Light sterile neutrino: the 2018 status

(1)

Stefano Gariazzo

IFIC, Valencia (ES) CSIC – Universitat de Valencia

[email protected] http://ific.uv.es/~gariazzo/

Light sterile neutrino:

the 2018 status

X CPAN Days, Salamanca, 29/10/2018

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1 Neutrino Oscillations - Some theory

2 Electron (anti)neutrino disappearence

3 Muon (anti)neutrino disappearence

4 Electron (anti)neutrino appearence

5 Global fit

6 Conclusions

(3)

5 Global fit

6 Conclusions

(4)

The Standard Model of Particle Physics

R/G/B2/3

1/2 2.3 MeV

up

u

R/G/B−1/3

1/2 4.8 MeV

down

d

−1

1/2 511 keV

electron

e

1/2

<2 eV

eneutrino

ν e

R/G/B2/3

1/2 1.28 GeV

charm

c

R/G/B−1/3

1/2 95 MeV

strange

s

−1

1/2 105.7 MeV

muon

µ

1/2

<190 keV

µneutrino

ν µ

R/G/B2/3

1/2 173.2 GeV

top

t

R/G/B−1/3

1/2 4.7 GeV

bottom

b

−1

1/2 1.777 GeV

tau

τ

1/2

<18.2 MeV

τneutrino

ν τ

±1

1 80.4 GeV

W

^±

1 91.2 GeV

Z

photon 1

γ

colo r

gluon 1

g

0 125.1 GeV

Higgs

H

graviton

strongnuclearforce(color) electromagneticforce(charge) weaknuclearforce(weakisospin) gravitationalforce(mass)

charge colors mass spin 6quarks(+6anti-quarks) 6leptons(+6anti-leptons)

12 fermions (+12 anti-fermions)

increasing mass→

5 bosons (+1 opposite chargeW)

standard matter unstable matter force carriers

Goldstone bosons

outside standard model

1

^st

2

^nd

3

^rd ^generation

[D. Galbraith & C. Burgard, 2012]

S. Gariazzo “Light sterile neutrino: the 2018 status” X CPAN days, 29/10/2018 1/21

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The Standard Model of Particle Physics

R/G/B2/3

1/2 2.3 MeV

up

u

R/G/B−1/3

1/2 4.8 MeV

down

d

−1

1/2 511 keV

electron

e

1/2

<2 eV

eneutrino

ν e

R/G/B2/3

1/2 1.28 GeV

charm

c

R/G/B−1/3

1/2 95 MeV

strange

s

−1

1/2 105.7 MeV

muon

µ

1/2

<190 keV

µneutrino

ν µ

R/G/B2/3

1/2 173.2 GeV

top

t

R/G/B−1/3

1/2 4.7 GeV

bottom

b

−1

1/2 1.777 GeV

tau

τ

1/2

<18.2 MeV

τneutrino

ν τ

±1

1 80.4 GeV

W

^±

1 91.2 GeV

Z

photon 1

γ

colo r

gluon 1

g

0 125.1 GeV

Higgs

H

graviton

strongnuclearforce(color) electromagneticforce(charge) weaknuclearforce(weakisospin) gravitationalforce(mass)

charge colors mass spin 6quarks(+6anti-quarks) 6leptons(+6anti-leptons)

12 fermions (+12 anti-fermions)

increasing mass→

5 bosons (+1 opposite chargeW)

standard matter unstable matter force carriers

Goldstone bosons

outside standard model

1

^st

2

^nd

3

^rd ^generation

[D. Galbraith & C. Burgard, 2012]

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Three Neutrino Oscillations

να=

3

X

k=1

Uαkνk (α=e, µ, τ)

U_αk described by 3 mixing anglesθ12, θ13, θ23 and one CP phase δ_CP Current knowledge of the 3 active ν mixing: [de Salas et al. (2018)]

NO: Normal Ordering,m1<m2<m3 IO: Inverted Ordering,m3<m1<m2

∆m²₂₁ = (7.55^+0.20_−0.16)·10⁻⁵eV²

|∆m²₃₁| = (2.50±0.03)·10⁻³eV² (NO)

