Status of Light Sterile Neutrinos Carlo Giunti INFN, Torino, Italy - - PowerPoint PPT Presentation

Status of Light Sterile Neutrinos Carlo Giunti

INFN, Torino, Italy

EPS-HEP2019 2019 European Physical Society Conference on High Energy Physics 10-17 July 2019, Ghent, Belgium

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 1/20

Short-Baseline Neutrino Oscillation Anomalies

Reactor Anomaly: ¯ νe → ¯ νx (∼ 3σ)

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

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

Gallium Anomaly: νe → νx (∼ 3σ)

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

LSND Anomaly: ¯ νµ → ¯ νe (∼ 4σ)

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 2/20

Efgective 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 ◮ ∆m2

SBL = ∆m2 41 ≃ ∆m2 42 ≃ ∆m2 43

◮ 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, Giunti, PRD 87, 113004 (2013) 113004]

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 3/20

Short-Baseline Reactor Neutrino Oscillations

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 − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 4/20

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% efgect on total fmux, but if it is an excess it increases the anomaly! ◮ No post-bump complete calculation

• f the neutrino fmuxes.

◮ Nominal Huber-Mueller fmux calculation uncertainty: ∼ 2.7%. ◮ Post-bump estimate of the fmux uncertainty due to unknown forbidden decays: ∼ 5%.

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

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 5/20

Reactor Fuel Evolution

◮ Reactor ¯ νe fmux produced by the β decays of the fjssion products of

235U 238U 239Pu 241Pu

◮ Efgective fjssion fractions: F235 F238 F239 F241 ◮ Cross section per fjssion (IBD yield): σf =

• k=235,238,239,241

Fk σf ,k

Burn-up (MWD/TU) 5000 10000 15000 20000 Fission fraction (%) 10 20 30 40 50 60 70 80 90 100 U

235

Pu

239

U

238

Pu

241

Others

0.24 0.26 0.28 0.30 0.32 0.34 0.36

F239

5.70 5.75 5.80 5.85 5.90 5.95 6.00 6.05

σf [10−43 cm2 / fission]

Best fit Average Model (Rescaled) Daya Bay

0.51 0.54 0.57 0.60 0.63

F235

Daya Bay

235

F 0.5 0.55 0.6 0.65 / fission]

2

cm

• 43

[10

f

y 5.7 5.8 5.9 6

Data Model (scaled by -6.0%) Best fit Identical spectra

239

F 0.25 0.3 0.35

RENO

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 6/20

0.26 0.28 0.30 0.32 0.34

239

F

5.7 5.8 5.9 6.0 6.1

f

σ

Daya Bay Data Daya Bay Fit RENO Data RENO Fit

2.5 − 2.0 − 1.5 − 1.0 −

239

/dF

f

σ d

1 2 3 4 5 6 7 8 9 10

f

σ

Daya Bay RENO Prediction

5.6 5.8 6.0 6.2 6.4

f

σ

1 2 3 4 5 6 7 8 9 10

2

χ Δ

[Giunti, Li, Littlejohn, Surukuchi, PRD 99 (2019) 073005, arXiv:1901.01807]

σf (F239) = ¯ σf + dσf dF239

• F239 − F 239
• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 7/20

F 239 σf / σf

HM

0.25 0.27 0.29 0.31 0.33 0.35 0.920 0.935 0.950 0.965 0.980

Daya Bay and RENO 235 239 235+239 OSC 235+OSC 239+OSC

235: r235 = 0.985 ± 0.015 χ2/NDF = 9.0/15 GoF = 88% 235+239:

• r235 = 0.923 ± 0.015

r239 = 0.975 ± 0.032 χ2/NDF = 8.7/14 GoF = 85%

σ235 [10−43 cm2/fission] σ239 [10−43 cm2/fission]

5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 3.5 4.0 4.5 5.0

Daya Bay RENO Combined 1σ 2σ 3σ

OSC: P¯

νe→¯ νe = 0.939 ± 0.024

χ2/NDF = 16.3/15 GoF = 37% 235+OSC: r235 = 0.938 ± 0.029 P¯

νe→¯ νe = 0.986 ± 0.022

χ2/NDF = 8.8/14 GoF = 85%

[Giunti, Li, Littlejohn, Surukuchi, arXiv:1901.01807]

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 8/20

◮ Daya Bay and RENO favor a suppression of the 235U fmux (235) over

• scillations (OSC).

◮ However, a better fjt is obtained with the hybrid model 235+OSC. ◮ Moreover, the addition of other reactor data favors oscillations or, better, 235U and/or 239U fmux suppression plus oscillations.

[Giunti, Ji, Laveder, Li, Littlejohn, JHEP 1710 (2017) 143, arXiv:1708.01133]

◮ Even if there are short-baseline neutrino oscillations, it is likely that the reactor antineutrino fmux calculations must be corrected (most likely the

235U fmux) to fjt:

• 1. The 5 MeV bump
• 2. The fuel evolution data

◮ The search for short-baseline neutrino oscillations needs model-independent information ⇑ ratios of spectra at difgerent distances

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 9/20

Reactor Spectral Ratios

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

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)

⋅ ⋅

|U e4|2 ∆m41

2 [eV2]

10−4 10−3 10−2 10−1 10−1 1 10

2σ NEOS DANSS−2018 NEOS+DANSS−2018 1σ 2σ 3σ

DANSS-2018

[PLB 787 (2018) 56, arXiv:1804.04046] 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

2018 model independent indication in favor of SBL oscillations NEOS: ∼ 1.7σ DANSS-2018: ∼ 2.7σ Combined: ∼ 3.5σ

[Gariazzo, Giunti, Laveder, Li, arXiv:1801.06467] [Dentler, Hernandez-Cabezudo, Kopp, Machado, Maltoni, Martinez-Soler, Schwetz, arXiv:1803.10661]

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 10/20

New DANSS results @ EPS-HEP 2019

Ratio of positron energy spectra at down and up detector positions (Full data set)

• The best 4ν point (ΔM2=0.35eV2, Sin2(2θ)=0.15, ∆Χ2 =7.8)

has CL of 1.8σ.

