νTokaiKamioka

Neutrino oscillation results from the T2K experiment

Kei Ieki, on behalf of the T2K collaboration

INPA seminar@LBNLFeb 26, 2014

1

Outline1. Neutrino oscillation2. The T2K experiment3. Oscillation analysis4. Latest results

2

1. Neutrino oscillation

3

Neutrino oscillation

4

UPMNS = 1 0𝑐23

−𝑠23

0𝑠23𝑐23

00

𝑐13 010

𝑠13𝑒− 𝑖𝛿𝐶𝑃

0𝑐13

0−𝑠13𝑒

𝑖𝛿𝐶𝑃

𝑐12 𝑠12𝑐120

001

−𝑠120

Mixing matrix depends on the mixing angles θ12, θ23, θ13 and the CP violating phase δCP.

()

The flavor of neutrino changes periodically as it propagates

νμ

νe

ντ

ν2

ν1

ν3

=

flavor eigenstates

mass eigenstates

time

time

UPMNS ×

Mixing matrix(PMNS matrix)

(m1)

(m2)

(m3)

What we already know

5

UPMNS ～0.82 0.55 0.16

-0.50 0.52 0.700.39-0.09 -0.65 0.70

θ12: ~34 θ23: ~45θ13: ~9δCP: unknown

Oscillation probability also depends on mass splittings: = ～ 7.5×10-5 eV2, 2.4×10-3 eV2

mass hierarchy (sign of ) is unknown.

What we already know

6

UPMNS ～0.82 0.55 0.16

-0.50 0.52 0.700.39-0.09 -0.65 0.70

θ12: ~34 θ23: ~45θ13: ~9δCP: unknown

Oscillation probability also depends on mass splittings: = ～ 7.5×10-5 eV2, 2.4×10-3 eV2

mass hierarchy (sign of ) is unknown.

• Is there a CP violation (δCP≠0) in the lepton sector?• Normal (>0) or inverted (<0) hierarchy?• Is θ23 equal to π/4 (maximal oscillation)?

Unanswered questions

Precision measurement of neutrino oscillation is important!

Neutrino oscillation experiments

7

Atmospheric neutrinos

Solar neutrinos

p-p fusion chain

νe νe

Accelerator neutrinos

Reactor neutrinos

𝜈𝑒𝜈𝑒

nuclear fission

θ23, θ12,

θ23, θ13,

θ12, θ13, δCP

Oscillation probabilities

8

𝑃 (𝜈𝑒→𝜈𝑒 ) 1−sin2 2𝜃13 sin2 Δ𝑚312 𝐿

4𝐸

• disappearance ()

• appearance ()

Reactor experiments ( from nuclear fission)

T2K ( from accelerator)

• disappearance ()

∝

Pure measurement of

Combining T2K and Reactor allows to measure δCP!

(: propagation length, : energy)

(sub-leading term)

+( matter   term )+…roughly proportional to 1/

Pure measurement of

Oscillation probabilities

roughly proportional to 1/

Combining T2K and Reactor allows to measure δCP!

(: propagation length, : energy)

9

𝑃 (𝜈𝑒→𝜈𝑒 ) 1−sin2 2𝜃13 sin2 Δ𝑚312 𝐿

4𝐸

• disappearance ()

• appearance ()

Reactor experiments ( from nuclear fission)T2K ( from accelerator)

• disappearance ()

∝

(sub-leading term)

+( matter   term )+…

P(νμ→νe)0.1

0.05

1 2 3Eν (GeV)

0

NH,δCP=0NH,δCP=π/2

IH,δCP=0IH,δCP=π/2

P(νμ→νμ)

sin2θ23=0.5,Δ=2.4×10-3 eV2

1 2 3Eν (GeV)

0.5

0

1

L=295km

L=295km

2. The T2K experiment

10

The T2K collaboration

11

CanadaTRIUMFU. AlbertaU. B. ColumbiaU. ReginaU. TorontoU. VictoriaU. WinnipegYork U.

FranceCEA SaclayIPN LyonLLR E. Poly.LPNHE Paris

GermanyAachen U.

PolandIFJ PAN, CracowNCBJ, WarsawU. Silesia, KatowiceU. WarsawWarsaw U. T.Wroklaw U.

