Exclusive measurement of the nonmesonic weak decay of the lambda(5)He hypernucleus.
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.
Kang
B H
BH
Department of Physics, Seoul National University, Seoul 151-742, Korea.
Bhang
H
H
Kim
E H
EH
Kim
J H
JH
Kim
M J
MJ
Yim
H J
HJ
Ajimura
S
S
Miyake
Y
Y
Aoki
K
K
Nagae
T
T
Noumi
H
H
Outa
H
H
Saha
P K
PK
Sato
Y
Y
Sekimoto
M
M
Toyoda
A
A
Banu
A
A
Fukuda
T
T
Hashimoto
O
O
Kameoka
S
S
Miura
Y
Y
Nakamura
S N
SN
Okayasu
Y
Y
Takahashi
T
T
Tamura
H
H
Tsukada
K
K
Watanabe
T
T
Hwang
J I
JI
Maruta
T
T
Nakamura
M
M
Okada
S
S
Park
H
H
Tanida
K
K