Accelerator Neutrino Oscillations Results and Prospects

1

Accelerator Neutrino Oscillations Results and Prospects

Koichiro NishikawaInstitute for Particle and Nuclear Studies

KEK

III International Pontecorvo Neutrino Physics School 16-26 September, 2006

2

• The present observations are good at discovering a surprise (if it is a large effect) for which small scale (controlled) experiments do not have enough sensitivity.

– Long baseline (100 – 108 km) size of earth, Sun size by luck

• They are however not good at measuring underlying parameters very precisely.

• Inherent uncertainties exist in calculation of various observables:

– Fluxes of solar neutrinos on Earth

• Nuclear reaction cross sections, chemical compositions, opacity, etc.

– Fluxes of atmospheric neutrinos

• Primary cosmic ray flux, nuclear interactions, etc.

• Find model-independent observables

– Solar neutrinos:

• Comparison of NC and CC interactions

• Spectral shape, day/night effect, etc

– Atmospheric neutrinos

• /e ratio

• Zenith angle distribution

3

Accelerator experiment• Neutrinos can be measured more than once

– Relative change of spectrum

• Effect of oscillation depend only on neutrino energy (fixed distance)

• Beam energy can be chosen – Type of detector– Neutrino energy determination method can be chosen

)E

Lm27.1(sin2sin.prob

222

4

Critical issues

• Only the product F(Ei) x (Ei) are measurable– Flux times cross section as a function of E

• The P(→ must be determined by minimizing the followings– (E) poorly known at low-medium energy

• Two measurements at different distances can reduce the the effect of ambiguities of cross sections

– Fnear(E) , Ffar(Edifferent from 1/r2 unless decay at rest• Different spectrum due to finite decay length and acceptanc

e at two distances – decay volume and distance– PID and Edetermination of observed events

• background processes (eps. NC, etc.) different in near, far

)E()(P)E(F)E(N

)E()E(F)E(Nfarfar

obs

nearnearobs

5

Neutrino beams from accelerator with existing technologies

Produce mesons by strong int. and let them decay in weak int.

1. Neutrinos from stopping ’s and ’s

(LSND KARMEN) unique spectrum of e

no problem of Far/Near, cross section, energy determination

2. Neutrinos from in-flight decays

• Wide Band Beam - sign selected by horn system but wide p band accepted, the highest intensity of CHORUS, NOMAD,K2K, MiniBooNE, MINOS, CGSN…..)

– Off-axis beam

• Dichromatic beam-momentum selected by B and Q mangets

– clean but the acceptance beam line limits intensity

6

Decay at Rest (DAR)

Small intrinsic e contaminationfew x 10-4

decay in flight contamination ?

Inverse beta decay well known

7

LSND/KARMEN Experiments

• 800MeV LINAC– 1mA – 600 sec width – 10msec rep.

• Mineral oil (Cherenkov pattern)

• prompt e and (2.2 MeV) p(n,)d

• 800MeV Rapid cycling syn– 200A– 200 nsec width– 20msec rep.

• Gd loaded scintillator

• prompt e and 7.8MeV) Gd(n,

•single measurement at one position•Ee+ from anti-e + p→e+ +n •unique spectrum for anti-e

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Signal and Background

9

Gamma Ray Distribution

10

LSND Final Results

11

KARMEN Distributions

12

With NOMAD and reactor experiments

13

sin2 2

m2 (

eV2 )It is impossible to have only 3 neutrinos

involved if all of the effects are the result of neutrino oscillations. Either some of the data are not due to oscillations,

or there must be at least one undiscovered “sterile” neutrino

or there must be CPT violation in the neutrino sector.

or exotic processes

‘Evidence’ of oscillations

e

e

31

23

22

23

21

22

213

232

221

mmmmmm

0mmm

14

15

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Experimental issue

• ‘MiniBooNE’ single detector

– compare the results with MC only

• signal = no muon, shower like events, not • Backgrounds = NC production, e in the beam

• PID e,

• Hadron production knowledge

– production by 8 GeV proton →normalization and HE components to interact with NC

– K to give Ke3 decay (K→e+ e)

17

A neutrino interaction model/E (10-38cm2/GeV)

