Measurement of Neutrino Oscillation with KamLAND:

Evidence of Spectral Distortion*

Jason Detwiler

Stanford University

SLAC Experimental Seminar

June 22, 2004

*T.Araki et al. arXiv:hep-ex/0406035 June 13, 2004

submitted to Phys. Rev. Lett.

T.Araki1, K.Eguchi1, S.Enomoto1, K.Furuno1, K.Ichimura1, H.Ikeda1, K.Inoue1, K.Ishihara1, T.Iwamoto1, T.Kawashima1, Y.Kishimoto1, M.Koga1, Y.Koseki1, T.Maeda1, T.Mitsui1, M.Motoki1, K.Nakajima1, H.Ogawa1, K.Owada1, J.-S.Ricol1, I.Shimizu1, J.Shirai1, F.Suekane1, A.Suzuki1, K.Tada1, O.Tajima1, K.Tamae1, Y.Tsuda1, H.Watanabe1, J.Busenitz2, T.Classen2, G.Keefer2, Z.Djurcic2, K.McKinny2, D-M.Mei2, A.Piepke2, E.Yakushev2, B.E.Berger3, Y-D.Chan3, M.P.Decowski3, D.A.Dwyer3, S.J.Freedman3, Y.Fu3, B.K.Fujikawa3, J.Goldman3, F.Gray3, K.M.Heeger3, K.T.Lesko3, K-B.Luk3, H.Murayama3, A.W.Poon3, H.M.Steiner3, L.A.Winslow 3, G.A.Horton-Smith4, C.Mauger4, R.D.McKeown4, P.Vogel4, C.E.Lane5, T.Miletic5, P.Gorham6, G.Guillian6, J.Learned6, J.Maricic6, S.Matsuno6, S.Pakvasa6, S.Dazeley7, S.Hatakeyama7, A.Rojas7, R.C.Svoboda7, B.D.Dieterle8, J.Detwiler9, G.Gratta9, K.Ishii9, N.Tolich9, Y.Uchida9, M.Batygov10, W.Bugg10, Y.Efremenko10, Y.Kamyshkov10, A.Kozlov10, Y.Nakamura10, C.R.Gould11, H.J.Karwowski11, D.M.Markoff11, J.A.Messimore11, K.Nakamura11, R.M.Rohm11, W.Tornow11, R.Wendell11, A.R.Young11, M.-J.Chen12, Y-F.Wang12, F.Piquemal13

1Research Center For Neutrino Science, Tohoku University, Sendai 980-8578, Japan

2Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA

3Physics Department, University of California at Berkeley and

Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA

4W.K.Kellog Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA

5Physics Department, Drexel University, Philadelphia, Pennsylvania 19104, USA

6Department of Physics and Astronomy, University of Hawaii at Manoa, Honolulu, Hawaii 96822 USA

7Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA

8Physics Department, University of New Mexico, Albuquerque, New Mexico 87131, USA

9Physics Department, Stanford University, Stanford, California 94305, USA

10Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA

11Triangular Universities Nuclear Laboratory, Durham, North Carolina 27708, USA and

Physics Department at Duke University, North Carolina State University, and the University of North Carolina at Chapel Hill

12Institute of High Energy Physics, Beijing 100039, People's Republic of China

13CEN Bordeaux-Gradignan, IN2P3-CNRS and University Bordeaux I, F-33175 Gradignan Cedex , France

The KamLAND Collaboration

Introduction

Reactor antineutrino experiments:

look for a flux deficit at a distance L

Nuclear reactor

Detector

L

ne

n?

Neutrino Oscillations

Write the weak states nl as a linear combination of mass eigenstates nj:



m

2

θ

MSW Effect*

ne, nm, nt

ne, nm, nt

q, e-

q, e-

ne

ne

e-

e-

Z0

W

* L. Wolfenstein, Phys. Rev. D 17, 2369 (1978)

S.P. Mikheev and A. Yu. Smirnov, Sov. J. Nucl. Phys. 42, 913 (1985)

L

osc

L

0

L

osc

L

0

L

osc

L

0

Solar Neutrino Oscillation Parameters

S.N. Ahmed et al. (SNO Collaboration), Phys. Rev. Lett. 92, 181301 (2004)

“LMA”

Losc ~ 102 km

Reactor Experiments

Control source and detector

Rock has L0 > Rearth → : Matter effects are negligible

Detect anti-neutrinos instead of neutrinos

However...

