Model-independent test of T violation in neutrino oscillations

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Model-independent test of T violation in neutrino oscillations

Based on

T. Schwetz and AS, arXiv:2106.16099

Alejandro Segarra

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Open questions: CP violation

• CPT in vacuum: CPV = TV

• Appearance required: P(ν_α ^→ ν_α) is T-invariant

• > 2 generations required: U_2x2 is a rotation - 1^st osc. max:

- 2^nd osc. max:

➢ Accelerator ν_μ to ν_e transition

• Matter effects induce environmental CPV

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3

Model-independent P

^αβ

: assumptions

Propagation of the three SM neutrino states is described by a hermitian Hamiltonian H(E; x), which depends on the neutrino energy E and in general on the matter density at the position x along the neutrino path

1.

A. Segarra

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Model-independent P

^αβ

: assumptions

Propagation of the three SM neutrino states is described by a hermitian Hamiltonian H(E; x), which depends on the neutrino energy E and in general on the matter density at the position x along the neutrino path

1.

For the experiments of interest, medium effects can be described to sufficient accuracy by a constant matter density which is approximately the same for all considered experiment

➢ Matter effects induce no TV 2.

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5

Model-independent P

^αβ

: assumptions

Propagation of the three SM neutrino states is described by a hermitian Hamiltonian H(E; x), which depends on neutrino energy E and in general on the matter density at the position x along the neutrino path

1.

➢ Matter effects induce no TV

➢ 2.

We allow for arbitrary (non-unitary) mixing of the energy eigenstates ν_i with the flavour states ν_α relevant for detection and production

3.

A. Segarra

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Model-independent P

^αβ

: assumptions

Propagation of the three SM neutrino states is described by a hermitian Hamiltonian H(E; x), which depends on neutrino energy E and in general on the matter density at the position x along the neutrino path

1.

➢ Matter effects induce no TV 2.

We allow for arbitrary (non-unitary) mixing of the energy eigenstates ν_i with the flavour states ν_α relevant for detection and production

3.

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The proposed TV test: are there L-odd terms?

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• Data P(L) at the same energy: same parameters

• Separate neutrino and antineutrino fits: different and

A. Segarra

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The proposed TV test: are there L-odd terms?

• Data P(L) at the same energy: same parameters

• Separate neutrino and antineutrino fits: different and

• Consider both ν_μ ^→ ν_μ and ν_μ ^→ ν_e (same , different ) - Disappearance is T invariant, fixes the frequencies - Appearance provides sensitivity to TV

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Necessary data points

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• 8 parameters: 6 real coefficients

2 independent frequencies, and

• 2 data points per baseline ( > 4 experiments)

A. Segarra

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Necessary data points

• 8 parameters: 6 real coefficients

2 independent frequencies, and

• 2 data points per baseline ( > 4 experiments)

• Zero-distance effects: near detectors provide L ≈ 0 ( > 3 exps.)

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How it works

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18 data points and best-fit curve without prior for delta=0, 90º.

Discuss delta = 90º frequencies values >> real ones

b.f. ω₂₁ = 7.7 ω₂₁ b.f. ω₃₁ = 1.2 ω₃₁

A. Segarra

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A 4

^th

assumption

4. We impose that the oscillation frequencies deviate only weakly from the ones corresponding to the standard three-flavour oscillation case

We include the prior term

with

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Dependence on the model

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Fit result depends on the true values of the parameters

• Oscillation probabilities depend on E

• Masses/mixings depend on the model

A. Segarra

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Realistic data: energy overlap

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Realistic data: energy overlap

15 A. Segarra

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Realistic data: energy overlap

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Realistic data: energy overlap

17 A. Segarra

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Realistic data: energy overlap

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Estimation of statistical uncertainties

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Number of signal events N_br

Near detector:

A. Segarra

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Data points (δ = 90º)

(295 km) (1100 km)

(1300 km) (540 km)

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10% energy resolution

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DUNE + T2HK + T2HKK + ESSνSB

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χ

²

values for δ = 90º

• Most sensitive bins: 0.75 and 0.85 GeV

• Energy resolution is crucial

Perfect [10%] energy resolution

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Dependence on δ

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What happens at 270º?

Disappearance:

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What happens for IH?

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Vacuum Invariance NH → IH

δ → π - δ

A. Segarra

Vacuum Invariance NH → IH

δ → π - δ

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What happens for (anti)neutrinos?

Vacuum Invariance

ν → ν

δ → 2π - δ

≈ ν ν

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Summary

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• T violation induces L-odd terms in the osc. Probability

• Can data be described by

• General parametrization:

- P(L) measurements at the same E with good ΔE - At least 3 different baselines: Korea is crucial!

• Neutrinos probe sinδ > 0, antineutrinos probe sinδ < 0 regardless of mass ordering

A. Segarra

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Model-independent test of T violation in neutrino oscillations