T2K NEUTRINO EXPERIMENT RECENT RESULTS AND PLANS

T2K NEUTRINO EXPERIMENT RECENT RESULTS AND PLANS

Alexander Izmaylov

Instituto de Fisica Corpuscular (UV and CSIC), Valencia, Spain on behalf of the T2K Collaboration

IX CPAN Days, October 23-25, Santander

Open questions:

• CP-violation in lepton sector? δ_CP value?

• Mass hierarchy(MH), “normal” (NH) or “inverted”(IH):

• m₁<m₂≪m₃ or m₃≪m₁<m₂?

• Octant of θ₂₃: <, > or = 45^o?

• Dirac/Majorana, steriles, CPT…

NEUTRINO OSCILLATIONS

Oscillations governed by

• three mixing angles:

• θ₁₂≈33^o, θ₁₃≈9^o, θ₂₃≈45^o

• two mass squared differences:

• Δm²₂₁≈7.5x10^-5eV² and |Δm²₃₂|≈2.5x10^-3 eV²

• source-detector baseline and neutrino energy

2

Atmospheric Accelerator Reactor Solar

Neutrino mixing:

Pontecorvo-Maki- Nakagawa-Sakata (PMNS) matrix

* PDG 2016

T2K (TOKAI-TO-KAMIOKA) EXPERIMENT

• World-leading neutrino physics project

• T2K — long-baseline neutrino oscillation accelerator experiment in Japan

• International collaboration:

• ~500 members, 63 institutes, 11 countries

3

09/11/16 J. Imber | LLR – Ecole Polytechnique 29

The T2K Collaboration

Canada TRIUMF

U. B. Columbia U. Regina

U. Toronto U. Victoria U. Winnipeg York U.

France CEA Saclay IPN Lyon LLR E. Poly.

LPNHE Paris

Germany Aachen U.

～ 500 members, 61 Institutes, 11 countries

Italy

INFN, U. Bari INFN, U. Napoli INFN, U. Padova INFN, U. Roma

Japan

ICRR Kamioka ICRR RCCN Kavli IPMU KEK

Kobe U.

Kyoto U.

Miyagi U. Edu.

Okayama U.

Osaka City U.

Tokyo Metropolitan U.

U. Tokyo

Poland

IFJ PAN, Cracow NCBJ, Warsaw

U. Silesia, Katowice U. Warsaw

Warsaw U. T.

Wroclaw U.

Russia INR

Spain

IFAE, Barcelona IFIC, Valencia

U. Autonoma Madrid

USA Boston U.

Colorado S. U.

Duke U.

Louisiana State U.

Michigan S.U.

Stony Brook U.

U. C. Irvine U. Colorado U. Pittsburgh U. Rochester U. Washington Switzerland

ETH Zurich U. Bern U. Geneva

United Kingdom Imperial C. London Lancaster U.

Oxford U.

Queen Mary U. L.

Royal Holloway U.L.

STFC/Daresbury STFC/RAL

U. Liverpool U. Sheffield U. Warwick

THE T2K COLLABORATION

Canada TRIUMF

U. B. Columbia U. Regina

U. Toronto U. Victoria U. Winnipeg York U.

France

CEA Saclay IPN Lyon LLR E. Poly.

LPNHE Paris

Germany Aachen

4 500 members, 63 institutes, 11 countries

Italy

INFN, U. Bari INFN, U. Napoli INFN, U. Padova INFN, U. Roma Japan

ICRR Kamioka ICRR RCCN Kavli IPMU KEK

Kobe U.

Kyoto U.

Miyagi U. Edu.

Okayama U.

Osaka City U.

Tokyo Institute of Tech Tokyo Metropolitan U.

U. Tokyo

Tokyo U. of Science Yokohama National U.

Poland

IFJ PAN, Cracow NCBJ, Warsaw

U. Silesia, Katowice U. Warsaw

Warsaw U. T.

Wroclaw U.

Russia INR RAS

Spain

IFAE, Barcelona IFIC, Valencia

U. Autonoma Madrid

USA

Boston U.

Colorado S. U.

Duke U.

Louisiana State U.

Michigan S.U.

Stony Brook U.