Total (NC+CC)

CC Total

CC quasi-elastic

DIS

CC single

NC single 0

E (GeV)

18

Intrinsic Intrinsic ννee (from K& (from K&μμ decay) decay) : 236 events: 236 events

OtherOtherννμμ mis-ID: 140 eventsmis-ID: 140 events

ππ00 mis-ID: 294 events mis-ID: 294 events(Neutral Current Interaction)(Neutral Current Interaction)

LSND-like e signal: 300 events

Approximate number of events Approximate number of events and Background expected in Mand Background expected in M

iniBooNEiniBooNE

Charged Current, Quasi-elasticCharged Current, Quasi-elastic 500,000 events500,000 events

Bac

kgro

und

Signal

~10-3 of total neutrino events

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SignalMis-IDIntrinsic νe

Δm2 = 1 ev2

Δm2 = 0.4 ev2

Sensitivity to a SignalSensitivity to a Signal

20

21

PID e seperation e-seperation

NUANCE adjustment

photon propagationin oil simulation

HARP data on K

22

23

24

25

26

27

28

Checking the reproducibilityof ’s, detector sim.

29

30

~10-3 of total neutrino events

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32

Accelerator-based Long Baseline Neutrino Oscillation Experiments

Long = distance>>decay region

33

Wide Band Beam• Maximum available neutrino intensity

• Protons hit target

• Pions produced at wide range of angles

• Magnetic horn to focus • Rock shield range out • beam travels through earth to the experiment

• decay / decay ~10-2 ,, Ke3→~1% e contamination

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Horn in K2K

200m

p+Al + + +

HELE

Need measurements of high energy (muon monitor)and low energy (neutrino events at near detector)secondary particle direction

35

Neutrino Beam

22

2

22

22

cm

cmcml

cmcmt

1

)0(E)(E

E5.0Em

mm)0(E

MeV35~m2

mmp,

m

E

)(cospp

sinpp

pt~35MeV/c

Typical characteristics

edecay vol.)• lifetime of ~ 0.01• production cross sectionof K/

~ 0.1 and Ke3 ~0.01 divergence ~ 10mrad/E(GeV)• Horn focuses to about a few mrad• Far/near is not scale as 1/r2

36

Neutrino event vertex distribution at 300m from target

Width

HE-LE

LE 0.5<EGeV HE 1<EGeV

cm

FWHM4m/300m~ 10 mrad

FWHM2m/300m~ 6 mrad

divergence is dominated by decay angle at these energies

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Critical issues (reminder)

• Only the product F(Ei) x (Ei) are measurable– Flux times cross section as a function of E

• The P(→ must be determined by minimizing the followings– (E) poorly known at low-medium energy

• Two measurements at different distances can reduce the the effect of ambiguities of cross sections

– Fnear(E) , Ffar(Edifferent from 1/r2 unless decay at rest• Different spectrum due to finite decay length and acceptanc

e at two distances – decay volume and distance– PID and Edetermination of observed events

• background processes (eps. NC, etc.) different in near,far

)E()(P)E(F)E(N

)E()E(F)E(Nfarfar

obs

nearnearobs

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Critical issues-1

• (E) poorly known at low-medium energy– Nuclear physics at GeV region

– Pauli blocking

– Nucleon Form factor

– Final state interaction inside nucleus

For several 100~1000km baseline

SciBooNEMinerva

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Quasi-elastic scattering cross-sections

• Two form factors

•MV fixed by e.m. (CVC)

•Axial V form factor

magenta Old MCred new MC

Cross-section ()

10-3

8 cm

2

/Ecm2/GeV)

1 10 100 GeV

n

pW 2

2V,A

2VA

M

q1

1f,f

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Data on charged current processes

• Not well known

• Especially 2~3 GeV

→SciBooNE

→Minerva

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Neutrino spectrum and the far/near ratio (in K2K)

beam

10-6

1.0 2.0

Far/Near Ratio

E(GeV)

beam MC w/PION Monitor Angular acceptance

(well collimated for HE)

Finite decay volume length (shorter for HE, Near better accep. for MH )

300m 250km

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Accelerator NeutrinosPresent Status

K2K (1999-2005　 Completed)

MINOS (2005-)

OPERA (2006-)

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• 1995– Proposed to study neutrino oscillation for atmospheric neutrinos anomaly.

