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H. Ray, University of Florida 1
MiniBooNE and the Hunt for Low Mass Sterile Neutrinos
H. Ray, University of Florida 2
Intriguing Mysteries• Need a dark matter candidate
• What about dark radiation? (2σ)– Excess relativistic energy density at decoupling
• SM has no way for νs to acquire mass
• Anomalous results from neutrino sector– Short baseline (SBL) oscillation appearance expt. excesses (2.8 –
3.8σ)– Reactor neutrino flux deficit (3σ)– Radioactive source (Ga) deficit (2.7 – 3.1σ)– IceCube flux deficit due to observed GRBs (3.7x lower)
H. Ray, University of Florida 3
Not One-Stop Shopping!
Sterile mass Allow ν to acquire mass
Dark Rad, SBL,
Reactor, Ga
Dark matter candidate
Find via a direct search
100 – 160 GeV YES NO NO NO
20 – 30 GeV YES NO NO YES
keV - GeV YES NO YES YES
eV YES YES NO YES
Gnineko, Gorbunov, Shaposhnikov, arXiv:1301.5516
H. Ray, University of Florida 4
Not All Compatible!
• Short baseline oscillation expt. excesses: ~1 eV• Reactor + Ga deficits: ~1 eV• Cosmology dark radiation candidate: ~1eV
• ex:– SBL compatible with CMB in 3+1, 3+2
– Incompatible with cosmological mass constraints from CMB, Large Scale Structure (sum of all ν masses < 0.3 – 0.6 eV)
– Can be compatible with LSS if include initial lepton asymmetry
Riemer-Sørensen, Parkinson, Davis, arXiv:1301.7102
H. Ray, University of Florida 5
What to Do?
• Propose experiments to further explore each anomaly
• Expts. to perform more precise measurements and searches for eV scale sterile neutrinos in reactors, radioactive decay, and SBL experiments
• My focus: SBL appearance results and prospects for the future
H. Ray 6
SBL Anomalies: LSND• 800 MeV proton beam + H20
target, copper beam stop
• 167 ton tank, liquid scintillator, 25% PMT coverage
• E ~20-50 MeV• L ~25-35 meters
• anti-e + p e+ + n – n + p d + (2.2 MeV)
H. Ray, University of Florida 7
SBL Anomalies: LSND
• LSND observed excess of anti-νe in an anti-νμ beam
• Excess: 87.9 ± 22.4 ± 6.0 (3.8σ)Phys. Rev. Lett. 77:3082-3085 (1996)Phys. Rev. C 58:2489-2511 (1998)Phys. Rev. D 64, 112007 (2001)
Fit to oscillation hypothesis
Backgrounds Posc = sin22θ sin2 1.27 Δm2 L
E
Δm2 = 1.2 eV2
sin22θ = 0.003
H. Ray, University of Florida 8
MiniBooNE vs LSNDLSND• (anti) Neutrino beam from
accelerator (DAR, average Eν 35 MeV)
• νμ too low E to make μ or π
• Proton beam too low E to make K
MiniBooNE• Neutrino beam from accelerator
(DIF, average Eν 800 MeV)
• Detector placed at 500 m from neutrino beam creation point, preserve LSND L/E
• New backgrounds: νμ CCQE and NC π0 mis-id for oscillation search
• New backgrounds: intrinsic νe from K decay (0.5% of p make K)
H. Ray, University of Florida 9
SBL Anomalies: MiniBooNE• 2.8σ antineutrino mode• 3.4σ neutrino mode• 3.8σ combined excess
– All in 200 – 1250 MeV range• 7σ stat – so not a statistical
fluctuation!
• Antineutrino excess consistent with LSND
• Neutrino excess not so much
• All backgrounds fully constrained • Need some new anomalous
background process to explain low energy excess, if not invoking a sterile neutrino explanation
Phys.Rev. Lett. 110, (2013) 16801
11.27 x 1020 POT
6.5 x 1020 POT
H. Ray, University of Florida 10
SBL Anomalies: Summary
Antonello, et al. arXiv:1307.4699
Δm2 = 3.14 eV2
sin22θ = 0.002Δm2 = 0.043 eV2
sin22θ = 0.88
H. Ray, University of Florida 11
Resolving the SBL Mystery
• Need definitive experiments – no more carving out small portions of the allowed sterile neutrino phase space– No longer good enough to see an excess or deficit – need to see
those wiggles!– Need to see wiggles as a function of energy!
