Review on Sterile Neutrinos Carlo Giunti INFN, Torino, Italy SSP - - PowerPoint PPT Presentation

SLIDE 1

Review on Sterile Neutrinos Carlo Giunti

INFN, Torino, Italy

SSP 2018 7th Symposium on Symmetries in Subatomic Physics 11-15 June 2018, Aachen, Germany

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 1/25

SLIDE 2

Beyond Three-Neutrino Mixing: Sterile Neutrinos

Losc = 4πE ∆m2

νe νµ ντ

∆m2

SOL

∆m2

ATM

. . . νs2 νs1 ∆m2

SBL

ν4 ν3 ν2 ν1 . . . ν5 m 1 eV2

≃ 2.5 × 10−3 eV2

≃ 7.4 × 10−5 eV2

10 20 30 86 88 90 92 94

Ecm [GeV] σhad [nb]

3ν 2ν 4ν

average measurements, error bars increased by factor 10

ALEPH DELPHI L3 OPAL

NLEP

νactive = 2.9840 ± 0.0082

Terminology: a eV-scale sterile neutrino means: a eV-scale massive neutrino which is mainly sterile

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 2/25

SLIDE 3

Sterile Neutrinos from Physics Beyond the SM

◮ Neutrinos are special in the Standard Model: the only neutral fermions ◮ Active left-handed neutrinos can mix with non-SM singlet fermions often

called right-handed neutrinos

◮ Light left-handed anti-νR are light sterile neutrinos

νc

R→νsL

(left-handed)

◮ Sterile means no standard model interactions

[Pontecorvo, Sov. Phys. JETP 26 (1968) 984]

◮ Active neutrinos (νe, νµ, ντ) can oscillate into light sterile neutrinos (νs) ◮ Observables:

◮ Disappearance of active neutrinos (neutral current deficit) ← CEνNS ◮ Indirect evidence through combined fit of data (current indication)

◮ Short-baseline anomalies + 3ν-mixing:

∆m2

21 ≪ |∆m2 31| ≪ |∆m2 41| ≤ . . .

ν1 ν2 ν3 ν4 . . . νe νµ ντ νs1 . . .

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 3/25

SLIDE 4

Effective 3+1 SBL Oscillation Probabilities

Appearance (α = β)

PSBL

(−)

να→

(−)

νβ

≃ sin2 2ϑαβ sin2 ∆m2

41L

4E

• sin2 2ϑαβ = 4|Uα4|2|Uβ4|2

Disappearance

PSBL

(−)

να→

(−)

να

≃ 1 − sin2 2ϑαα sin2 ∆m2

41L

4E

• sin2 2ϑαα = 4|Uα4|2

1 − |Uα4|2

U = Ue1 Ue2 Ue3 Ue4 Uµ1 Uµ2 Uµ3 Uµ4 Uτ1 Uτ2 Uτ3 Uτ4 Us1 Us2 Us3 Us4               SBL

◮ 6 mixing angles ◮ 3 Dirac CP phases ◮ 3 Majorana CP phases ◮ CP violation is not observable in SBL

experiments!

◮ Observable in LBL accelerator exp.

sensitive to ∆m2

ATM [de Gouvea et al, PRD 91 (2015)

053005, PRD 92 (2015) 073012, arXiv:1605.09376; Palazzo et al, PRD 91 (2015) 073017, PLB 757 (2016) 142; Kayser et al, JHEP 1511 (2015) 039, JHEP 1611 (2016) 122] and solar exp. sensitive

to ∆m2

SOL [Long, Li, CG, PRD 87, 113004 (2013) 113004]

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 4/25

SLIDE 5

3+1: Appearance vs Disappearance

◮ Amplitude of νe disappearance:

sin2 2ϑee = 4|Ue4|2 1 − |Ue4|2 ≃ 4|Ue4|2

◮ Amplitude of νµ disappearance:

sin2 2ϑµµ = 4|Uµ4|2 1 − |Uµ4|2 ≃ 4|Uµ4|2

◮ Amplitude of νµ → νe transitions:

sin2 2ϑeµ = 4|Ue4|2|Uµ4|2 ≃ 1 4 sin2 2ϑee sin2 2ϑµµ quadratically suppressed for small |Ue4|2 and |Uµ4|2 ⇓ Appearance-Disappearance Tension

