Japanese-American Cooperative Emulsion Experiment /JACEE/

The instrumentation and results of long duration balloon flights carried out jointly by U.S. and Japan researchers to examine high energy cosmic rays are reported. Basic detector geometries are 2.5 sq m sr with operation at altitudes with 3-4 g/sq cm pressure, with observations thus far of over 100 hr. Energies from 2-100 TeV are recorded for nucleus-nucleus and hadron-nucleus interactions, and searches are made for new particle or interactions. The detector is an emulsion chamber which comprises doubly-coated nuclear emulsions on 800 micron thick methacryl substrates, X-ray films, etchable detectors, low density spacers, and lead sheets. Segmentation of the instrument into a primary charge module, a target section, a spacer section, and a lead-emulsion calorimeter allows accurate charge measurement for primary nuclei, reliable energy resolution, and a large geometrical factor for collecting high energy events. A primary Ca nucleus of 300 TeV has been observed.