Optical selection of straws for the MPD endcap tracker

An optical method for estimating deviation from the linearity of straws with a diameter of 4 mm and a length of 60 cm mounted in the ring frames of a detector is described. The maximum permissible deviation from linearity of straws is 400 μm, and the amplitudes of signals from a 55 Fe source vary along the straws by no more than 9%. The results of this optical-linearity checkup agree fairly well with the data obtained using a more accurate method (the measurement of amplitude characteristics with a 55 Fe source) for determining the deviation of a straw from the anode axis.