Search for electron neutrino appearance in a 250 km long-baseline experiment.
We present a search for electron neutrino appearance from accelerator-produced muon neutrinos in the K2K long-baseline neutrino experiment. One candidate event is found in the data corresponding to an exposure of 4.8 x 10(19) protons on target. The expected background in the absence of neutrino oscillations is estimated to be 2.4+/-0.6 events and is dominated by misidentification of events from neutral current pi(0) production. We exclude the nu(micro) to nu(e) oscillations at 90% C.L. for the effective mixing angle in the 2-flavor approximation of sin((2)2theta(microe)( approximately 1/2sin((2)2theta(13))>0.15 at Deltam(2)(microe)=2.8 x 10(-3) eV(2), the best-fit value of the nu(micro) disappearance analysis in K2K. The most stringent limit of sin((2)2theta(microe)<0.09 is obtained at Deltam(2)(microe)=6 x 10(-3) eV(2).
Ahn
M H
MH
Department of Physics, Seoul National University, Seoul 151-742, Korea.
Aoki
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S
Ashie
Y
Y
Bhang
H
H
Boyd
S
S
Casper
D
D
Choi
J H
JH
Fukuda
S
S
Fukuda
Y
Y
Gran
R
R
Hara
T
T
Hasegawa
M
M
Hasegawa
T
T
Hayashi
K
K
Hayato
Y
Y
Hill
J
J
Ichikawa
A K
AK
Ikeda
A
A
Inagaki
T
T
Ishida
T
T
Ishii
T
T
Ishitsuka
M
M
Itow
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Y
Iwashita
T
T
Jang
H I
HI
Jang
J S
JS
Jeon
E J
EJ
Joo
K K
KK
Jung
C K
CK
Kajita
T
T
Kameda
J
J
Kaneyuki
K
K
Kato
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I
Kearns
E
E
Kibayashi
A
A
Kielczewska
D
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Kim
B J
BJ
Kim
C O
CO
Kim
J Y
JY
Kim
S B
SB
Kobayashi
K
K
Kobayashi
T
T
Koshio
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Y
Kropp
W R
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Learned
J G
JG
Lim
S H
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Lim
I T
IT
Maesaka
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H
Maruyama
T
T
Matsuno
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S
Mauger
C
C
Mcgrew
C
C
Minamino
A
A
Mine
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S
Miura
M
M
Miyano
K
K
Morita
T
T
Moriyama
S
S
Nakahata
M
M
Nakamura
K
K
Nakano
I
I
Nakata
F
F
Nakaya
T
T
Nakayama
S
S
Namba
T
T
Nambu
R
R
Nishikawa
K
K
Nishiyama
S
S
Noda
S
S
Obayashi
Y
Y
Okada
A
A
Oyama
Y
Y
Pac
M Y
MY
Park
H
H
Saji
C
C
Sakuda
M
M
Sarrat
A
A
Sasaki
T
T
Sasao
N
N
Scholberg
K
K
Sekiguchi
M
M
Sharkey
E
E
Shiozawa
M
M
Shiraishi
K K
KK
Smy
M
M
Sobel
H W
HW
Stone
J L
JL
Suga
Y
Y
Sulak
L R
LR
Suzuki
A
A
Suzuki
Y
Y
Takeuchi
Y
Y
Tamura
N
N
Tanaka
M
M
Totsuka
Y
Y
Ueda
S
S
Vagins
M R
MR
Walter
C W
CW
Wang
W
W
Wilkes
R J
RJ
Yamada
S
S
Yamamoto
S
S
Yanagisawa
C
C
Yokoyama
H
H
Yoo
J
J
Yoshida
M
M
Zalipska
J
J