Post on 24-Feb-2016
description
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
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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)
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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
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The T2K collaboration
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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
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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
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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
35
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
42
# 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
43
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
47
# 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!