RussiaINR

U. SheffieldU. Warwick

USABoston U.Colorado S. U.Duke U.Louisiana S. U.Stony Brook U.U. C. IrvineU. ColoradoU. PittsburghU. RochesterU. Washington

SpainIFAE, BarcelonaIFIC, Valencia

SwitzerlandETH ZurichU. BernU. Geneva

United KingdomImperial C. LondonLancaster U.Oxford U.Queen Mary U. L.STFC/DaresburySTFC/RALU. Liverpool~500 members,

59 Institutes, 11 countries

ItalyINFN, U. BariINFN, U. NapoliINFN, U. PadovaINFN, U. Roma

JapanICRR KamiokaICRR RCCNKavli IPMUKEKKobe U.Kyoto U.Miyagi U. Edu.Osaka City U.Okayama U.Tokyo Metropolitan U.U. Tokyo

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• Discovery of νμ νe

We observed νμ νe with 7.3σ significance in 2013!• Precise measurement of νμ νμ

Updated result reported on Feb 18

Main goals

νμ νe,μ,τ

Far Detector(Super-Kamiokande)

Near Detector(ND280)

J-PARC

295km

High intensity νμ beam & giant water Cherenkov detector SK

~40m

μ

p

π+

The T2K experimentθ13, δCP

θ23, Δ

J-PARC

13

LINAC

3 GeVRCS

Main RingSynchrotron(30 GeV)

νμ beam to SK

Near detectors

FastExtraction

production target

J-PARC = Japan Proton Accelerator Research Complex

J-PARC neutrino beam

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p beam

Magnetic horns

Decay volume

Beamdump

Muonmonitor

ND280

INGRID

μ+ νμ

νμ

To SKπ+

π+μ+ off-axis

on-axis0m 118m 280m

- High intensity 30GeV proton beam- Pions are focused by magnetic horns

- Off-axis beam: direction of the beam is shifted by ~2.5 degrees.

Energy spectrum peaked at oscillation maximum.BG ν interaction modes for νμνe at high energy are reduced.

ν energy spectrum

Oscillation prob.

carbon target

ν-N cross section

T2K νμ flux (no osc.)

Total

CCQECC1π (res)

NC1π0 (res)

CC other

NC other

ν detection at near/far detectors

15

𝜈𝑙𝑙−

𝑊𝑝

● CCQE (Charged Current Quasi Elastic)

● CC1π (Charged Current 1π)

𝜈𝑙𝑙−

𝑊𝑁π

• Main interaction mode in T2K • Eν can be reconstructed from

pl and θl

● NC1π0 (Neutral Current 1π0)

𝑍𝜈𝑙

𝜈𝑙

π0𝛾𝛾

In the oscillation analysis, neutrinos are detected through Charged Current (CC) interactions.

Uncertainty of the cross sections strongly affects the oscillation analysis.

Near detectors

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● ND280 (off-axis) ν beam flux & cross section measurement

● INGRID (on-axis) ν beam direction, stability measurement

Measures the neutrino beam at 280m downstream from the neutrino production target

INGRID

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1.5m

~10m

~10m

Beam center

• Large mass & large volume• 16 identical modules (14 in cross)• Iron/scintillator layers

Monitor n beam profile/rate.

νμμ

ND280

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0.2T magnet

TPC1FGD1 FGD2

TPC2 TPC3

μ

+SMRD

νμ

FGD

- Scintillator bars (~1 ton for FGD1)- ν target & tracking

- Time Projection Chambers- 3D tracking, momentum measurement, PID

TPC

Combination of many detectors to measure ν beam flux & cross section.

Super-Kamiokande (SK)

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𝜈𝑒

e-~40m

Measure ν interactions after oscillation.

-like

1-ring e-like/μ-like events are selected for νμ→νe/νμνμ analysis.

-like

• 50 kton water Cherenkov detector (FV: 22.5 kton)1000m underground Kamioka mine

• Identify e/μ from Cherenkov ring shape

Inner detector~11100 20’’ PMTs

Outer detector~2000 8’’ PMTs(veto external BG)

e μ

Brief history of T2K

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• 6.6×1020 protons on target (~8% of the final goal) collected/analyzed.• Beam power has steadily increased and reached 220kW continuous

operation with a world record of 1.2×1014 protons per pulse.