U. C. Irvine U. Colorado U. Pittsburgh U. Rochester U. Washington Switzerland

U. Bern U. Geneva

United Kingdom Imperial C. London Lancaster U.

Oxford U.

Queen Mary U. L.

Royal Holloway U.L.

STFC/Daresbury STFC/RAL

U. Liverpool U. Sheffield U. Warwick

T2K Experiment International Collaboration

T2K (TOKAI-TO-KAMIOKA) EXPERIMENT

• Spanish groups provide important and in many ways crucial contributions to the experiment

• Near Detector:

• Magnet operations (IFAE), TPCs (IFAE and IFIC), near detector calibration, reconstruction and analysis

• Conveners of the groups responsible of the data-taking coordination, neutrino interactions modelling, tracking, analysis framework development, “exotics” physics

searches

• UAM actively participates in the Super-Kamiokande calibrations + future work on Gd addition

5

T2K DESIGN

• Near and Far detectors

• Off-axis (anti)muon-neutrino beam

• Energy peaked at oscillation maximum (E~0.6 GeV)

• Neutrino and antineutrino enhanced modes via horn polarity switching

• Dominant process for ν detection: charged-current quasi-elastic interactions (CCQE)

• Reduced intrinsic ν_e contamination (≲1%)

• Reduced backgrounds from high-energy tail

6

NEUTRINO OSCILLATIONS IN T2K

“Disappearance" channel

• Precise measurement of “atmospheric” parameters θ₂₃ and Δm²₃₂ and CPT test via ν vs anti-ν analysis

7 P (⌫

! ⌫

) ' 1 (cos

✓

sin

2✓

) sin

✓

m

L 4E

◆

“Appearance” channel: measuring θ₁₃ and probing CP-violation (CPV)

• Leading term defines the octant of θ₂₃: <, > or = 45^o

• Sub-leading term accounts for CPV: enhanced effect when comparing neutrino and antineutrino data

Leading term

From Phys. Rev. D64 (2001) 053003

CP-violating

“+” sign for anti-ν

P (⌫

! ⌫

) ' sin

2✓

sin

✓

⇥ sin

[(1 x) ] (1 x)

+O(↵

)

m²₃₁

↵ = | m²₂₁

m²₃₁| ⇠ 1

30 = m²₃₁L 4E

CP-conserving

+↵ cos

⇥ sin 2✓

sin 2✓

sin 2✓

⇥ cos sin[x ] x

sin[(1 x) ] (1 x)

↵ sin

⇥ sin 2✓

sin 2✓

sin 2✓

⇥ sin sin[x ] x

sin[(1 x) ] (1 x)

* T2K leading efforts

Accumulated POT

0 5 10 15 20 25

2010 2011 2012 2013 2014 2015 2016

Run1 Run2 Run3 Run4 Run5 Run6 Run7 Run8

Beam Power (kW)

0 100 200 300 400 500 1020

×

Total Accumulated POT for Physics -Mode Beam Power

ν

-Mode Beam Power ν

23 January 2010 – 12 April 2017 Total POT: 22.54 x 10²⁰

ν mode POT: 14.93 x 10²⁰ (66.2%) ν mode POT: 7.62 x 10²⁰ (33.8%) _

T2K DATA TAKING

• POT (Protons on Target) for present results (Jan 2010 - April 2017):

• 14.93x10²⁰(ν mode) + 7.62x10²⁰(anti-ν mode) POT (66.2% : 33.8%)

8 2017:

stable operation at ~470 kW 2010:

start operation

T2K results release:

νμ 1^st release

νe app 3.1σ

νe app 7.3σ

1^st constraint on δCP

ν_μ highest precision on θ23 Summer 2016 results Summer 2017 results

2017:

doubled

ν-mode

statistics!