[Okada, Yasuda, IJMPA 12 (1997) 3669; Bilenky, CG, Grimus, EPJC 1 (1998) 247]

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 5/25

SLIDE 6

Gallium Anomaly

Gallium Radioactive Source Experiments: GALLEX and SAGE νe Sources: e− + 51Cr → 51V + νe e− + 37Ar → 37Cl + νe Test of Solar νe Detection: νe + 71Ga → 71Ge + e− E ≃ 0.75 MeV E ≃ 0.81 MeV

0.7 0.8 0.9 1.0 1.1

R = N exp N cal

Cr1 GALLEX Cr SAGE Cr2 GALLEX Ar SAGE

R = 0.84 ± 0.05

LGALLEX = 1.9 m LSAGE = 0.6 m ∆m2

SBL 1 eV2 ≫ ∆m2 ATM

≈ 2.9σ deficit

[SAGE, PRC 73 (2006) 045805; PRC 80 (2009) 015807; Laveder et al, Nucl.Phys.Proc.Suppl. 168 (2007) 344, MPLA 22 (2007) 2499, PRD 78 (2008) 073009, PRC 83 (2011) 065504]

◮ 3He + 71Ga → 71Ge + 3H cross section measurement

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

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 6/25

SLIDE 7

Reactor Electron Antineutrino Anomaly

[Mention et al, PRD 83 (2011) 073006]

New reactor ¯ νe fluxes: Huber-Mueller (H-M)

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

L [m] R = N exp N cal

10 102 103 0.70 0.80 0.90 1.00 1.10 1.20

R = 0.934 ± 0.024

Bugey−3 Bugey−4+Rovno91 Chooz Daya Bay Double Chooz Gosgen+ILL Krasnoyarsk Nucifer Palo Verde RENO Rovno88 SRP

≈ 2.8σ deficit

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 7/25

SLIDE 8

L [m] Pνe→νe

1 10 102 103 0.70 0.80 0.90 1.00 1.10 1.20

DC DC DB DB R R

E ≈ 4MeV − sin22ϑee = 0.1 ∆m41

2 = 0.1 eV2

∆m41

2 = 0.5 eV2

∆m41

2 = 1.0 eV2

Bugey−4 Rovno91 Rovno88 Bugey−3 Gosgen ILL Krasnoyarsk SRP Nucifer

∆m2

SBL 0.5 eV2 ≫ ∆m2 ATM ◮ SBL oscillations are averaged at the Daya Bay, RENO, and Double

Chooz near detectors = ⇒ no spectral distortion

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 8/25

SLIDE 9

Reactor Antineutrino 5 MeV Bump

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

(Data - MC) / MC

0.1 − 0.1 0.2

[RENO, arXiv:1511.05849]

Visible Energy (MeV) 1 2 3 4 5 6 7 8 0.25 MeV Data / Predicted 0.6 0.8 1.0 1.2 1.4

Data No oscillation Reactor flux uncertainty Total systematic uncertainty = 0.090

13

θ 2

2

Best fit: sin

[Double Chooz, arXiv:1406.7763] [Daya Bay, arXiv:1508.04233]

◮ Cannot be explained by neutrino

• scillations (SBL oscillations are

averaged in RENO, DC, DB).

◮ It is likely due to a theoretical

miscalculation of the spectrum.

◮ Heretic solution: detector energy

• nonlinearity. [Mention et al, PLB 773 (2017) 307]

◮ ∼ 3% effect on total flux, but if it is

an excess it increases the anomaly!

◮ No post-bump complete calculation

• f the neutrino fluxes.

