Recent Results from KamLAND

Jason Detwiler

Stanford University

December 15, 2003

K.Eguchi, S.Enomoto, K.Furuno, J. Goldman, H.Hanada, H.Ikeda, K.Ikeda, K.Inoue, K.Ishihara, W.Itoh, T.Iwamoto, T.Kawaguchi, T.Kawashima, H.Kinoshita, Y.Kishimoto, M.Koga, Y.Koseki, T.Maeda, T.Mitsui, M.Motoki, K.Nakajima, M.Nakajima, T.Nakajima, H.Ogawa, K.Owada, T.Sakabe, I.Shimizu, J.Shirai, F.Suekane, A.Suzuki, K.Tada, O.Tajima, T.Takayama, K.Tamae, H.Watanabe

Tohoku University

J.Busenitz, Z.Djurcic, K.McKinny, D-M.Mei, A.Piepke, E.Yakushev

University of Alabama

B.E.Berger, Y-D.Chan, M.P.Decowski, D.A.Dwyer, S.J.Freedman, Y.Fu, B.K.Fujikawa, K.M.Heeger, K.T.Lesko, K-B.Luk, H.Murayama, D.R.Nygren, C.E.Okada, A.W.Poon, H.M.Steiner, L.A.Winslow

LBNL/UC Berkeley

G.A.Horton-Smith, R.D.McKeown, J.Ritter, B.Tipton, P.Vogel

California Institute of Technology

C.E.Lane, T.Miletic

Drexel University

P.Gorham, G.Guillian, J.Learned, J.Maricic, S.Matsuno, S.Pakvasa

University of Hawaii

S.Dazeley, S.Hatakeyama, M.Murakami, R.C.Svoboda

Louisiana State University

B.D.Dieterle, M.DiMauro

University of New Mexico

J.Detwiler, G.Gratta, K.Ishii, N.Tolich, Y.Uchida

Stanford University

M.Batygov, W.Bugg, H.Cohn, Y.Efremenko, Y.Kamyshkov, A.Kozlov, Y.Nakamura

University of Tennessee

L.De Braeckeleer, C.R.Gould, H.J.Karwowski, D.M.Markoff, J.A.Messimore, K.Nakamura, R.M.Rohm, W.Tornow, A.R.Young

TUNL

Y-F.Wang

IHEP, Beijing

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:

Oscillation probability for 2 flavors (e.g. ne, nm):

q

Dm2

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)

Solar Neutrino Mixing Parameters

Neutrinos On Earth

Control source and detector

Sun: L0 ~ 200 km << Rsun; Rock: L0 ~ 104 km > Rearth

 Matter effects much less significant

Neutrino beams

sensitivity to small Dm2 requires very large L

appearance possible

collimated source

Reactors

sensitive to very small Dm2

disappearance only

 limited sin22q sensitivity

4p source

Reactors In Japan

KamLAND uses

the entire Japanese

nuclear power

industry as a 180 GWth

long­baseline source!

KamLAND

80% of total flux from

baselines 140-210 km

Kashiwazaki

Takahama

Ohi

55% of total flux from:

235U Fission

Stable nuclei with A

most likely from

fission:

92 protons and 142 neutrons are shared between X1 and X2

and

98 protons

136 neutrons

On average, 6 n must decay to 6 p to reach stable matter.

> 99.9% of n 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

observed spectrum

[interactions / MeV ton day]

ne + p  n + e+

cross section*

(~10-42 cm2)

emitted

spectrum

3

neutrinos with E < 1.8 MeV

are not detected

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

From Bugey 3: short baseline (L = 15 m, 40 m), 1.5 x 105 events

Previous Results

Previous Results

Antineutrino Flux at KamLAND

Flux Calculation Systematics (%)

ne

ne

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

The KamLAND Detector

KamLAND Trigger

Muons:

all tubes hit

Singles threshold:

200 PMT's hit (~0.7 MeV)

Coincidence, prescale threshold: 120 PMT's hit

Waveform Analysis

Samples (~1.5ns)

ADC counts (~120 V)

Blue: raw data

red: pedestal

green: pedestal subtracted

KamLAND Data

Event Display:

through­going muon

color is pulseheight

all tubes illuminated

KamLAND Data

Stopped muon

KamLAND Data

Cherenkov ring from

“edge clipper”

