Sterile Neutrinos at the eV Scale Whence, Where, and Whither? - PowerPoint PPT Presentation

Sterile Neutrinos at the eV Scale Whence, Where, and Whither? Joachim Kopp (CERN & University of Mainz, Germany) KEK—KIAS—NCTS Theory Workshop | つくば市 | December 4—7, 2018

In this Talk The Neutrino Flavor Anomalies LSND & MiniBooNE: Anomalous ν μ → ν e oscillations? Reactor and Gallium Anomalies: Where are the missing ν e ? Sterile Neutrinos: Global Status Cosmological Constraints (and how to evade them) � 2

The Neutrino Flavor Anomalies A Hint for Sterile Neutrinos?

Anomalies in Short Baseline Oscillations � 4

Anomalies in Short Baseline Oscillations LSND / MiniBooNE: anomalous oscillations ν µ → ν e LSND 2001 MiniBooNE 2018 � 4

Anomalies in Short Baseline Oscillations LSND / MiniBooNE: anomalous oscillations ν µ → ν e Reactor & Gallium Experiments: anomalous disappearance ν e Mention et al., 1101.2755 DANSS Collaboration @ Neutrino 2018 � 4

Anomalies in Short Baseline Oscillations LSND / MiniBooNE: anomalous oscillations ν µ → ν e Reactor & Gallium Experiments: anomalous disappearance ν e Baselines too short for SM oscillations! Mention et al., 1101.2755 DANSS Collaboration @ Neutrino 2018 � 4

Sterile Neutrinos Definition: sterile neutrino = SM singlet fermion Very generic extension of SM can be leftover of extended gauge multiplet Useful phenomenological tool can explain ν masses (seesaw mechanism, m ~ TeV…M Pl ) can explain cosmic baryon asymmetry (leptogenesis, m ≫ 100 GeV) can explain dark matter (m ~ keV) can explain oscillation anomalies (m ~ eV) 
 Promote mixing matrix to 4 x 4, oscillation formula unchanged: X ⇥ � � ⇤ U ∗ α j U β j U α k U ∗ P α → β = − i E j − E k T β k exp j,k � 5

The Reactor Anomaly ν̅ e flux from nuclear reactors is ~ 3.5% (~ 3 σ ) below prediction ➟ oscillations of ν̅ e into sterile neutrinos ν̅ s ? Mueller et al. 1101.2663, Huber 1106.0687 � 6

The Reactor Anomaly ν̅ e flux from nuclear reactors is ~ 3.5% (~ 3 σ ) below prediction ➟ oscillations of ν̅ e into sterile neutrinos ν̅ s ? 2 = 0.44 eV 2 , sin 2 2 θ 14 = 0.13 Δ m 2 = 1.75 eV 2 , sin 2 2 θ 14 = 0.10 Δ m observed / no osc. expected 1.1 2 = 0.9 eV 2 , sin 2 2 θ 14 = 0.057 Δ m 1 Gosgen 0.9 Gosgen Bugey3 Bugey3,4 Krasn Rovno SRP Bugey3 Krasn Rovno, SRP Krasn Gosgen 0.8 ILL 0.7 10 100 distance from reactor [m] � 6

Predicting Reactor Neutrino Fluxes ν̅ e flux from nuclear reactors is ~ 3.5% (~ 3 σ ) below prediction ➟ oscillations of ν̅ e into sterile neutrinos ν̅ s ? Predicting reactor ν̅ e fluxes: Use measured β spectra from 235 U, 238 U, 239 Pu, 241 Pu fission Convert to ν̅ e spectrum For single β decay: E ν = Q — E e Reality: thousands of decay branches, many not known precisely Use (incomplete) information from nuclear data tables … … complemented by a fit to “effective decay branches” Mueller et al. 1101.2663, Huber 1106.0687 � 7

Corrections to Reactor Neutrino Fluxes ν̅ e flux from nuclear reactors is ~ 3.5% below prediction Important corrections ν̅ e Finite size of nucleus e L σ µ ν ν L ) W µ ν L ⊃ (¯ Weak magnetism Screening of nuclear charge: Z → Z eff Radiative corrections ( γ emission) Non-equilibrium effects in measured β spectra Neutron lifetime uncertainty Mueller et al. 1101.2663, Huber 1106.0687 � 8

