Higher-statistics measurement of the branching ratio for the decay K sub L sup 0 r arrow. mu. mu

With a significant increase in experimental sensitivity, we have observed an additional 281 {ital K}{sub {ital L}}{sup 0}{r arrow}{mu}{mu} events after a background subtraction of 19{plus minus}6 events. Normalizing this sample to the simultaneous observation of the decay {ital K}{sub {ital L}}{sup 0}{r arrow}{pi}{sup +}{pi}{sup {minus}}, we obtain the branching ratio {ital B}({ital K}{sub {ital L}}{sup 0}{r arrow}{mu}{mu})=(7.6{plus minus}0.5(stat){plus minus}0.4(syst)){times}10{sup {minus}9}. Combining these data with our previously published sample containing 87 events yields {ital B}({ital K}{sub {ital L}}{sup 0}{r arrow}{mu}{mu})=(7.0{plus minus}0.5){times}10{sup {minus}9}.