• Need them to be cost-effective• Preferably short-term, to use as input to longer-term
projects
12
Proposed Experiments
H. Ray, University of Florida
de Gouvea et al, arXiv:1310.4340
RUNNING• MicroBooNE
• MINOS+
PROPOSED• ICARUS /
NESSIE
• J-PARC
• LAr1-ND / LAr1
• MiniBooNE+
• nuSTORM
• OscSNS
H. Ray, University of Florida 13
MiniBooNE Low-E Excess
• Largest backgrounds in region of excess are muon neutrino Neutral Current – mis-ID neutral pions and gammas that look identical to e+/e- in our detector
H. Ray, University of Florida 14
MiniBooNE Low-E Backgrounds
• Both NC backgrounds are constrained by in-situ measurements
• NC π0 directly measured• NC γ (radiative Δ decay) constrained to NC π0
• Also, recent theoretical calculations agree with MBPhys. Rev. D 81 (2010) 013005
H. Ray, University of Florida 15
MiniBooNE Low-E Backgrounds
• Both NC backgrounds are constrained by in-situ measurements
• NC π0 directly measured• NC γ (radiative Δ decay) constrained to NC π0
• Also, recent theoretical calculations agree with MBPhys. Rev. D 81 (2010) 013005
H. Ray, University of Florida 16
MiniBooNE Low-E Excess• Photons or electrons?
MicroBooNE MiniBooNE+
H. Ray, University of Florida 17
Booster Neutrino Beam at FNAL
dirt
target and horn(174 kA)
π+
π-
K+
K0
✶
✶
μ+
✶
decay region(50 m)
oscillations?
FNAL booster(8 GeV protons)
Neutrinos from pions decaying in flightMean neutrino E ~500 MeV
H. Ray, University of Florida 18
MicroBooNE
• 170 ton LAr TPC, ~450 m from neutrino creation point• Beautiful separation between electrons and photons
• Different target nucleus from MiniBooNE• Lower event rates – same POT exposure as MB ν dataset means only a few
10s of events• Has less self-shielding b/c smaller, may be more prone to dirt backgrounds
• Will begin collecting data ~this summer• Run for 3 years, 2.2e20 POT / year, neutrinos only
1 GeV electron shower 1 GeV π0 decay
H. Ray, University of Florida 19
MiniBooNE+• Add scintillator to MiniBooNE to enable
reconstruction of 2.2 MeV neutron-capture photons
• Re-run neutrino mode oscillation search
• Neutron-capture enables separation of CC oscillation events from NC backgrounds– CC: e + n e- + p
• 1-10% of all interactions will produce a neutron
– NC: μ + 12C Δ or π0 + p or n • equal chances of getting n or p• n + p d + 2.2 MeV
Reconstructed vs True Eν, Signal
Reconstructed vs True Eν, Backgrounds
arXiv 1310.0076
H. Ray, University of Florida 20
MiniBooNE+• Need to know the (1-10%) vs 50% very well for this
analysis!
• These numbers come from previous data/models
• Will measure in MB+
• Can measure n fraction in νμ CC events (not the oscillation channel)
• Can measure n fraction in pristine NC π0 events
H. Ray, University of Florida 21
MiniBooNE+• Same as previous analysis, same
excess
• Require n-capture events– Red: if excess is truly due to CC νe
events, excess disappears– Blue: if excess is truly due to a NC
process (ie not oscillations), excess remains
• Yields 3.5σ NC/CC separation for this test, for combined 5σ MB excess
H. Ray, University of Florida 22
MiniBooNE+ and MicroBooNE• Complementary Effort• MicroBooNE: use photon/electron separation • MB+: use nucleons (neutrons), no energy threshold
• MicroBooNE: precision tracking, low event rates• MB+: Cerenkov/calormetric reconstruction, higher event rates
• MB+: larger fiducial volume, concurrent running may help with dirt backgrounds
• Important to keep 800 ton MB (CH2) running in the BNB as the event rates will be higher than any of the new or proposed LAr devices. Very important to understand any changes in beam.
