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KamLAND (Anti-Neutrino Status)
The 10th International Conference on Topics in Astroparticle and Underground Physics
Sep. 14, 2007Itaru Shimizu (Tohoku Univ.)
T. Ebihara,1 S. Enomoto,1 K. Furuno,1 Y. Gando,1 K. Ichimura,1 H. Ikeda,1 K. Inoue,1 Y. Kibe,1 Y. Kishimoto,1 M. Koga,1Y. Konno,1 A. Kozlov,1 Y. Minekawa,1 T. Mitsui,1 K. Nakajima,1, K. Nakajima,1 K. Nakamura,1 K. Owada,1 I. Shimizu,1J. Shirai,1 F. Suekane,1 A. Suzuki,1 K. Tamae,1 S. Yoshida,1 J. Busenitz,2 T. Classen,2 C. Grant,2 G. Keefer,2 D.S. Leonard,2D. McKee,2 A. Piepke,2 M.P. Decowski,3 S.J. Freedman,3 B.K. Fujikawa,3 F. Gray,3, L. Hsu,3, R. Kadel,3 K.-B. Luk,3H. Murayama,3 T. O’Donnell,3 H.M. Steiner,3 L.A. Winslow,3 D.A. Dwyer,4 C. Jillings,4, 、 C. Mauger,4 R.D. McKeown,4
C. Zhang,4 B.E. Berger,5 C.E. Lane,6 J. Maricic,6 T. Miletic,6 M. Batygov,7 J.G. Learned,7 S. Matsuno,7 S. Pakvasa,7J. Foster,8 G.A. Horton-Smith,8 A. Tang,8 S. Dazeley,9, K. Downum,10 G. Gratta,10 K. Tolich,10 W. Bugg,11 Y. Efremenko,11Y. Kamyshkov,11 O. Perevozchikov,11 H.J. Karwowski,12 D.M. Markoff,12 W. Tornow,12 K. M. Heeger,13 F. Piquemal,14 and J.-S. Ricol14
(KamLAND Collaboration)
KamLAND Collaboration
1Research Center for Neutrino Science, Tohoku University, Sendai 980-8578, Japan2Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA3Physics Department, University of California at Berkeley andLawrence Berkeley National Laboratory, Berkeley, California 94720, USA4W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA5Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA6Physics Department, Drexel University, Philadelphia, Pennsylvania 19104, USA7Department of Physics and Astronomy, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA8Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA9Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA10Physics Department, Stanford University, Stanford, California 94305, USA11Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA12Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA and Physics Departments at Duke University, North Carolina State University, and the University of North Carolina at Chapel Hill13Department of Physics, University of Wisconsin, 1150 University Avenue, Madison, WI 53706, USA14CEN Bordeaux-Gradignan, IN2P3-CNRS and University Bordeaux I, F-33175 Gradignan Cedex, France
Kamioka
Outer water tank
Inner tank
1,000 ton LS
34% photo-coverage with1325 17” and 554 20” PMTs
~ 180 km baseline
P (νe → νe) = 1− sin2 2θ sin2(1.27∆m2[eV2]l[m]
E[MeV])
2 flavor neutrino oscillation most sensitive region
!m2 = (1/1.27) · (E[MeV]/L[m]) · (!/2)
! 3" 10!5eV2
reactor neutrino : sensitive to LMA solution
Kamioka Liquid Scintillator Anti-Neutrino DetectorKamLAND
観測エネルギー (MeV)1.0 2.6 8.50.4 太陽ニュートリノ 地球ニュートリノ 原子炉ニュートリノ 超新星ニュートリノ
e-
e-νx
νxsolar neutrino
n
pν̄e
e+
γ
γ
γ
anti-neutrino detection by inverse beta-decay
prompt
delayed
mean capture time ~ 200 µsec on proton
reactor neutrinogeo neutrino
neutrino detection by electron scattering
solar neutrino geo neutrino reactor neutrino supernova neutrino
observed energy (MeV)Physics Target in KamLAND
Reactor and Geo Neutrino Analysis
3(R/6.5m)
0 0.2 0.4 0.6 0.8 1
Pro
mpt
Ener
gy
(M
eV)
1
2
3
4
5
6
7
8
-410
-310
-210
-110
1
10
210
accidental
fast-neutron reactor neutrino