◮ Nominal Huber-Mueller flux

calculation uncertainty: ∼ 2.5%.

◮ Guessed true flux uncertainty: ∼ 5%.

[Hayes and Vogel, ARNPS 66 (2016) 219]

◮ Bottom line: the status of the

reactor anomaly is controversial!

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 9/25

SLIDE 10

NEOS

[PRL 118 (2017) 121802 (arXiv:1610.05134)]

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)

1 2 3 4 5 6 7 10 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)

2

(1.73 eV , 0.142)

2

(2.32 eV

(c)

⋅ ⋅

◮ Hanbit Nuclear Power Complex in

Yeong-gwang, Korea.

◮ Thermal power of 2.8 GW. ◮ Detector: a ton of Gd-loaded

liquid scintillator in a gallery approximately 24 m from the reactor core.

◮ The measured antineutrino event

rate is 1976 per day with a signal to background ratio of about 22.

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 10/25

SLIDE 11

DANSS

[Solvay Workshop, 1 December 2017; La Thuile 2018, 3 March 2018; Neutrino 2018, 8 June 2018]

◮ Installed on a movable platform

under a 3 GW reactor.

◮ Large neutrino flux. ◮ Reactor shielding of cosmic rays. ◮ Variable source-detector distance

with the same detector! Down = 12.7 m Up = 10.7 m

Positron Energy [MeV] Ratio Down/Up

1.0 2.0 3.0 4.0 5.0 6.0 7.0 0.64 0.68 0.72 0.76 DANSS No−Oscillations Oscillations Best Fit

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 11/25

SLIDE 12

Model-Independent ¯ νe SBL Oscillations

[Gariazzo, CG, Laveder, Li, PLB 782 (2018) 13, arXiv:1801.06467]

sin22ϑee ∆m41

2 [eV2]

10−3 10−2 10−1 1 10−1 1 10

2σ DANSS NEOS NEOS+DANSS 1σ 2σ 3σ

∼ 3.7σ ∆m2

41 = 1.29 ± 0.03

sin2 2ϑee = 0.049 ± 0.011 sin2 ϑ14 = |Ue4|2 sin2 ϑ14 = 0.012 ± 0.003 sin2 ϑ13 = 0.022 ± 0.001

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 12/25

SLIDE 13

Comparison with the Reactor and Gallium Anomalies

sin22ϑee ∆m41

2 [eV2]

10−3 10−2 10−1 1 10−1 1 10

2−3σ (solid−dashed) Reactor Anomaly Gallium Anomaly NEOS+DANSS 1σ 2σ 3σ

◮ 3σ agreement. ◮ 2σ tension. ◮ Small overestimate of the

reactor fluxes.

◮ Small overestimate of the

GALLEX and SAGE efficiencies.

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 13/25

SLIDE 14

Global Model-Independent νe and ¯ νe Disappearance

sin22ϑee ∆m41

2 [eV2]

10−3 10−2 10−1 1 10−1 1 10

MIνeDis 1σ 2σ 3σ STEREO (1yr, 2σ) PROSPECT (3+3yr, 3σ) SoLiD (1+3yr, 3σ) KATRIN (90% CL)

◮ NEOS and DANSS. ◮ Reactor rates with free 235U

and 239Pu fluxes: r235 and r239.

◮ Gallium data with free

GALLEX and SAGE efficiencies: ηG and ηS.

◮ New reactor experiments:

STEREO, Neutrino-4, SoLiD, PROSPECT

◮ Kinematic ν4 mass

measurement: KATRIN

[See also Dentler, Hernandez-Cabezudo, Kopp, Machado, Maltoni, Martinez-Soler, Schwetz, arXiv:1803.10661]

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 14/25

SLIDE 15

Neutrino-4 [PPNS 2018]

bVÛ `Û

—Ž–• ƒ•‘ˆ

• ‹•

…Š™‡ › …–‹•‰

STEREO [arXiv:1806.02096 and Neutrino 2018]

10−2 10−1

sin2(2θee)

1 101

∆m2

41(eV 2) RAA 95% C.L. RAA 99% C.L. RAA: Best fit STEREO Exclusion Sensitivity (66 days) : 90% C.L. STEREO Exclusion (66 days) : 90% C.L.

