A NEW LIMIT ON THE FLUX OF COSMIC ANTIHELIUM

Abstract A very sensitive search for cosmic-ray antihelium was performed using data obtained from three scientific flights of the BESS magnetic rigidity spectrometer. We have not observed any antihelium; this places a model-independent upper limit (95% C.L.) on the antihelium flux of 6×10 −4 m −2 sr −1 s −1 at the top of the atmosphere in the rigidity region 1 to 16 GV, after correcting for the estimated interaction loss of antihelium in the air and in the instrument. The corresponding upper limit on the He /He flux ratio is 3.1 ×10 −6 , 30 times more stringent than the limits obtained in similar rigidity regions with magnetic spectrometers previous to BESS.