light sterile neutrinos: the evidence jonathan link virginia tech
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Light Sterile Neutrinos: The Evidence Jonathan Link Virginia Tech Workshop on Neutrinos at the SNS Oak Ridge National Lab 5/2/12. Outline. Sterile Neutrinos in Theory and Phenomenology Evidence from Particle Physics Evidence from Cosmology Proposed Future Experiments. - PowerPoint PPT PresentationTRANSCRIPT
Light Sterile Neutrinos: The Evidence Light Sterile Neutrinos: The Evidence
Jonathan LinkJonathan Link
Virginia TechVirginia Tech
Workshop on Neutrinos at the SNS Workshop on Neutrinos at the SNS
Oak Ridge National Lab Oak Ridge National Lab
5/2/125/2/125/2/20125/2/2012Jonathan LinkJonathan Link
5/2/20125/2/2012Jonathan LinkJonathan Link
OutlineOutline
1. Sterile Neutrinos in Theory and Phenomenology
2. Evidence from Particle Physics
3. Evidence from Cosmology
4. Proposed Future Experiments
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Sterile NeutrinosSterile Neutrinos
A sterile neutrino is a lepton with no ordinary electroweak interaction except those induced by mixing.
Active neutrinos:
LEP Invisible Z0 Width is consistent with only three light active neutrinos
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ν3
ν2ν1
m22
m12
mas
s2
But there is evidence for 3 different m2 scales.
Atmospheric
Solar
ν3
ν2ν1
m22
m12
mas
s2
ν4
m32
Atmospheric
Solar
LSND
Sterile NeutrinosSterile Neutrinos
Three neutrinos allow only 2 independent Δm2 scales.
A sterile neutrino is a lepton with no ordinary electroweak interaction except those induced by mixing.
LSND LSND ννμμ→→ ν νee Appearance Appearance
Event Excess: 32.2 ±9.4 ±2.3
Stopped π+ beam 30 meters baseline The detector was downstream of the target.
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KARMEN KARMEN ννμμ→→ ν νee Appearance Search Appearance Search
Stopped π+ beam 18 meters baseline The detector was slightly behind the target.
15 candidate events agree with background expectation
Joint LSND & KARMEN analysis
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Bugey Bugey ννee Disappearance Disappearance
Reactor Neutrinos 15, 40 and 95 m baselines
Sensitivity from absolute rate and near/far comparisons
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Pee = Pes + Peμ + Peτ
Atmospheric
Sterile
ν1m1
2
ν3
ν2
m22
ν4
m32
Solar
Mixing with a Fourth, Mostly Sterile, Mass EigenstateMixing with a Fourth, Mostly Sterile, Mass Eigenstate
Ue42 Uμ4
2 Uτ42 Us4
2
Pμe
= sin2(1.27Δm32L/E)sin22θ4Ue4
2 Uμ42
The appearance probability:
The disappearance probability:
Comparing appearance (like LSND) and disappearance probabilities (like Bugey) requires some care…
If Ue4≈Uμ4 and Us4 ≈ 1 then Pee ≈ 2√Pμe
Pee ≈ Pes = 4Ue42 Us4
2 sin2(1.27Δm32L/E)
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Bugey Bugey ννee Disappearance Disappearance
Reactor Neutrinos 15, 40 and 95 m baselines
Sensitivity from absolute rate and near/far comparisons
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Assuming Ue4=Uμ4
MiniBooNE MiniBooNE ννμμ→→ ν νee Appearance Search Appearance Search
Found No Significant Excess Consistent with LSND
π+ decay in flight beam ~500 m baseline
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MiniBooNE MiniBooNE ννμμ→→ ν νee Appearance Search Appearance Searchπ- decay in flight beam ~500 m baseline
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ννμμ and and ννμμ Disappearance DisappearanceNeutrino and antineutrino disappearance rates should be equal
(Assuming CPT is conserved)
MiniBooNE and SciBooNE Two
Baseline Analysis
Neutrinos
Antineutrinos
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Gallium Anomaly (Gallium Anomaly (ννee Disappearance) Disappearance)The solar radiochemical detectors GALLEX and SAGE used intense EC sources (51Cr and 37Ar) to “calibrate” the νeGa cross section.
The average ratio of measurement to theory is
R=0.86±0.05
Or
R=0.76 .
Bahcall does not calculate a theory uncertainty.
The deficit may be due to sterile neutrino oscillations.
