Measurement of Neutrino Oscillation
with KamLAND:
Evidence of Spectral Distortion
hep-ex 0406035 (June 2004) submitted to PRL
see also http://neutrino2004.in2p3.fr/ (G. Gratta)
三井唯夫(東北大学ニュートリノ科学研究センター)
for the KamLAND collaboration
第15回「宇宙ニュートリノ」研究会、東京大学宇宙線研究所
2004年6月24日• 4.7 times larger statistics than the first result(162 ton-yr -> 766.3 ton-yr)

First result v.s. present result
First res. Present res.

Exposure (ton-yr)
Live time (day)162145.1

766.3
515.1

May 4 - Oct 6,2002

May 9, 2002
- Jan 11, 2004

Fiducial (radius)
5m5.5 mNeutrino observed / 54258
no-oscillation/ 86.8 / 365.2
Significance of
99.95% 99.995%
Disappearance
Significance of53 %99.9 %
Spectral distortion

x 4.7x 3.55
x 1.33

KamLAND Detector

Prompt2700m.w.e.

20m
DelayedPresent result (5.5m)
First result (5m)~200 µsec

20m

a few /day in KamLAND!

!

Thermal power, Burn-up,
Fuel change record data,
Simple model of reactor
core.
" fission rate
" energy spectrum@KamLAND
Korea(2.3+- 0.2% @N(ν) )Improvement of Vertex Fitter• NFirst result5m

Present result
Fiducial 5.5m

Balloon shape
1.2 < E < 1.6MeV (40K γ energy region)
K. Ichimura, I. Shimizu, K. Inoue－2 < z < 2m (equator)
Pumpkin shape observed!
with reconstructed vertex
distribution

south

Number of valleys = 44
Balloon ropeeast

northwestφ1.2 < E < 1.6MeV (40K γ energy region)－90°< φ < 90°

Balloon rope

topequatorbottomθImprovement of Energy Fitter∆E/E [%]Position dependence (spallation neutron)±0.4%
FiducialR [cm]All effects are 3-dimensionally understood, calibrated:
R2, transparency of scintillator, shade of balloon ropes, etc

Time dependence (Spallation neutron)∆E/E [%]• Relative calibrationis performed foreach run(1 run ~= 1 day)using 40K peaks• Stable for 2 years

2002

2003
month/dayyr

2004

Two-photoelectron peak found by energy fitter

17’’PMT

20’’PMT• Energy fitter knows
expected number ofphotoelectrons for each
event, each PMT, because
he fits energy bycomparing it with actuallyobserved.
• Energy fitter detected a 2p.e. peak for the first time,by choosing µ ~ 2 events,
showing that his
expectation is very
accurate.

Nonlinearity calibration (Cherenkov/Birks)

12B β− spectrum is used: good for e+(previously, only gammas)
12B

Best fit model

Energy scale error of 2.6-MeV e+
5-m fiducial

5.5-m fiducial

Cherenkov/Birks (statistic)

0.35

0.35

Cherenkov/Birks (systematic)

0.93

0.93

Time dependence

1.3

1.3

Position dependence

0.85

0.92

20’’ PMT non-linearity

0.8

0.8

Total

2.01 %

2.04 %

Improvement of Energy Fitter• Systematic error: almostsame as the first result• Reliability increased byemploying 12B βcalibration• Position uniformity and its
reliability increased

First result

Estimate of total volume and fiducial fraction

Scintillator volume measured 3 times

Tanks in the
purification system

The detector(3000 m3 tank)Flow meter at thelevel-4 entranceEnergy dependence of fiducial volume8

He9Li coincidence
5.5m
Delayed(2.2MeV)

Prompt(>4MeV)

Energy dependence ofvertex at 5.5m
< 5cm
±2.7% energy-dependent
volume error

5.5m

Time variation of fiducial volume12B<±1.5%

Stable for 2 years

Spallation cut“showering muon”
Q - (dE/dx)MIP x (track length)> 106 photoelectrons (~3 GeV)
~ 1/30 of all muons---> all volume 2 sec veto

