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Data sample and data reduction

The physics data set consists of runs 3155, 3191, 3192. Runs 3155 and 3191 are valid beam triggered runs; 3192 is a central trigger run. Runs 3156, 3190 and 3200 are empty target runs of the same field polarity as the physics runs; runs 3157, 3187 and 3188 are empty target runs of the opposite field polarity. The magnetic spectrometer setting for all runs is 4 GeV/c. A cut on CX veto counter (Section 3.4.1) was used to safeguard against non-target interactions and beam halo. Contamination of the detector by $\delta$-electrons is a major problem discussed in subsection 6.2. Due to the presence of the dipole magnetic field, only one half of the detector is $\delta$-contaminated. The problem therefore is solved by ignoring that half in the analysis altogether. In the negative runs, the left (looking along the beam) side of the detector is $\delta$-free. Only that side was used for the analysis. Out of its 256 channels, 252 were operating normally and 4 were dead. Whenever an amplitude sum is quoted, it is from those 252 channels only. The range of calibrated amplitude sum between -25 MeV and 95 MeV was split into 12 bins of equal (10MeV) width; events outside this range were not used. The power spectra of local fluctuations were analyzed in each bin. Event mixing was done separately in each bin. More detailed information about the data sample is given in Table 6.1.