Disappearance only → limited q sensitivity

4p source

Reactors In Japan

KamLAND uses

the entire Japanese

nuclear power

industry as a 180 GWth

long­baseline source!

Kashiwazaki

Takahama

Ohi

55% of total flux from:

KamLAND

Mt. Ikenoyama

~1km high

Reactors In Japan

80% of total flux from baselines 140-210 km

The KamLAND Detector

Chimney

Liquid Scintillator

(1 kton)

Containment Vessel

(diam. 18m)

Outer Detector

Outer Detector

PMTs

Calibration Device

LS Balloon

(diam. 13m)

Buffer Oil

1879 Inner Detector PMTs

(34% coverage)

Event Signature

Coincidence signal: detect

Prompt: e+ energy + annihilation 

Delayed: n-capture g

p

e+

511 keV γ

511 keV γ

n

2.2 MeV γ

p

d

Dt ~ 210 μs

ne

Event Signature

Coincidence signal: detect

Prompt: e+ energy + annihilation 

Delayed: n-capture g

e+

511 keV γ

511 keV γ

2.2 MeV γ

Dt ~ 210 μs

ne

Event Reconstruction

(color is time)

Reconstruct event position and energy from PMT-hit timing and total light collected

Calibration

Calibrate energy and position reconstruction with radioactive gamma sources

visible

Calibration

12B

12N

τ=29.1ms

Q=13.4MeV

τ=15.9ms

Q=17.3MeV

μ

Tagged cosmogenics are also used for calibration

Fit to data gives 12B:12N ~ 100:1

68Ge

65Zn

60Co

n-p

n-12C

Energy Scale

Correct for Birk's quenching, Cherenkov emission, light absorption/optics

Event Selection

Time correlation: 0.5 ms < Dt < 1 ms

Vertex correlation: DR < 2 m

Delayed event energy: 1.8 MeV < Ed < 2.6 MeV

Prompt event energy: 2.6 MeV < Ep < 8.5 MeV

Spherical fiducial volume: Rp, Rd < 5.5 m

Total efficiency: 89.8 ± 1.5 %

e+

511 keV γ

511 keV γ

2.2 MeV γ

Dt ~ 210 μs

ne

Data Collection

369.7

Oct - Jan 11

2004

Run B

515.1

Mar 9, 2002 –

Jan 11, 2004

Data-set presented here

Jan/Feb 2003

Mar 9 – Oct 6

2002

Jan 2002

Dates

Live time

(days)

-

Electronics upgrade & 20” PMT commissioning

145.4

Run A

(data-set of 1st paper)*

-

Start data taking

Exposure: 766.3 ton∙yr (4.7 times our previous result)

*K.Eguchi et al. (KamLAND Collaboration), Phys. Rev. Lett. 90, 021802 (2003).

Prompt/Delayed Event Energies

Eprompt (MeV)

Fiducial Cut

5.5 m fiducial cut

Fiducial Volume and Systematic

neutrons

Fiducial Volume and Systematic

12B/12N

Backgrounds

Accidentals: 2.69 ± 0.02 events

off-time window selection

random event pairing

“swap” Ep/Ed cuts*

Correlated backgrounds: spallation products

veto full detector for 2s after showering/bad-m

apply 2s veto in 3m-radius tube along good-m tracks

→ 9.7% correction to exposure

Remaining correlated backgrounds:

8He/9Li: 4.8 ± 0.9 events

fast n: < 0.89 events

Total Backgrounds: 7.5 ± 1.3 events

*Y.-F.Wang et al., Phys. Rev. D 62, 013012 (2000)

> 99.9% of ne are

produced by fissions of

235U, 238U, 239Pu, 241Pu

Reactor Fuel Cycle

Simulation Inputs

Economics pushes the uncertainty on the power to < 1%

ne Spectra

235U, 239Pu, and 241Pu: ne spectra are derived from b-spectra measurements

A. A. Hahn et al., Phys. Lett. B218, 365 (1989)

K. Schreckenbach et al., Phys. Lett. B160, 325 (1985)

238U: no measurements are available, so we must rely on calculations

P. Vogel et al., Phys. Rev. C52 (2498)

The Detected ne Spectrum

* P. Vogel and J. F. Beacom, Phys. Rev. D60, 053003 (1999)

νe+p→n+e+ cross

section (10-43 cm2)*

Eν (MeV)

Reactor νe spectrum (a.u.)