(α, n) reaction
S/N5 m 5.5 m
¹²C*
¹⁶O*reactor neutrino
geo neutrino
(2.6 - 8.5 MeV, R 5.5 m)
(0.9 - 2.6 MeV, R 5.0 m)
(1) efficient accidental background rejection(2) combined analysis of reactor and geo neutrinos
S / B ratio map (energy v.s. radius)
large accidental B.G.caused by external γ-raysAnalysis improvement
previous result
separated analysis window for reactor and geo neutrinos
Anti-Neutrino Event Selection
(MeV)promptE
0 1 2 3 4 5 6 7 8
Eff
icie
ncy
(%
)
0
10
20
30
40
50
60
70
80
90
100
Fig
ure
of
Mer
it
0
1
2
3
4
5
6
7
8
9
10
Efficiency
Figure of Merit
Detection efficiency
efficiency decreasecaused by largeraccidental BG
efficiency
Figure of Merit
(a) Accidental B.G. discrimination
Lratio = fν / (fν + faccidental)discriminator based on 5 parameters (Ed, ΔR, ΔT, Rp, Rd)
(b) µ spallation cut• ΔTµ > 2 s after showing µ (ΔQ > 106 p.e.)• ΔTµ > 2 s or ΔL > 3 m after non-showering µ
Likelihood Ratio
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Fig
ure
of
Mer
it
4
4.5
5
5.5
6
6.5
7
7.5
8
Likelihood Ratio
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Events
/ B
in
-510
-410
-310
-210
-110
1
10 anti-neutrino(reactor, geo)
accidentalbackground
maximum “Figure of Merit”Lratio > 0.967
generated by MC simulation
2.2 < Eprompt < 2.3 MeV
Figure of Merit
f : PDF
preliminary
Selection : Maximize “Figure of Merit”S!
S + Baccidental
Systematic Uncertainty
Detector related Reactor related
Fiducial volume 1.8%Energy scaleL-selection eff.OD vetoCross section
1.5%0.6%0.2%0.2%
νe spectra 2.4%Reactor powerFuel compositionLong-lived nucleiTime lag
2.1%1.0%0.3%
0.01%
2.4% 3.4%
Total systematic uncertainty : 4.1%
“full volume” calibration lowered the fiducial volume error(4.7% in previous analysis)preliminary
R [cm]0 100 200 300 400 500 600
Bia
s [c
m]
-5
-4
-3
-2
-1
0
1
2
3
4
5
Ge68
R [cm]0 100 200 300 400 500 600
Bia
s [c
m]
-5
-4
-3
-2
-1
0
1
2
3
4
5
Co60
source deployment
Full Volume Calibrationz-axis
off-axis
“4pi calibration” system for the off-axis source deployment
bias < 3 cm
bias < 3 cm
68Ge
60Co
even
t rat
e (a
rbitr
ary)
bias < 3 cm corresponds to 1.8% volume uncertainty
cross-checked by12B/12N uniformity
z-axis
z-axis
off-axis
off-axis
visible energy [MeV]1 2 3 4 5 6 7 8e
ve
nts
/Me
V/a
lph
a
0
2
4
6
-610!
13C(α, n)16O
13C16O
n
α
d
γ (2.22MeV)
precoil proton
γ (6.1MeV) or e+e-(6.0MeV)
prompt
delayed16O
6.049MeV 0+6.130MeV 3-
0+
natural abundance1.1%
12C(n, nγ)12C
Q = 2.2MeV
12Cn
γ prompt(4.4MeV)
(α, n) Background Estimation
alpha energy [MeV]
0 1 2 3 4 5
cro
ss s
ecti
on
[b
arn
]
-610
-510
-410
-310
-210
-110
1
S. Harissopulos et al.
neutron yield difference < 4%
JENDL
cross section measurement
Estimation uncertainty
11% for ground state20% for excited state
Po13C source calibration
ground state1st excited state2nd excitted state
(α, n) background estimation163.3 ± 18.0 events for ground state
18.7 ± 3.7 events for excited state
expected rate in no oscillation [events/day]
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
ob
serv
ed
rate
[even
ts/d
ay]
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
events/day
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Rate Analysis above 2.6 MeV
Observed events
No osci. expectedBackground
Ratio = (obs. - B.G.) / No osci.
expe
cted i
n no o
scilla
tion c
ase
90% C.L.
