KamLAND and Neutrino Physics

1
KamLAND and Neutrino Physics

• Introduction neutrinos and
• neutrino oscillation
• Atmospheric oscillation
• Solar oscillation
• Reactor antineutrinos
• and KamLAND
• Other measurements
• with KamLAND
• Neutrino Future

Inside of KamLAND before oil filling
2
What is a neutrino?

• One of the fundamental particles in the
• Standard Model of particle physics
• Spin-1/2 fermion
• Very small mass
• gt zero mass in the Standard Model!
• No charge (electromagnetic or color)
• Very weakly interacting
• gt usually travel through the earth
• without interacting
• Very common
• 108 neutrinos per cubic meter!
• Produced in the big bang, supernovae, the sun,
• cosmic ray showers in the atmosphere, radioactive
  decays,

3
Neutrino History

• The neutrino was proposed by
• Pauli in 1939 to conserve
• energy and angular momentum
• in nuclear beta decay
• A two-body decay should give a
• single electron energy, but the
• spectrum is continuous

Dear Radioactive Ladies and Gentlemen
F. A. Scott,Phys. Rev. 48,391 (1935)
4
Neutrino History

• Neutrinos are very difficult to
• detect Pauli first thought
• they could never be detected!
• The (anti)neutrino was first
• detected by Reines and Cowan
• in 1956.
• Neutrino source nuclear reactor
• Savannah River, South Carolina
• Antineutrinos detected through
• inverse beta decay
• ne p ? e n
• Two signals in coincidence
• e signal energy loss, annihilation with an
  electron
• two 511 keV gammas
• n signal delayed gamma from neutron capture

Poltergeist detector
5
Neutrino Oscillation

• The Standard Model includes three neutrino
  flavor states
• ne, nm, nt, defined by how they interact
• If neutrinos have mass, the neutrino mass states
  can be different
• n1, n2, n3, with masses m1, m2, m3
• The two basis states are related by a unitary
  transformation
• called the MNSP (Maki-Nakagawa-Sakata-Pontecorv
  o) matrix
• (analogous to the CKM matrix for quarks)
• Each mass state has a different time evolution

6
Two-Flavor Oscillation

• Suppose we only have to consider two flavors
• If I start with a pure nm state, then after it
  travels a distance L it is
• The probability to detect the state as a nm
  after distance L is
• The phases interfere with each other
• to produce the oscillation
• Only get interference if the masses differ

Dm2 in eV2 L in km or m E in GeV or MeV
7
Two-Flavor Oscillation

• For Dm2 2 x 10-3 eV2
• At long distances, the oscillations average out

1
nm survival probability
1 sin22q23
Log scale!
8
Atmospheric Neutrino Oscillation

• Introduction neutrinos and
• neutrino oscillation
• Atmospheric oscillation
• Solar oscillation
• Reactor antineutrinos
• and KamLAND
• Other measurements
• with KamLAND
• Neutrino Future

Super-Kamiokande
9
Atmospheric Neutrinos

• Cosmic-ray showers in the earths
• atmosphere produce nm, ne
• In an underground detector,
• atmospheric neutrinos from
• different directions have
• different baselines
• Oscillation changes the fraction
• of neutrinos detected
• vs. zenith angle
• Detectors like Super-K can detect
• neutrinos through charged-current
• interactions in the detector
• ne ? e, nm ? m

10
Super-Kamiokande

• 50 ktons of water 1000 m
• underground in central Japan
• Detects rings of Cerenkov light
• from charged particles
• Light collected by PMTs
• (photomultiplier tubes)

• Super-K is the successor to
• the Kamiokande experiment,
• which was originally built to
• search for proton decay

Super-K event display
11
Super-K Results

• Super-K sees all the ne expected, but a lot of
  nm are missing!
• In fact, half of the neutrinos are missing from
  the far
• side of the earth
• The mixing appears to be maximal q23 ? 45