Observed spectrum (a.u.)

Short baseline (L = 15 m, 40 m), 1.5 x 105 events

Bugey 3

B.Achkar et al., Phys. Lett. B 374, 243 (1996).

Bookkeeping...

Japanese research reactors / spent fuel / rest of the world: 1.1 ± 0.5%

4.8

7.8·103

17.4

6

986

Yonggwang

6.1

9.9·103

11.5

4

712

Ulchin

South Korea

4.6

7.5·103

9.2

4

735

Kori

4.3

7.1·103

8.2

4

709

Wolsong

5.1

8.3·103

6.0

3

561

Ikata

6.3

1.0·104

3.8

2

401

Simane

9.3

1.5·104

6.5

3

431

Onagawa

2.1

3.4·103

5.3

2

830

Sendai

4.8

7.8·103

10.1

4

755

Genkai

1.4

2.3·103

3.3

2

783

Tomari

31.1

5.1·104

14.2

6

349

Fukushima1

55.2

9.0·104

1.6

1

88

Sika

29.5

4.8·104

13.2

4

345

Fukushima2

62.5

1.0·105

4.5

2

138

Tsuruga

Total Nominal

Japan

74.3

1.2·105

10.2

4

191

Takahama

114.3

1.9·105

13.7

4

179

Ohi

62.0

1.0·105

4.9

3

146

Mihama

62.0

1.0·105

10.6

4

214

Hamaoka

181.7

3.3

24.3

Ptherm

(GW)

1.3·106

1.6·104

4.1·105

Flux

(cm-2 s-1)

803.8

70

-

10.1

1

295

Tokai2

254.0

7

160

Kashiwazaki

Rate noosc*

(yr-1 kt-1)

Cores

(#)

Dist (km)

Site

Survival Probability

ne

Events observed: 258

No oscillation expectation:

365 ± 24 (syst)

Background: 7.5 ± 1.3

Average survival probability:

0.686 ± 0.044 (stat) ± 0.045 (syst)

ne disappearance at 99.995% C.L.

Time Variation

Source-Signal Correlation

Expected for no oscillations

Energy Spectrum

Best oscillation fit:

Dm2 = 8.3 x 10-5 eV2

sin22q = 0.83

c2 for 20 equal probability bins:

18.3 (18 d.o.f.)

A rescaled no-oscillation spectrum is excluded at 99.89% C.L.

L/E Spectrum

N / Nno-osc

L/E Spectrum

*V.Barger et al. Phys. Rev. Lett. 82 (1999) 2640

†E.Lisi et al., Phys. Rev. Lett. 85 (2000) 1166

*

†

c2 = 30.1/18

c2 = 28.6/18

N / Nno-osc

Oscillation Parameter Contours

Best fit:

Dm2 = 8.3 x 10-5 eV2

sin22q = 0.83

Maximal mixing disfavored at

79% C.L.

LMA II disfavored at 99.6% C.L.

LMA 0 disfavored at 94% C.L.

Shape-Only Contours

Best fit:

Dm2 = 8.3 x 10-5 eV2

sin22q = 0.98

Comparison with Previous Results

This result:

Dm2 = 8.3 x 10-5 eV2

sin22q = 0.83

Previous result:

Dm2 = 6.9 x 10-5 eV2

sin22q = 1.0

Include MSW Matter Effects

Global Solar + KamLAND Analysis

Conclusions

Factor ~4.7 increase in exposure strengthens our previous findings of antineutrino disappearance

Correlated variation of the signal with source modulations observed at a moderate C.L.

Fit to neutrino oscillation is decent, while fits to no-oscillation, rescaled no-oscillation, decay, and decoherence are poor due to significant spectral distortion

Global solar + KamLAND analysis excludes LMA II and gives a precision measurement of the oscillation parameters

Statistics are on the same level as systematics; future work will focus on reducing systematics

Stay tuned for more physics from KamLAND!

this is all solar combined

on “nuebar rather than nu”: mention both CPT invariance and uncorrelated systematics

2003-07-03T08:59:45