A MWPC with highly segmented cathode pad readout☆

We have developed a device to perform precise automated measurements of the relative wire separations in a planar wire chamber. The measurement scheme involves slowly passing the wire chamber through a laser beam directed onto a photodiode. The measured position of the chamber as a function of time is then correlated with the photodiode response to yield the relative wire positions with a mean accuracy of better than 10 μm (FWHM). The operational principles, system components, and results from our studies are discussed.

An investigation of MWPCs with interpolating chevron shaped cathode pad readout has been carried out as part of the R&D for the particle tracking system of the PHENIX detector at RHIC. Two prototype chambers were designed and constructed. Their response to minimum ionizing particles was tested with secondary beams from the AGS accelerator system at the Brookhaven National Laboratory. Results on resolution, differential non-linearity and overall performance for different chevron patterns and cell geometries are presented.

First results of the second coordinate readout in a 4 mm diameter straw made with resistive Kapton are presented. Operational parameters such as gas gain, stability of response and, most importantly, position resolution of the longitudinal avalanche coordinate measured with an external strip electrode readout were studied with argon-ethane, argon-isobutane and argon-DME gas mixtures. Typical resolution of 85 μm σ was obtained for X-rays of a 7.4 keV average energy from an X-ray generator. Experimental limitations on position resolution along the wire are discussed.