12
Is it oscillation?

• Another analysis of Super-K data vs. L/E instead
  of zenith angle,
• using a subset of events with good L/E
  resolution
• Dip at first oscillation minimum, later
  maxima/minima smeared out
• Oscillation preferred to other explanations of
  deficit
• Better Dm2 resolution than standard zenith-angle
  analysis

13
Accelerator measurements

• Atmospheric neutrino oscillations have also
  been measured with
• neutrino beams produced by accelerators
• Two experiments (so far!)
• K2K, Japan
• beam from KEK to Super-K
• MINOS, US beam from Fermilab to Soudan
• gt MINOS first results just released!
• Both experiments send nm beams, look for
• disappearance
• MINOS detect neutrinos
• through CC interactions
• in steelscintillator
• detector with B-field

MINOS far detector
14
Oscillation Parameters

• Measurements of the atmospheric neutrino
  oscillation
• parameters q23, Dm23 with atmospheric neutrinos
• and with accelerator neutrinos give consistent
  results
• MINOS will improve the measurement further

• Measurements of the atmospheric neutrino
  oscillation
• parameters q23, Dm23

New MINOS result
15
Solar Neutrino Oscillation

• Introduction neutrinos and
• neutrino oscillation
• Atmospheric oscillation
• Solar oscillation
• Reactor antineutrinos
• and KamLAND
• Other measurements
• with KamLAND
• Neutrino Future

The Sun, imaged with neutrinos by Super-K
16
Neutrinos from the Sun

• Nuclear fusion in the sun produces neutrinos
  with a
• complicated energy spectrum multiple processes
  involved
• Much lower energy than atmospheric neutrinos
• Solar neutrino experiments have been
• sensitive to different energy regions

7
91
0.2
0.008
John Bahcall
17
Radiochemical Experiments

• ne capture on select radioisotopes
• Chlorine ne 37Cl ? e 37Ar gt 814 keV
• Gallium ne 71Ga ? e 71Ge gt 233 keV
• Detect decays of capture daughters
• Sensitive only to integrated ne flux above
  threshold
• Results
• Homestake (Cl) ?Cl/SSM 0.34 ? 0.03
• SAGEGALLEX/GNO ?Ga/SSM 0.54 ? 0.03
• The ratios disagree! Suppression varies with
  energy.
• (SSM is Standard Solar Model,
• BP00 Bahcall/Pinsonneault,Astrophys. J. 555,
  990, 2001)

Ray Davis
18
Kamiokande Super-K

• Water-Cerenkov, detects forward-scattered
• electrons from neutrino-electron elastic
  scattering
• nx e ? nx e
• All three neutrino flavors ne, nm, nt can
  interact, but the
• ne cross-section is much higher because there are
  both
• charged-current and neutral-current contributions
• Only sensitive to most energetic 8B solar
  neutrinos
• Detect of electron energy
• and direction
• Flux result
• ?SK/SSM 0.465 ? 0.015
• Constant suppression no time variation or
  energy distortion detected

Koshiba Masatoshi
19
MSW Effect

• How can oscillation explain different
  suppression factors at
• different energies?
• We need one more ingredient the MSW Effect
• (Mikheyev-Smirnov-Wolfenstein)
• Propagation through matter modifies the ne
  survival probability.
• nes can interact with matter in ways that nm,
  nt cannot.
• The energy eigenstates in matter are not the
  same as in vacuum!
• The MSW effect is also sensitive to the sign of
  Dm2
• is m1 or m2 heavier?

20
MSW for World Leaders

• Neutrino propagation difference between
• matter and vacuum
• Forward scattering off matter
• is different for ne vs. nm,t
• MSW effect changes the
• ne survival probability
• Useful limiting cases
• Below critical energy
• vacuum oscillations dominate
• Above critical energy
• matter effects dominate
• Critical energy 1.8 MeV for LMA, 8B
• Goes as 1/Dm2
• Can get large suppression from small mixing
  angles!

21
Multiple Regions

• With neutrino oscillations
• and the MSW effect, multiple
• regions of parameter space
• fit the data!