Brief history of T2K

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● First indication of νμ→νe

(Significance to exclude θ13=0: 2.5σ) PRL107,041801 (2011)● First νμ→νμ result from T2K PRD 85, 031103 (2012)

● “Evidence” of νμ→νe

(Significance: 3.1σ) PRD 88, 032002 (2013)

● Updated νμ→νμ result PRL 111, 211803 (2013)

● “Discovery” of νμ→νe

(Significance: 7.3σ) PRL 112, 061802 (2014)

● Updated νμ→νμ

world’s best θ23 measurement　　 (paper will be ready soon)

Stability of the beam

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Stability of ν interaction rate normalized by # of protons (INGRID)

Stability of ν beam direction (INGRID)

• Neutrino rate per POT is stable to 0.7% over run period• Neutrino beam direction is stable < 1mrad (<2% shift in the ν energy)

over run period

Note: Dataset includes 0.21x1020 POT with 250 -> 205kA horn operation (13% flux reduction at peak)

3. Oscillation analysis

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Overview of the analysis

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Comparison of SK eventsMC Data

⑤ Oscillation analysis

③ Constraints from ND280

② Constraints from external data

④ SK event selection

① flux, -N interaction prediction

①,② Flux & interaction prediction

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i) ν flux prediction

Hadron production prediction is weighted so that interactions match external data.(NA61/SHINE, Eitchen et al., Allaby et al.)

● Flux simulation

①,② Flux & interaction prediction

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overlaid plot

Predicted flux (SK)

Near (ND280) and Far (SK) fluxes are highly correlated SK flux can be constrained by ND280 measurement

Flux SK/ND280 correlation

Predicted flux (ND280)

● Predicted flux

i) ν flux prediction

peaked around0.6 GeV

~1% of νe

(BG for νμ→νe)

①,② Flux & interaction prediction

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Systematic error sources

SK flux has 10-15% uncertainties from 0.1 to 5 GeV

Systematic errors

● Systematic errors

i) ν flux prediction

①,② Flux & interaction prediction

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ii) ν-N interaction prediction

● Interaction simulation

𝜈𝑙

𝑙

W

Nπ

NEUT simulation code - Cross section prediction for different interaction modes: CCQE, π production via resonance (CC1π, NC1π) etc. - Fermi-Gas model for nuclei - FSI: Interactions of hadrons in the final state (π absorption etc.)

ν-N cross section

T2K νμ flux (no osc.)

Total

CCQECC1π (res)

NC1π0 (res)

CC other

NC other

①,② Flux & interaction prediction

● Systematic parametersWe use effective parameters (axial mass form factor MA, normalization parameters etc.) with uncertainties that span the base model and data, and allow the ND280 to constrain the model.

𝐹 𝐴 (𝑞2 )= 𝐹 𝐴(0)

(1+ 𝑞2

𝑀 𝐴2 )

2

Axial form factor:Past measurements of MA

QE

MAQE 1.21±0.45 GeV/c2

CCQE norm 1±0.11

Parameters (CCQE)

29

ii) ν-N interaction prediction

①,② Flux & interaction prediction

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● Systematic parameters

CC1π+NC1π0

MARES 1.41±0.22 GeV/c2

CC1π norm 1.15±0.32

NC1π0 norm 0.96±0.33

Parameters (resonant π)For the resonant π production models, we use MiniBooNE data and fit to NEUT predictions.

ii) ν-N interaction prediction

③ Constraints from ND280

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TPC1FGD1 FGD2

TPC2 TPC3

CC0πCC1π+

CC other

μμ + π+

μ + hadrons

CC0π μ momentumCC1π+ μ momentum CC other μ momentum

We measure the muon momentum and angular distributions in three samples. Constrain the uncertainties for different interaction modes

CCQEResonant π

Deep Inelastic Scattering (DIS)

DIS

③ Constraints from ND280

32

CC0π μ momentum distribution

We fit the muon momentum and angular distributions to constrain the flux × cross section.

