light sterile neutrinos: fact or ﬁction?

Light sterile neutrinos:

fact or fiction?

Patrick Huber

Center for Neutrino Physics – Virginia Tech

IBS conference Dark World

KAIST Munji Campus, Daejon, Korea

October 30 – November 3, 2017

P. Huber – VT CNP – p. 1

Evidence in favor

• LSND ν̄µ → ν̄e

• MiniBooNE ν̄µ → ν̄e and νµ → νe

• T2K νe → νe• Gallium νe → νe• Reactors νe → νe


Disappearance and appearance

νµ → νe requires that the sterile neutrino mixes withboth νe and νµ

⇒ there must be effects in both νe → νe and νµ → νµ

Up to factors of 2, the energy averaged probabilitiesobey

Pµe . (1− Pµµ)(1− Pee)


LSND and MiniBooNE

P (ν̄µ → ν̄e) ≃ 0.003


Fermilab SBN

Reco. Energy (GeV)0.5 1 1.5 2 2.5 3

Eve

nts

/ GeV

0

500

1000

1500

2000

2500 ICARUS-T600, 600m = 0.0014)eµθ 22, sin 2 = 1.6 eV2m∆Signal: (

Statistical Uncertainty OnlyNominal, 6.6e20 POT

eν → µ

eν → +K

eν → 0K

γNC Single

CCµνDirt

Cosmics

Figure courtesy D. Schmitz and C. Adams

Signal to noise not so different from LSND. . . will anear detector of completely different design help?


JSNS2

Pion decay at restat JSNS, Gd-dopedscintillator.

JSNS2, 2017

Direct test of the LSND result → should have beeddone 20 years ago!

see talk by Soo-Bong Kim


Gallium anomaly

25% deficit of νe from radioactive sources at shortdistances

• Effect depends on nuclear matrix element

• R is a calibration constant


Nuclear matrix elements


The reactor anomaly

Distance (m)10

210

310

0.6

0.8

1.0

1.2

Previous data

Daya Bay

World Average

Exp. Unc.σ1-

Flux Unc.σ1-

Data

/ P

red

ictio

n

Previous average

R = 0.943 +- 0.008 (exp.)

Daya Bay’s reactor flux

previous short baseline

Daya Bay R = 0.947 ± 0.022

Daya Bay, 2014

Mueller et al., 2011, 2012 – where are all theneutrinos gone?


Contributors to the anomaly

6% deficit of ν̄e from nuclear reactors at shortdistances

• 3% increase in reactor neutrino fluxes

• decrease in neutron lifetime

• inclusion of long-lived isotopes (non-equilibriumcorrection)

The effects is therefore only partially due to the fluxes,but the error budget is clearly dominated by the fluxes.


Neutron lifetime

range used in past reactor analyses

PDG 2012

æ

æ

æà

à

à

à

à

à

ìì

lifetime data from Wietfieldt & Greene, Rev. Mod. Phys. 83 H2011L 1173

Mention

etal.

1985 1990 1995 2000 2005 2010 2015860

870

880

890

900

910

-2

-1

0

1

2

3

year

neut

ron

lifet

ime@sD

IBD

cros

sse

ctio

nch

ange@%D


Neutrinos from fission

N=50 N=82

Z=50

235U

239Pu

stable

fission yield

8E-5 0.004 0.008


β-branches


β-spectrum from fission

235U foil inside the HighFlux Reactor at ILL

Electron spectroscopywith a magnetic spec-trometer

Same method used for239Pu and 241Pu

For 238U recent measure-ment by Haag et al., 2013

Schreckenbach, et al. 1985.P. Huber – VT CNP – p. 14

Virtual branches

æ æ æ æ æ

7.0 7.2 7.4 7.6 7.8 8.0 8.210-6

10-5

10-4

10-3

10-2

Ee @MeVD

coun

tspe

rbi

n

E0=9.16MeV, Η=0.115

æ

æ

æ

æ

æ

7.0 7.2 7.4 7.6 7.8 8.0 8.210-6

10-5

10-4

10-3

10-2

Ee @MeVDco

unts

per

bin

E0=8.09MeV, Η=0.204

æ

æ

æ

æ

æ

7.0 7.2 7.4 7.6 7.8 8.0 8.210-6

10-5

10-4

10-3

10-2

Ee @MeVD

coun

tspe

rbi

n

E0=7.82MeV, Η=0.122

1 – fit an allowed β-spectrum with free normalization η and

endpoint energy E0 the last s data points

2 – delete the last s data points

3 – subtract the fitted spectrum from the data

4 – goto 1

Invert each virtual branch using energy conservation into a

neutrino spectrum and add them all. e.g. Vogel, 2007P. Huber – VT CNP – p. 15

Reactor antineutrino fluxes

ILL inversionsimple Β-shape

our result1101.2663

2 3 4 5 6 7 8-0.05

0.00

0.05

0.10

0.15

EΝ @MeVD

HΦ-Φ

ILLL�Φ

ILL

Shift with respect to ILL results, due to

a) different effective nuclear charge distributionb) branch-by-branch application of shape corrections