LMA
SMA
LOW
VAC
22
Sudbury Neutrino Observatory

• Heavy-water-Cerenkov detector, 5 MeV threshold
• Three different n detection modes
• CC (charged current) ne D ? p p e ne
  only
• NC (neutral current) nx D ? p n nx all
  three flavors!
• ES (elastic scattering) nx e ? nx
  e (same as Super-K)
• With the NC mode, SNO measures the total solar
  neutrino flux directly
• Neutron detection done in three different ways
• Phase I (D2O phase) 2H n ? 3H g (6.25
  MeV) 25
• add NaCl
• Phase II (salt phase) 35Cl n ? 36Cl g (8.6
  MeV) 83
• NaCl out, Neutral Current Detectors (NCDs) in
• Phase III (NCD phase) n detection via 3He
  proportional counters
• 45 neutron detection efficiency, but much
  cleaner S/B
• Complicated analysis the three signals are all
  backgrounds to each other

23
SNO

• NC, CC, ES rates all measured
• NC sees full SSM flux
• Solar neutrino problem solved
• 5.3s appearance of nm,t in a ne beam
• Ratio of CC to NC strongly
• constrains the mixing angle q12
• CC/NC 0.306 ? 0.026 ? 0.024

24
Motivation for KamLAND

• With MSW matter effects,
• solar neutrino oscillation
• constraints allowed several
• very different regions of
• mixing parameter space
• A reactor antineutrino
• experiment with a baseline
• 200 km could measure or
• rule out LMA oscillation
• After first SNO results,
• global analyses of all solar
• data favored LMA
• gt Not true when KamLAND
• was first proposed!

LMA
SMA
LOW
VAC
25
Reactor Antineutrinos

• Introduction neutrinos and
• neutrino oscillation
• Atmospheric oscillation
• Solar oscillation
• Reactor antineutrinos
• and KamLAND
• Other measurements
• with KamLAND
• Neutrino Future

Kashiwazaki-Kariwa Nuclear Power Station Tokyo
Electric Power Company Largest Nuclear Power Site
in the World Largest Antineutrino source for
KamLAND
26
Reactor Antineutrinos

• Nuclear power plants produce electron
  antineutrinos ne
• through the b-decay of fission fragments
• Antineutrinos detected through
• inverse b-decay
• ne p e n
• Spectral shape is a convolution
• of reactor ne spectrum with
• inverse b-decay cross-section
• Delayed coincidence signal
• Prompt positron
• Delayed neutron

• Nuclear power plants produce electron
  antineutrinos _
• through the b-decay of fission fragments
• Antineutrinos detected through
• inverse b-decay
• _
• Spectral shape is a convolution
• of reactor _
• inverse b-decay cross-section

Inverse b-decay cross-section
1.8 MeV threshold
27
CHOOZ

• Previous reactor antineutrino experiment,
• 1 km baseline
• Originally designed to search for ne oscillation
  with
• parameters in the atmospheric mixing range
• Neutrons detected though capture on Gd
• No deficit observed

• Previous reactor antineutrino experiment,
• 1 km baseline
• Originally designed to search for _
• parameters in the atmospheric mixing range
• Neutrons detected though capture on Gd
• No deficit observed
• Energy distribution consistent with
• expected spectrum from reactors

Backgrounds measured with reactor off
28
KamLAND

• KamLAND (Kamioka Liquid-scintillator
  AntiNeutrino Detector)
• Designed to measure or rule out neutrino
  oscillations
• at the solar LMA parameters with a
• terrestrial antineutrino source nuclear
  reactors
• KamLAND is located in the
• same mine near Kamioka,
• Japan as Super-K, in the
• former site of Kamiokande
• Previous reactor neutrinos
• flux measurements shown
• with flux vs. distance
• prediction from LMA

LMA prediction
29
KamLAND Collaboration
Tohoku University, Sendai, Japan University of
Alabama University of California at Berkeley
/ Lawrence Berkeley National Lab. California
Institute of Technology Drexel University Universi
ty of Hawaii at Manoa Kansas State
University Louisiana State University Stanford
University University of Tennessee Triangle
Universities Nuclear Laboratory Institute of
High Energy Physics, Beijing, China CENBG,
Bordeaux, France
30
Why Japan?
Convenience!
31
Why Japan?
KamLAND uses the entire Japanese nuclear
power industry as a longbaseline source
KamLAND
80 of flux from baselines 140210 km
32
Effects of Oscillations

• Oscillations change both the
• rate and energy spectrum of
• detected events
• Multiple reactors at different
• baselines complicate the signal
• Reactor operation data is critical!