χ2 / ndf = 3.1 / 4
2002 2003 2004 2005 2006 2007
period for “KamLAND 2004”
985
154963
0.594 ± 0.020(stat) ± 0.026(syst)
515 days
total 1491 days
8.5σ disappearance significance
χ2 / ndf = 11.8 / 4 Fit with a horizontal line
(1.9% C.L.)
Fit constrained through B.G. expected
976 days
updated
preliminary
“Reactor” rate analysis (2.6 MeV threshold)
(see Poster Sessions : Ichimura and Minekawa et al.)
(MeV)promptE
Ev
ents
/ 0
.42
5 M
eV
0
50
100
150
200
250
300
0 1 2 3 4 5 6 7 8
KamLAND data
no oscillation
best-fit oscillation
accidental
O16
,n)!C(13
e"Expected Geo
best-fit osci. + BG
e"+ Expected Geo
Energy Spectrum above 0.9 MeVprevious result (above 2.6 MeV)
best-fit
geo neutrinos “Geo + Reactor” combined analysis
preliminary
Observed events
No osci. expectedBackground
1609
2178
276(w/o geo neutrino)
exposure : 2881 ton-year (3.8 × 766 ton-year for “KamLAND 2004”)
χ2 / ndf = 21.0 / 16 (18.0% C.L.)
Scaled no oscillation spectrum is excluded at 5.2σ
goodness of fit using equal probability bins
χ2 / ndf = 63.9 / 17best-fitno osci.
(Ichimura and Minekawa et al.)
free parameter : geo neutrinos (U, Th) = (39.3, 29.4) events
(tan2θ, Δm2) = (0.56, 7.58 × 10-5 eV2)
(km/MeV)e!
/E0L
20 30 40 50 60 70 80 90 100
Rat
io
0
0.2
0.4
0.6
0.8
1
1.2
1.4 KamLAND databest-fit osci.
e!best-fit osci. + Expected Geo
L/E plotRatio = (observed - B.G.) / (no osci. expected)
preliminary
consistent with geo neutrino expectationfrom an earth model
Distortion effect is clearly illustrated by L/E plotL0 : a fixed baseline (180 km)
20% geo neutrinoflux uncertainty(a claim based on the geology)
w/o geo neutrino
(km/MeV)e!
/E0L
0 10 20 30 40 50 60 70
Rat
io
0
0.2
0.4
0.6
0.8
1
1.2
1.4 KamLAND data CHOOZ databest-fit osci.
e!best-fit osci. + Expected Geo
preliminary
1st 2nd 3rd
KamLAND covers the 2nd and 3rd maximum
Neutrino Oscillationprevious result (above 2.6 MeV)
characteristic of neutrino oscillation
hypothetical single reactorat 180 km
short baselineexperiment
(km/MeV)e!
/E0L
0 10 20 30 40 50 60 70
Rat
io
0
0.2
0.4
0.6
0.8
1
1.2
1.4 KamLAND data CHOOZ databest-fit osci.
e!best-fit osci. + Expected Geo
preliminary
1st 2nd 3rd
Alternate Hypothesisprevious result (above 2.6 MeV)
oscillation
Δχ2 = 34.5
Δχ2 = 45.0
V. D. Barger et al., Phys. Rev. Lett. 82, 2640 (1999)
E. Lisi et al, Phys. Rev. Lett. 85, 1166 (2000)
decoherence
decay
best model is neutrino oscillation
(km/MeV)e!
