Improved limits on nu(e) emission from mu+ decay.
We investigated mu(+) decays at rest produced at the ISIS beam stop target. Lepton flavor (LF) conservation has been tested by searching for nu(e) via the detection reaction p(nu(e),e(+))n. No nu(e) signal from LF violating mu(+) decays was identified. We extract upper limits of the branching ratio (BR) for the LF violating decay mu(+)-->e(+)+nu(e)+nu(-) compared to the standard model (SM) mu(+)-->e(+)+nu(e)+nu(mu) decay: BR<0.9(1.7) x 10(-3) (90% C.L.) depending on the spectral distribution of nu(e) characterized by the Michel parameter rho=0.75(0.0). These results improve earlier limits by one order of magnitude and restrict extensions of the SM in which nu(e) emission from mu(+) decay is allowed with considerable strength. The decay mu(+)-->e(+)+nu(e)+nu(mu) often proposed as a potential source for the nu(e) signal observed in the LSND experiment can be excluded.
Armbruster
B
B
Institut für Kernphysik, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany.
Drexlin
G
G
Eitel
K
K
Jannakos
T
T
Kleinfeller
J
J
Maschuw
R
R
Oehler
C
C
Plischke
P
P
Reichenbacher
J
J
Steidl
M
M
Zeitnitz
B
B
Gemmeke
H
H
Kleifges
M
M
Eichner
C
C
Ruf
C
C
Bodmann
B A
BA
Finckh
E
E
Hössl
J
J
Jünger
P
P
Kretschmer
W
W
Wolf
J
J
Booth
N E
NE
Blair
I M
IM
Edgington
J A
JA