STUDY OF CAPILLARY TRACKING DETECTORS WITH POSITION-SENSITIVE PHOTOMULTIPLIER READOUT

Measurements have been carried out on light yield and attenuation leng th in glass capillaries filled with new liquid scintillators (LS) and compared with analogous measurements made on 0.5 mm diameter plastic f ibres Kuraray SCSF-38 and 3HF. It is found that, at a distance of 1 m, the light output in the capillary filled with green LS based on 1-met hylnaphthalene doped with a new dye 3M15 is greater by a factor of 2 t o 3 than for plastic fibres. A tracking detector consisting of a capil lary bundle read out by a 100 channel position-sensitive microchannel plate photomultiplier (2MCP-100) has been built and tested in the labo ratory using a cosmic ray trigger. A comparison has been made between the performance of such a detector and that of a similar one, read out by a 96 channel Philips XP1724/A photomultiplier. It was found that a bundle made of 20 mu m diameter capillaries with a tapered end giving a magnification of 2.56, filled with the new IPN+3M15 liquid scintill ator, read out by the 2MCP-100, provides a space resolution of sigma = 170 mu m, a two-track resolution of the same value and a hit density of n = 1.9/mm for tracks crossing the detector at a distance of 20 cm from the photocathode. If the same detector is read out by the Philips XP1724/A, the space resolution becomes 200 mu m, the two-track resolu tion 600 mu m and the hit density n = 1.7/mm. The worse performance in the latter case is caused by the larger crosstalk compared with that of the 2MCP-100 PSPM, The results indicate that a LS-filled capillary detector is a very promising device for fast fibre tracking.