H. Ray, University of Florida 23
SBL Anomalies
MINOS+ LAr1ICARUS
OscSNS
nuSTORM
J-PARC
LSND, MB ((anti)νμ (anti)νe, (anti)νe app)sensitive to combo of θ14 and θ24
Reactors (νe disappearance)sensitive to θ14
MINOS+ (νμ or anti-νμ CC disappearance) sensitive to θ24, little sensitivity to
θ14
H. Ray, University of Florida 24
Liquid Argon At Fermilab• Uses MiniBooNE’s beamline
• microBooNE can distinguish electrons from photons
• need 2nd detector to tell if the excess occurs at a distance or is intrinsic to the beam
• microBooNE won’t collect anti-ν data because of their smaller size– lower xsec means almost no events or too long to run
H. Ray, University of Florida 25
LAr1-ND
C. Adams, et al., arXiv:1309.7987
• 100 m = in existing SciBooNE enclosure
• 40 ton fiducial volume LArTPC
• 4.9 m length, along the beam direction (7 m wide, ~11.5 m high)
• muon detector downstream
• Use as prototype development for LBNE technology
• 1 kton LArTPC at 700 m
• Run for last year of microBooNE’s run, collect 2.2e20 POT
• Total run time will have 48 events in microB, 310 in LAr1-ND, assuming MB ν mode excess, and that the excess is not L dependent (vs MB’s 129)
H. Ray, University of Florida 26
LAr1-ND
4σ coverage of best fit point around 1 eV2, with full microBooNE data set and 1 year of LAr1-ND running
C. Adams, et al., arXiv:1309.7987
H. Ray, University of Florida 27
ICARUS at FNAL
• 2 detectors, one at ~150 m and one at 700 m– T150 = 200 tons of Ar (100 ton fiducial)– T600 = 760 tons of Ar (430 ton fiducial)– Can’t use SciBooNE Hall – need a new hole in ground
• Near = larger mass than LAr1-ND• Far = less mass than LAr1, plus B field (1T)
• Need 2 years from funding agency green-light to upgrade, then move to FNAL– Thermal shields, external insulation, pmts photo-detectors, B
fieldarXiv:1312.7252
H. Ray, University of Florida 28
ICARUS at FNAL
Neutrino Run6.6e20 POT
Anti-Neutrino Run +B
field11e20
POT
H. Ray, University of Florida 29
NuMI Neutrino Beam at FNAL
• Movable target and magnetic focusing horn– Tunable neutrino beam energy– Run in neutrino, anti-neutrino mode
Graphite target
H. Ray, University of Florida 30
MINOS+
• Long baseline experiment• L/E ~500 km/GeV (atm. Δm2)
• 2 detectors: near & far• Magnetized, tracking sampling calorimeters
• Measure Δm223, sin2(2θ23) for ν, anti-ν
Graphite target
H. Ray, University of Florida 31
MINOS+• Runs MINOS near and far detectors in the
NuMI medium energy configuration– 3 yrs, starting 2013
• CC disappearance between both detectors• Exploring odd dip for MINOS• NC events for sterile search (θ34)
Green: excluded by νμ disappearanceBlue: excluded by NC disappearance
MINOS+ Fermilab Proposal 1016
H. Ray, University of Florida
OscSNS
32
- absorbed by target
+ DARMono-Energetic!= 29.8 MeV
E range up to 52.8 MeV
• Spallation Neutron Source at Oak Ridge
• ~1 GeV protons+Hg target (1.4 MW)
• Free source of neutrinos
H. Ray, University of Florida 33
OscSNS Detector• Homogeneous liquid scintillator detector
– Mineral oil + b-PBD– 8 m diameter x 20.5 m length– ~800 tons, 25% PMT coverage
– Flexible arm deployment system for 1 – 50 MeV
calibration sources – 16N, 8Li, 252Cf
• 60 m in the backward direction, ~150 degrees from incident proton beam
Proton beam
OscSNS Detector HallarXiv:1307.7097
H. Ray, University of Florida 34
OscSNS nm -> ne Experiment vs LSND
• More Detector Mass (x5)
• Higher Intensity Neutrino Source (x2)
• Lower Duty Factor (x1000) (less cosmic background)
• Separation of nm & ne / anti-nm fluxes with timing
• Negligible DIF Background (backward direction)
• Lower Neutrino Background (~x2) (60m vs 30m)
• For LSND parameters, expect ~100-200 ne oscillation events & ~50 background events per year!