FITTED FLUX PARAMETERS

30

➤ Fitted flux parameters are generally near their nominal value of 1.0

➤ Most of the fitted flux parameters fall within their assigned 1 sigma prior uncertainty

Super-K Neutrino Mode Flux Super-K Antineutrino Mode Flux

Neutrino Energy (GeV) Neutrino Energy (GeV)

NEAR DETECTOR MEASUREMENTS

• On-axis detector INGRID

• Iron-scintillator layers

• Day-by-day monitoring of the

ν beam position and rate

9

• Off-axis detector ND280

• Detectors in 0.2 T B field

• Tracker:

• Time projection chambers

• Scintillator fine-grained detectors

Super-K flux parameters

ND280 ANALYSIS

10

• Fit to ND280 samples constrains

neutrino flux and cross-section model

• Reduce systematic uncertainty for oscillation analysis: ≈12%→≈6%

ν_μ FGD1CC-0π

FGD1 νμ CC-1π

Example samples

CCQE CC1π

FAR DETECTOR MEASUREMENTS SUPER-KAMIOKANDE (SUPER-K)

• 50 kton water-Cherenkov tank

• Separate e/ μ-like rings:

• <1% misidentified μ as e

• π

rejection

• No magnetic field

11

• 5 Super-K samples used for analysis

• 1-ring μ and e-like events in ν and anti- ν modes + CC1π e-like for ν mode

μ -like e-like

CCQE

http://www.ps.uci.edu/~tomba/sk/tscan/pictures.html http://www.ps.uci.edu/~tomba/sk/tscan/pictures.html

CC1π

1-e ring

with a delayed e-ring

T2K DATA

ND280 data

Beam monitors INGRID

Super-K data

DATA FITS

ND280 fit

SuperK fit

MC

MODELS

ND280 model

Neutrino

interactions model

Neutrino flux model

Super-K model

EXTERNAL DATA

Neutrino interactions

Hadron production:

NA61/CERN

T2K ANALYSIS STRATEGY

12

Final oscillation results

+

* Two approaches:

frequentist and

Bayesian (MCMC) to

obtain/present final results

2017 ANALYSIS IMPROVEMENTS

13

• Neutrino interactions modelling is rapidly developing → changes may affect the results

• Huge efforts in recent years to improve NEUT (Acta Phys. Polon. B42477 (2009)) neutrino generator used in T2K

• Multi-nucleon processes: Valencia 2p-2h model (Phys.Rev. C83(2011) 045501)

• Improved model for CCQE with inclusion of long-range correlations in nucleus (Random Phase Approximation, RPA calculation)

• 2017 analysis: new parametrisation of uncertainties for multi-nucleon and RPA

• On-going checks of results robustness: preliminary systematics parameters used!

• Small effect on δ

but larger for “atmospheric” parameters

• Super-Kamiokande event reconstruction

• New algorithm (fitQun) applied for all analysis samples

• (Re-)optimised the fiducial volume cuts

• ~30% increase in “effective” statistics

FV params

T2K FAR DETECTOR SAMPLES

14

ν-mode anti-ν-mode

ν μ ν e ν e

CC1π

* T2K Preliminary

ν μ

_

ν _ e Energy distribution

ANALYSIS RESULTS: ATMOSPHERIC PARAMETERS θ 23 AND Δ m 2 32

15

• 2016 analysis (joint fit of 5 samples with reactor constraint for θ

):

• Compatible and consistent results with other experiments

• Consistent results for P(ν

→ ν

) and P(ν

→ ν

): CPT conserved

• 2017 analysis: work on-going to study the effect from systematics uncertainties of the neutrino interactions modelling

Phys.Rev. D96 (2017) no.1, 011102

2016 analysis

2016 analysis

ANALYSIS RESULTS: ATMOSPHERIC PARAMETERS θ 23 AND Δ m 2 32

16

• Joint analysis with reactor constraint

• Data prefers upper octant and normal mass hierarchy

• Caveat: preliminary systematic uncertainties → tests on-going

23) (θ

sin2

0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7

)-4 c2 | (eV 322 m∆|

2.3 2.35 2.4 2.45 2.5 2.55 2.6 2.65 2.7

−3

×10

Normal - 68CL Normal - 90CL Inverted - 68CL Inverted - 90CL Best fit

T2K Run1-8 Preliminary

Final systematics pending

Posterior probabilities from Bayesian analysis

* Doubled ν-mode

statistics for 2017 analysis!

Final systematics still pending!

