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

We report the first measurement of the K+K-, pi+pi- frequencies for pBAR annihilations at rest in a gaseous H-2 target at low pressure (5 mbar). We have obtained:f(pipi)=(4.26+/-0.11) X 10(-3), f(KK)=(0.46+/-0.03)X10(-3). The ratio R=f(KK)/f(pipi) has also been measured at a pressure of 2 mbar. Comparison with previous measurements shows that f(KK) decreases monotonically with the target density but its value at 5 mbar is still higher than the value with L X-rays in coincidence.