/E0L
0 10 20 30 40 50 60 70
Rat
io
0
0.2
0.4
0.6
0.8
1
1.2
1.4 KamLAND data CHOOZ databest-fit osci.
e!best-fit osci. + Expected Geo
preliminary
1st 2nd 3rd
Alternate Wavelengthprevious result (above 2.6 MeV)
LMA I
LMA 0 and LMA II are disfavored at more than 4σ
LMA II
LMA 0
-110 1
-410
KamLAND
95% C.L.
99% C.L.
99.73% C.L.
best fit
SNO
95% C.L.
99% C.L.
99.73% C.L.
best fit
10 20 30 40
!1 !2 !3 !4
!5
!6
5
10
15
20
!1
!2
!3
!4
"2tan 2#$
)2 (
eV
2m
$2#
$
Oscillation Parameters
LMA II
KamLAND only
> 6σ
preliminary
small matter effectSNO KamLAND
LMA 0> 4σ
(marginalized error)
tan2θ = 0.56
Δm2 = 7.58 × 10-5 eV2
+0.14−0.09
+0.21−0.20
12! 2sin
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
)2
eV
-5 (
10
2 m
"
6
6.5
7
7.5
8
8.5
9
3 neutrino effect
same result for Δm2
preliminary
3 neutino2 neutino
0.2 0.3 0.4 0.5 0.6 0.7 0.85
6
7
8
9
10
11
12-510×
!2tan
)2 (e
V2
m"
KamLAND + Solar95% C.L.99% C.L.99.73% C.L.global best fit
!2tan
)2
eV
-5 (
10
2m
"
0.2 0.3 0.4 0.5 0.6 0.7 0.85
6
7
8
KamLAND + SNO
95% C.L.
99% C.L.
99.73% C.L.
best fit
KamLAND 2004 This resultPrecise measurement of Δm2
Δm2 is measured at 2.8% precision by KamLAND
preliminary
KamLAND + SNO
tan2θ = 0.49
Δm2 = 7.59 × 10-5 eV2
+0.07−0.05
+0.20−0.21
Δm2 : systematic uncertainty 2.0%dominated by linear energy scale uncertainty
Δm2 = 7.9 × 10-5 eV2+0.4−0.3
tan2θ = 0.40+0.07−0.05
Th + N
UN
50 100 150 200
2!
"
0
5
10
15
20
Th + N
UN
50 100 150 200
2!
"
0
5
10
15
20
(MeV)promptE
Ev
ents
/ 0
.42
5 M
eV
0
50
100
150
200
250
300
0 1 2 3 4 5 6 7 8
KamLAND data
no oscillation
best-fit oscillation
accidental
O16
,n)!C(13
e"Expected Geo
best-fit osci. + BG
e"+ Expected Geo
Geo Neutrino Estimation
+27.3−27.2U+Th = 74.9 event
TNU (Terrestrial Neutrino Unit) = events/1032 target-proton/year
(previous result : 57.4 TNU)+32.0−30.0
39.4 TNU+14.4−14.3
preliminary
geo neutrinos (U, Th)Analysis : KamLAND (rate + shape + time) + SNO
Th/U mass ratio fixed : 3.9
Reference model (16 TW)
U : 56.2 event (28.9 TNU)Th : 13.1 event (7.6 TNU)
model expected69.3 events (36.5 TNU)
preliminary
Summary• KamLAND improved sensitivity to νe observation.
• In the reactor neutrino analyses, we showed
• Geo neutrino flux is measured with better precision.
- Oscillatory shape including 2nd and 3rd maximum- Exclusion of LMA II and 0 at more than 4σ C.L.- Precise measurement of oscillation parameters.
KamLAND only tan2θ = 0.56 Δm2 = 7.58 × 10-5 eV2+0.14−0.09
+0.21−0.20
KamLAND + SNO tan2θ = 0.49 Δm2 = 7.59 × 10-5 eV2+0.07−0.05
+0.20−0.21
data-set : 766 ton-yr → 2881 ton-yrE threshold : 2.6 MeV → 0.9 MeVsyst. uncertainty : 6.5% → 4.1%
(α, n) B.G. uncertainty :
100% → 20% (excited state)32% → 10% (ground state)