Selected references to this lecture:

Kamland papers:

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

K.Eguchi et al., Phys. Rev. Lett.92, 071301 (2004),

T. Araki et al., hep-ex/0406035 .

General review:

C. Bemporad, G. Gratta, and P. Vogel., Rev. Mod. Phys. 74, 297 (2002).

• Pontecorvo already in 1946 suggested touse nuclear reactors in order to performneutrino experiments.• Indeed, in 1953-1959 Reines and Cowanshowed that neutrinos are real particlesusing nuclear reactors as a source.• Since then, reactors, powerful sourceswith ~6x1020 /s electron antineutrinos

emitted by a modern ~3.8 GWthermal reactor,have been used often in neutrino studies.• The spectrum is well understood….

Electron antineutrinos are produced bythe decay of fission fragments

Reactor spectrum:1) Fission yields Y(Z,A,t), essentially all known2) decay branching ratios bn,i(E0

i) for decay branch i,

with endpoint E0i , some known but some (particularly

for the very short-lived and hence high Q-value)unknown.3) decay shape, assumed allowed shape, known P(E,E0

i,Z) or for electrons Ee= E0 – E

dN/dE = n Yn(Z,A,t) i bn,i(E0i) P(E,E0

i,Z) and a similar formula for electrons.

If the electron spectrum is known, it can be `converted’into the antineutrino spectrum.

Spectrum Uncertainties

Theory onlyKlapdor and Metzinger, 1982

Beta calibratedSchreckenbach, 1985Hahn, 1989

Bemporad, Gratta, and Vogel, RMP 74, 297 (2002)

Results of Bugey experiment (1996)

Reactor spectra

Detecting reactor antineutrinos;low detection threshold required

Detector reaction e + p -> e+ + n, positron spectrum measured

Cross sectionknown to ~0.2%,see Vogel & Beacom,Phys. Rev. D60,053003

The survival probability of electron

antineutrinos of energy E producedat the distance L from the detector is

Pee(E,L) = 1 – sin2(2)sin2(m2L/4E

The experiment become sensitive to

oscillations if m2L/E ~ 1,

proof of oscillations is Pee(E,L) < 1.

To study oscillations, use the disappearance test:

Probability ofoscillations isproportional tosin2(m2L/4E).Since for thereactors E~4MeV,the sensitivity tom2 is inverselyproportional tothe distance L.

History of reactor neutrino oscillation search:

• Discovery of oscillations of atmospheric

neutrinos implies m2 ~ (2-3)x10-3 eV2,

thus indicating that reactor experiments

with L ~ (1-3) km should be performed

(Chooz and Palo Verde).

• Also, the preferred `solution’ to the solar

neutrino deficit implies m2 ~ (5-10)x10-5 eV2,

thus indicating that reactor experimentswith L ~ 100 km should be performed(KamLAND)

~180 km

~80 GW : 6% of world nuclear power

~25GW : most powerful station

in the world

Ｃｏｌｌａｂ

ｏｒａｔｏｒ

KamLAND Collaboration

13 institutions & 93 members

KamLAND Experiment

180 km

300

antineutrinos from the Sun . . .

A brief history of KamLANDA brief history of KamLAND

DatesDatesLive timeLive time

(days)(days)

Start data takingStart data taking Jan 2002Jan 2002 --

Run ARun A

(data-set of 1(data-set of 1stst paper) paper)Mar 9 – Oct 6Mar 9 – Oct 6

20022002145.4145.4**

Electronics upgrade & Electronics upgrade & 20” PMT commissioning20” PMT commissioning Jan/Feb 2003Jan/Feb 2003 --

Run BRun BOct - Jan 11Oct - Jan 11

20042004369.7369.7

Data-set presented Data-set presented herehere††

Mar 9, 2002 –Mar 9, 2002 –

Jan 11, 2004Jan 11, 2004515.1515.1

* Was 1

45

.1 w

ith

old

an

aly

sis

† † T.Araki et al,T.Araki et al, arXiv:hep-ex/0406035 Jun 13, 04arXiv:hep-ex/0406035 Jun 13, 04 submitted to Phys Rev Lettsubmitted to Phys Rev Lett

A limited range of baselines contribute to the fluxA limited range of baselines contribute to the fluxof reactor antineutrinos at Kamiokaof reactor antineutrinos at Kamioka