(Assuming Dm2 < 1 eV2)
H. Ray, University of Florida 35
Oscillation Goals
• anti-nm -> anti-ne appearance
• ne -> ns disappearance
• nm -> ns disappearance
• nall -> ns disappearance
H. Ray, University of Florida
Appearance Sensitivity
36
anti-nm anti-ne appearance sensitivity for 1 & 3 years of running:
anti-ne p e+ n; n p d g (2.2 MeV)
LSND & KARMENAllowed
LSND & KARMENAllowed
CONTINUOUS!
Already at 5σ!
50% detector efficiency, ~85% Ee cut efficiency, oscillation probability of 0.26%
H. Ray, University of Florida 37
Appearance Sensitivity
Assuming 5y of data & sin22q = 0.005, Dm2=1 eV2Assuming 5y of data & sin22q = 0.005, Dm2=4 eV2
L/E (m/MeV) L/E (m/MeV)
Statistical errors, 20% bgd
P(
n m ->
n e )
CONTINUOUS!50% detector efficiency, ~85% Ee cut efficiency, oscillation probability of 0.26%
H. Ray, University of Florida 38
Disappearance Sensitivity
ne C e- Ngs , Ngs Cgs e+ ne
Assuming 5y of data & sin22q = 0.15, Dm2 = 1 eV2 Assuming 5y of data & sin22q = 0.15, Dm2 = 4 eV2
L/E (m/MeV) L/E (m/MeV)
P(
n e ->
n s )
50% detector efficiency
Statistical errors, 1% bgdCONTINUOUS!
H. Ray, University of Florida
J-PARC Neutrino Beamline• Spallation Neutron Source at J-PARC
• Muons DAR to produce neutrinos
• Primarily μ+ e+ anti-νμ νe
• 50 ton fiducial mass liquid scintillator detector at 17 m
• Use CCQE appearance analysis (anti-νμ anti-νe)
• Use νe CC disappearance
• Above ground, may have issues with neutron backgrounds
4 years operation
Blue = 5σ CLGreen = 3σ CL
T. Maruyama et al., arXiv:1310.1437
H. Ray, University of Florida 40
Sensitivitiesνμ νe, νe νμ appearance searches
neutrino and anti-neutrino modes
App only fit + LBL reactors, Kopp, Machado, Maltoni, Schwetz, arXiv:1303.3011
Global fit, Giunti, Laveder, Li, Long, arXiv:1308.5288
• ICARUS curve is for CERN, not FNAL
• Difference in opinion of how to do fits
de Gouvea et al, arXiv:1310.4340
Abazajiana, et al. arXiv:1204.4219
H. Ray, University of Florida 41
Event Rates
LAr1-ND100 m
ICARUS150 m, E < 5 GeV
ICARUS700 m, E < 5
GeV
MiniBooNE200 to 1250 MeV
OscSNS J-PARC
νμ CC Inclusive(anti-νμ)
2,500,000(291,000)
387,000(56,900)
νe CC Inclusive(anti-νe)
26,200(1,780)
4,460(312)
νμ νe
app (1.15 eV2, 1.5e-3)
310 signal322 bgd
400, 380 signal 2,520, 1860 bgd(E < 5 GeV, 2 GeV)
233 sig (expect)162 sig (obs)
790 bgd
anti-νe p e+ n app (1.2 eV2, 3e-3)
100 sig (expect) 78 sig (obs)
400 bgd
480 signal168 bgd
337 signal494 bgd
νe + 12C e- 12Ngs
dis9412 signal
96 bgd22,934
2.2e20 POT (1 yr, full run)
200 – 475 MeV
Neutrino: 6.6e20 POT (3 yr full run)Anti-neutrino: 11e20 POT (5 yr full run)
12e22 POT(4 yrs, full run)
10.96e23 POT(4 yrs)same as ICARUS
H. Ray, University of Florida 42
Cost Estimates
de Gouvea et al, arXiv:1310.4340
J-PARC μ-DAR anti-νμ anti-νe app. J-PARC small (~<5 M) Same target nucleon
as LSND, MB
Shorter-term
H. Ray, University of Florida 43
Summary and Conclusions• Many outstanding mysteries in the neutrino sector
• Even mysteries that indicate a similar solution aren’t compatible
• Need new era of 5σ, definitive, and cost-effective experiments to explore & resolve
• Many experiments on the horizon, need to decide as a community what to push, to get full funding
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