+0.09−0.08
(Bahcall)
(Haxton)
Giunti & Laveder
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Reactor AnomalyReactor AnomalyNew analyses (blue and red) of the reactor νe spectrum predict a 3% higher flux than the existing calculation (black).
HuberMeuller et al.
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Bugey RevisitedBugey RevisitedThe constraint from rate goes away.
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Cosmology and the Number of NeutrinosCosmology and the Number of Neutrinos
The energy density of neutrinos is proportional to the number of neutrino families, Neff :
The expansion rate of the radiation dominated era of the early universe depends on the density of relativistic particles.
This can be measured in:
• Large Scale Structure (LSS)
• Cosmic Microwave Background (CMB)
• Big-Bang Nucleosynthesis (BBN)
effN
Future Experiments: SourcesFuture Experiments: Sources
Intense radioactive sources (EC, fission fragments) plus low energy detectors to search for νe and νe disappearance.
Elastic Scattering: Borexino, SNO+Cr
Charged Current: LENS, Baksan, Ce-LAND, Borexino, Daya Bay
Neutral Current: RICOCHET
Most use existing detectors (low cost)
Potential for oscillometry (imaging the oscillation wave)
R&D needed on sources (especially in the U.S.)
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Future Experiments: ReactorsFuture Experiments: Reactors
Several ideas for new reactor experiments. Some, piggy-backing on safe guards measurements are under construction now.
Nucifer, SCRAAM, Stereo, PIK…
Need to be very close to the reactor core.
Small cores are advantageous.
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Future Experiments: Stopped Future Experiments: Stopped ππ Beams Beams
Direct test of LSND anomaly.
OscSNS: Improved LSND (Off beam axis, lower duty factor, gadolinium?)
LSND-Reloaded: Gd-loaded Super-K plus cyclotron. Possibility of oscillometry.
What if LSND is new physics but not oscillations? This may be the only approach that is sensitive.
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Future Experiments: Decay in Flight BeamsFuture Experiments: Decay in Flight Beams
MiniBooNE was a decay in flight experiment. Proposed experiment in this class include
MicroBooNE, BooNE, LArLAr NESSiE, νSTORM
Most of these are two detector experiments which will fix the greatest difficulty with MiniBooNE. With a muon decay beam, νSTORM may not need a near detector.
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Conclusions and PerspectivesConclusions and Perspectives
• There is a great deal of interest in latelyWorkshop on Beyond Three Family Neutrino Oscillations, LNGS, April 2011Short-Baseline Neutrino Workshop, Fermilab, May 2011Sterile Neutrinos at the Crossroads Workshop, Virginia Tech, Sept. 2011Future Short Baseline Neutrino Experiments −Needs & Options, Fermilab, March 2012Light Sterile Neutrinos: A White Paper, arXiv:1204.5379, April 2012
• There are many hints of sterile neutrinos in particle physics:LSND, MiniBooNE ν, Gallium, Reactor Flux
• There are many null or ambiguous results as well:KARMEN, Bugey, MiniBooNE ν, Accelerator Disappearance
• There are several proposals/concepts for new, hopefully definitive tests of the Δm ~ 1 eV2 sterile neutrino hypothesis.
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Conclusions and PerspectivesConclusions and Perspectives
The hints for light sterile neutrinos from particle physics and cosmology are certainly not definitive − individually or combined
But
They can’t just be ignored. This situation calls for further, definitive investigation.
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Supplemental Slides
Sterile Neutrinos at the Crossroads WorkshopSterile Neutrinos at the Crossroads Workshop
Workshop ObjectiveThe goal of this workshop was to bring together experts in the various sub-disciplines − such as nuclear and particle theory and experiment, cosmology, and neutrino phenomenology − in order to critically review the evidence for and against sterile neutrinos and to discuss the need or otherwise to pursue dedicated new experiments and possibly new strategies.
Virginia Tech, September 26-28, 2011
~60 participants, 28 talks and 9 poster with lots of time for discussion
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Sterile Neutrino White PaperSterile Neutrino White Paper
Outline:1. Theory and Motivation (editors Barenboim & Rodejohann)
2. Astrophysical Evidence (Abazajian & Wong)
3. Evidence from Oscillation Experiments (Koop & Louis)
4. Global Picture (Lasserre & Schwetz)
5. Requirements for Future Experiments (Fleming & Formaggio)
6. Appendix: Possible Future Experiments (Huber & Link)
Written from an international perspective for an audience including both the scientific community and funding agencies.
Visit http://cnp.phys.vt.edu/white_paper/
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