T2KK/T2KO 実験での質量階層性、CP位相測定の可能性

T2KK/T2KO 実験での質量階層性、CP 位相測定の可能性

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Yoshitaro Takaesu U of Tokyo

Introduction

Questions in neutrino physics

• Dirac or Majorana?• mass scale & its origin?• Sterile neutrinos?• CP violation in the lepton sector?• Majorana CP phase?• Dirac CP phase?

• mass hierarchy?

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Questions in neutrino physics

• Dirac or Majorana?• mass scale & its origin?• Sterile neutrinos?• CP violation in the lepton sector?• Majorana CP phase?• Dirac CP phase?

• mass hierarchy?

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Fix unknowns as possible as we can.

We know them. But really don’t know them.

Further motivations for MH and Dirac CP phase

• Needed for determination of neutrino mass in hierarchical case from cosmology and beta decay exp. results.

• Define scope for future neutrinoless double beta decay experiments.

• Reduce uncertainty for CP phase measurements significantly.

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⌃imi m2� = ⌃i|Uei|2m2

i

Mass hierarchy

Dirac CP phase• provide a solution for CP violation source in Leptogenesis.

• via flavour dependent CP asymmetry for M1 << 10^12 GeV.

• Constrain flavor symmetry models for neutrino mixing pattern.[Perke, Petcov, Riotto, PRD and NPB 2007]

Our knowledge on neutrino sector Three light flavor mixing

Mass differences

normal inverted

Mass hierarchy: NH or IH

[PDG:Phys.Rev. D86 (2012) 010001] 6

U =

Majorana phaseUnknown

irrelevant to neutrinooscillation

Hints on MH and Dirac CP phase

around 90° seems to be disfavoured by T2K + reactor (theta_13).

MINOS favours around 90° but lower statistics.

MH and Dirac CP phase are still less constrained.

1403.0867

Global FitForero et.al1205.4018

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1502.01550

• T2K (LBL, 22.5kt WC) (2011 ~ )• Nova (LBL, 14kt LAr) (2014 ~ )

• INO (atm, 50kt Iron) (2018 ~ )• JUNO (react, 20kt LSci) (2020 ~ )

• RENO50 (react, 18kt LSci) (2020 ~ )• ORCA (atm, 3Mt Ocean) (2020 ~ )• PINGU (atm, 3Mt Ice) (2021 ~ )• DUNE (LBL, 40kt LAr) (2024 ~ )• T2HK (LBL, 560kt WC) (2025 ~ ) • ESSnuSB (LBL, 500kt WC) (2030 ~ )

Oscillation Experiments for MH / Dirac CP phase

T2K/T2HK&

DUNE%

Nova%

PINGU&

INO

RENO50

ESSnuSB

Operating

Approved

Proposed

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Neutrino Beam Exp.

We assume POT/year ( sec) with 40 GeV proton beam.

focusing beamνµ (νµ )

p

Neutrino beam is produced by colliding protons on target. The total neutrino flux is expressed by POT (Protons On Target). ( like Luminosity @ collider )

0.64 MW

(Talk by T.Nakaya @Flavor of New Physics (2015.3.9))

Current: 0.32 MWPlan: 0.75 MW in 5years

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Oscillation Probability: disappearance mode

(Up to linear terms of are retained in A and B)

CP phase sensitive terms are subdominant.-> almost insensitive to CP phase

Effect of Mass hierarchy (sign of Delta_31) is too small comparing to 1 -> almost insensitive to Mass hierarchy

However, this mode is important to constrain using its large number of events.

sin ✓23

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Matter effect terms enhances sign difference of .

Oscillation Probability

(Up to linear terms of are retained in A and B)

Amplitudecorrection

Phasecorrection

Matter Effect

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term typically has larger coefficient than term. LBL exp. are more sensitive to than .


Ae ' 0.2

✓⇢̄

3 g/cm3

◆✓E

GeV

◆�0.47

✓L/1000 km

E/GeV

◆sin �CP

Be '�0.28

✓⇢̄

3 g/cm3

◆✓L

1000 km

◆+0.23

✓L/1000 km

E/GeV

◆cos �CP

Higher neutrino E has better sensitivity to the mass hierarchy for a fixed baseilne L.The sensitivity to CP phase is increased for lower E. -> Need to cover lower neutrino energy/higher peaks.