Antineutrino Candidate

Prompt Signal

E = 3.20 MeV

Delayed Signal

E = 2.22 MeV

t = 111 s

R = 34 cm

(color is time)

Calibrations

Radioactive gamma sources inserted in detector to

calibrate energy and position reconstruction

68

65

60

Autoradiography of KamLAND

Chimney activity

Central thermometers

Balloon surface contamination

Bottom flange / plumbing

Reconstruction Performance

R = 5.0 m

R = 5.0 m radius

fiducial volume

estimation from spallation neutron uniformity

Energy scale determined from radioactive source calibrations

Event Selection

Time correlation: 0.5 ms < Dt < 660 ms

Vertex correlation: DR < 1.6 m

Delayed event energy: 1.8 MeV < Edel < 2.6 MeV

Spherical fiducial volume: R < 5 m

Z-axis: r > 1.2 m

Total efficiency: 78.3 ± 1.6 %

e+

511 keV γ

511 keV γ

2.2 MeV γ

Dt = 210 μs

ne

Backgrounds

Accidental bg estimated from shifted time window 0.020-20 seconds

0.0086 ± 0.0005 events

×

×

×

Cosmogenic Backgrounds

Muon track reconstruction reveals the balloon boundary

2700 m.w.e. overburden cuts muon rate to ~0.3Hz

Muons leave neutrons which can fake the signal

Veto detector for 2 ms after muons

Muons also create longer lived (> 100 ms) neutron emitters

Veto 3m cylinder around muon track for 2 s

For high energy muons (> 3 GeV), veto entire detector for 2 s

Correction to livetime: 11.4%

Residual correlated background: 1 ± 1 event

Prompt/Delayed Event Energies

Estimated Contributions to the Systematic Uncertainty (%):

Systematic Uncertainties

ne

For no oscillations, in 145.1 live-days we expect

86.8 ± 5.6 events (1 ± 1 bg)

Measured Event Rate

We observe...

54

Measured Event Rate

LMA

no osc

Solar Neutrino Mixing Parameters

Event Spectrum

Fit to Oscillation Parameters

All contours at 95% CL

Best fit parameters:

Dm2 = 6.9 x 10-5 eV2

sin22q = 1.0

Time Variation of Flux

Expected Sensitivity

3-Flavor Mixing

solar + KamLAND:

q12 ~ 30°

Dm212 ~ 10-4 eV2

atmospheric n:

q23 ~ 45°

Dm223 ~ 3 x 10-3 eV2

q13 < 10°

Dm213 ~ ± 3 x 10-3 eV2

future accelerator/reactor

neutrinoless

double beta decay

High Energy ne Sources

Solar sources

spin flavor precession: ne  nm,t  ne

ne decay to ne

Other sources

WIMP annihilation

Supernova relic neutrinos

Energy Scale Above 5 MeV

12B decay spectrum

High Energy Backgrounds

±

±

±

±

8

9

ne

High Energy Systematics

High Energy Electron-Antineutrinos

High Energy ne Results

No events detected in 0.28 kton-yr exposure with 1.1 ± 0.4 background expected

ne flux < 2.8 x 10-4 times solar 8B neutrino flux

 improvement by a factor of ~30

As a limit on spin flavor precession:

mn < 1.3 x 10-10 mB x [100 kG / BsT(0.05 Rs)]

(best limit from MUNU: mn < 1.0 x 10-10 mB)

Conclusions

KamLAND observed, for the first time, disappearance of electron antineutrinos in a laboratory-style experiment

Assuming CPT invariance, this result excludes solar neutrino oscillation solutions except LMA at > 99.95% CL

No detected events between 8 - 15MeV puts a limit on any electron antineutrino flux at KamLAND in that energy range

Limit on from the sun improved by factor of ~30

More results are on the way (updated reactor, geoneutrinos, neutron production...)

ne

Reactor

Far Detector

L ~ 1000m

ne

n?

q13 at Reactors

Near Detector

L ~ 100m

from Huber et al.

First discussed by L.A.Mikaelyan and V.V.Sinev,

Phys. Atom. Nucl. 63, 1002 (2001)

Also see P. Huber et al., arXiv:hep-ph/0303232

and the more comprehensive list at

http://kmheeger.lbl.gov/theta13/references.html

Jason Detwiler

2003-07-03T08:59:45