PROSPECT [arXiv:1806.02784 and Neutrino 2018]

2 −

10

1 −

10 1

14

θ 2

2

sin

1 −

10 1 10 ]

2

[eV

41 2

m ∆

PROSPECT Exclusion, 95% CL PROSPECT Sensitivity, 95% CL SBL + Gallium Anomaly (RAA), 95% CL

SoLiD [arXiv:1806.02461 and Neutrino 2018]

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 15/25

SLIDE 16

0.90 0.92 0.94 0.96 0.98 1.00 0.85 0.90 0.95 1.00 1.05 1.10

r235 r239

Free r235, r239 2 4 6 8

∆χ2

2 4 6 8

∆χ2

MIνeDis 1σ 2σ 3σ

0.5 0.6 0.7 0.8 0.9 0.5 0.6 0.7 0.8 0.9

ηG ηS

2 4 6 8

∆χ2

2 4 6 8

∆χ2

MIνeDis 1σ 2σ 3σ

◮ Indication of r235 < 1. ◮ Likely small overestimate of the GALLEX and SAGE efficiencies.

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 16/25

SLIDE 17

LSND

[PRL 75 (1995) 2650; PRC 54 (1996) 2685; PRL 77 (1996) 3082; PRD 64 (2001) 112007]

¯ νµ → ¯ νe 20 MeV ≤ E ≤ 52.8 MeV ∆m2

SBL 0.1 eV2 ≫ ∆m2 ATM ◮ Well-known and pure source of ¯

νµ p

800 MeV

+ target → π+

at rest

− − − → µ+ + νµ µ+ − − − →

at rest e+ + νe + ¯

νµ ¯ νe + p → n + e+ Well-known detection process of ¯ νe

◮ ≈ 3.8σ excess ◮ But signal not seen by KARMEN at

L ≃ 18 m with the same method

[PRD 65 (2002) 112001]

L ≃ 30 m

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 17/25

SLIDE 18

MiniBooNE

¯ νµ → ¯ νe

[PRL 110 (2013) 161801]

LSND signal

νµ → νe

[arXiv:1805.12028]

LSND signal

◮ Purpose: check the LSND signal ◮ Different L ≃ 541 m ◮ Different 200 MeV ≤ E 3 GeV ◮ Similar L/E ⇐

⇒ oscillations

◮ No money, no Near Detector ◮ Agreement with LSND for

E 475 MeV

◮ Low-energy anomaly to be

checked by MicroBooNE

◮ Pragmatic Approach:

E > 475 MeV

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 18/25

SLIDE 19

All MiniBooNE Data

sin22ϑeµ ∆m41

2 [eV2]

10−4 10−3 10−2 10−1 1 10−2 10−1 1 10 102

Combined 1σ 2σ 3σ

2 σ LSND MiniBooNE

Pragmatic MiniBooNE

sin22ϑeµ ∆m41

2 [eV2]

10−4 10−3 10−2 10−1 1 10−2 10−1 1 10 102

Combined 1σ 2σ 3σ

2 σ LSND MiniBooNE

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 19/25

SLIDE 20

Pragmatic ¯ νµ → ¯ νe and νµ → νe Appearance

sin22ϑeµ ∆m41

2 [eV2]

10−4 10−3 10−2 10−1 1 10−2 10−1 1 10 102

Combined 1σ 2σ 3σ

2 σ LSND MiniBooNE KARMEN NOMAD BNL−E776 ICARUS OPERA

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 20/25

SLIDE 21

νµ and ¯ νµ Disappearance

sin22ϑµµ ∆m41

2 [eV2]