= (2.42^+0.03_−0.04)·10⁻³eV² (IO) sin²(θ₁₂) = 0.320^+0.020_−0.016

sin²(θ13) = 0.0216^+0.008_−0.007 (NO)

= 0.0222^+0.007_−0.008 (IO) sin²(θ23) = 0.547^+0.020_−0.030 (NO)

= 0.551^+0.018_−0.030 (IO) First hints forδ_CP'3/2π

0.2 0.3 0.4

sin²θ₁₂ 0 5 10 15 20

∆χ2

0.4 0.5 0.6

sin²θ₂₃

0.016 0.02 0.024 0.028 sin²θ₁₃

7 8

∆m²₂₁ [10^-5eV²] 0

5 10 15 20

∆χ2

2.2 2.4 2.6

|∆m²₃₁| [10^-3eV²]

0 0.5 1 1.5 2

δ/π

see also: http://globalfit.astroparticles.es

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Two types of neutrinos

ν

_α

ν

_β

source L detector

ν₁ ν2

ν3

|ν_αi=U_αk|ν_ki

flavor neutrinos ν_α massive neutrinosν_k

Pνα→νβ(L) =|hν_α|ν(L)i|²=^X

k,j

UβkU^∗_αkU^∗_βjUαjexp −i∆m_kj²L 2E

!

∆m_ij² =m²_i −m²_j

(8)

A large family

In principle, previous discussion is valid forN neutrinos only constraint: there are exactly

three flavor neutrinos in the SM

[LEP, Phys. Rept. 427 (2006) 257, arXiv:hep-ex/0509008]

Nν^(Z⁾= 2.9840±0.0082 through the measurement

of the Z resonance e⁺e⁻ −→Z −→ ^X

a=e,µ,τ

νaν¯a

0 10 20 30

86 88 90 92 94

E_cm [GeV]

σhad[nb]

3ν 2ν

4ν

average measurements, error bars increased by factor 10

ALEPH DELPHI L3 OPAL

neutrinosα >3 must be sterile

sterile neutrino = SM singlet: no couplings with other SM particles

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A large family

In principle, previous discussion is valid for N neutrinos N×N mixing matrix,N flavor neutrinos, N massive neutrinos







|ν_ei

|ν_µi

|ν_τi

|ν_s₁i . . .







=







U_e1 U_e2 U_e3 U_e4 ... U_µ1 U_µ2 U_µ3 U_µ4 Uτ1 Uτ2 Uτ3 Uτ4

Us11 Us12 Us13 Us14

. . . . ..













|ν₁i

|ν₂i

|ν₃i

|ν₄i . . .







(10)

A large family

In principle, previous discussion is valid forN neutrinos N×N mixing matrix,N flavor neutrinos,N massive neutrinos







|ν_ei

|ν_µi

|ν_τi

|ν_s₁i . . .







=







U_e1 U_e2 U_e3 U_e4 ... U_µ1 U_µ2 U_µ3 U_µ4 Uτ1 Uτ2 Uτ3 Uτ4

Us11 Us12 Us13 Us14

. . . . ..













|ν₁i

|ν₂i

|ν₃i

|ν₄i . . .







Our case will be 3 (active)+1 (sterile), a perturbation of 3 neutrinos case

ν

_α

ν

_β

source L detector

ν₁ ν2

ν₃ ν4

m₄ m_`

` = 1,2,3

∆m²₄₁'1 eV² ' ∆m²₄₂ ' ∆m²₄₃

6 angles

3Dirac CP phases

3 Majorana CP phases

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Short BaseLine (SBL)

P_ν_α→ν_β(L) =|hν_α|ν(L)i|²=^X

k,j

U_βkU^∗_αkU^∗_βjU_αjexp −i∆m²_kjL 2E

!

Ifm₄m_`, faster oscillations

ν4 oscillations are averaged in most neutrino oscillation experiments Effect of 4th neutrino only visible as global normalization

Short BaseLine (SBL) oscillations: ∆m²₄₁L E '1 At SBL, oscillations due to∆m²₂₁ and|∆m²₃₁|do not develop

(12)

Short BaseLine (SBL)

k,j

!