Isotope-Dependent Fluxes � 9

Isotope-Dependent Fluxes Reactor fuel composition evolves with time (“burnup”) Daya Bay 1704.01082 � 9

Isotope-Dependent Fluxes Reactor fuel composition evolves with time (“burnup”) Effective fraction of 239 Pu fissions W th,r ¯ P 6 P ee,r f i,r ( t ) r =1 L 2 r E r ( t ) F i ( t ) = W th,r ¯ P 6 P ee,r Daya Bay 1704.01082 r =1 L 2 r E r ( t ) � 9

Isotope-Dependent Fluxes Reactor fuel composition evolves with time (“burnup”) Measure inverse β decay rate as function of F 239 Sterile Neutrino: same deficit for all isotopes 
 Flux Misprediction: isotope-dependent deficits Daya Bay 1704.01082 � 9

Sterile Neutrinos or Flux Uncertainty? Daya Bay 1704.01082 � 10

Sterile Neutrinos or Flux Uncertainty? 235 U prediction off 239 Pu prediction OK Daya Bay 1704.01082 � 10

Sterile Neutrinos or Flux Uncertainty? 235 U prediction off 239 Pu prediction OK Sterile Neutrino Models Daya Bay 1704.01082 � 10

Sterile Neutrinos or Flux Uncertainty? � 11


 
 Sterile Neutrinos or Flux Uncertainty? Full analysis: Compare fit with free 235 U, 238 U, 239 Pu, 241 Pu fluxes 
 to fit with fixed fluxes + ν s 
 Δχ 2 = 7.9 � 11


 
 Sterile Neutrinos or Flux Uncertainty? Full analysis: Compare fit with free 235 U, 238 U, 239 Pu, 241 Pu fluxes 
 to fit with fixed fluxes + ν s 
 Δχ 2 = 6.3 (with theoretical uncertainties) Dentler Hernández JK Maltoni Schwetz 1709.04294 � 11


 
 Sterile Neutrinos or Flux Uncertainty? Full analysis: Compare fit with free 235 U, 238 U, 239 Pu, 241 Pu fluxes 
 to fit with fixed fluxes + ν s 
 Δχ 2 = 6.3 (with theoretical uncertainties) But both hypothesis yield excellent goodness of fit Fluxes within errors + ν s : p = 0.18 Fluxes free : p = 0.73 Δχ 2 (sterile neutrino vs. free fluxes) : p = 0.007 Dentler Hernández JK Maltoni Schwetz 1709.04294 � 11

Caveats Daya Bay method assumes flux from each isotope is time and burnup-independent. � 12


 Caveats Non-Equilibrium Effects Non-Linear Isotopes Some relevant decays are Neutron capture 
 out of equilibrium 
 on fission products 90 Sr 90 Y t 1/2 =29 yrs t 1/2 =2.7 days Q=0.55 MeV Q=2.2 MeV 90 Zr Extra neutron flux/burnup Extra t -dependence 
 dependence in ν flux in ν flux Jaffke Huber 1510.08948, Huber Sharma, in preparation � 13

Improved Analysis Huber Sharma, in preparation � 14

Improved Analysis χ 2 ( Δχ 2 ) 1/2 Best Fit 5.8 Uncorrected Model 15.0 3 σ Corrected Model 8.5 1.6 σ Huber Sharma, in preparation � 14

Sterile Neutrinos Global Status

Global Fit to ν e and ν̅ e Disappearance 95 % , 99 % CL 10 1 2 dof All 2 [ eV 2 ] � e disapp 10 0 � m 41 All Reactors C12 G a l l i u m Solar 10 - 1 10 - 3 10 - 2 10 - 1 | U e4 2 Dentler Hernández JK Maltoni Schwetz 1709.04294 Dentler Hernández JK Machado Maltoni Martinez Schwetz, in preparation � 16