• Best point in old data (ΔM2=1.33 eV2) is also shown

ΔM2=0.35 eV2, Sin2(2θ)=0.15 ∆Χ2 =7.8 ΔM2=1.33 eV2, Sin2(2θ)=0.03 ∆Χ2 =4.3

Preliminary

[Danilov @ EPS-HEP 2019]

|U e4|2 ∆m41

2 [eV2] DANSS−2019 Best Fit Solar 2σ bound

10−4 10−3 10−2 10−1 10−1 1 10

2σ NEOS DANSS−2018 NEOS+DANSS−2018 1σ 2σ 3σ

◮ The DANSS-2019 best fjt has too large mixing. ◮ The agreement between NEOS and DANSS has diminished. ◮ Reactor indications in favor of SBL oscillations seem to be fadind away. ◮ We wait independent checks of PROSPECT, STEREO and SoLiD.

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 11/20

The Gallium Anomaly Revisited

[Kostensalo, Suhonen, Giunti, Srivastava, arXiv:1906.10980]

◮ New JUN45 shell-model calculation of the cross section of νe + 71Ga → 71Ge + e−

|U e4|2 ∆m41

2 [eV2] 90% CL Bahcall Haxton Frekers JUN45

10−3 10−2 10−1 10−1 1 10

|U e4|2 ∆m41

2 [eV2] Reactors 1σ 2σ 3σ

Gallium − JUN45 68.27% CL (1σ) 90.00% CL 95.45% CL (2σ) 99.00% CL 99.73% CL (3σ)

10−3 10−2 10−1 10−1 1 10

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 12/20

¯ νµ → ¯ νe and νµ → νe Appearance

sin22ϑeµ = 4|U e4|2|U µ4|2 ∆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 − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 13/20

νµ and ¯ νµ Disappearance

|U µ4|2 ∆m41

2 [eV2]

10−3 10−2 10−1 10−2 10−1 1 10 102

3σ CDHSW CCFR ATM SB−MB νµ SB−MB νµ IceCube DeepCore MINOS+ Combined [Gariazzo, Giunti, Ternes, in preparation]

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 14/20

Global 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 = 4|U e4|2|U µ4|2 ∆m41

2 [eV2]

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

Global Fit 1σ 2σ 3σ 3σ Dis App

◮ νµ → νe is quadratically suppressed! ◮ Global Fit: χ2/NDF = 831.7/797 GoF = 19% χ2

PG/NDFPG = 42.8/2

GoFPG = 5 × 10−10 ← ◮ Similar tension in 3 + 2, 3 + 3, . . . , 3 + Ns

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

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 15/20

Global 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 = 4|U e4|2|U µ4|2 ∆m41

2 [eV2]

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

Global Fit 1σ 2σ 3σ 3σ Dis App

◮ νµ → νe is quadratically suppressed! ◮ Global Fit: χ2/NDF = 831.7/797 GoF = 19% χ2

PG/NDFPG = 42.8/2

GoFPG = 5 × 10−10 ← ◮ Similar tension in 3 + 2, 3 + 3, . . . , 3 + Ns

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

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 16/20

Global Fit Without MiniBooNE

sin22ϑeµ = 4|U e4|2|U µ4|2 ∆m41

2 [eV2]

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

Global Fit 1σ 2σ 3σ 3σ Dis App

Without MiniBooNE

χ2/NDF = 768.9/763 GoF = 43% χ2

PG/NDFPG = 28.7/2

GoFPG = 6 × 10−7 ←

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 17/20

Global Fit Without LSND

sin22ϑeµ = 4|U e4|2|U µ4|2 ∆m41

2 [eV2]

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

Global Fit 1σ 2σ 3σ 3σ Dis App

Without LSND

χ2/NDF = 802.9/793 GoF = 40% χ2

PG/NDFPG = 22.1/2

GoFPG = 2 × 10−5 ←

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 18/20

Global Fit Without LSND and MiniBooNE

sin22ϑeµ = 4|U e4|2|U µ4|2 ∆m41

2 [eV2]

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

Global Fit 1σ 2σ 3σ 3σ Dis App

Without MiniBooNE and LSND

χ2/NDF = 727.4/759 GoF = 79% χ2

PG/NDFPG = 0/2

GoFPG = 1 ←

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 19/20

Conclusions

◮ Neutrinos can be powerful messengers of new physics beyond the SM as the existence of light sterile neutrinos indicated by the reactor, Gallium and LSND anomalies. ◮ Exciting 2018 model-independent indication of light sterile neutrinos at the eV scale from the NEOS and DANSS experiments in approximate agreement with the reactor and Gallium anomalies. ◮ 2019 DANSS data do not confjrm the 2018 indication and the reactor indications in favor of SBL oscillations seem to be fadind away. ◮ Important checks in the near future by the reactor experiments PROSPECT, STEREO, SoLid. (Neutrino-4?) ◮ Independent tests through the efgect of m4 in β-decay (KATRIN), electron-capture (ECHo, HOLMES) and ββ0ν-decay experiments. ◮ The MINOS+ bound (if correct) disfavors the LSND and MiniBooNE short-baseline νµ → νe signals. ◮ Status of Light Sterile Neutrinos? They do not seem to feel well.

• C. Giunti − Status of Light Sterile Neutrinos − EPS-HEP2019 − Ghent − 13 July 2019 − 20/20