Light sterile neutrinos: fact or fiction?
Transcript of 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
P. Huber – VT CNP – p. 2
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)
P. Huber – VT CNP – p. 3
LSND and MiniBooNE
P (ν̄µ → ν̄e) ≃ 0.003
P. Huber – VT CNP – p. 4
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?
P. Huber – VT CNP – p. 5
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
P. Huber – VT CNP – p. 6
Gallium anomaly
25% deficit of νe from radioactive sources at shortdistances
• Effect depends on nuclear matrix element
• R is a calibration constant
P. Huber – VT CNP – p. 7
Nuclear matrix elements
P. Huber – VT CNP – p. 8
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?
P. Huber – VT CNP – p. 9
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.
P. Huber – VT CNP – p. 10
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
P. Huber – VT CNP – p. 11
Neutrinos from fission
N=50 N=82
Z=50
235U
239Pu
stable
fission yield
8E-5 0.004 0.008
P. Huber – VT CNP – p. 12
β-branches
P. Huber – VT CNP – p. 13
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
P. Huber – VT CNP – p. 16
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!
P. Huber – VT CNP – p. 17
Same for allBased on JEFF fission yields and using ENSDFspin-parity assignments
P. Huber – VT CNP – p. 18
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?
P. Huber – VT CNP – p. 20
Latest result of Daya Bay
Daya Bay, 2017
Only an issue ifthe predictionof Pu239 in theHuber+Muellermodel is correct.Hayes et al., 2017
P. Huber – VT CNP – p. 21
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
P. Huber – VT CNP – p. 23
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
P. Huber – VT CNP – p. 24
NEOS vs Daya Bay
� �
�
� �
���� � �
�
�
� ���
�
�
�
��
�
�
�
����
�
���
�
�
��
�
���
�
��
����
���
�
�
�
�
��
���
�
��
��
�
�
��
�
�
�
�
�
�
��
�
�
�
�
� �
�
� �
���� � �
�
�
� ���
�
�
�
��
�
�
�
����
�
���
�
�
��
�
���
�
��
����
���
�
�
�
�
��
���
�
��
��
�
�
��
�
�
�
�
�
�
��
�
�
�
�
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.
P. Huber – VT CNP – p. 25
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.
P. Huber – VT CNP – p. 26
DANSS and NEOS
Dentler et al. 2017
This is a spectral effect independent of rate and shapepredictions!
P. Huber – VT CNP – p. 27
Reactor fit
Dentler et al. 2017
Closed 2σ contourseven without usinga flux prediction.
P. Huber – VT CNP – p. 28
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
P. Huber – VT CNP – p. 29
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.
P. Huber – VT CNP – p. 30
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!
P. Huber – VT CNP – p. 32
Questions?
P. Huber – VT CNP – p. 33
NuFact 2018
We invite you to NuFact 2018, August 2018, atVirginia Tech, Blacksburg, VA.
P. Huber – VT CNP – p. 34
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
P. Huber – VT CNP – p. 35