• 1999– Started taking data.

• 2000 – Detected the less number of neutrinos than the expectation at a distance of

250 km. Disfavored null oscillation at the 2 level.• 2002

– Observed indications of neutrino oscillation. 　　 The probability of null oscillation is less than 1%.

• 2004– Confirm neutrino oscillation at the Confirm neutrino oscillation at the level with both a deficit of level with both a deficit of and and

the distortion of the Ethe distortion of the E spectrum. spectrum.

• 2004 Nov.6– Terminated K2K due to horn trouble and high residual radiation level

Brief history of K2K

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K2K experiment

monitormonitor

Near detectors(ND)

+

Target+Horn200m

decay pipe

SK

100m ~250km

12GeV protons

~1011/2.2sec(/10m10m)

~106/2.2sec(/40m40m)

~1 event/2 days

Signal of oscillation at K2K Reduction of events Distortion of energy spectrum

(monitor the beam center)

E

LmP

22 27.1

sin2sin

E

~105 /2 days

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Particle detection at 250km away

(BG: 1.6 events within 500s 2.4×10-3 events in 1.5s)

TSKTspill

GPS

SKTOF=0.83msec

112 events

Decay electron cut.

20MeV Deposited Energy

No Activity in Outer DetectorEvent Vertex in Fiducial VolumeMore than 30MeV Deposited Energy

Analysis Time Window

500sec

5sec

TDIFF. (s)

-0.2TSK-Tspill-TOF1.3sec

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Analysis Overview

Observation #, p and

interaction MCMeasurement(E), int.

KEK

Far/Near Ratio (beam MC with mon.+ HARP )

Observation# and E

rec.

Expectation# and E

rec.

(sin22, m2)

SK

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Overall normalization error on Nsk for Nov99~

(Event)

Stat 0.28 0.37%

KT 3.32 4.37%

SK 2.28 3.00%

Flux +2.81

-2.59

F/N +4.26

-5.55

NC/CC +0.15

-0.23

nQE/QE +0.38

-0.61

CT 0.46 0.60%

Total +6.53

-7.37

5.34%

KT: dominated by FV errorSK: also.

Errors

HARP~1 %

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Pion Monitor: pion distribution after horn

Measure Momentum / Angle Dist. of π’s Just after Horn/Target

+Well known π Decay Kinematics +Well Defined Decay Volume Geometry

⇒Predict　 νμ Energy Spectrum at Near Site Far Site 　

Ring Image Gas Cherenkov Detector (Index of Refraction is Changeable)

To Avoid Severe Proton Beam Background,νμ Energy Information above 1GeV is Available(β of 12GeV Proton ~ β of 2GeV π)

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Good agreement with old data. (Cho et.al.)

Beam MC based on Cho et al.

Error 　assignment based on this measurements

p

w1 w2 w3 w4 …..: :

: :p, gives two C-light peaksfit withwi • C-light)

index of refraction : p thresholdposition of ring :

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Thin target data need assumption of secondary interaction in targetTotal cross section of p-AlHorn magnetic field ambiguityProton beam profile

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spectrum shape

HARP, Pion monitor and MC comparison

Far/Near ratio vs E

52

NEUT: K2K Neutrino interaction MC

• CC quasi elastic (CCQE)

– Smith and Moniz with MA=1.1GeV

• CC (resonance) single (CC-1)

– Rein and Sehgal’s with MA=1.1GeV

• DIS

– GRV94 + JETSET with Bodek and Yan

g correction.• CC coherent

– Rein&Sehgal with the cross section rescale by J. Marteau

• NC

+ Nuclear Effects

/E (10-38cm2/GeV)

Total (NC+CC)

CC Total

CC quasi-elastic

DISCC single

NC single 0

E (GeV)

53

Near detector measurements

• 1KT Water Cherenkov Detector (1KT)

• Scintillating-fiber/Water sandwich Detector (SciFi)

• Lead Glass calorimeter (LG) before 2002

• Scintillator Bar Detector (SciBar) after 2003

• Muon Range Detector (MRD)

Muon range detector

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1KT Flux measurement• The same detector technology as Super-K.