13) (θ

sin2

15 20 25 30 35

−3

×10

(Radians) CPδ

−3

−2

−1 0

1 2

3 Normal - 68CL

Normal - 90CL Inverted - 68CL Inverted - 90CL Best fit

T2K Run1-8 Preliminary

Final systematics pending

13) (θ

sin2

10 15 20 25 30 35 40 45 50

−3

×10

(Radians) CPδ

−3

−2

−1 0

1 2

3 Normal - 68CL

Normal - 90CL Inverted - 68CL Inverted - 90CL Best fit

PDG 2016

T2K Run1-8 Preliminary

Final systematics pending

ANALYSIS RESULTS: θ 13 MEASUREMENTS

17

• Good agreement with reactor experiments

• T2K best fit (NH): sin

θ

= 0.0277

• PDG 2016: sin

θ

= 0.0210±0.0011

• Sensitivity to δ

with T2K data only

• Large CPV favoured

Reactor constraint:

sin²θ13=0.0210±0.0011

T2K only

Final systematics pending

Final systematics pending

(rad) δCP

−3 −2 −1 0 1 2 3

ln(L)∆-2

0 5 10 15 20 25 30

Normal Inverted

T2K Run1-8 Preliminary

Final systematics pending

ANALYSIS RESULTS: δ CP

18

• Exclude CP conservation in lepton sector sin(δ_CP)=0 at 2σ level

• Observed events favour large CPV (δ_CP =-1.83 radians for NH) and normal mass hierarchy

• 2σ CL regions:

• Normal mass hierarchy: [-2.98, -0.6] radians

• Inverted mass hierarchy: [-1.54, -1.19] radians T2K+Reactor

_

2σ intervals

neutrino (top)

antineutrino (bottom)

ν

ν

_

T2K-II Protons-On-Target Request

JFY

2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027

MR Beam Power [kW]

0 200 400 600 800 1000 1200

1400 21 POT]Integrated Delivered Protons [10

0 5 10 15 20 25 30 35 40 45

POT]21 . [10 July)−(Oct.Delivered Protons / Period

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

MR Power Supply upgrade

T2K-II Protons-On-Target Request

T2K FUTURE PROSPECTS

19

• 7.8x10²¹ POT approved (expected by ~2021)

• Gain “effective” statistics: new CC-nonQE, multi-ring samples: already ~30% with new SK reconstruction

• Decrease systematic uncertainties: new ND280 samples + analysis improvements

• T2K phase-II proposal to start in ~2021 and run till 2026 (Hyper-Kamiokande time?):

• Collect ~20x10²¹ POT

• Beam power: 450 kW → 750kW → 1.3 MW

• Near detector upgrade

Current data taking

Accumulated POT

0 5 10 15 20 25

2010 2011 2012 2013 2014 2015 2016

Run1 Run2 Run3 Run4 Run5 Run6 Run7 Run8

Beam Power (kW)

0 100 200 300 400 500 1020

×

Total Accumulated POT for Physics -Mode Beam Power

ν

-Mode Beam Power ν

23 January 2010 – 12 April 2017 Total POT: 22.54 x 10²⁰

ν mode POT: 14.93 x 10²⁰ (66.2%) ν mode POT: 7.62 x 10²⁰ (33.8%) _

T2K FUTURE PROSPECTS: SENSITIVITY

20

• Exclude CP conservation at more than 3 σ level for δ

= -π/2 and NH

• Significant improvement in the precision for atmospheric parameters

Unknown MH

T2K FUTURE PROSPECTS:

NEAR DETECTOR UPGRADE

• Reduction of systematic uncertainties is crucial

• 18% (2011) → 9% (2014) → 6% (2016) → 4%(2020..)?

• ND280 measurements are important

21

• Possible upgrade of T2K near detector:

target date ~2020

• New design (work on-going):

• improve acceptance + reduce threshold for low momentum particles (e.g. protons)

• Test detectors in J-PARC for target design:

• INGRID water module (2016)

• WAGASCI/Baby-MIND (from 2017)

Reference design 3σ

+ TOF detectors

T2K preliminary NH and δ_CP=-π/2

SUMMARY

• T2K is working steadily on its quest on filling neutrino puzzle

• For 2017 analysis doubled ν statistics since 2016 + additional ~30% with new Super-K event reconstruction

• With ≃22.5x10

POT (~30% of expected POT):

• Measurement of sin

θ

in agreement with reactor data

• First! exclusion of CP-conservation at 2σ level

• Short term plans:

• Continuous data-taking with beam power increase to 750 kW

• New analysis samples to increase statistics and improve systematics

• T2K Phase-II proposed, extended run for ~2020-2026. Smooth transition to Hyper-K time

• With 20x10

POT reach 3σ exclusion of CP conservation for certain δ

and MH

• Near detector upgrade to further reduce systematic uncertainties

22

Thank You

23

NEUTRINO OSCILLATIONS IN T2K

At T2K baseline (L~295km, E~0.6GeV):

• CPV: ≈ ±30% effect

• Mass hierarchy: ≈ ±10% effect

24

(GeV) Eν

0.5 1 1.5 2 2.5 3

Osc. Prob

0 0.02 0.04 0.06 0.08 0.1

flux νµ

Off-axis 2.5°

, NH, ν

=0° δcp

, NH, ν

=270° δcp

, NH, ν

=0° δcp

, NH, ν

=270° δcp

νe µ→ , ν νe µ→ ν

Large CPV effect Small matter

CP PHASE/

CHANNEL

δ

= - π/2 Enhance Suppress

δ

=π /2 Suppress Enhance

P(⌫_µ ! ⌫_e) P(¯⌫_µ ! ⌫¯_e)

δ

and mass hierarchy (MH) both cause differences in ν and anti-ν oscillations

T2K NEUTRINO FLUX PREDICTION

• Simulation: FLUKA, GCALOR and GEANT3

• Tuned to external data: NA61/SHINE (CERN)

• Measurement of pion/kaon production of 31 GeV/c proton beam with carbon target

• Thin target (4%λ) and T2K replica target

• Reduction of uncertainties: ~30% to ~10%

• Intrinsic ν

25 Replica target results are being

incorporated into analysis

T2K NEUTRINO INTERACTIONS MODEL

• NEUT neutrino generator

• Model tuned to external data: MiniBooNE, MINERνA, bubble chambers`

• CCQE: Relativistic Fermi Gas (weighted from Spectral Function) + relativistic Random Phase Approximation for nuclear system

• Multinucleon processes (2p2h) included based on J.Nieves model, Phys. Lett. B 707, 72 (2012)

• Pre-(ND280)fit uncertainty for Super-K: ~7.5%

26

Anti- ν

ν

ON-AXIS NEAR DETECTOR INGRID

• T2K utilises off-axis neutrino beam:

• Important to monitor beam intensity and direction

27

• Iron/scintillator detector to measure beam profile and rate

• Day-by-day monitoring

• Direction stable within 1 mrad

(~2% shift in peak energy)

ND280 ANALYSIS: ν -MODE

28

• ND280 samples in FGD1 and FGD2: ν_μ interactions in ν mode running

• CC-0π: muon and no pions in the final state

• CC-1π: muon and π⁺ in the final state

• CC-Other: all other CC interactions (DIS dominated)

CC-1πFGD1 FGD1

CC-Other CC-0πFGD1

ND280 ANALYSIS: ANTI- ν -MODE

29

• ND280 samples in FGD1 and FGD2

• CC-1tracks and CC-Ntrack samples

• μ

samples and μ

to constrain “wrong-sign” background

FGD1

μ⁺ FGD1

μ^-

FGD1μ⁺ FGD1

μ^-

ND280 INPUTS TO OSCILLATION ANALYSIS (2016)

• Each model parameter (flux + neutrino interactions) has its uncertainty

• Fit to ND280 data constrains flux and cross-section model, uncertainties propagated to SK as covariance

• Significant reduction of systematic uncertainties

30

Total NSK Fraction Uncertainty, % νμ νe ainti-νμ anti-νe

Flux ^{W/O ND280} 7.6 8.9 7.1 8.0

Cross section ^{W/O ND280} 7.7 7.2 9.3 10.1

Flux and cross

section ^{W/ ND280} 2.9 4.2 3.4 4.6

Final/sec. hadronic

interactions ^— 1.5 2.5 2.1 2.5

Far detector ^— 3.9 2.4 3.3 3.1

Total ^{W/O ND280} 12.0 11.9 12.5 13.7

Total W/ ND280 5.0 5.4 5.2 6.2

* T2K Preliminary

2016 ANALYSIS RESULTS: θ 23 AND Δ m 2 32

31

• Joint analysis with reactor constraint:

sin

2θ

=0.085±0.05

• T2K data consistent with maximal mixing

• Compatible with other experiments (intervals for fixed mass hierarchy)