Example spectra (L.A.Winslow) Top Dm2
1.5?10-4, tan2q 0.41 (LMA II) Bottom Dm2
0.7?10-4, tan2q 0.41 (LMA I) top 4 reactors
at full thermal power only
33
KamLAND Detector

• 1 kton liquid scintillator
• Mineral oil buffer
• outside 120-mm
• nylon balloon
• 1879 PMTs
• 1325 17" fast
• 554 20" efficient
• Water Cerenkov
• Outer Detector
• Event position from
• light arrival times
• 20 cm resolution
• Event energy from
• total light yield

Rock
Calibration Systems
Electronics (E-Hut)
PMTs
18m Steel Sphere
13m Nylon Balloon
Outer Detector
34
Rapid Construction
First results released December 9, 2002
35
Neutrino Events in KamLAND

• Inverse b-decay _
• Prompt e signal
• Because the neutron is so much heavier than the
  positron,
• E(kinetic)e ? E_ _
• Positron loses energy by ionization and then
• annihilates with an electron, giving off two
  511 keV gammas
• Total energy deposited Eprompt ? E_
• Delayed n capture
• The neutron thermalizes in the detector
• Thermal neutron captures on a proton
• Edelayed 2.2 MeV
• Capture time 200 ms
• Liquid scintillator emits light when energy is
  deposited,
• light yield (almost!) linear with energy

• Inverse b-decay ne p e n
• Prompt e signal
• Because the neutron is so much heavier than the
  positron,
• E(kinetic)e ? En (mn mp) ? En 1.8 MeV
• Positron loses energy by ionization and then
• annihilates with an electron, giving off two
  511 keV gammas
• Total energy deposited Eprompt ? En 0.8 MeV
• Delayed n capture
• The neutron thermalizes in the detector
• Thermal neutron captures on a proton
• Edelayed 2.2 MeV
• Capture time 200 ms
• Liquid scintillator emits light when energy is
  deposited,
• light yield (almost!) linear with energy

36
KamLAND Data Analysis

• PMT pulses (few mV) are digitized
• as waveforms
• Analyze waveforms to extract pulse
• arrival times (at the 1 ns level) and
• total pulse charges
• Vertexing we determine the
• position of the energy deposition
• from the timing information
• 20 cm resolution
• Energy we determine the event
• energy from the sum of pulse
• charges essentially counting PE
• 6.2/?E(MeV) resolution

12-channel KAMFEE board
37
Antineutrino Candidate
two events in delayed coincidence
(color is time)
Prompt (e) event E 3.20 MeV
Delayed (neutron) event E 2.22 MeV
Dt 111 ms DR 34 cm
38
Backgrounds

• Accidentals
• two unrelated singles events
• that mimic a coincidence signal
• gt 2.69 ? 0.02 events pass cuts
• Spallation backgrounds
• produced by cosmic-ray muon
• interactions
• gt 9Li, 8He 4.8 ? 0.9 events
• gt Fast neutrons lt 0.89 events
• 13C(a,n)16O (more later)
• due to contamination of scintillator with 210Pb
  alpha emitter!
• gt 10.3 7.1 events
• Geoneutrinos (more later!)
• antineutrinos from decays of radioactive
  elements in the earth
• gt all below 2.6 MeV analysis threshold
• Total 17.8 7.3 events in 515.1 days

singles background in one-day run
39
Event Selection

• Fiducial volume
• Rprompt, Rdelayed lt 5.5m
• Coincidence
• 0.5 lt DT lt 1000 msec
• DR lt 2 m
• Energy cuts
• positron 2.6 lt Eprompt lt 8.5 MeV
• analysis window above 2.6 MeV
• neutron 1.8 lt Edelayed lt 2.6 MeV
• Spallation cuts after muons (0.3 Hz)
• DTmuon lt 2 msec
• DTmuon lt 2 sec within 3m of muon
• or if muon showers gt 106 PE
• Total event selection efficiency 89.8