– Sensitive to low energy neutrinos.

– Sensitive for NC

KT

SK

KT

SK

KT

SKobsKTSK M

M

dEEE

dEEENN

)()(

)()(exp

Far/Near Ratio (by MC)~1×10-6

M: Fiducial mass MSK=22,500ton, MKT=25ton: efficiency SK-I(II)=77.0(78.2)%, KT=74.5%

NSKexp=158.4 NSK

obs=112+11.6 -10.0

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Near Detector Spectrum Measurements

• 1KT– Fully Contained 1 ring (FC1R) sample.

• SciBar– 1 track, 2 track QE (p≤25), 2 track nQE (2 track nQE (pp>25>25)) wher

e one track is • SciFi

– 1 track, 2 track QE (p≤25), 2 track nQE (p>30) where one track is

(p) for 1track, 2trackQE and 2track nQE samples

(E), nQE/QE

56

0-0.5 GeV

0.5-0.75GeV

0.75-1.0GeV

1.0-1.5GeV

••

••

E QE (MC) nQE(MC)

MC templatesKT data

P (MeV/c)

(

MeV

/c)

• flux KEK(E) (8 bins)• interaction (nQE/QE)

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Flux measurements2=638.1 for 609 d.o.f

– ( E< 500) = 0.78 0.36– ( 500 E < 750) = 1.01 0.09– ( 750 E <1000) = 1.12 0.07– (1000 E <1500) = 1.00 (1500 E <2000) = 0.90 0.04– (2000 E <2500) = 1.07 0.06– (2500 E <3000) = 1.33 0.17– (3000 E ) = 1.04 0.18– nQE/QE = 1.02 0.10

The nQE/QE error of 10% is assigned based on the sensitivity of thefitted nonQE/QE value by varying the fit criteria.

>10(20 ) cut: nQE/QE=0.95 0.04• standard(CC-1 low q2 corr.): nQE/QE=1.02 0.03

• No coherent: =nQE/QE=1.06 0.03

(E) at KEK

E

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Super-K oscillation analysis

• Total Number of events

• Erec spectrum shape of FC-1ring- events

• Systematic error term

)(),2sin,(),2sin,(

),2sin,(22

2

xsyst

xshape

xnorm

x

fLfmLfmL

fmL

f x : Systematic error parameters

Normalization, Flux, and nQE/QE ratio are in fx

Near Detector measurements, Beam constraint, beam MC estimation, and Super-K systematic uncertainties.

59

Log Likelihood difference from the minimum.

sin22m2[eV2]

lnL lnL- 68%- 90%- 99%

- 68%- 90%- 99%

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disappearance versus E shape distortion

sin22sin22

m2[e

V2]

m2[e

V2]

NSK (#) E shape

Both disappearance of Both disappearance of and the distortion of and the distortion of EE spectrum have the consistent result. spectrum have the consistent result.

61

sin22

0.002

0.004

0.006

0.0 0.2 0.4 0.6 0.8 1.0

Normalized by area

Nobs=112 Nexp=158.4

+9.4-8.7

Distortion of the neutrino spectrum

Rate

Best fitsin22=1m2 =2.77 x 10-3

Allowed region

Null oscillation hypothesis excluded at 4.4

62

K2K upper bounds on →e

limitlimit

sensitivitysensitivity

K2K-I+II (#obs.=1, #B.G.=1.70)K2K-I+II (#obs.=1, #B.G.=1.70)upper limit (90% CL)upper limit (90% CL) sinsin2222ee=0.13 =0.13 @2.8e-3 eV@2.8e-3 eV22

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Conclusion

• K2K Oscillation analysis on June99 ~November 6 , 05 full data

1. Long Baseline experiment can be done!

2. Both SK rate reduction and Erec shape distortion has been

observed3. Null oscillation hypothesis has been excluded by 4.41 m2=1.88~3.48x10-3eV2 for sin22=1 @ 90%CL5. sin22, m2 are consistent with atmospheric neutrino results6. e-appearance search is limited by statistics, upper limit (9upper limit (9

