First observation of K{L}-->pi{+/-}e{-/+}nue{+}e{-}.
This Letter is the first report of the K{L}-->pi{+/-}e{-/+}nue{+}e{-} decay. Based on 19 208+/-144 events, we determine the branching fraction, B(K{L}-->pi{+/-}e{-/+}nue{+}e{-}M_{e{+}e{-}}>5 MeV/c{2},E{e{+}e{-}}{*}>30 MeV)=(1.285+/-0.041)x10{-5}, and Gamma(K{e3ee}M{e{+}e{-}}>5 MeV/c{2})/Gamma(K{e3})=[4.57+/-0.04(stat)+/-0.14(syst)]x10{-5}. This ratio agrees with a theoretical prediction based on chiral perturbation theory (ChPT) calculated to O(p{4}). The measured kinematical distributions agree with those predicted by just ChPT O(p{4}), but show significant disagreement with ones predicted by leading-order ChPT.
Abouzaid
E
E
The Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA.
Arenton
M
M
Barker
A R
AR
Bellantoni
L
L
Blucher
E
E
Bock
G J
GJ
Cheu
E
E
Coleman
R
R
Corcoran
M D
MD
Cox
B
B
Erwin
A R
AR
Escobar
C O
CO
Glazov
A
A
Golossanov
A
A
Gomes
R A
RA
Gouffon
P
P
Hsiung
Y B
YB
Jensen
D A
DA
Kessler
R
R
Kotera
K
K
Ledovskoy
A
A
McBride
P L
PL
Monnier
E
E
Nelson
K S
KS
Nguyen
H
H
Niclasen
R
R
Phillips
D G
DG
Ping
H
H
Ramberg
E J
EJ
Ray
R E
RE
Ronquest
M
M
Santos
E
E
Slater
W
W
Smith
D
D
Solomey
N
N
Swallow
E C
EC
Toale
P A
PA
Tschirhart
R
R
Velissaris
C
C
Wah
Y W
YW
Wang
J
J
White
H B
HB
Whitmore
J
J
Wilking
M J
MJ
Winstein
B
B
Winston
R
R
Worcester
E T
ET
Worcester
M
M
Yamanaka
T
T
Zimmerman
E D
ED
Zukanovich
R F
RF