Sterile neutrino oscillation

Sterile neutrino oscillation Sterile neutrino oscillation

at a neutrino factoryy

Ken-ichi Fuki Ken ichi Fuki

(Tokyo Metropolitan University )

Andrea Donini (IFT Madrid (UAM/CSIC)) Work in collaboration with

Andrea Donini (IFT, Madrid (UAM/CSIC)),

Davide Meloni (Rome III U. & INFN, Rome3 ),

Jacobo Lopez-Pavon (IFT, Madrid (UAM/CSIC)),

Osamu Yasuda (TMU)

1 1 Four flavor neutrino with LSND 1. Four flavor neutrino

1.1. Four flavor neutrino with LSND

(2+2) scheme

(2+2) scheme

m₃² m₄²

Excluded by solar ν

m ²

Excluded by solar ν and atm ν （4.9σ）

(3+1) scheme

m₁² m₂

m₄² Strongly disfavored by SBL disappearance

m₃2²

pp data （3.1σ）

m₁² m₂²

1.2.1. Four flavor neutrino without LSND

Large θ

is allowed θ

and θ

are small.

In contrast, g

Donini-Maltoni-Meloni-Migliozzi-Terranova arXiv:0704.0388v2

,

14 16 18 20

30 35 40

8 10 12 14

θ 14 20

25

θ 34

2 4 6 8

5 10 15

0 2 4 6 8 10 12 14 16 18 20

θ₁₃

0 2

0 2 4 6 8 10 12 14 16 18 20

θ₂₄

0 5

1.2.2. Sensitivity limit at the CNGS/OPERA

Large g θ

is still allowed

Nominal intensity of 4.5 x 10¹⁹ pot/yr

14 θ₂₃ = 45°, δ₃ = 0°

1 2 3× 5

10 ³⁵

40

θ₂₃ = 45°, δ₃ = 0°

p y

8 10 12

4 × 1× 2××× 1

25 30

4

× 1

99%CL 99%CL

4 6 θ 14 8

10 15

θ 34 20 1

× 2

× 3

× 10× 5

0 2 4 6 8 10 12 14

0 2 4

0 2 4 6 8 10 12 14

0 5 10

0 2 4 6 8 10 12 14

θ₁₃ ^{0 2 4 6} θ₂₄^{8 10 12 14}

Donini-Maltoni-Meloni-Migliozzi-Terranova arXiv:0704.0388v2

2 1 1st order expansion of probabilities in matter

2. (3+1)scheme at Neutrino Factory

2.1. 1st order expansion of probabilities in matter

ν e decouples !!

2.2. Set up

P （ ν μ →ν μ ）

P （ ν μ →ν τ ）

P （ ν μ →ν μ ）

Set up:

relevant

I t 2 x 10²⁰ muon decay / yr x 4 yr / baseline

L=3000km, 7500km

Input:

Δm²₄₁ > 0.1eV²

Hybrid-emulsion / Magnetized iron calorimeter of 50 kton

“HYBRID MIND”

A maximal muon energy = 50 GeV No CP phases

“HYBRID-MIND”

No background / No systematic errors Ref. Cervera @ GOLDEN’07 for HYBRID-MIND；

100 % efficiency for both ε_μ and ετ

~90% ~25%

De Lellis @ GOLDEN’07 for MAGNETIZED ECC

In reality 90% 25%

VERY PRELIMINAR ANALYSIS

In reality

2.3. Sensitivity in θ 13 , θ 14 ,θ 24 and θ 34

Very low sensitivity to θ₁₃ and θ₁₄ High sensitivity in θ₂₄ and θ₃₄

1) Highest sensitivity in θ34 from the 7500km

2). Highest sensitivity in θ24 from the 3000km baseline

1). Highest sensitivity in θ34 from the 7500km baseline

baseline

10

8

6

θ 14 3000km+7500km

90%CL

4

2

90%CL

θ

θ θ 0

0

10 8

6 4

2

0 θ₁₃

ν e decouples !!

θ₁₃=θ₁₄=0

2.4. Contribution of P(ν

→ν

） and P(ν

→ν

）

at 3000km at 3000km

Sensitive to both θ24 and θ34

3-flavor

4-flavor Θ24=10°

Θ34=25°

Pμτ

90%CL

No sensitivity to θ34, only to θ24

4-flavor 3-flavor

Θ24=10°

Pμμ

Θ34=25°

2.5. Contribution of P(ν

→ν

） and P(ν

→ν

）

at 7500km at 7500km

Sensitivity to both θ24y and θ34

Θ34=25°

Θ24=10°

τ

90%CL 3-flavor

4 flavor

Pμτ

4-flavor

Sensitivity to both θ24 and θ34

3-flavor 4-flavor

Θ24=10° Θ34=25°

Pμμ

Θ34=25

3. Summary

• Golden and Silver channels are not optimal to study 3+1Golden and Silver channels are not optimal to study 3 1 sterile neutrinos.

ν_μ→ ν_μ and ν_μ→ ν_τ are the relevant channels.

• We have performed a preliminary analysis at a two-baseline (L=3000km+7500km) 50GeV nufact with ideal HYBRID-MIND detectors (no background and 100% efficiency)

detectors (no background and 100% efficiency).

θ₃₄ sensitivity down to 〜 4°and θ₂₄ sensitivity down to 〜 1°at 90%CL.

1 at 90%CL.

Highest sensitivity in θ₃₄ from the 7500km baseline and Highest sensitivity in θ₂₄ from the 3000km baseline.

Hi h t iti it i θ f th d h l t

Highest sensitivity in θ₂₄ from the ν_μ→ ν_μ and ν_μ→ ν_τchannels at 3000km.

Highest sensitivity in θ₃₄ from the ν_μ→ ν_μ and ν_μ→ ν_τchannels at 7500km.

Th h l h hi h iti it i θ d θ t b th 3000k

The channel ν_μ→ ν_τ has a high sensitivity in θ₃₄ and θ₂₄ at both 3000km and 7500km, even though the event number is not large .

The ν_μμ→ ν_μμ channel alone gives g θ₂₄₂₄

< 1

< 5

It is very important to have a reasonable efficiency for

τ