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)