CC1π

CC other

DataBefore fitAfter fit

③ Constraints from ND280

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Cross-section parametersSK nm flux

• ND280 fit reduces both flux and cross-section model uncertainties individually

• Flux and cross-section parameters are anti-correlated after these fits because the constraint is a rate at ND280

④ SK event selection

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νμ→νμ

1. T2K beam timing & Fully contained(no activities in OD)

2. Inside fiducial volume (>2m from wall)3. 1 μ-like Cherenkov ring4. Reconstructed μ momentum > 200MeV/c

(for good μ/e separation)5. Number of decay electron (μe) ≤ 1

m-likee-like

2. 1 μ-like ring cut5. Decay electrons ≤ 1

νμ μ

④ SK event selection

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νμ→νe

1. T2K beam timing & Fully contained(no activities in OD)

2. Inside fiducial volume (>2m from wall)3. 1 e-like Cherenkov ring4. Visible energy Evis > 100MeV/c

(Evis : electron energy deposit in ID)Reject NC BG, decay e from μ)

5. Number of decay electron (μe) = 06. Reconstructed ν energy Erec < 1250 MeV

(Suppress intrinsic νe contamination in the νμ beam )

7. NCπ0 BG rejection cut

4.Visible energy cut

6.Erec<1250 MeV cut

Next page

④ SK event selectionνμ→νe

𝑍𝜈𝜇π0𝛾𝛾

𝜈𝜇

e-like ring

NCπ0 background

● NCπ0 rejection cut

undetectedOld method

Force to find the second ring, based on the PMT charge information.Invariant mass of π0 is required to be less than 105 MeV/c2.

New method (2013~)

Use new event reconstruction algorithm “fiTQun”. It is a likelihood fit which determines all of the track parameters (position, momentum, particle ID) at the same time, based on the timing and charge of the PMTs.

36π0 invariant mass (MeV/c2)

fiTQun NCπ0 rejection

ln()

selectNew cut reduces NCπ0 BG by ~70%,with only 2% loss of the signal.

4. Latest results

37

νμνμ measurement

38

Expected νμ events (no osc.): 446±23 events

Observed 120 νμ candidate events.

νμ energy spectrum Ratio to no oscillations

Updated result reported on Feb 18! (3.01×10206.57×1020 POT)

νμνμ measurement

39

sin2θ23=0.5, eV2/c4 125.9

Expected number of events

Observed: 120

Error sources Errorν flux & cross section (constrained by ND280) 2.7%

ν-N cross section (not constrained by ND280) 4.9%

SK detector & Final state interaction 5.6%

Total 8.1%

Systematic errors on number of νμ events

(assuming δCP=0, sin2θ23=0.5, Δ=2.4×10-3eV2/c4)

Eν distribution with errors

Reconst. E (GeV)

w/o ND280 constraintw/ ND280 constraint

(sin2q23, Dm232)=(0.5, 2.4×10-3 eV2)

* The dominant uncertaintiesaffecting T2K Dm2

32 precision such as binding energy/SK energy scale are not shown in the left table of # of events since they don’t affect overall normalization.

events

νμνμ measurement

• Lively discussion motivated by CCQE cross section inconsistency between MiniBooNE/other experiment

• Not incorporated directly into analysis– But we have a large systematic uncertainty (100%) on decays of D

resonances w/ prompt p absorption (“p-less D-decay”). It has similar impact on neutrino energy reconstruction as a 100% uncertainty in the multi-nucleon interaction model (Nieves model)

– Dedicated MC study shows the impact on oscillation analysis is small relative to our current statistical error.

40

Multi-nucleon systematic error

νμνμ measurement

• Lively discussion motivated by CCQE cross section inconsistency between MiniBooNE/other experiment

• Not incorporated directly into analysis– But we have a large systematic uncertainty (100%) on decays of D

resonances w/ prompt p absorption (“p-less D-decay”). It has similar impact on neutrino energy reconstruction as a 100% uncertainty in the multi-nucleon interaction model (Nieves model)

– Dedicated MC study shows the impact on oscillation analysis is small relative to our current statistical error.

41

Multi-nucleon systematic error

νμνμ fit method

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# of events Enrec dist. Syst. Osc. param.

