title: Exclusive measurement of the nonmesonic weak decay of the lambda(5)He hypernucleus.
abstract: We performed a coincidence measurement of two nucleons emitted from the nonmesonic weak decay of lambda(5)He formed via the 6Li(pi+, K+) reaction. The energies of the two nucleons and the pair number distributions in the opening angle between them were measured. In both np and nn pairs, we observed a clean back-to-back correlation coming from the two-body weak reactions of lambda p --> np and lambda n --> nn, respectively. The ratio of the nucleon pair numbers was N(nn)/N(np) = 0.45 +/- 0.11(stat) +/- 0.03(syst) in the kinematic region of cos theta(NN) < -0.8. Since each decay mode was exclusively detected, the measured ratio should be close to the ratio of gamma(lambda p --> np)/gamma(lambda n --> nn). The ratio is consistent with recent theoretical calculations based on the heavy meson and/or direct-quark exchange picture.
authors.affiliation: Department of Physics, Seoul National University, Seoul 151-742, Korea.
authors.forename: B H
authors.initials: BH
authors.lastname: Kang
authors.forename: H
authors.initials: H
authors.lastname: Bhang
authors.forename: E H
authors.initials: EH
authors.lastname: Kim
authors.forename: J H
authors.initials: JH
authors.lastname: Kim
authors.forename: M J
authors.initials: MJ
authors.lastname: Kim
authors.forename: H J
authors.initials: HJ
authors.lastname: Yim
authors.forename: S
authors.initials: S
authors.lastname: Ajimura
authors.forename: Y
authors.initials: Y
authors.lastname: Miyake
authors.forename: K
authors.initials: K
authors.lastname: Aoki
authors.forename: T
authors.initials: T
authors.lastname: Nagae
authors.forename: H
authors.initials: H
authors.lastname: Noumi
authors.forename: H
authors.initials: H
authors.lastname: Outa
authors.forename: P K
authors.initials: PK
authors.lastname: Saha
authors.forename: Y
authors.initials: Y
authors.lastname: Sato
authors.forename: M
authors.initials: M
authors.lastname: Sekimoto
authors.forename: A
authors.initials: A
authors.lastname: Toyoda
authors.forename: A
authors.initials: A
authors.lastname: Banu
authors.forename: T
authors.initials: T
authors.lastname: Fukuda
authors.forename: O
authors.initials: O
authors.lastname: Hashimoto
authors.forename: S
authors.initials: S
authors.lastname: Kameoka
authors.forename: Y
authors.initials: Y
authors.lastname: Miura
authors.forename: S N
authors.initials: SN
authors.lastname: Nakamura
authors.forename: Y
authors.initials: Y
authors.lastname: Okayasu
authors.forename: T
authors.initials: T
authors.lastname: Takahashi
authors.forename: H
authors.initials: H
authors.lastname: Tamura
authors.forename: K
authors.initials: K
authors.lastname: Tsukada
authors.forename: T
authors.initials: T
authors.lastname: Watanabe
authors.forename: J I
authors.initials: JI
authors.lastname: Hwang
authors.forename: T
authors.initials: T
authors.lastname: Maruta
authors.forename: M
authors.initials: M
authors.lastname: Nakamura
authors.forename: S
authors.initials: S
authors.lastname: Okada
authors.forename: H
authors.initials: H
authors.lastname: Park
authors.forename: K
authors.initials: K
authors.lastname: Tanida