Measurement of anti-p p pi+pi- and anti-p p->K+K- annihilation frequencies in a 5mb hydrogen gas target

We report the first measurement of the K +K-, 7r + 7r- frequencies for ~ annihilations at rest in a gaseous H 2 target at low pressure (5 mbar). We have obtained: f~= (4.26+0.11 ) × 10 -3, fKK = (0.46+0.03) × 10 -3. The ratio R=fKK/f~, has also been measured at a pressure of 2 mbar. Comparison with previous measurements shows that fKK decreases monotonically with the target density but its value at 5 mbar is still higher than the value with L X-rays in coincidence. Antiproton-proton annihilations at rest occur from the 1So spin singlet and 3S1 spin triplet S-wave initial states with principal quantum number n >~ 1 and from the lp~ spin singlet and 3P o, 3P 1 and 3P 2 spin triplet P