10−3 10−2 10−1 1 10−2 10−1 1 10 102

99% CL CDHSW (1984) CCFR (1984) ATM SB−MB νµ (2012) SB−MB νµ (2012) IceCube (2016) MINOS (2016) MINOS+ (2017)

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 21/25

SLIDE 22

3+1 Appearance-Disappearance Tension

νe DIS sin2 2ϑee ≃ 4|Ue4|2 νµ DIS sin2 2ϑµµ ≃ 4|Uµ4|2 νµ → νe APP sin2 2ϑeµ = 4|Ue4|2|Uµ4|2 ≃ 1

4 sin2 2ϑee sin2 2ϑµµ

sin22ϑeµ ∆m41

2 [eV2]

10−4 10−3 10−2 10−1 1 10 10−4 10−3 10−2 10−1 1 10

Global Fit 1σ 2σ 3σ 3σ Dis App

◮ νµ → νe is quadratically suppressed! ◮ Global Fit without MINOS+

χ2

PG/NDFPG = 7.8/2 ⇒ GoFPG = 2%

◮ Similar tension in 3+2, 3+3, . . . , 3+Ns

[CG, Zavanin, MPLA 31 (2015) 1650003]

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 22/25

SLIDE 23

New Bound from MINOS+

[arXiv:1710.06488] )

24

θ (

2

sin

4 −

10

3 −

10

2 −

10

1 −

10 1

)

2

(eV

41 2

m ∆

4 −

10

3 −

10

2 −

10

1 −

10 1 10

2

10

3

10

POT MINOS

20

10 × 10.56 POT MINOS+

20

10 × 5.80 mode

µ

ν MINOS & MINOS+ data 90% C.L. ) σ and 2 σ 90% C.L. Sensitivity (1

)

24

θ (

2

sin

4 −

10

3 −

10

2 −

10

1 −

10 1

)

2

(eV

41 2

m ∆

4 −

10

3 −

10

2 −

10

1 −

10 1 10

2

10

3

10

POT MINOS

20

10 × 10.56 POT MINOS+

20

10 × 5.80 mode

µ

ν data 90% C.L. MINOS & MINOS+ MINOS 90% C.L. IceCube 90% C.L. Super-K 90% C.L. CDHS 90% C.L. CCFR 90% C.L. SciBooNE + MiniBooNE 90% C.L. Gariazzo et al. (2016) 90% C.L.

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 23/25

SLIDE 24

Effects of MINOS+

sin22ϑµµ ∆m41

2 [eV2]

10−3 10−2 10−1 1 10

3σ Global Fit without MINOS+ MINOS+ Global Fit with MINOS+

sin22ϑeµ ∆m41

2 [eV2]

10−4 10−3 10−2 10−1 1 10 10−4 10−3 10−2 10−1 1 10

Global Fit 1σ 2σ 3σ 3σ Dis App

◮ χ2 PG/NDFPG = 18.3/2 ⇒ GoFPG = 0.01%

← Intolerable tension!

◮ The MINOS+ bound (if correct) disfavors the LSND ¯

νµ → ¯ νe signal.

[See also Dentler, Hernandez-Cabezudo, Kopp, Machado, Maltoni, Martinez-Soler, Schwetz, arXiv:1803.10661]

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 24/25

SLIDE 25

Conclusions

◮ Exciting model-independent indication of light sterile neutrinos at the eV

scale from the NEOS and DANSS experiments = ⇒ New Physics beyond the Standard Model!

◮ Agreement with the Reactor and Gallium Anomalies =

⇒ Needed revision of the 235U calculation and small decrease of the GALLEX and SAGE efficiencies.

◮ Can be checked in the near future by the reactor experiments STEREO,

Neutrino-4, SoLid, PROSPECT.

◮ Independent tests through effect of m4 in β-decay (KATRIN) and

ββ0ν-decay.

◮ The MINOS+ bound (if correct) disfavors the LSND ¯

νµ → ¯ νe signal.

• C. Giunti − Review on Sterile Neutrinos − SSP 2018 − 11 June 2018 − 25/25