Measurement of neutrino oscillation with KamLAND: evidence of spectral distortion.
We present results of a study of neutrino oscillation based on a 766 ton/year exposure of KamLAND to reactor antineutrinos. We observe 258 nu (e) candidate events with energies above 3.4 MeV compared to 365.2+/-23.7 events expected in the absence of neutrino oscillation. Accounting for 17.8+/-7.3 expected background events, the statistical significance for reactor nu (e) disappearance is 99.998%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance and prefers the distortion expected from nu (e) oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives Deltam(2)=7.9(+0.6)(-0.5)x10(-5) eV(2). A global analysis of data from KamLAND and solar-neutrino experiments yields Deltam(2)=7.9(+0.6)(-0.5)x10(-5) eV(2) and tan((2)theta=0.40(+0.10)(-0.07), the most precise determination to date.
Araki
T
T
Research Center for Neutrino Science, Tohoku University, Sendai 980-8578, Japan.
Eguchi
K
K
Enomoto
S
S
Furuno
K
K
Ichimura
K
K
Ikeda
H
H
Inoue
K
K
Ishihara
K
K
Iwamoto
T
T
Kawashima
T
T
Kishimoto
Y
Y
Koga
M
M
Koseki
Y
Y
Maeda
T
T
Mitsui
T
T
Motoki
M
M
Nakajima
K
K
Ogawa
H
H
Owada
K
K
Ricol
J-S
JS
Shimizu
I
I
Shirai
J
J
Suekane
F
F
Suzuki
A
A
Tada
K
K
Tajima
O
O
Tamae
K
K
Tsuda
Y
Y
Watanabe
H
H
Busenitz
J
J
Classen
T
T
Djurcic
Z
Z
Keefer
G
G
McKinny
K
K
Mei
D-M
DM
Piepke
A
A
Yakushev
E
E
Berger
B E
BE
Chan
Y D
YD
Decowski
M P
MP
Dwyer
D A
DA
Freedman
S J
SJ
Fu
Y
Y
Fujikawa
B K
BK
Goldman
J
J
Gray
F
F
Heeger
K M
KM
Lesko
K T
KT
Luk
K-B
KB
Murayama
H
H
Poon
A W P
AW
Steiner
H M
HM
Winslow
L A
LA
Horton-Smith
G A
GA
Mauger
C
C
McKeown
R D
RD
Vogel
P
P
Lane
C E
CE
Miletic
T
T
Gorham
P W
PW
Guillian
G
G
Learned
J G
JG
Maricic
J
J
Matsuno
S
S
Pakvasa
S
S
Dazeley
S
S
Hatakeyama
S
S
Rojas
A
A
Svoboda
R
R
Dieterle
B D
BD
Detwiler
J
J
Gratta
G
G
Ishii
K
K
Tolich
N
N
Uchida
Y
Y
Batygov
M
M
Bugg
W
W
Efremenko
Y
Y
Kamyshkov
Y
Y
Kozlov
A
A
Nakamura
Y
Y
Gould
C R
CR
Karwowski
H J
HJ
Markoff
D M
DM
Messimore
J A
JA
Nakamura
K
K
Rohm
R M
RM
Tornow
W
W
Wendell
R
R
Young
A R
AR
Chen
M-J
MJ
Wang
Y-F
YF
Piquemal
F
F