0% CL)0% CL) 　　 sinsin2222ee=0.13 @2.8=0.13 @2.8 ｘｘ 1010-3-3 eV eV22

7. Many studies on low energy neutrino interaction continue

64

MINOS experiment

• Two neutrino detectors• Long baseline neutrino oscillation exp

eriment• Fermilab’s NuMI beamline

735 km

65

Neutrino beamline

• 120 GeV protons hit graphite target• Two magnetic horns focus positive pions and kaons • Mesons decay in flight in evacuated decay pipe giving rise to almost pure υμ beam• Adjustable neutrino beam energy

νμTarget

HornsDecay Pipe

Absorber

Hadron Monitor

Muon Monitors

Rock

μ+π+

10 m 30 m675 m

5 m 12 m 18 m

Z. Pavlovic

66

Adjustable beam energy

• Changing target position changes neutrino beam energy

• 10 cm most favorable for oscillation analysis

• Data in other configurations used for systematic studies

• LE event composition: – 92.9% υμ

– 5.8% υμ

– 1.3% υe / υe

• After target replacement run at 9cm

- 10 cm

- 100 cm

- 250 cm

Target position:

67

MINOS Detectors

• Functionally identical– 2.54cm thick steel planes– 4.1×1cm scintillator strips– Multianode PMT readout– Magnetized B~1.3T

Coil

Near Detector

Far Detector

• Near Detector:– 1 km from target– 1 kton– 282 steel and 153 scintillator pla

nes

• Far Detector:– 735 km from target– 5.4 kton– 484 steel/scinitllator planes

68

Neutrino interactions

CC Event NC Event

•long track + hadronic activity at vertex

•short event, often diffuse

3.5m 1.8m

Monte CarloMonte Carlo

υμ μ

X X

υ υ • Likelihood procedure used to differentiate between NC and CC events

• NC contaminations in lowest energy bins

Eυ = Eshower+Pμ

69

Event classification

• Good agreement between data and MC for input variables

y=E shw/E υ

70

Event Classification

Event Classification Parameter

rejected asNC like

71

Tuning hadron production MC for ND data

• Fit ND data from all beam configurations : various Target-horn configuration

• Simultaneously fit νμ and νμ spectra(Use MIPP data in future)

υμ LE010/185kALE010/185kA LE100/200kA LE250/200kA

72

Beam matrix method

• Construct beam matrix using MC

• Use Near Detector data to predict the “unoscillated” spectrum at the Far detector

• Spectrum known at 2-4% level

X

=

73

Observed FD events

• Energy dependant deficit

Data SampleFD

Data

Expected(MC)

Data/Prediction(Matrix Method)

All 563 738±30 0.76 (4.4 )

(<10 GeV) 310 496±20 0.62 (6.2 )

(<5 GeV) 198 350 ±14 0.57 (6.5

74

Far Detector Data timing to spill time

• Time stamping of the neutrino events is provided by two GPS units

• Timing of neutrino candidates consistent with spill signal

• Easy to separate cosmic muons (0.5Hz)

• Time distribution is as expected

NuM

I onl

y m

ode

75

Systematic errors

• Systematic shifts in the fitted parameters are computed using MC “data samples” (at best fit point)

UncertaintyShift in Δm2

(10-3 eV2)

Shift in

sin2(2θ)

Near/Far normalization 4% 0.065 <0.005

Absolute hadronic energy scale 10% 0.075 <0.005

NC contamination 50% 0.010 0.008

All other systematic uncertainties 0.041 <0.005

Total systematic (summed in quadrature) 0.11 0.008

Statistical error (data) 0.17 0.080

76

Far spectrum

• Best fit for 2.5x1020 POT

423200160

232 c/eV1038.2||

..Δm

080232 00.1)2(sin .

2 /n.d.f = 41.2/34 = 1.2

77

Allowed region

• Fit is constrained to physical region: sin2(223)≤1

080232 00.1)2(sin .

