Neutrino Science at Berkeley Lab: Understanding Neutrino Oscillations Model-Independent Evidence for the Flavor First Evidence for the Disappearance Change of Solar Neutrinos at SNO of Reactor Antineutrinos at KamLAND KamLAND (Kamioka Liquid Scintillator Anti-Neutrino Detector) is a 1-kton liquid scintillator detector in the Kamioka mine in central Japan designed to measure the antineutrino flux from nearby nuclear power plants. KamLAND detects reactor electron antineutrinos through

inverse β-decay of νe on protons.

The Sudbury Neutrino Observatory (SNO) is an imaging water With 1000 tons of heavy water, SNO Cherenkov detector located 2 km underground in the Creighton observes the interactions of solar 8B mine in Sudbury, Ontario, Canada. neutrinos through 3 different interaction KamLAND measured 61% of the expected antineutrino channels. Neutrino interactions with 8 flux. In the 50-year history of reactor neutrino physics, SNO SNO deuterium give SNO unique sensitive to all ! ! KamLAND has found first evidence for the 7 ES CC active neutrino flavors. disappearance of reactor electron antineutrinos. 6 5 SNO 4 !NC SSM 3 !NC Evidence for Neutrino Oscillations 2 1 The observed flavor change of 0 solar electron neutrinos in 0 1 2 3 4 5 6 6 !e (10 cm-2 s-2) SNO and the measurement of 2.0 antineutrino disappearance at NNeeuuttrraall-Current EElalassttiic Scattering Chaarrggeedd-Current Current (NC) Scattering (ES) Current (CC) KamLAND provide evidence Region favored by

l 1.5

a for the oscillation of neutrinos ) n solar experiments

ν g i 0 0 S

(under the assumption of CPT P o

B 1.0 SSM n / i r t

M invariance). KamLAND’s result u S e 5.3 S σ N ( C C shap e narrows the allowed neutrino 0.5 constrained oscillation parameters to the C C shap e unconstrained 0.0 ‘Large-Mixing-Angle’ solution

νe+ νµ+ντ νe + 0.15 (νµ+ντ) νe and strongly disfavors other possible mechanisms of In 2002, SNO found that 2/3 of all solar electron neutrino flavor change. Ratio of the measured νe flux to the expected reactor νe flux. neutrinos change their flavor en route to Earth and Before KamLAND After KamLAND The dashed line is the expectation for no neutrino

are detected as muon or tau neutrinos in the Solar neutrino experiments favor the KamLAND’s observation of νe disappearance oscillations. The dotted curve is representative of a best-fit Sudbury Neutrino Observatory. ‘Large-Mixing-Angle’ oscillation solution. eliminates other oscillation solutions. ‘Large-Mixing-Angle’ oscillation solution.

Understanding the UMNS Determining the Last Undetermined Mixing Angle: Neutrino Mixing Matrix A Reactor Neutrino Experiment to Measure θ13 Past, Present and Future Experiments Results of the SNO solar neutrino experiment, the KamLAND reactor With multiple detectors and a antineutrino experiment, and the evidence from the Super-Kamiokande variable baseline a next- atmospheric neutrino experiment have established the massive nature of generation reactor neutrino νe νe,µ,τ neutrinos and point to a novel phenomenon called neutrino oscillations. experiment has the opportunity to discover sub-dominant In the framework of neutrino oscillations the mass and flavor eigenstates of 3 neutrino oscillations and make a < 1 km 1-2.5 km active species are related through the UMNSP matrix. measurement of θ13.

# Ue1 Ue2 Ue3 & % ( U U U U = % µ1 µ2 µ 3( % ( Dirac phase Majorana phases U U 2 2 $ "1 " 2 U" 3 ' ' * 2 2 %m31 L 4 2 2 %m21 L # & # *i, CP & # & # & 1 0 0 cos)13 0 e sin)13 cos)12 sin)12 0 1 0 0 Pee "1# sin 2$13 sin # cos $13 sin 2$12 sin ) , 2-3 neutrino detectors with variable % ( % ( % ( % i / 2 ( 0 cos sin 0 1 0 sin cos 0 0 e - 0 4E 4E = % )23 )23 ( +% ( +% * )12 )12 ( +% ( & ( & + baseline % ( % i, CP ( % ( % i- / 2+i. ( $ 0 *sin)23 cos)23' $ *e sin)13 0 cos)13 ' $ 0 0 1' $ 0 0 e '

atmospheric ν solar ν present ! present θ is central to neutrino oscillation physics accelerator ν reactor and accelerator ν solar ν 0νββ experiments 13 future future future future! 1500 ft A variety of experiments are needed to determine all elements of the neutrino • Why are the mixing angles large, maximal, and small?

mixing matrix. The angle θ13 associated with the subdominant oscillation is still underground ν detectors undetermined! • Is there CP, T, or CPT violation in the lepton sector? nuclear reactor solar θ = 33° large 12 • Is there a connection between the lepton and the atmospheric θ23 = ~ 45° maximal 2 baryon sector? CHOOZ + SK tan θ13 < 0.03 at 90% CL small … at best

Future reactor neutrino experiments with multiple detectors have the opportunity • Understanding the role of neutrinos in the early to measure the last undetermined mixing angle θ13 . Knowing θ13 will be critical for Universe: Can leptogenesis explain the baryon establishing the feasibility of CP violation searches in the lepton sector. Diablo Canyon, California - An Ideal Site? asymmetry?

Acknowledgements: We thank Lawrence Berkeley National Laboratory, the Sudbury Neutrino Observatory, Inco Ltd., and the Kamioka mining company. This work is supported by the Department of Energy. August 2003