APPearance (α6=β)

(−)ν_α source

of⁽⁻⁾ν_α

(−)ν_β detect different

flavor⁽⁻⁾ν_β

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Short BaseLine (SBL)

k,j

!

APPearance (α6=β)

(−)ν_α source

of⁽⁻⁾ν_α

DISappearance

(−)ν_α source

of⁽⁻⁾ν_α

(−)ν_s goes undetected

(14)

Short BaseLine (SBL)

k,j

!

APPearance (α6=β)

(−)ν_α source

of⁽⁻⁾ν_α

DISappearance

(−)ν_α source

of⁽⁻⁾ν_α

(−)ν_s goes undetected CP violation cannot be observed in SBL experiments!

(15)

New mixings in the 3+1 scenario







Ue1 Ue2 Ue3 Ue4

U_µ1 U_µ2 U_µ3 U_µ4 U_τ1 U_τ2 U_τ3 U_τ4 Us11 Us12 Us13 Us14





 4×4 mixing matrix:

(16)

New mixings in the 3+1 scenario







Ue1 Ue2 Ue3 Ue4





ϑ14

ϑ24

ϑ₃₄

(17)

New mixings in the 3+1 scenario







Ue1 Ue2 Ue3 Ue4





ϑ14

ϑ24

ϑ₃₄ DISappearance

P₍₋₎^SBL

ν_α→ (−)

ν_α

'1−sin²2ϑααsin²

∆m²₄₁L 4E

sin²2ϑαα= 4|U_α4|²(1− |U_α4|²)

(−)νe →⁽⁻⁾νe

reactor gallium

|U_e4|² = sin²ϑ14

(−)ν_µ→⁽⁻⁾ν_µ accelerator atmospheric

|U_µ4|² = cos²ϑ₁₄sin²ϑ₂₄

(18)

New mixings in the 3+1 scenario







Ue1 Ue2 Ue3 Ue4





ϑ14

ϑ24

ϑ₃₄ DISappearance

P₍₋₎^SBL

ν_α→ (−)

ν_α

'1−sin²2ϑααsin²

∆m²₄₁L 4E

sin²2ϑαα= 4|U_α4|²(1− |U_α4|²)

(−)νe →⁽⁻⁾νe

reactor gallium

|U_e4|² = sin²ϑ14

(−)ν_µ→⁽⁻⁾ν_µ accelerator atmospheric

|U_µ4|² = cos²ϑ₁₄sin²ϑ₂₄

APPearance

P₍₋₎^SBL

ν_α→ (−)

ν_β

'sin²2ϑαβsin²

∆m²₄₁L 4E

sin²2ϑ_αβ = 4|U_α4|²|U_β4|²

(−)ν_µ→⁽⁻⁾ν_e

LSND MiniBooNE

KARMEN OPERA

. . .

sin²2ϑeµ= 4|U_e4|²|U_µ4|² quadratically suppressed!

for small|U_e4|²,|U_µ4|²

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5 Global fit

6 Conclusions

(20)

Gallium anomaly

Gallium radioactive source experiments: GALLEX andSAGE L'1.9 m L'0.6 m

e⁻+⁵¹Cr→⁵¹V +ν_e

ν_e sources: e⁻+³⁷Ar→³⁷Cl +ν_e

νe+⁷¹Ga→⁷¹Ge +e⁻

E '0.75 MeV E '0.81 MeV

In the detector:

71Ge 3/2⁻

1/2⁻ 5/2⁻ 3/2⁻

71Ga

500 keV

232 keV 175 keV

cross sections of the transitions from

[Krofcheck et al., PRL 55 (1985) 1051]

[Frekers et al., PLB 706 (2011) 134]

[SAGE, 2006][Laveder, 2007][Giunti&Laveder, 2011]

(21)

