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MiniBooNE and the Hunt for Low Mass Sterile Neutrinos

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  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) • IceCubeflux deficit due to observed GRBs (3.7x lower) H. Ray, University of Florida

  3. Not One-Stop Shopping! 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, University of Florida


  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

  7. SBL Anomalies: LSND Fit to oscillation hypothesis • LSND observed excess of anti-νe in an anti-νμ beam • Excess: 87.9 ± 22.4 ± 6.0 (3.8σ) Δm2 = 1.2 eV2 sin22θ = 0.003 Backgrounds Posc = sin22θ sin2 1.27 Δm2 L E Phys. Rev. Lett. 77:3082-3085 (1996) Phys. Rev. C 58:2489-2511 (1998) Phys. Rev. D 64, 112007 (2001) H. Ray, University of Florida

  8. MiniBooNE vs LSND LSND • (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: νμCCQE and NC π0mis-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 11.27 x 1020 POT 6.5 x 1020 POT Phys.Rev. Lett. 110, (2013) 16801 H. Ray, University of Florida

  10. SBL Anomalies: Summary Δm2 = 0.043 eV2 sin22θ = 0.88 Δm2 = 3.14 eV2 sin22θ = 0.002 Antonello, et al. arXiv:1307.4699 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 H. Ray, University of Florida

  12. Proposed Experiments • RUNNING • MicroBooNE • MINOS+ • PROPOSED • ICARUS / NESSIE • J-PARC • LAr1-ND / LAr1 • MiniBooNE+ • nuSTORM • OscSNS de Gouvea et al, arXiv:1310.4340 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(radiativeΔ decay) constrained to NC π0 Also, recent theoretical calculations agree with MB Phys. 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(radiativeΔ decay) constrained to NC π0 Also, recent theoretical calculations agree with MB Phys. Rev. D 81 (2010) 013005 H. Ray, University of Florida

  16. MiniBooNE Low-E Excess • Photons or electrons? MiniBooNE+ MicroBooNE H. Ray, University of Florida

  17. Booster Neutrino Beam at FNAL π- oscillations? π+ ✶ μ+ ✶ K0 ✶ K+ target and horn (174 kA) FNAL booster (8 GeV protons) decay region (50 m) dirt Neutrinos from pions decaying in flight Mean 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+ LAr1 ICARUS • LSND, MB ((anti)νμ (anti)νe, (anti)νeapp) • sensitive to combo of θ14and θ24 • Reactors (νe disappearance) • sensitive to θ14 • MINOS+ (νμor anti-νμ CC disappearance) • sensitive to θ24, little sensitivity to θ14 OscSNS J-PARC nuSTORM 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 • 100 m = in existing SciBooNEenclosure • 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 ktonLArTPC 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) C. Adams, et al., arXiv:1309.7987 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 SciBooNEHall – 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 field arXiv:1312.7252 H. Ray, University of Florida

  28. ICARUS at FNAL Anti-Neutrino Run +B field 11e20 POT Neutrino Run 6.6e20 POT H. Ray, University of Florida

  29. NuMI Neutrino Beam at FNAL Graphite target • Movable target and magnetic focusing horn • Tunable neutrino beam energy • Run in neutrino, anti-neutrino mode H. Ray, University of Florida

  30. MINOS+ Graphite target • 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 H. Ray, University of Florida

  31. MINOS+ Green: excluded by νμ disappearance Blue: excluded by NC disappearance • 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) MINOS+ Fermilab Proposal 1016 H. Ray, University of Florida

  32. OscSNS • Spallation Neutron Source at Oak Ridge • ~1 GeV protons+Hg target (1.4 MW) • Free source of neutrinos - absorbed by target Mono-Energetic! = 29.8 MeV E range up to 52.8 MeV + DAR 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 Proton beam • 60 m in the backward direction, ~150 degrees from incident proton beam OscSNS Detector Hall arXiv:1307.7097 H. Ray, University of Florida

  34. OscSNS nm -> neExperiment vs LSND (Assuming Dm2 < 1 eV2) • More Detector Mass (x5) • Higher Intensity Neutrino Source (x2) • Lower Duty Factor (x1000) (less cosmic background) • Separation of nm & ne / anti-nmfluxes with timing • Negligible DIF Background (backward direction) • Lower Neutrino Background (~x2)(60m vs30m) • For LSND parameters, expect ~100-200ne oscillation events &~50background events per year! 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

  36. Appearance Sensitivity 50% detector efficiency, ~85% Ee cut efficiency, oscillation probability of 0.26% CONTINUOUS! • anti-nm anti-ne appearance sensitivity for 1 & 3 years of running: anti-ne p  e+ n; n p  d g (2.2 MeV) Already at 5σ! LSND & KARMEN Allowed LSND & KARMEN Allowed H. Ray, University of Florida

  37. Appearance Sensitivity 50% detector efficiency, ~85% Ee cut efficiency, oscillation probability of 0.26% CONTINUOUS! Statistical errors, 20% bgd Assuming 5y of data & sin22q = 0.005, Dm2=1 eV2 Assuming 5y of data & sin22q = 0.005, Dm2=4 eV2 P(nm-> ne) L/E (m/MeV) L/E (m/MeV) H. Ray, University of Florida

  38. Disappearance Sensitivity 50% detector efficiency CONTINUOUS! Statistical errors, 1% bgd neC 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 P(ne-> ns) L/E (m/MeV) L/E (m/MeV) H. Ray, University of Florida

  39. J-PARC Neutrino Beamline • 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 • Spallation Neutron Source at J-PARC • Muons DAR to produce neutrinos • Primarily μ+ e+ anti-νμ νe 4 years operation Blue = 5σ CL Green = 3σ CL T. Maruyama et al., arXiv:1310.1437 H. Ray, University of Florida

  40. Sensitivities νμ νe, νe  νμ appearance searches neutrino and anti-neutrino modes • ICARUS curve is for CERN, not FNAL • Difference in opinion of how to do fits App only fit + LBL reactors, Kopp, Machado, Maltoni, Schwetz, arXiv:1303.3011 Abazajiana, et al. arXiv:1204.4219 Global fit, Giunti, Laveder, Li, Long, arXiv:1308.5288 de Gouvea et al, arXiv:1310.4340 H. Ray, University of Florida

  41. Event Rates 10.96e23 POT (4 yrs) 2.2e20 POT (1 yr, full run) 200 – 475 MeV same as ICARUS Neutrino: 6.6e20 POT (3 yr full run) Anti-neutrino: 11e20 POT (5 yr full run) 12e22 POT (4 yrs, full run) H. Ray, University of Florida

  42. Cost Estimates J-PARC μ-DAR anti-νμ anti-νe app. J-PARC small (~<5 M) Same target nucleon as LSND, MB Shorter-term de Gouvea et al, arXiv:1310.4340 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 H. Ray, University of Florida