Over the data periodOver the data periodReported hereReported here

Korean reactorsKorean reactors3.4±0.3%3.4±0.3%

Rest of the worldRest of the world+JP research reactors+JP research reactors

1.1±0.5%1.1±0.5%

Japanese spent fuelJapanese spent fuel0.04±0.02%0.04±0.02%

- Induced Neutrons & Spallation-12B/12N

12B12N

T (T-T), L

L < 3m

Tagged cosmogenics can be used for calibrationTagged cosmogenics can be used for calibration

1212BB

1212NN

Fit to data shows that12B:12N ~ 100:1

τ=29.1msQ=13.4MeV

τ=15.9msQ=17.3MeV

μ

Radioactivity in liquid scintillator

238U: 214Bi → 214Po → 210Pb β+γ α τ=28.7 m τ=237 μs E=3.27 MeV E=7.69 MeV

232Th: 212Bi → 212Po → 208Pb β+γ α τ=87.4 m τ=440 ns E=2.25 MeV E=8.79 MeV

238U: (3.5±0.5)∙10-18 g/g needed 10-14 g/g232Th: (5.2±0.8)∙10-17 g/g

τ=(219±29) μs Expected: 237 μs

Note: The best background in 76Ge decay

detectors is at present ~0.2 counts/(keV kg y).

Expressing the background in the liquid scintillator

in KamLAND in the same units, and for

energies 2-3 MeV, one finds value ~10 times

smaller going out to 5.5 m radius and ~20 times

smaller for 5 m radius

%Total LS mass 2.1Fiducial mass ratio 4.1Energy threshold 2.1Tagging efficiency 2.1Live time 0.07Reactor power 2.1Fuel composition 1.0Time lag 0.28e spectra 2.5Cross section 0.2# of target protons < 0.1

Total Error 6.4 %

Systematic Uncertainties E > 2.6 MeV

5 % : goal

4. 6

Very clean measurementVery clean measurement

AccidentalAccidentalbackgroundbackground

Expect 1.5 n-Expect 1.5 n-1212CCcapturescaptures

Second KamLAND paper

2003 saw a substantial dip in reactor antineutrino flux2003 saw a substantial dip in reactor antineutrino flux

90% CL90% CL

Good correlation with reactor fluxGood correlation with reactor flux

Expe

cted

for no

osc

illat

ions

Expe

cted

for no

osc

illat

ions

(But a horizontal line still gives a decent fit with χ2=5.4/4)

Fit constrainedFit constrainedthrough knownthrough known

backgroundbackground

χ2=2.1/4

~0.03 for~0.03 for3TW3TW

hypotheticalhypotheticalEarth coreEarth core

reactorreactor

In CHOOZit waspossibleto determinebackgroundby this effect.

Inconsistent with simple 1/RInconsistent with simple 1/R22 propagation propagation at 99.995% CLat 99.995% CL

BackgrounBackgroundd

EventsEvents

AccidentalAccidentalss

2.69±0.02.69±0.022

88He/He/99LiLi 4.8±0.94.8±0.9

μμ-induced -induced nn

<0.89<0.89

TotalTotal 7.5±1.37.5±1.3

Observed events 258No osc. expected 365±24(syst)Background 7.5±1.3

ResultsResults

(Observed-Background)/Expected = 0.686±0.044(stat)±0.045(syst)(Observed-Background)/Expected = 0.686±0.044(stat)±0.045(syst)

Caveat: this specific number does not have an absolute meaning in KamLAND, Caveat: this specific number does not have an absolute meaning in KamLAND, since, with oscillations, it depends on which reactors are on/offsince, with oscillations, it depends on which reactors are on/off

(766.3 ton·yr,(766.3 ton·yr, ~4.7~4.7 the statistics of the first paper) the statistics of the first paper)

Second paper

Decay chain leading to 210Po:

222Rn (3.8d) 218Po (3.1m) 214Pb (27m) 214Bi,214Bi (20m) 214Po (164s) 210Pb (22.3y) 210Bi,210Bi (5d) 210Po (138d) 206Pb(stable)

The long lifetime of 210Pb causes its accumulation.The from 210Po decay then interact with 13C inthe scintillator by 13C(,n)16O making unwantedbackground. There is only ~10-11g of 210Pb infhe fiducial volume, enough however to cause1.7x109 decays in 514 days.