= norm × shape × syst × osc

Note: sin2q13, sin2q12, Dm221 are constrained by PDG2012. dCP is unconstrained.

Maximum likelihood fit based on:• Number of νμ events• distribution

DataBest fit

Position: Dm232

DataBest fitNo oscillation

Depth: sin22q23

νμνμ result

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Previous T2K resultPRL 111, 211803 (2013)

2D confidence regions

T2K new

[NH]

Great improvement from the previous T2K result!T2K favors maximal mixing

1D intervals

q23 [NH] [42.6, 48.9] [40.9, 50.7]

q23 [IH] [42.5, 48.8] [40.8, 50.5]

Best fit: (sin2q23, D)=(0.514, 2.51×10-3 eV2)　 　　　　 (sin2q23, D)=(0.511, 2.48×10-3 eV2) 　　　　　　　

Normal hierarchy (NH)Inverted hierarchy (IH)

νμνμ result

44

T2K measures q23 with the world-leading precision!

Comparison w/ other experiments

Normal hierarchy

Inverted hierarchy

νμνe measurement

45

Observed 28 νe candidate events.

Reconstructed νe energy distribution

Expected backgrounds: 4.9±0.6 events

0 1000500Energy (MeV)

T2K νμ flux

νμνe measurement

46

sin22θ13=0.0, δCP=0 4.9

sin22θ13=0.1, δCP= 17.2

sin22θ13=0.1, δCP=0 21.6

sin22θ13=0.1, δCP= 25.7

Expected number of events

Observed: 28

Error sources ErrorNeutrino flux & cross section (constrained by ND280) 2.9%

Neutrino cross section (not constrained by ND280) 7.5%

SK detector & Final state interaction & γ-N interaction 3.5%

Total 8.8%

Systematic errors on number of νe events

(assuming δCP=0, sin2θ23=0.5, Δ=2.4×10-3eV2/c4)

NCπ0 BG: 0.9Intrinsic νe contamination BG: 3.4

νμνe fit method

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# of events (pe,θe) dist. Syst. Osc. param.

= norm × shape × syst × osc

Note: sin2q23, are constrained by T2K νμνμ measurement with 3.01×1020 POT.

Maximum likelihood fit based on:• Number of νe events• (pe, θe) distribution

(MeV/c)0 400 800 1200

60

120

0

(deg

rees

)

180

sin22θ13=0.1(CCQE dominated)

(MeV/c)0 400 800 1200

sin22θ13=0.0(BG only)

distribution

νe

e-

θe

P(νμνe) = sin22θ13sin2θ23sin2

+(CPV term)+…

νμνe result (sin22θ13)

48

Best fit for normal (inv.) hierarchy: sin22θ13 = ()

Electron momentum and angular distribution

(Assuming δCP=0. sin2θ23 and Δ are constrained by T2K νμνμ measurementwith 3.01×1020 POT)

Significance to exclude θ13=0: 7.3σ

“Discovery” of νμνe

(6.57×1020 POT, normal hierarchy)

νμνe result (δCP vs. sin22θ13)

49

68% and 90% allowed region of sin22θ13 for each value of δCP

Normal hierarchy

Inverted hierarchy

Fit performed for different values of δCP.

(sin22θ13=0.098±0.013)

(sin2θ23 and Δ are constrained by T2K νμνμ measurement with 3.01×1020 POT)

NOTE: These are 1D contours for various value of δCP, not 2D contours

νμνe result, combined with reactor

50

Combined with reactor measurement (sin22θ13=0.098±0.013 from PDG2012)

90% CL excluded region

Normal hierarchy: 　　　 0.19π ～ 0.80πInverted hierarchy:　 　 π ～ 0.97π, 　 0.04π ～ π

This is an important step towards the discovery of CP violation in the lepton sector!

Regions above these lines (derived by Feldman-Cousins method) are excluded with 90% C.L.

δCP negative log likelihood curve

90% excluded regions

Best fit

Summary

51

• νμνμ

Latest result updated on Feb 18. World’s best measurement of θ23!