Gallium anomaly

Gallium radioactive source experiments: GALLEX andSAGE L'1.9 m L'0.6 m

e⁻+⁵¹Cr→⁵¹V +ν_e

ν_e sources: e⁻+³⁷Ar→³⁷Cl +ν_e

νe+⁷¹Ga→⁷¹Ge +e⁻

E '0.75 MeV E '0.81 MeV

In the detector:

71Ge 3/2⁻

1/2⁻ 5/2⁻ 3/2⁻

71Ga

500 keV

232 keV 175 keV

cross sections of the transitions from

[Krofcheck et al., PRL 55 (1985) 1051]

[Frekers et al., PLB 706 (2011) 134]

Test detection of solar νe

0.70.80.91.01.1

R=NexpNcal

Cr1 GALLEX

Cr SAGE

Cr2 GALLEX

Ar SAGE

R=0.84±0.05

'2.9σ deficit

[SAGE, 2006][Laveder, 2007][Giunti&Laveder, 2011]

(22)

Reactor Antineutrino Anomaly (RAA)

2011: new reactor ¯νe fluxes by HuberandMueller+ (HM)

[Huber, PRC 84 (2011) 024617] [Mueller et al., PRC 83 (2011) 054615]

Previous reactor rates evaluated with new fluxes⇒ deficit

L [m]

R=NexpNcal

10 10² 10³

0.700.800.901.001.101.20

R=0.934±0.024

Bugey−3 Bugey−4 Chooz

Daya Bay Double Chooz Gosgen

ILL Krasnoyarsk Nucifer

Palo Verde RENO Rovno88

Rovno91 SRP

'2.8σ deficit

Suppression at detector due to active-sterile oscillations?

[PRD 83 (2011) 073006]

(23)

Can we trust the HM fluxes?

2014:

Visible Energy (MeV)

1 2 3 4 5 6 7 8

0.25 MeVData / Predicted

0.6 0.8 1.0 1.2 1.4

Data No oscillation Reactor flux uncertainty Total systematic uncertainty

= 0.090 13 2θ Best fit: sin2

[Double Chooz, arxiv:1406.7763]

[Daya Bay, arxiv:1508.04233]

Prompt Energy [MeV]

1 2 3 4 5 6 7 8

Events / 0.2 MeV ⁵⁰⁰⁰

10000 15000

Data MC Near (a)

Prompt Energy 1 2 3 4 5 6 7 8 0

200 400 600

800 Fast neutron Accidental

8He

9Li/

Prompt Energy (MeV)

1 2 3 4 5 6 7 8

(Data - MC) / MC

−0.1 0 0.1

0.2 1 2 3 4 5Prompt Energy (MeV)6 7 8

Events / 0.2 MeV ⁵⁰⁰

1000 1500

Data MC Far (b)

Prompt Energy 1 2 3 4 5 6 7 8 0

50 100

Fast neutron Accidental

8He

9Li/

252Cf

Prompt Energy (MeV)

1 2 3 4 5 6 7 8

(Data - MC) / MC

−0.1 0 0.1 0.2

[RENO, arxiv:1511.05849]

bump in the spectrum around5 MeV!

cannot be explained by SBL oscillations (averaged at the observed distances)

many attempts of possible explanations, how to clarify the issue?

(24)

Can we trust the HM fluxes?

2014:

Visible Energy (MeV)

1 2 3 4 5 6 7 8

0.25 MeVData / Predicted

0.6 0.8 1.0 1.2 1.4

Data No oscillation Reactor flux uncertainty Total systematic uncertainty

= 0.090 13 2θ Best fit: sin2

[Double Chooz, arxiv:1406.7763]

[Daya Bay, arxiv:1508.04233]

Prompt Energy [MeV]

1 2 3 4 5 6 7 8

Events / 0.2 MeV ⁵⁰⁰⁰

10000 15000

Data MC Near (a)

Prompt Energy 1 2 3 4 5 6 7 8 0

200 400 600

800 Fast neutron Accidental

8He

9Li/

Prompt Energy (MeV)

1 2 3 4 5 6 7 8

(Data - MC) / MC

−0.1 0 0.1

0.2 1 2 3 4 5Prompt Energy (MeV)6 7 8

Events / 0.2 MeV ⁵⁰⁰

1000 1500

Data MC Far (b)

Prompt Energy 1 2 3 4 5 6 7 8 0

50 100

Fast neutron Accidental

8He

9Li/

252Cf

Prompt Energy (MeV)

1 2 3 4 5 6 7 8

(Data - MC) / MC

−0.1 0 0.1 0.2

[RENO, arxiv:1511.05849]

bump in the spectrum around5 MeV!

cannot be explained by SBL oscillations (averaged at the observed distances)

many attempts of possible explanations, how to clarify the issue?