Forbidden decays

ΡpHrL

ΡnHrL

ΨHrL

EΒ=10MeV

A=140

l=0

l=1

l=2

0 5 10 15 20

r @fmD

e,ν̄ final state can forma singlet or triplet spinstate J=0 or J=1

Allowed:s-wave emission (l = 0)

Forbidden:p-wave emission (l = 1)or l > 1

Significant dependence on nuclear structure inforbidden decays→ large uncertainties!


Same for allBased on JEFF fission yields and using ENSDFspin-parity assignments


Look at past dataa Experiment fa

235fa

238fa

239fa

241R

expa,SH

σexpa

[%] σcora

[%] La [m]

1 Bugey-4 0.538 0.078 0.328 0.056 0.932 1.4 1.4 15

2 Rovno91 0.606 0.074 0.277 0.043 0.930 2.8 1.8 18

3 Rovno88-1I 0.607 0.074 0.277 0.042 0.907 6.4 3.8 18

4 Rovno88-2I 0.603 0.076 0.276 0.045 0.938 6.4 3.8 18

5 Rovno88-1S 0.606 0.074 0.277 0.043 0.962 7.3 3.8 18

6 Rovno88-2S 0.557 0.076 0.313 0.054 0.949 7.3 3.8 25

7 Rovno88-3S 0.606 0.074 0.274 0.046 0.928 6.8 3.8 18

8 Bugey-3-15 0.538 0.078 0.328 0.056 0.936 4.2 4.1 15

9 Bugey-3-40 0.538 0.078 0.328 0.056 0.942 4.3 4.1 40

10 Bugey-3-95 0.538 0.078 0.328 0.056 0.867 15.2 4.1 95

11 Gosgen-38 0.619 0.067 0.272 0.042 0.955 5.4 3.8 37.9

12 Gosgen-46 0.584 0.068 0.298 0.050 0.981 5.4 3.8 45.9

13 Gosgen-65 0.543 0.070 0.329 0.058 0.915 6.7 3.8 64.7

14 ILL 1 0 0 0 0.792 9.1 8.0 8.76

15 Krasnoyarsk87-33 1 0 0 0 0.925 5.0 4.8 32.8

16 Krasnoyarsk87-92 1 0 0 0 0.942 20.4 4.8 92.3

17 Krasnoyarsk94-57 1 0 0 0 0.936 4.2 2.5 57

18 Krasnoyarsk99-34 1 0 0 0 0.946 3.0 2.5 34

19 SRP-18 1 0 0 0 0.941 2.8 0.0 18.2

20 SRP-24 1 0 0 0 1.006 2.9 0.0 23.8

21 Nucifer 0.926 0.061 0.008 0.005 1.014 10.7 0.0 7.2

22 Chooz 0.496 0.087 0.351 0.066 0.996 3.2 0.0 ≈ 1000

23 Palo Verde 0.600 0.070 0.270 0.060 0.997 5.4 0.0 ≈ 800

24 Daya Bay 0.561 0.076 0.307 0.056 0.946 2.0 0.0 ≈ 550

25 RENO 0.569 0.073 0.301 0.056 0.946 2.1 0.0 ≈ 410

26 Double Chooz 0.511 0.087 0.340 0.062 0.935 1.4 0.0 ≈ 415

Giunti, 2016P. Huber – VT CNP – p. 19

What does this tell us?

Giunti, 2016

Is U235 odd?Are the error bars for U235 just smaller?


Latest result of Daya Bay

Daya Bay, 2017

Only an issue ifthe predictionof Pu239 in theHuber+Muellermodel is correct.Hayes et al., 2017


The 5 MeV bump

•

•

•

Seen by all three reactor experiments

Tracks reactor power

Seems independent of burn-upP. Huber – VT CNP – p. 22

Recent neutrino measurements

In Daya Bay, RENO and Double Chooz, the distanceis such that all sterile oscillations are averaged away –no confusion between nuclear physics and newphysics

The statistics in the Daya Bay near detectors is around1 million events

In combination, this should provide a good test of ourability to compute reactor fluxes


NEOSE

vents

/day/1

00 k

eV

20

40

60 Data signal (ON-OFF)

Data background (OFF)

