The cosmic-ray electron and positron spectra measured at 1 Au during solarminimum activity

We report on a new measurement of the cosmic-ray electron and positron spec tra. The data were collected by the balloon-borne experiment CAPRICE94, whi ch was flown from Lynn Lake, Canada, on 1994 August 8-9 at an altitude corr esponding to 3.9 g cm(-2) of average residual atmosphere. The experiment us ed the NMSU-WIZARD/CAPRICE94 balloon-borne magnet spectrometer equipped wit h a solid radiator Ring Imaging Cerenkov (RICH) detector, a time-of-flight system, a tracking device consisting of drift chambers and multiwire propor tional chambers, and a silicon-tungsten calorimeter. This was the first tim e a RICH detector was used together with an imaging calorimeter in a balloo n-borne experiment. A total of 3211 electrons, with a rigidity at the spect rometer between 0.3 and 30 GV, and 734 positrons, between 0.3 and 10 GV, we re identified with small backgrounds from other particles. The absolute ene rgy spectra were determined in the energy region at the top of the atmosphe re between 0.46 and 43.6 GeV for electrons and between 0.46 and 14.6 GeV fo r positrons. We found that the observed positron spectrum and the positron fraction are consistent with a pure secondary origin. A comparison of the t heoretically predicted interstellar spectrum of electrons shows that the in jection spectrum of primary electrons is steeper than that of the nucleonic components of cosmic rays. Furthermore, the observed electron and positron spectra can be reproduced from the interstellar spectra by a spherically s ymmetric model for solar modulation; hence, the modulation is independent o f the sign of the particle charge.