Model independent information!

(i.e. take ratio of spectra at different distances)

(25)

NEOS

Single detector experiment

Prompt Energy [MeV]

1 2 3 4 5 6 7 8

Events /day/100 keV

10 20 30 40 50

60 ^ε

−3 10

−2 10

−1 10

Neutrino Energy [MeV]

2 3 4 5 6 7 8 12

Prompt Energy [MeV]

1 2 3 4 5 6 7 10

Data signal (ON-OFF) Data background (OFF)

(H-M-V) ν MC 3

(Daya Bay) ν MC 3 (a)

Prompt Energy [MeV]

1 2 3 4 5 6 7 10

Data/Prediction

0.9 1.0 1.1

NEOS/H-M-V Systematic total (b)

Prompt Energy [MeV]

1 2 3 4 5 6 7 10

Data/Prediction

0.9 1.0

1.1 NEOS/Daya Bay

Systematic total

, 0.050) (1.73 eV2

, 0.142) (2.32 eV2

(c)

⋅

Ratio to DayaBay measurement to be model independent

[PRL 118 (2017) 121802]

(26)

DANSS

Single movable detector

Positron energy, MeV

1 2 3 4 5 6 7

Ratio Bottom/Top

0.64 0.66 0.68 0.7 0.72 0.74 0.76 0.78

∼3σ preference for 3+1 oscillations

Detector can be at∼10.5,∼11.5 or ∼ 12.5 mfrom reactor core

[D.Svirida@NOW2018]

[arxiv:1804.04046]

(27)

Model-independent fit of

⁽⁻⁾

ν

_e

DIS

NEOS +DANSS

s i n²2ϑ

ee

∆m412 [eV2 ]

10⁻³ 10⁻² 10⁻¹ 1

10⁻¹ 1 10

2σ DANSS NEOS

NEOS+DANSS 1σ 2σ 3σ

The NEOSand DANSS region perfectly overlap at

∆m₄₁² ' 1.3 eV² sin²2ϑee ' 0.05 sin²ϑ₁₄ ' 0.01

[SG et al., PLB 782 (2018) 13]

(28)

Model-independent fit of

⁽⁻⁾

ν

_e

DIS

DANSS + NEOS+ RAA+ Gallium

s i n²2ϑ

ee

∆m412 [eV2 ]

10⁻³ 10⁻² 10⁻¹ 1

10⁻¹ 1

10 ₂₋₃_σ (solid−dashed) Reactor Anomaly Gallium Anomaly

NEOS+DANSS 1σ 2σ 3σ

DANSS + NEOS do not agree with GalliumandRAA

[SG et al., PLB 782 (2018) 13]

(29)

Model-independent fit of

⁽⁻⁾

ν

_e

DIS

All data:

s i n²2ϑ

ee

∆m412 [eV2 ]

10⁻³ 10⁻² 10⁻¹ 1

10⁻¹ 1

10 ₂₋₃_σ (solid−dashed) NEOS+DANSS

MIν_eDis 1σ 2σ 3σ

Fit dominated by DANSS + NEOS

[SG et al., PLB 782 (2018) 13]

(30)

5 Global fit

6 Conclusions

(31)

IceCube and DeepCore

IceCube ^{O(10 km)}^.^L^.^O(10⁴^km)

∼ 2×10⁴ High energy µevents 320 GeV < E < 20 TeV

10⁻² 10⁻¹ 10⁰

sin²2θ24

10⁻² 10⁻¹ 10⁰ 10¹

∆m

2 412/eV

IceCube 99% CL Exclusions IC86 rate+shape IC86 shape only (blind result) IC59 result