PARAMETER/MASS HIERARCHY

NORMAL MASS HIERARCHY

INVERTED MASS HIERARCHY

sin

2θ

| Δ m

|

(x10

eV

/c

)

2016 CPT INVARIANCE TEST: ν μ AND anti- ν μ DISAPPEARANCE

• Strategy

• Assign independent oscillation parameters for antineutrinos

• Neutrino samples constrain “wrong-sign” background

• Test CPT: θ

≠θ

and Δm

≠Δm

• Consistent results for P(ν

→ ν

) and P(ν

→ ν

): CPT conserved

32

_ _

_ _

NH IH

2016 COMPARISON WITH NOVA BEST- FIT

ν-mode anti-ν-mode 33

ν

μ -like

ν

e-like anti-ν

e-like anti- ν

μ -like

NEW SAMPLE: CC1 𝛑

34

• ν

e-like single ring events

• Require additional ring from Michel electron

• Energy with 2-body kinematics with Δ baryon

• Applied only for ν-mode running

• Gain ~10% more statistics (MC)

• 15 events observed

• Total 5 samples available for T2K analysis

ν

CC1π-like 15 events

CCQE CC1π

EVENT RATES

• Largely in line with the prediction for δ

= -π/2

35

• Generally within statistical and systematic uncertainties

• p-value: ~0.42

• More observed e-like CC1π events15 than maximum expectation 6.92

TOTAL SYSTEMATICS UNCERTAINTIES

• Total systematics uncertainties (%) used in 2017 analysis

36

ROBUSTNESS OF T2K ANALYSIS RESULTS

37

• Neutrino interaction modelling is a rapidly developing media

• Study potential bias in the T2K oscillation analysis due to the

choice of neutrino interaction model and investigate variations that are not yet implemented

in the fit model

• Produce fake data studies by varying parts of the interaction model

• Fit using the model without the variations

• Evaluate biases in the fitted oscillation parameters

• Use different data sets:

• Discrepancies between models and data that may indicate deficiencies in models

• Planned improvements to models not yet available in oscillation fitting framework

FAKE DATA STUDIES IN T2K

38

• Use different data sets:

• Data-driven variation generated based on the pre-fit data/prediction discrepancy in ND280 (and external data, e.g. Minerva)

• Variations produced with different assumptions of the axial form factor

• Variations that cover discrepancies in pion spectrum observed in ND280

• Variations to probe new pion production model

ND280

fit results

EXAMPLE OF ND280 DATA-DRIVEN FAKE DATA STUDIES

39

• Use excess of data over prediction prior to ND280 fitting

• Assign observed access to three different interactions

• CCQE enhanced

• 2p2h with intermediate Δ resonate (2p2h-Δ)

• Pure nucleon-nucleon correlations (2p2h-nonΔ)

• Use excess to predict event rates in ND280 and Super-Kamiokande

T2K preliminary T2K preliminary

EXAMPLE OF ND280 DATA-DRIVEN FAKE DATA STUDIES

40

• Example studies for the fake-data studies produced for Asimov data sample

• Used in analysis to get sensitivity values

• Values set to PDG-2016 data and best fit values from the previous T2K analysis

FAKE DATA STUDIES

EFFECT ON “ATMOSPHERIC” PARAMETERS

41

• Bias of Δm

to lower values and sin

θ

to max mixing

• Narrow contour obtained for fake data studies

• Studying whether should incorporate these effects of variations as an additional systematic uncertainty

• No conclusive statement yet

T2K preliminary T2K preliminary

FAKE DATA-STUDIES EFFECT ON δ CP

42

• Right: Compare nominal MC and the fake data

• Left: shift data Δχ

according to difference observed in fake data study

• Max change/shift to the confidence interval/mean point: ≃ 2%

• Small effect on δ

limits

T2K preliminary Fake-data for

Δ-2p2h

T2K preliminary

IMPACT OF SAMPLES ON δ CP

43

• Take data samples out 1 at a time and replace with nominal Monte Carlo prediction → check the change on limits

• Largest effect from e-like CC1π sample

T2K preliminary