40
Event Selection

• Delayed vs. prompt energy

Neutron capture on 12C
Neutron capture band
(First publication plot)
Accidental background
41
Systematic Errors
Fiducial Volume 4.7 Energy threshold 2.3 Cut
efficiencies 1.6 Livetime 0.06 Reactor
power 2.1 Reactor fuel composition 1.0 Antineutrin
o spectra 2.5 Cross section 0.2 Total 6.5
(Systemic errors from second reactor publication)
42
First Reactor Antineutrino Result

• Observed neutrino disappearance
• (NobsNBG)/Nno-osc 0.611 ? 0.085 (stat) ?
  0.041 (syst)
• Probability that 86.8 events would
• fluctuate down to 54 is lt 0.05
• Standard _
• ruled out at the
• 99.95 confidence level
• PRL

• Observed neutrino disappearance
• (NobsNBG)/Nno-osc 0.611 ? 0.085 (stat) ?
  0.041 (syst)
• Probability that 86.8 events would
• fluctuate down to 54 is lt 0.05
• Standard ne propagation
• ruled out at the
• 99.95 confidence level
• PRL 90, 021802 (2003)
• Cover of PRL ?
• Over 1000 citations!

curve, shaded region global-fit solar LMA
43
Rate Shape Analysis

• Fit prompt (positron) energy spectrum above 2.6
  MeV with
• full reactor information (power, fuel, flux),
  2-flavor mixing
• Energy spectrum was consistent with constant
  suppression
• but the absence of distortions constrained
  oscillation parameters

44
Mixing Parameter Constraints
45
Second KamLAND Result

• Added more data, improved analysis tools,
• expanded the fiducial volume, understood (a,n)
  background
• Second KamLAND reactor antineutrino paper
• published March 4, 2005 PRL 94, 081801 (2005)
• Statistical significance of disappearance
  99.998 (was 99.95)
• 258 candidates seen / 365.2 expected
• (NobsNBG)/Nno-osc 0.658 ? 0.044 (stat) ? 0.047
  (syst)
• (ratio not directly comparable
• to previous result due to time
• variations in reactor baselines!)
• Unbinned maximum-likelihood fit
• Data now show shape distortion
• at 99.6 significance

46
Rate vs. Flux

• KamLAND cant turn the reactors off to measure
  backgrounds
• and confirm directly that the signal is from
  reactors
• However, the reactor antineutrino flux has
  varied significantly
• during KamLAND operation
• Consistent with reactor antineutrinos

90 C.L. region
47
L0/E Plot

• Oscillation depends on L/E
• KamLAND doesnt measure L, but the
• flux distribution has a strong peak
• A typical value L0180 km is used
• This is really a 1/E plot
• Oscillations smeared out in 1/E
• Goodness of fit
• 0.7 - decay
• 1.8 - decoherence
• 11.1 - oscillation
• (0.4 - constant suppression)
• Data prefer oscillation to other
• hypotheses

Data vs. No-oscillation expectation
48
Second KamLAND Result

• KamLAND data in agreement with global fits to
  solar
• neutrino results
• KamLAND alone now measures Dm2 7.90.6 x 10-5
  eV2
• Global analysis of KamLAND Dm2 7.90.6 x 10-5
  eV2
• plus solar data gives tan2q 0.400.10

• KamLAND data in agreement with global fits to
  solar
• neutrino results
• KamLAND alone now measures Dm2 7.9-0.5
• Global analysis of KamLAND Dm2 7.9-0.5
• plus solar data gives tan2q 0.40-0.07