[PRL 117 (2016) 071801]

(32)

IceCube and DeepCore

10⁻² 10⁻¹ 10⁰

sin²2θ24

10⁻² 10⁻¹ 10⁰ 10¹

∆m

2 412/eV

[PRL 117 (2016) 071801]

DeepCore

IceCube string DeepCore string

Corridor DeepCore

1000 m

Dust layer

bad optical properties

Veto cap 10 DOMs 10 m vertical spacing

DeepCore 50 HQE DOMs 7 m vertical spacing

0.01 0.02 0.03 Absorption [ 1 / m ]0.04

1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 Depth [ m ]

(33)

IceCube and DeepCore

10⁻² 10⁻¹ 10⁰

sin²2θ24

10⁻² 10⁻¹ 10⁰ 10¹

∆m

2 412/eV

[PRL 117 (2016) 071801]

DeepCore

∼ 5×10³ tracklike events 6 GeV . E . 60 GeV

10⁻³ 10⁻² 10⁻¹

|Uµ4|²= sin²θ24 0.00

0.05 0.10 0.15 0.20 0.25 0.30

|Uτ4|2=sin2θ34·cos2θ24

SK, NO (2015), 90 % C.L.

SK, NO (2015), 99 % C.L.

IceCube, NO (2016), 90 % C.L.

IceCube, NO (2016), 99 % C.L.

IceCube, IO (2016), 90 % C.L.

IceCube, IO (2016), 99 % C.L.

0 2 4 6 8

−2∆lnL

90% C.L.

99% C.L.

0 2 4 6 8

−2∆ lnL

90%C.L. 99%C.L.

[PRD 95 (2017) 112002]

Both also constrain|U_τ4|²

(34)

MINOS & MINOS+

Near (ND,' 500 m) and far (FD,' 800 km) detector

10-2 10^-1 1 10 10² 10³

〉) µν→µν P(〈

0 0.2 0.4 0.6 0.8 1

ND FD

µ CC ν

1 2 10

10 10² 10 1

Reconstructed energy (GeV)

10-2 10^-1 1 10 10² 10³

〉) sν→µν 1 - P(〈

0 0.2 0.4 0.6 0.8 1

3-flavor prob.

= 0.05 eV2 41

m2

∆ = 0.50 eV2 41

m2

∆ = 5.00 eV2 41

m2

∆

ND FD

NC

L / E (km / GeV) [PRL 117 (2016) 151803]:

far-to-near ratio

[arxiv:1710.06488]: full two-detectors fit

1 GeV . E . 40 GeV, peak at 3 GeV

(35)

MINOS & MINOS+

10-2 10^-1 1 10 10² 10³

〉) µν→µν P(〈

0 0.2 0.4 0.6 0.8 1

ND FD

µ CC ν

1 2 10

10 10² 10 1

Reconstructed energy (GeV)

10-2 10^-1 1 10 10² 10³

〉) sν→µν 1 - P(〈

0 0.2 0.4 0.6 0.8 1

3-flavor prob.

= 0.05 eV2 41

m2

∆ = 0.50 eV2 41

m2

∆ = 5.00 eV2 41

m2

∆

ND FD

NC

L / E (km / GeV) [PRL 117 (2016) 151803]:

far-to-near ratio

[arxiv:1710.06488]: full two-detectors fit

1 GeV . E . 40 GeV, peak at 3 GeV

Systematics:

24) θ

2( sin

−3

10 10⁻² 10⁻¹ 1

)2 (eV412m∆

−4

10

−3

10

−2

10

−1

10 1 10 102

103

90% C.L. Sensitivity Statistics only Energy Scale Hadron Production Cross Sections Backgrounds Other Systematics Total Systematics

POT MINOS 1020

× 10.56

POT MINOS+

1020

× 5.80

mode simulation νµ

[arxiv:1710.06488]

(36)

MINOS & MINOS+

10-2 10^-