5.5m

3m cylinder cut“non-showering muon”
other muon good reconstructed---> 2 sec 3-m cylinder“bad reconstructed muon”
track reconstruction failed
but, from charge, Nhit,
it should be a muon---> all volume 2 sec veto

Spallation cut
Vetotime by muon

5.5m

3m cylinder cut• ID muon veto (2msec)• Bad reconstructed muon veto (2sec)• Showering muon veto (2sec)• Non-showering muon veto(2sec, 3m cylinder cut)
Spallation events (8He9Li)
Showering muon
350 → 0.2
Non-showering muon86→ 5.7
Rejection efficiency for 8He9Li = 98.7%
Dead time (x volume ratio) = 9.7%

Muon fitter improved
93.8% neutrons are in r=3m column
from the previous muon

Non-showering µLivetime for each run~ 90%

Livetime
Runtimenoisy runHalf-badrun
Run Number

Livetime
RuntimeLivetime

Vertex fitter efficiency• Probability of vertex
failure < 0.1 %• Simple algorithm(vertex should benear to the early-hitPMT) assures highreliability of vertex
reconstruction

Systematic Error• Almost same asthe first result(6.4 %)

Background: long-lived delayed-n β-decay
9Li (8He)Time spectrum
After “showering µ”
Tagged delayed coincidence
Fit: τ=214±22 ms
9Li 257 ms
8He 172 ms• Large statictics ->found that most are
9Li (8He < 15%@90% C.L.)
both from time andenergy spectra

Energy spectrum of 9Li
After “showering µ”

9Li events in the final neutrino sample
used in the analysisagree• 4.8 ± 0.9
estimated fromspallation cutefficiency• 4 (the best fit)energy spectrumof the final
neutrino sample

Extracting fast neutron sample
Fast n energy spectrum
Choosing events with
Outer Detector (OD) hit
greater or equal to 5
Energy spectrum
Position dependence-> OD veto efficiency
no-OD muon (rock muon)(Monte Carlo)
Currently, upper limit:< 0.89 in the data sample

yranimile n vertex distribution
prFastBackground
Background

EventsAccidentals

2.69±0.02

8He/9Li

4.8±0.9

μ-induced n<0.89Total

7.5±1.3

Delayed coincidence events:
the neutrino sample

Present result v.s. first result
Present result 1 box = 1 bin

Quality: the same
Sample increased
First result 1 point = 1 event

4.7-times statistics
53 %.C.L. -> 99.89 % C.L.
(spectral distortion)

First result

Data and scaled no-oscillation
shape consistent at 53% C.L

Verification of the final neutrino sample
The 258 events• Event reconstruction
quality & near-event
distribution checked
after the final
neutrino sample fixed• All events have beenverified by physicists.
(not a selectioncriterion)

“Reconstructed Event Display” to check event qualityΤime v.s. distance from theobtained vertex point to each
PMT. Points are data, curves areexpected by the vertex fitter withthe universal speed of light.
ToF-subtracted time spectrum. Widthis from scintillation time profile.
Charge v.s. distance. r -2 effect isdominant, with all the effects(transparency, shade etc) are also
included in the expected curves.
Occupancy v.s. distance. Saturation curve characteristic toPoisson statistics are seen indata and expected curves.
Distribution of charge dividedby expected. Width is from
PMT charge distribution.

PromptDelayed17’’
20’’
1 datapoint :
30 to 50
PMTs

Correlation
betweenprompt anddelayedevents.

ν 4.5 MeV••

One of neutrino candidates.
Timing, Charge, Occupancy
dependence on distance from thereconstructed vertex point arequite consistent with isotropic
scintillation light emission.

Flasher••••Flasher events can be easily
distinguished from real events.
Because flasher is real lightemission, timing and charge
distributions show roughly similarbehavior.
However, chi square is very bad,probably because it’s not isotropicemission, and has different wave
length spectrum.
Usually, flasher is identified withvery large charge in only one PMT,
but in this analysis, that “flashingPMT” is excluded from the data,
and flasher can still be identified
with bad distribution of other PMTs.