H-M (flux uncertainty)

err)σH-M + excess fit (1

Full uncertainty

Prompt Energy [MeV]2 3 4 5 6 7

Ratio to P

redic

tion

0.9

1

1.1

5 MeV excessNEOS Preliminary

Y. Oh, ICHEP 2016

24m from a large core(power reactor), con-firms bump


NEOS vs Daya Bay

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1 2 3 4 5 6 70.95

1.00

1.05

1.10

1.15

Eprompt [MeV]

R

1 2 3 4 5 6 7

0.95

1.00

1.05

Eprompt [MeV]R

NE

OS/R

Daya

Bay

Huber, 2017

There is more U235 in NEOS, since core is fresh ⇒

3− 4 σ evidence against Pu as sole source of bump,but equal bump size is still allowed at better than 2 σ.


NEOS and sterile neutrinos

adapted from NEOS, 2016

NEOS reports a limit,but their best fit oc-curs at sin2 2θ = 0.05and ∆m2 = 1.73 eV2

with a χ2 value6.5 belowthe no-oscillation hy-pothesis.

DANSS has a similar result.


DANSS and NEOS

Dentler et al. 2017

This is a spectral effect independent of rate and shapepredictions!


Reactor fit

Dentler et al. 2017

Closed 2σ contourseven without usinga flux prediction.


Global fit

sin22ϑeµ

∆m

412 [e

V2]

10−4

10−3

10−2

10−1

1

10

+

+

PrGlo17

1σ

2σ

3σ

3σ

App

Dis

(a)sin

22ϑee

∆m

412 [e

V2]

10−2

10−1

1

10−1

1

10

+

PrGlo17

1σ

2σ

3σ

3σ

νe Dis

Dis

(b)sin

22ϑµµ

∆m

412 [e

V2]

10−2

10−1

1

10−1

1

10

+

PrGlo17

1σ

2σ

3σ

3σ

νµ Dis

Dis

(c)

Gariazzo et al., 2017


Finding a sterile neutrino

All pieces of evidence have in common that they areless than 5σ effects and they may be all due to theextraordinary difficulty of performing neutrinoexperiments, if not:

• N sterile neutrinos are the simplest explanation

• Tension with null results in disappearanceremains

Due to their special nature as SM gauge singletssterile neutrinos are strong candidates for being aportal to a hidden sector – significant experimentalactivity.


MiniBooNE reloaded?

(−)νe →

(−)νe

sin22ϑee

∆m

412

[e

V2]

10−2

10−1

1

10−1

1

10

+

KATRIN − 2σ

CeSOX (95% CL)

BEST (95% CL)

IsoDAR@KamLAND (5yr, 3σ)

IsoDAR@C−ADS (5yr, 3σ)

DANSS (1yr, 95% CL)

NEOS (0.5yr, 95% CL)

Neutrino−4 (1yr, 95% CL)

PROSPECT phase 1 (3yr, 3σ)

PROSPECT phase 2 (3yr, 3σ)

SoLiD phase 1 (1yr, 95% CL)

SoLiD phase 2 (3yr, 3σ)

STEREO (1yr, 95% CL)

(−)νµ →

(−)νe

sin22ϑeµ

∆m

412 [e

V2]

10−4

10−3

10−2

10−1

1

10

+

3+1 PrGLO

1σ

2σ

3σ

SBN (3yr, 3σ)nuPRISM (3σ)

JSNS2 (3σ)

(−)νµ →

(−)νµ

sin22ϑµµ

∆m

412

[e

V2]

10−2

10−1

1

10−1

1

10

+

3+1 PrGLO

1σ

2σ

3σ

SBN (3yr, 3σ)KPipe (3yr, 3σ)

Giunti, Neutrino 2016

. . . and that assumes all is going according to plan!P. Huber – VT CNP – p. 31

Summary

Tension in global fits

• Maybe more complicated than sterile neutrino

• And/or not all data is right

• Lots of nuclear physics uncertainties

With NEOS and DANSS we have a positive indicationfrom reactors independent of flux predictions.

In combination, light sterile neutrinos are one of thebest cases for New Physics, anywhere!


Questions?


NuFact 2018

We invite you to NuFact 2018, August 2018, atVirginia Tech, Blacksburg, VA.


The Department of Physics at Virginia Tech invitesapplications for a tenure-track faculty position inParticle Physics Phenomenology with a focus onneutrinos and dark matter.

Email: [email protected]: +1 (540) 231 8727URL: http://listings.jobs.vt.edu/postings/79786


light sterile neutrinos: fact or ﬁction?

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