LMA II LMA I
49
Now and Then
PDG 2000
KamLAND solar 2005
50
Reactor Experiment Future

• The reactor antineutrino analysis will continue
  to improve!
• Rate analysis and mixing angle determination are
  now
• systematics limited
• 6.5 systematic uncertainty dominated
• by 4.7 fiducial volume systematic
• Work now focused on reducing
• systematic uncertainties
• Dm2 resolution comes from distortions
• in the energy spectrum, which are
• not as sensitive to our systematics
• gt still statistics limited
• More statistics can help reduce systematics!
• Already have 2x the published dataset
• New approaches no FV cut at high energy,
• go below 2.6 MeV by including geoneutrinos
• Purification will eliminate (a,n) background

statistics limited
systematics limited
51
4p Calibration System

• We are building a 4p calibration system to
• directly calibrate vertex reconstruction
• and energy response in the full fiducial volume.
• Currently can only deploy calibration
• sources along the z-axis
• Absence of off-axis calibration source
• data means that the fiducial volume
• systematic must be estimated
• indirectly
• Hope to calibrate off-axis this summer

52
More Physics with KamLAND

• Introduction neutrinos and
• neutrino oscillation
• Atmospheric oscillation
• Solar oscillation
• Reactor antineutrinos
• and KamLAND
• Other measurements
• with KamLAND
• Neutrino Future

KamLAND on the cover of Nature, July 28, 2005
53
More Physics with KamLAND
cosmological neutrinos
solar neutrinos
geological neutrinos
reactor neutrinos
Energy (MeV)
antineutrinos
neutrinos antineutrinos
neutrinos
Mountain above the Kamioka mine that
houses KamLAND and Super-K Mozumi is in the
foreground, Where both KamLAND and Super-K have
offices and remote control rooms
54
Geoneutrinos

• KamLAND is sensitive to geological antineutrinos
• Antineutrinos are produced in the decay chains
• of uranium (238U) and thorium (232Th)
• These isotopes are present is the silicate
  earth
• (i.e. continental crust) at typical
  concentrations
• 238U 20 ppb
• 232Th 80 ppb
• 41 ratio
• Expected to be
• absent from the core
• present in lower concentrations
• in the mantle, ocean crust
• Decays are a major source of heat
• 1/3 total heat flow?

55
Geoneutrinos

• MC map of geoneutrino sources that KamLAND
  could
• see (including oscillations!)
• Signal dominated by local sources
• 25 within 50 km
• 50 within 500 km

model of distribution of geoneutrinos
at detectable at KamLand
structure of the Earth
56
Geoneutrinos

• Geoneutrino spectrum endpoint is 2.6 MeV
• gt Origin of 2.6 MeV cut
• in reactor analysis
• Geoneutrino analysis requires
• tighter cuts vs. reactor analysis
• understanding
• low-energy backgrounds
• oscillation parameters!
• The 13C(a,n)16O background is very
• important for this analysis!

57
13C(a,n)16O

• 13C(a,n)16O cross section 10-7
• KamLAND scintillator contains 210Pb
• a long-lived radon decay product
• 210Pb decay chain produces as
• 210Pb ? 210Bi ? 210Po ? 206Pb a
• Total a decays in dataset few x 109
• Produces fast neutron background
• mostly below 2.6 MeV
• gt prompt signal from recoil protons
• as the neutron thermalizes
• gt delayed signal is neutron capture
• Most of the background above 2.6 MeV is from an
• excited state of 16O populated by 13C(a,n)16O
• prompt 6 MeV gamma

13C(a,n)16O
n(12C,12C)n
58
Geoneutrino Result

• Fit to data in geoneutrino region
• (plotted vs. antineutrino E,
• rather than positron event E)
• Points data
• Light solid fit
• Red 238U chain geoneutrino fit
• Green 232Th chain geoneutrino fit
• Dark solid total non-geoneutrino
• Light blue reactor neutrino background
• Brown dotted (a,n) background
• Purple accidentals
• Confidence intervals
• total geoneutrinos vs. relative fraction
• This result opens a new field!
• The measurement will be greatly improved by
• scintillator purificaton