Badness: ν v.s. unphysical events•taadalitr
Pa

•

•

All the unphysical events
studied here are clearly
separated from neutrino samples
or AmBe calibration data.
No veto BG shows continuous
distribution. Even if muon vetofails, it doesn’t fake only goodbackground but also makes
background with high badness.
All neutrino events are good as aresult (we didn’t apply any cut
using badness)Near events distributionenergy∆r from theprompt event
Rbadness
promptglobal trigger
delayed trigger
muon
residual charge±3.5 s±100 ms
Time from the prompt±3 ms

A typical spallation event•High
energy(>4MeV),and highbadness
event
clusternear theprompt
delayedpair

Systematic errors of spectral shape•••0.35% (energy scalenonlinearity)
2.7% (possible energy
dependence of the fiducial
volume, approximated bylinear function)~1.4 % (reactor spectrum)1-σ points - best fit

Analysis method
・Rate analysis
χ2 Rate =(Ratio observed － Ratio expected (sin22θ , ∆m2))2σstat 2 + σsyst 2

σstat , σsyst : Sigma of the observed ratio

・Shape analysis
χ2 Shape = －2 log L Shape (sin22θ , ∆m2, NBG , α)+ χ2 BG(NBG ) + χ2 distortion(α)
NBG : accidental and spallation backgroundsα: energy scale, ν spectrum error

・Rate+Shape analysis
χ2 Rate + Shape = χ2 Rate + χ2 ShapeRatio: (observed - BG) / no-oscillation• Rescaled no-oscillation == arbitrary constantobviously doesn’t fit the dataRatio v.s. L0/E
oscillating nearly 1 wave length(with short-base-line data,1.5 wave length)
Present result

First result andprevious experiments
L0=180 km

More exotic, non-oscillations models for the antineutrinochannel start being less favored by data
Decay*excluded at
95% CL
Decoherence†
excluded at94% CL*V.Barger et al. Phys. Rev. Lett. 82 (1999) 2640
†E.Lisi et al., Phys. Rev. Lett. 85 (2000) 1166

Neutrino decay and decoherence

・Neutrino decay

ν2 → X (sterile), ∆m122 ~ 0 casemL) )2
P( νe → νe ) = (cos2θ + sin2θ exp( －2τE・Neutrino decoherence∆m122 ~ 0 case

1L2
P( νe → νe ) = 1 －sin 2θ (1－exp(－γ0 E ) )2
Shape distortion
Testing good ness of fit
Neutrino oscillation
Neutrino decay
Neutrino decoherence

Which one is more likely ?

2003 saw a substantial dip in reactor antineutrino flux

Good correlation with reactor flux

90% CLedtcepxErfonosniotllaicos

Fit constrained
through known
backgroundχ2=2.1/4~0.03 for3TW
hypothetical
Earth corereactor(But a horizontal line still gives a decent fit with χ2=5.4/4)

Un-binned likelihood fit to 2-flavor oscillations
LMA2 excluded
at 99.6% CL∆m2=8.3·10-5 eV2
sin22θ=0.83

tan2θ=0.41“LMA0” disfavoredat 94% CL

This result

First KamLAND result∆m2=8.3·10-5 eV2
sin22θ=0.83∆m2 = 6.9 x 10-5 eV2
sin2 2 θ = 1.0

Combined solar ν – KamLAND 2-flavor analysis

0.6 × 10 −5 eV 2
∆m122 = 8.2 +− 0 .50.09
tan 2 θ12 = 0.40 +− 0.07

Includes (small) matter effects

Unknown very far reactor:
doesn’t change the result much
• e.g. hypothetical“georeactor” at thecenter of the Earth• The same energy
spectrum as normal
reactors but nospectral distortion
because it’s very far.
• Intensity: freeparameter -> result
didn’t change somuchSummary of reactor νe oscillation
by KamLAND• 4.7 times larger statistics than the first result• Spectral shape distortion observed at 99.9 % C.L.
• Oscillatory behavior of shape distortion observed:
other models don’t fit the observed distortion(e.g. neutrino decay disfavored at 95 % C.L. )• Two-flavor neutrino oscillation:– KamLAND best fit: ∆m2 = 8.3#10-5 eV2
tan2θ = 0.41
– Global analysis : ∆m2 = 8.2 +0.6-0.5 #10-5 eV2
tan2θ = 0.40 +0.09-0.07