� ν μ → ν e appearance 99 % CL OPERA ( 2013 ) ICARUS ( 2014 ) 10 1 2 dof Mini - BooNE � NOMAD 2 [ eV 2 ] E776 + solar LSND 10 0 � m 41 Combined KARMEN MiniBooNE � 10 - 1 w / o DiF LSND Combined 10 - 3 10 - 2 10 - 1 sin 2 2 � � e Dentler Hernández JK Machado Maltoni Martinez Schwetz, in preparation � 17

� ν μ → ν e appearance 99 % CL OPERA ( 2013 ) ICARUS ( 2014 ) 10 1 2 dof Mini - BooNE � NOMAD 2 [ eV 2 ] E776 + solar LSND 10 0 � m 41 Global fit to ν e appearance data consistent. Combined KARMEN MiniBooNE � 10 - 1 w / o DiF LSND Combined 10 - 3 10 - 2 10 - 1 sin 2 2 � � e Dentler Hernández JK Machado Maltoni Martinez Schwetz, in preparation � 17


 
 
 
 
 
 
 Relation Between Oscillation Channels Oscillation channels are related: 
 P ν e → ν e ' 1 � 2 | U e 4 | 2 (1 � | U e 4 | 2 ) P ν µ → ν µ ' 1 � 2 | U µ 4 | 2 (1 � | U µ 4 | 2 ) P ν µ → ν e ' 2 | U e 4 | 2 | U µ 4 | 2 4 π E/ ∆ m 2 41 ⌧ L ⌧ 4 π E/ ∆ m 2 (for ) 31 Models can be over-constrained. � 18

Global Fit in 3+1 Model 99 % CL S 2 dof H D 10 1 C (-) / � � (-) �� e (-) � e Free Fixed 2 [ eV 2 ] 10 0 � m 41 MINOS / MINOS + M B d i s a p p 10 - 1 Null DC + SK results + IC combined 10 - 2 10 - 1 | U � 4 2 Dentler Hernández JK Machado Maltoni Martinez Schwetz, in preparation see also works by Collin Argüelles Conrad Shaevitz, e.g. 1607.00011, Gariazzo Giunti Laveder Li, e.g. 1703.00860 � 19

Global Fit in 3+1 Model Reactor + Gallium Anomalies, 99 % CL S 2 dof H LSND, MiniBooNE D 10 1 C (-) / � � (-) �� e (-) � e Free Fixed 2 [ eV 2 ] 10 0 � m 41 MINOS / MINOS + M B d i s a p p 10 - 1 Null DC + SK results + IC combined 10 - 2 10 - 1 | U � 4 2 Dentler Hernández JK Machado Maltoni Martinez Schwetz, in preparation see also works by Collin Argüelles Conrad Shaevitz, e.g. 1607.00011, Gariazzo Giunti Laveder Li, e.g. 1703.00860 � 19

Global Fit in 3+1 Model 99 % CL CDHS 2 dof 10 1 (-) / � � (-) �� e (-) � e Free Fixed 2 [ eV 2 ] 10 0 � m 41 MINOS / MINOS + MB disapp 10 - 1 Null DC + SK results + IC combined Dentler et al. 
 10 - 2 10 - 1 in preparation | U � 4 2 χ 2 / dof Δ χ 2 glob Δ χ 2 PG / dof p PG ν μ disapp 468.9 / 504 5.9 ν e app+disapp 628.6 / 537 17.5 Combined 1120.9 / 1109 23.4 / 2 8.3 × 10 -6 � 20

Global Fit in 3+1 Model 99 % CL CDHS 2 dof 10 1 (-) / � � (-) �� e (-) � e Free Fixed 2 [ eV 2 ] Parameter Goodness-of-Fit Test: 10 0 � m 41 Quantifies penalty for combining data sets MINOS / MINOS + MB disapp Maltoni Schwetz hep-ph/0304176 10 - 1 Null DC + SK results + IC combined Dentler et al. 
 10 - 2 10 - 1 in preparation | U � 4 2 χ 2 / dof Δ χ 2 glob Δ χ 2 PG / dof p PG ν μ disapp 468.9 / 504 5.9 ν e app+disapp 628.6 / 537 17.5 Combined 1120.9 / 1109 23.4 / 2 8.3 × 10 -6 � 20