• νμνe

Best fit: sin22θ13 = () for normal (inverted) hierarchy Significance to exclude θ13=0: 7.3σ. “Discovery” of νμνe ! T2K+Reactor δCP 90% CL excluded region: 0.19π ～ 0.80π (-π ～ -0.97π, -0.04π ～ π) for normal (inverted) hierarchy

Prospect• Expected improvements:

– νμ→νe & νμ→νμ joint fit analysis will be ready soon– Neutrino interaction model implementations ongoing

(spectral function, multi-nucleon etc.)• Data taking:

– Anti-ν test run is forecast : Switch horn current in 2014– LINAC upgrade is done (181400MeV)– Future MR upgrade to operate at 750 kW

• ν-N cross section measurements: Charged current interaction measurements (νμCCQE, νμ CC inclusive, νμ CC coherent π, νe CC inclusive etc. at ND280, INGRID) will be released.

52

Backup slides

53

54

Koseki-san’s slides @ T2K collaboration meeting, Sep, 2013

Expected POT is estimated based on the information.

sin2q23/Dm232 1s Precision vs. POT

55

50% POT n + 50% POT anti-nSolid Lines: no sys. err.Red Dashed: with conservative projected sys. err. (~7% n, ~14% anti-n)

Statistical limit of 1s precision at full POT • sin2q23 (q23): ~0.045 (~2.6°)• Dm2

32: ~4×10-5 eV2

Assuming true: sin22q13=0.1, dCP=0°, sin2q23=0.5, Dm232=2.4×10-3 eV2, [NH]

q13 constrained by d(sin22q13) = 0.005

[NH] Normal hierarchy, [IH] Inverted hierarchy

now

~2016

now

~2016

Precisions will drastically improve over the next few years.

Appearance 90% C.L. Sensitivity

56

[NH] Normal hierarchy, [IH] Inverted hierarchy

7.8×1021 POT (50% POT n + 50% POT anti-n)Solid Lines: no sys. err., Dashed: with 2012 sys. err. (~10% ne, ~13% nm)

Case study (1): True dCP = 0° Case study (2): True dCP = -90°

Assuming true: sin22q13=0.1, sin2q23=0.5, Dm232=2.4×10-3 eV2, [NH]

T2Kw/ Reactord(sin22q13)

= 0.005

T2K only

Sensitivity for Resolving sindCP≠0

57

7.8×1021 POT (50% POT n + 50% POT anti-n)

True[NH]

True[NH]

True[IH]

True[IH]

No sys. err. w/ 2012 sys. err. (~10% ne, ~13% nm)

Assuming true: sin22q13=0.1, Dm232=2.4×10-3 eV2

q13 constrained by d(sin22q13) = 0.005

[NH] Normal hierarchy, [IH] Inverted hierarchy

58

T2K + NOnA Sensitivity for Resolving sindCP≠0

Assuming 5% (10%) normalization uncertainty on signal (background)Assuming true: sin22q13=0.1, Dm2

32=2.4×10-3 eV2, q13 constrained by d(sin22q13) = 0.005

[NH] Normal hierarchy, [IH] Inverted hierarchy

Region where sind=0 can beexcluded by 90% C.L.

solid(dash): w/o (w/) systematics

NOnA

T2K

Both T2K/NOnA -> full POT (50% POT n + 50% POT anti-n)Shown in [NH] case.

Sensitivity to resolve sind=0

59

T2K + NOnA Sensitivity to Mass HierarchyBoth T2K/NOnA -> full POT (50% POT n + 50% POT anti-n)Shown in [NH] case.

Assuming true: sin22q13=0.1, Dm232=2.4×10-3 eV2, q13 constrained by d(sin22q13) = 0.005

Red: T2K alone, Blue: NOnA alone, Black: T2K + NOnA

[NH] Normal hierarchy, [IH] Inverted hierarchy

Region where MH can bedistinguished by 90% C.L.

Sensitivity to resolve MH

solid(dash): w/o (w/) syst.

NOnA

60

CC0π sample

ND280 νe Measurement• Interactions in FGD and particle ID in TPC• Major background: photons from π0 decays• Fit CC0π, CC1π+CCother and γ sideband

γ sample fit prefers scale factor of 0.77±0.02(stat)

CC1π+ + CCother sample

measured flux 1.06 0.06(stat) 0.08(syst)predicted flux

e

e

nn

Intrinsic beam ne background prediction is validated!