dE/dx PROTOTYPE TEST*

A small prototype of a multiwire dE/dx detector was tested in SLAC's test beam. The basic concept of the detector was similar to the JADE drift cell design. The purpose of the test was to decide on some design parameters for a full size prototype, which is now in construction. Introduction Our motivation was to concentrate on the particle identification below 4 GeV/c which is about the limit of most of the particle distributions at PEP energies. In particular, we wanted to explore the possibility of identifying particles using a dE/dx technique in the HRS magnet. This technique was in a competition, with Cerenkov counters, proposed by the Michigan group.1 The available space allowed us to use only about 70 cm of active length. Our test chamber reported in this paper had 47 samples, each 1.5 cm long. This would allow a reasonable n/e identification below 4 GeV/c, a/p identification below 1.2 GeV/c and above 3 GeV/c, n/k identification below 800 MeV/c, if we would operate at atmospheric pressure. Although some of these regions can be covered by TOF and shower counter techniques, obviously not all particles could be identified by a single device in a multi-prong environment. The type of chamber we decided to investigate resembles the JADE type of detector.2 This type of chamber proved to be useful as a tracking device, however, there are still some questions left about its usefulness as a dE/dx device in the relativistic rise region. We felt that its concept is attractive because in addition to tracking and dE/dx measurement, it has features which limit the number of wires required and it could perform well in a high multiplicity environment. This project had three stages. In the first stage we investigated the properties of several gases in a single sample test chamber, 3 in the second stage we tested the chamber which had full size in the x-y plane and only 10 cm long in the z-direction (most of the data reported in this paper comes from this test), and finally, we constructed a full size chamber, which is now being tested. Description of the Prototype The basic dimensions of the test cell are shown in Fig. 1. The active length of the wires was only 10 cm (z-direction in conventional storage ring sense). Each sample length along the track was 1.5 cm, and there were 47 samples in total. To limit …