±


T2KK / T2KO

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As an Example of next generation neutrino beam experiments

T2KK and T2KO

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T2KK: 100 kton in Korea and SK [hep-ph/0410229, 0504026, 0901.1517, 1001.5165] T2KO: 100 kton in Oki island and SK [0804.2111, 1209.2763]

* SK (22.5kton) is also used as a second detector

SK

T2K(250 km)

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• Longer baseline than T2K to enhance sensitivity to the MH• Wide band beam for sensitivity to (phase) as well as (amplitude).

T2KK and T2KO

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SK22


T2KO(650 km)

100

T2KK and T2KO

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SK22


T2KK(1000 km)

100

Beam profiles

νµ beam

Korea and Oki detectors cover wider energy range than SK.sensitive to term (phase) as well as term (Amp.). But more NC π0 BG from the high energy tail

K.Hagiwara, T.Kiwanami, N.Okamura, K.Senda hep-ph/1209.2763

Flux * Cross section

Energy distributions: νe appearance mode (NH)

Total eventsCCQE signalnon-CCQE signalNC π0 BGmiss-ID neutrino BG

SK

T2KO

T2KK

T2KK and T2KOcan observe the 2nd oscillation peakas well as the 1st peak.

Energy distributions: νe appearance mode (IH)

Total eventsCCQE signalnon-CCQE signalNC π0 BGmiss-ID neutrino BG

SK

T2KO

T2KK

T2KK and T2KOcan observe the 2nd oscillation peakas well as the 1st peak.

Mass Hierarchy

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Sensitivity to Mass Hierarchy

T2KK 2.5°OAB@SK

T2KO

MH can be determined with > 3 sigma for T2KK in 5 years run.

We need luck to determine MH with T2KO in 5 years run.

Sensitivity strongly depends on CP phase and 2-3 angle.

Sensitivity of other experiments to MH1311.1822

1401.2046

Sensitivity of other experiments to MH

DUNE

Full 5yrs run

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PINGUORCA

Nova +T2KESSnuSB 2+8yrs

Hyper-K 10yrs

Sensitivity of other experiments to MH

RENO-50INO

Dirac CP phase

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T2K122 (just for comparison with T2KK and T2KO)

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T2K122: 100 kton added to SK

SK22


T2K122(295 km)

100

degeneracy in

Sensitivity to CP phases (global picture)The sensitivity to the CP phase measurement is fully expressed intest vs. true plane.

4 9Exclusion contours

corresponds to CP measurement accuracy in previous slidesT2KK

3°OABT2KK2.5°OAB

T2KO T2K122

sin �CP

T2KK & T2KO have better sensitivity than T2K122around ±60°, ±120°.

CP measurement with and beam Longer baseline helps to resolve degeneracy in

termdue to

Poor accuracydue to the degeneracy

T2KK 3°OAB

T2KK 2.5°OAB

T2KO T2K122

Using around 2.5:2.5 beam ratio, CP phase can be measured with 20° - 50° (T2KK) and 20° - 45° (T2KO) accuracy.

T2KK 3°OAB T2KK 2.5°OAB

T2KO T2K122

CP measurement with and beam

Sensitivity of LBL experiments to Dirac CP phaseT2KK (10yrs)

T2K+Nova

T2KK (5yrs)

T2KK/T2KO-like experiment can fill gap btw Nova/T2K and Hyper-K/DUNE, if realized.

(DUNE)

T2KO* modified plot in 1309.7022

for 45% of (T2KK)

for 25% of (T2KO) for 33% of (T2K122)

Sensitivity to CP violation detection

The region of the CPV detection is also clearly seen.

4 9Exclusion contours

CPV

CPV detection with

Sensitivity to CPV in 5years

T2KK3°OAB

T2KK2.5°OAB

T2KO T2K122

Statistics matters

CPV sensitivity:T2K122 > T2KO > T2KK

Sensitivity of LBL experiments to CPV

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DUNE 10yrESSnuSB 2+8 yr: 1309.7022

Hyper-K 10yrs

SummaryThere are many on-going efforts to determine the neutrino mass hierarchy and Dirac CP violating phase in the lepton sector.

Mass hierarchy will be determined with 3-5 sigma.

We discussed sensitivity of neutrino beam experiments to MH and CP phase, considering T2KK/T2KO like experiment as an example.

CP phase will be measured with 20° - 50° accuracy.

MH will be fixed in the next decade, but it will take more time tomeasure CP phase accurately and establish CPV.

Using 100kton WC detector at ~1000 km distance with 5*10^21 POT neutrino beam flux,

(atm. & react. exp. can also contribute.)

(Neutrino beam exp. plays a crucial role.)

T2KK/T2KO 実験での質量階層性、CP位相測定の可能性

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