59
KamLAND Solar Phase

• Goal is a direct measurement of the solar 7Be
  neutrino flux
• Tough measurement
• single ES event nx e ? nx e
• need very low background to
• statistically extract the signal
• Solar Standard Model (SSM)
• 7Be prediction is at the 10 level
• gt This measurement is not expected
• to improve the determination of
• mixing parameters
• gt Measurement will improve the SSM
• 7Be neutrino energy is below the MSW transition
• gt survival probability is different than 8B n
• seen by Super-K, SNO
• gtgtgt verification of MSW effect ltltlt
• gt check for something unexpected?

91
7
0.2
0.008
John Bahcall
60
KamLAND Solar Phase

• KamLAND scintillator has very low U, Th levels
  from initial
• purification, but other contaminants must be
  reduced substantially
• 106 85Kr - present in atmosphere, from N2
  bubbling
• 105 210Pb, 210Bi from radon contamination
• A great deal of RD progress on purification
• approaches distillation, adsorption, heating
• The upgrade has been (very well!) funded
• in Japan. Full-scale purification system
• is under construction. Purification will
• start this fall!

Distillation Test System
61
KamLAND Solar Phase

• Signal and backgrounds
• 7Be signal now 106 below backgrounds
• 85Kr, 210Bi b, 210Po a
• Other benefits of purification
• Eliminates 13C(a,n)16O background for
• reactor antineutrinos, geoneutrinos
• Enhances supernova signals by
• adding singles detection below 1MeV

62
Other Physics at KamLAND

• Spallation production of neutrons,
  delayed-coincidence
• backgrounds e.g. 9Li, other products e.g. 12B
• Understanding these processes is important for
  future
• experiments e.g. reactor measurement of q13
• Higher-energy antineutrinos
• Searches for antineutrinos above the reactor
  endpoint
• Solar antineutrinos best existing limit
• PRL 92, 071301 (2004)
• Supernova relic neutrinos
• Nucleon decay searches
• First paper on search for neutrons in nuclei
  decaying
• to invisible modes
• PRL 96, 101802 (2006)
• Work on other neutron modes, proton decay to K
  modes

63
The Neutrino Future

• Introduction neutrinos and
• neutrino oscillation
• Atmospheric oscillation
• Solar oscillation
• Reactor antineutrinos
• and KamLAND
• Other measurements
• with KamLAND
• Neutrino Future

Cover of the APS report on the Future of Neutrino
Physics
64
2-flavor oscillation?

• Why can we get away with only considering
  two-flavor
• Oscillation to describe solar and atmospheric
  mixing data?
• Consider the parameters
• Atmospheric Solar Reactor
• Dm2 2-3 x 10-3 eV2 8 x 10-5 eV2 8 x
  10-5 eV2
• L lt 1.3 x 107 m 1.5 x 1011 m 105 m
• E GeV 1-10 MeV 1-10 MeV
• Solar Dm2 is much smaller than atmospheric
  Dm2
• the oscillation is slower. Atmospheric
  neutrinos would have
• to travel much further to see it.
• ne in solar and reactor experiments arent
  affected by the
• amtopheric oscillation known from CHOOZ
• All oscillation results to date are described by
  only 4 parameters!

65
General picture

• The MNSP picture.
• We know
• q12, Dm2 from solar mixing
• q23, Dm2 from atmospheric mixing
• limits on the absolute mass scale
• (cosmology, tritium endpoint,
• neutrinoless double-beta decay)
• We dont know
• absolute mass scale or hierarchy
• Mixing angle of third oscillation,
• described by q13, Dm2
• 3x3 Unitary matrix has a phase d
• CP violation in the lepton sector?

