A new measurement of the cosmic ray electron spectrum from 10 GEV to 300 GEV

We have measured the spectrum of cosmic ray electrons with a new instrument that combines a transition radiation detector with a shower detector. The transition radiation detector provides unique identification of individual electrons and good discrimination against protons. At the same time, it allows the construction of a large area instrument (0.48 m2 ster) and consequently makes possible a measurement of improved statistical accuracy. The instrument has been calibrated with electron beams of 5-300 GeV at Fermilab, thus eliminating energy dependent biases. A first balloon flight yielded 30 hours of data at an altitude of 5 g/cm2. We shall describe the design of the instrument, the accelerator calibrations, and the analysis of the balloon flight data. The spectrum of electrons is found to be significantly steeper than that of protons over the whole energy range. (author)