;
• Calibration constants are calculated by the formula $C$_i=N_i/<A_i-P_i> , where $N$_i=200 for the Preshower channels, and $N$_i=300 for the Shower channels;
• All of distributions histograms, results of fittings, _i-P_i> and $C$_i constants values changing in channels are plotted on the display.

After the execution of cosmic_cal_paw.kumac program, the following resulting files are created:

cosmic_cal.ps -- a postscript file, containing all of graphics, which are plotted on the display during execution;

cosmic_calib.dat -- an ASCII file, containing values of calibration constants $C$_i , computed on cosmic data, and parameters of Gauss, by which these constants distributions are fitted.

  
Figure 2: Values of calibration constants computed on cosmic rays data for Preshower (a), and Shower (b) channels versus channel number. These coefficients values distributions for Preshower (c), and Shower (d) channels.

In Fig.2 four pictures among that, which are plotted during execution of program cosmic_cal_paw.kumac, are shown. Fig.2(a) and Fig.2(b) show graphics of values of calibration constants computed on cosmic rays data for Preshower and Shower channels, accordingly. These coefficients values distributions in Fig.2(c) for Preshower and Fig.2(d) for Shower allow to estimate an accuracy of shower detector channels amplitudes equalization. These pictures show that channels amplitudes was equalized and stays with the good accuracy for the most of shower detector modules.