423200160

232 c/eV1038.2||

..Δm

2 /n.d.f = 41.2/34 = 1.2

)3.2( 2min

)61.4( 2min

78

Unconstrained fit

2-32 eV10 26.2 Δm

07.12sin2 2 /n.d.f = 40.9/34 = 1.2

79

Summary

• Analyzed data using 2.5×1020 POT

• Systematic errors well under control

• MINOS disfavors no disappearance hypothesis by 6.2σ (<10GeV)

• Best fit to oscillation hypothesis yields:

• Forthcoming results:

– υμ → υe search

– υμ → υs search

423200160

232 c/eV1038.2||

..Δm

080232 00.1)2(sin .

80

Forthcoming improvements • Use antineutrinos + neut

rinos• Expanded FD fiducial v

olume• Improved event reconstr

uction + selection• 3.5×1020POT through 8/

07• Next year significant pr

oton accelerator improvements– 4.6×1020ppp (demons

trated in MI)

81

K2K and MINOS have established neutrino oscillation in muon-neutrino disappearance

as observed in atmospheric neutrino observation in Super-Kamiokande

82

Collaboration :

13countries 37 Institutes

An Emulsion-Counter Hybrid experiment for Tau neutrino Appearance

Detection.

OPERA 　

OPERA Detector

CNGS Beam

730km

CNGS First Neutrino to Gran Sasso at 2006 August

Current phase: Installation of Emulsion target (ECC Bricks)

83

84

85

Expected signal and background in OPERA in 5 years

mrad

I.P.=5-20m

86

Beam events:~horizontal tracksBeam angle:3.35° from below

Cosmic rays muons

Tracks zenith angle (no beam timing requirement)

319 on-spill events are observed

¾ muons coming from the rock¼ neutrino interactions in the detector (CC+NC)

The observed numbers are consistent with the expectation

Detector live-time ~95%

First neutrino : Muons from Neutrino Interactions 2006 August

Recorded "Rock Muon" event

CERN

87

Summary• First CNGS Neutino in 2006: total 8.2x1017 pot

– Electric detector's performance was confirmed.– Succeeded to connect tagged muons from the Electric detect

or to the Emulsion target (CS and ECC).

• Current status in Gran Sasso: ECC brick production and installation is going on.– Current production and insertion Speed ~300ECC/day about

1/3 of planned. Need speed up 700ECC/day. – until the end of April 2007

• CNGS 2007 run is planned in this Autumn.– OPERA will start the Physics RUN with 60,000ECC bricks.– ~300 neutrino interaction ~10 charm events for decay det

ection and analysis. And <1 Tau neutrino event.

88

Three generation neutrinos

89

Current status of neutrino mass and mixingsAnything new?

Solar + KamLAND

J.W.F. Valle, hep-ph/0410103J.W.F. Valle, hep-ph/0410103

12, m122 23, m32

2 13, m312

Only upper limit on 13

No info. on AtmosphericMINOS、 K2K

90

Three Flavor Mixing in Lepton Sector

3

2

1CPMMNSVU

e

100

0

0

0

010

0

0

0

001

U 1212

1212

1313

1313

2323

2323PMNS cs

sc

ces

esc

cs

sci

i

e

Weak eigenstates m1

m2

m3

mass eigenstates

100

0e0

00e

V 2

1

i

i

CPM

12, 23, 13

+ (+2 Majorana phase)

m122, m23

2, m132

cij = cosij, sij=sinij

91

Present Knowledge

solar neutrino (SK,SNO), reactor (KamLAND) Matter effect fix the sign of m2 12

07.00.842sin 122 0meV103.8m 2

12252

12

atm. neutrino (SK), long-baseline (K2K,MINOS)Oscillation probability sqaured is measured

545

00.196.02sin

23

232

reactor neutrino exp.(CHOOZ), K2K, MINOS

limit)(upper 16.02sin 132

to be the larger component in e

to be the larger component in e unkowneV105.2m 232

13

unkowneV105.2m 23223

92

Three ambiguities

232 2sin 2323 （（ octantoctant ） ） and and

2 fold ambiguity for 2 fold ambiguity for

MNS13 , undeterminedundetermined

213m sign of m2

1 ３

2 fold ambiguity for mass

“best fit” 23 =45 : no octant ambiguity

11

22

33

93

Regardless of ‘ambiguities,only the measurements of can open the

next phases of progress