• The MNSP picture.
• We know
• q12, Dm12
• q23, Dm23
• limits on the absolute mass scale
• (cosmology, tritium endpoint,
• neutrinoless double-beta decay)
• We dont know
• absolute mass scale or hierarchy
• Mixing angle of third oscillation,
• described by q13, Dm13

66
Many open questions!

• Do we really understand the atmospheric and
  solar mixing?
• What is q13?
• Can we measure CP violation in the lepton
  sector?
• Can such CP violation and leptogenesis explain
  why the
• universe is made of matter?
• What is the neutrino mass hierarchy?
• What is the absolute neutrino mass scale?
• Are neutrinos their own antiparticles?
• Are they Dirac fermions like all the other
  quarks and leptons,
• or are they Majorana fermions?
• Are there more than three neutrinos? (LSND?)
• Are there other surprises in neutrino physics?
  (e.g. magnetic moments?)
• Why are neutrinos so light?
• What does this tell us about fundamental physics?

67
Neutrinoless Double-Beta Decay

• Majorana neutrinos are their own antiparticles
• If neutrinos are Majorana, double-beta
• decay can proceed by a loop diagram
• with no neutrinos in the final state
• This process is sensitive to a Majorana mass,
• a weighted sum over all three masses, all
• mixing angles, dCP, plus new phases
• (weighted by Ue1, Ue2, Ue3 m1, m2 dominate)
• Several experiments have been proposed
• EXO, Majorana, CUORE
• Technically challenging!

68
Reactor measurement of q13

• High-precision short-baseline reactor experiment
• Goal is to measure the subdominant q13
  oscillation in
• ne disappearance down to sin22q13 of 0.01
• The best limits now come from CHOOZ.
• CHOOZ was a high-precision measurement, 2.7
  systematics.
• Measurement requires systematics
• below the 1 level
• How do we do better?
• Use two detectors to cancel flux,
• detector uncertainties
• The disappearance effect
• depends only on q13
• no matter (hierarchy!) effects,
• ambiguities from dCP

• High-precision short-baseline reactor experiment
• Goal is to measure the subdominant q13
  oscillation in
• _

Pee
detector 1
Pee
detector 2
nuclear reactor
Distance (km)
69
Off-axis accelerator q13, dCP

• With the right accelerator beam, we can measure
  q13 , dCP
• in nm ? ne appearance
• Rate depends on multiple unknown parameters
• q13, dCP, and matter effects (hierarchy)
• Measurement will be done in Japan T2K
• proposed in the US NOnA
• Experiments are complementary to reactor q13 and
  to each other

70
Broadband accelerator - VLBNO

• Instead of going off-axis to get sharp energy
  peaks, use
• a beam with a broad energy band and see effects
  vs. energy
• Measure all neutrino oscillation parameters in
  one experiment
• Example Brookhaven AGS-based Super Neutrino
  Beam,
• powered by AGS upgrade to 1-2 MW
• Megaton-class Water Cherenkov detector at NSF
  DUSEL site

71
Broadband accelerator beams - VLBNO

• Instead of going off-axis to get sharp energy
  peaks, use
• a beam with a broad energy band and see effects
  vs. energy
• Measure all neutrino oscillation parameters in
  one experiment
• Brookhaven AGS-based Super Neutrino Beam,
• powered by AGS upgrade to 1-2 MW
• Megaton-class Water Cherenkov detector at NSF
  DUSEL site

talk by Tom Kirk
72
Conclusions
KamLAND made the first observation of reactor
antineutrino disappearance Current KamLAND
results show disappearance at the 99.998 CL and
spectral shape distortion at 99.6. Solar
oscillation mixing results have gone from
allowed regions spanning many orders of
magnitude to parameter measurement Reactor
results will continue to improve precision
measurement of basic physics parameters KamLAND
is gearing up to measure solar 7Be
neutrinos test of MSW explanation do we really
understand the data? Next-generation reactor
antineutrino experiments will play a critical
role in understanding neutrinos Very exciting
time! KamLAND public data release http//www.awa
.tohoku.ac.jp/KamLAND/datarelease/2ndresult.html