A NEW LIMIT ON THE FLUX OF COSMIC ANTIHELIUM

A very sensitive search for cosmic-ray antihelium was performed using data obtained from three scientific flights of the BESS magnetic rigid ity spectrometer. We have not observed any antihelium; this places a m odel-independent upper limit (95% C.L.) on the antihelium flux of 6 x 10(-4) m(-2)sr(-1)s(-1) at the top of the atmosphere in the rigidity r egion 1 to 16 GV, after correcting for the estimated interaction loss of antihelium in the air and in the instrument. The corresponding uppe r limit on the <(He)over bar>/He flux ratio is 3.1 x 10(-6), 30 times more stringent than the limits obtained in similar rigidity regions wi th magnetic spectrometers previous to BESS. (C) 1998 Published by Else vier Science B.V.