Ratio of Measured to Expected e Flux from Reactor Neutrino

ExperimentsLMA: m2 = 5.5x10-5 eV2

sin2 2 = 0.833

G.Fogli et al., PR D66, 010001-406,(2002)

Energy spectrum now adds substantial informationEnergy spectrum now adds substantial information

Best fit toBest fit tooscillations:oscillations:

ΔΔmm22=8.3·10=8.3·10-5-5 eV eV22

sinsin2222θθ=0.83=0.83

StraightforwardStraightforwardχχ22 on the histo on the histo

is is 19.6/1119.6/11

Using equalUsing equalprobability binsprobability bins

χχ22/dof=18.3/18/dof=18.3/18(goodness(goodness

of fit is 42%)of fit is 42%)

A fit to a simple rescaled reactor spectrumA fit to a simple rescaled reactor spectrumis excluded at 99.89% CL (is excluded at 99.89% CL (χχ22=43.4/19)=43.4/19)

Second paper

m2 = 6.9 x 10-5 eV2

sin2 2 = 1.0

This resultThis result

ΔΔmm22=8.3·10=8.3·10-5-5 eV eV22

sinsin2222θθ=0.83=0.83

First KamLAND resultFirst KamLAND result

Combined solar Combined solar νν – KamLAND 2-flavor analysis – KamLAND 2-flavor analysis

Includes (small) matter effectsIncludes (small) matter effects

07.009.040.0tan

105.06.02.8

122

25212

eVm

KamLAND uses a range of L and KamLAND uses a range of L and it cannot assign a specific L to each eventit cannot assign a specific L to each event

Nevertheless the ratio of detected/expectedNevertheless the ratio of detected/expectedfor Lfor L00/E (/E (or 1/Eor 1/E) is an interesting quantity, as it decouples) is an interesting quantity, as it decouples

the the oscillation patternoscillation pattern from the reactor energy spectrum from the reactor energy spectrum

no oscillation expectationno oscillation expectation

HypotheticalHypotheticalsingle 180kmsingle 180km

baselinebaselineexperimentexperiment

ConclusionsConclusions

Data consistent with large flux swings in 2003Data consistent with large flux swings in 2003

Welcome to precision neutrino physics !Welcome to precision neutrino physics !

Together with solar Together with solar νν

Spectrum distortions now quite significant, shape-only very powerfulSpectrum distortions now quite significant, shape-only very powerful

Best KamLAND fit to oscillations Best KamLAND fit to oscillations ΔΔm=8.3·10m=8.3·10-5-5 eV eV22, sin, sin2222θθ=0.83=0.83LMA2 is now excludedLMA2 is now excluded

KamLAND reactor exposure: 766.3 ton·yr (470% increase)KamLAND reactor exposure: 766.3 ton·yr (470% increase)

07.009.040.0tan;105.0

6.02.8 122252

12

eVm

What’s next?•Purification of liquid scintillator; remove 85Kr and 210Pb (low energy background) and attempt to observe solar 7Be e

(feasibility studies under way).•Determine or constrain the flux of solar antineutrinos and of the geoneutrinos. Study the neutron production by muons.•In a different reactor experiment (two detectors, one close and another at ~1-2 km) determine or constrain the unknown mixing angle 13. That is a whole different story.

What next in reactor neutrino studies?

Future Reactor Measurements

Apollonio et al., EPJ C27, 331 (2003)

Chooz reached at ~1 km 2.8% statistical error 2.7% systematic error

Next generation search forTheta-13 needs to achieve~1% errors

A high sensitivity search for e from the Sun and other sources at KamLAND

hep-ex/0310047, Phys. Rev. Lett. 92, 071301 (2004)

No events found between8.3-14.8 MeV for 0.28kt-yexposure. Assuming the8B spectrum shape, thislimits the antineutrino fluxto 2.8x10-4 of the SSM 8Bflux. This represents a factor of30 improvement over thebest previous limit.

Thanks to Atsuto Suzuki, Patrick Decowski,

Gianni Fiorentini, Andreas Piepke and

Giorgio Gratta who made some of the

figures used in this talk.