MiniBooNE and the Hunt for Low Mass Sterile Neutrinos 1H. Ray, University of Florida

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) 2H. Ray, University of Florida

Not One-Stop Shopping! 3H. Ray, University of Florida Sterile massAllow ν to acquire mass Dark Rad, SBL, Reactor, Ga Dark matter candidate Find via a direct search 100 – 160 GeVYESNO 20 – 30 GeVYESNO YES keV - GeVYESNOYES eVYES NOYES Gnineko, Gorbunov, Shaposhnikov, arXiv:

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 4 Riemer-Sørensen, Parkinson, Davis, arXiv: H. Ray, University of Florida

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 Florida5

H. Ray6 SBL Anomalies: LSND 800 MeV proton beam + H 2 0 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)

SBL Anomalies: LSND LSND observed excess of anti-ν e in an anti-ν μ beam Excess: 87.9 ± 22.4 ± 6.0 (3.8σ) H. Ray, University of Florida Phys. Rev. Lett. 77: (1996) Phys. Rev. C 58: (1998) Phys. Rev. D 64, (2001) 7 Fit to oscillation hypothesis Backgrounds P osc = sin 2 2θ sin Δm 2 L E Δm 2 = 1.2 eV 2 sin 2 2θ = 0.003

MiniBooNE vs LSND LSND (anti) Neutrino beam from accelerator (DAR, average E ν 35 MeV) ν μ too low E to make μ or π Proton beam too low E to make K MiniBooNE Neutrino beam from accelerator (DIF, average E ν 800 MeV) Detector placed at 500 m from neutrino beam creation point, preserve LSND L/E New backgrounds: ν μ CCQE and NC π 0 mis-id for oscillation search New backgrounds: intrinsic ν e from K decay (0.5% of p make K) H. Ray, University of Florida8

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 H. Ray, University of Florida9 Phys.Rev. Lett. 110, (2013) x POT 6.5 x POT

SBL Anomalies: Summary 10 Antonello, et al. arXiv: H. Ray, University of Florida Δm 2 = 3.14 eV 2 sin 2 2θ = Δm 2 = eV 2 sin 2 2θ = 0.88

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 Florida11

Proposed Experiments 12 H. Ray, University of Florida de Gouvea et al, arXiv: RUNNING MicroBooNE MINOS+ PROPOSED ICARUS / NESSIE J-PARC LAr1-ND / LAr1 MiniBooNE+ nuSTORM OscSNS

H. Ray, University of Florida13 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 Florida14 MiniBooNE Low-E Backgrounds Both NC backgrounds are constrained by in-situ measurements NC π 0 directly measured NC γ (radiative Δ decay) constrained to NC π 0 Also, recent theoretical calculations agree with MB Phys. Rev. D 81 (2010)

H. Ray, University of Florida15 MiniBooNE Low-E Backgrounds Both NC backgrounds are constrained by in-situ measurements NC π 0 directly measured NC γ (radiative Δ decay) constrained to NC π 0 Also, recent theoretical calculations agree with MB Phys. Rev. D 81 (2010)

MiniBooNE Low-E Excess Photons or electrons? H. Ray, University of Florida16 MicroBooNE MiniBooNE+

Booster Neutrino Beam at FNAL H. Ray, University of Florida dirt target and horn (174 kA) π+ π- K+K+ K0K0 ✶ ✶ μ+ ✶ decay region (50 m) oscillations? FNAL booster (8 GeV protons) 17 Neutrinos from pions decaying in flight Mean neutrino E ~500 MeV

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 H. Ray, University of Florida18 1 GeV electron shower1 GeV π 0 decay

H. Ray, University of Florida19 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 + 12 C  Δ   or π 0 + p or n equal chances of getting n or p n + p  d MeV  Reconstructed vs True Eν, Signal Reconstructed vs True Eν, Backgrounds arXiv

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 ν μ CC events (not the oscillation channel) Can measure n fraction in pristine NC π 0 events H. Ray, University of Florida20

MiniBooNE+ Same as previous analysis, same excess Require n-capture events –Red: if excess is truly due to CC ν e 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 Florida21

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 (CH 2 ) 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 Florida22

SBL Anomalies 23H. Ray, University of Florida MINOS+ LAr1 ICARUS OscSNS nuSTORM J-PARC LSND, MB ((anti)ν μ  (anti)ν e, (anti)ν e app) sensitive to combo of θ 14 and θ 24 Reactors (ν e disappearance) sensitive to θ 14 MINOS+ (ν μ or anti-ν μ CC disappearance) sensitive to θ 24, little sensitivity to θ 14

Liquid Argon At Fermilab Uses MiniBooNE’s beamline microBooNE can distinguish electrons from photons need 2 nd 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 Florida24

LAr1-ND H. Ray, University of Florida25 C. Adams, et al., arXiv: 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)

LAr1-ND H. Ray, University of Florida26 4σ coverage of best fit point around 1 eV 2, with full microBooNE data set and 1 year of LAr1-ND running C. Adams, et al., arXiv:

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 field H. Ray, University of Florida27 arXiv:

ICARUS at FNAL H. Ray, University of Florida28 Neutrino Run 6.6e20 POT Anti-Neutrino Run +B field 11e20 POT

NuMI Neutrino Beam at FNAL H. Ray, University of Florida29 Movable target and magnetic focusing horn –Tunable neutrino beam energy –Run in neutrino, anti-neutrino mode Graphite target

MINOS+ H. Ray, University of Florida Long baseline experiment L/E ~500 km/GeV (atm. Δm 2 ) 2 detectors: near & far Magnetized, tracking sampling calorimeters Measure Δm 2 23, sin 2 (2θ 23 ) for ν, anti-ν 30 Graphite target

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 (θ 34 ) H. Ray, University of Florida31 Green: excluded by ν μ disappearance Blue: excluded by NC disappearance MINOS+ Fermilab Proposal 1016

OscSNS 32  - absorbed by target  + DAR Mono-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

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 – 16 N, 8 Li, 252 Cf m in the backward direction, ~150 degrees from incident proton beam Proton beam OscSNS Detector Hall arXiv:

OscSNS  -> e Experiment vs LSND More Detector Mass (x5) Higher Intensity Neutrino Source (x2) Lower Duty Factor (x1000) (less cosmic background) Separation of  & e / anti-  fluxes with timing Negligible DIF Background (backward direction) Lower Neutrino Background (~x2) (60m vs 30m) For LSND parameters, expect ~ e oscillation events & ~50 background events per year! (Assuming  m 2 < 1 eV 2 ) H. Ray, University of Florida34

Oscillation Goals anti-  -> anti- e appearance  e -> s disappearance   -> s disappearance  all -> s disappearance H. Ray, University of Florida35

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

Appearance Sensitivity 37 Assuming 5y of data & sin 2 2  = 0.005,  m 2 =1 eV 2 Assuming 5y of data & sin 2 2  = 0.005,  m 2 =4 eV 2 L/E (m/MeV) Statistical errors, 20% bgd H. Ray, University of Florida CONTINUOUS! 50% detector efficiency, ~85% E e cut efficiency, oscillation probability of 0.26%

Disappearance Sensitivity 38 e C  e - N gs, N gs  C gs e + e Assuming 5y of data & sin 2 2  = 0.15,  m 2 = 1 eV 2 Assuming 5y of data & sin 2 2  = 0.15,  m 2 = 4 eV 2 L/E (m/MeV) H. Ray, University of Florida 50% detector efficiency Statistical errors, 1% bgd CONTINUOUS!

J-PARC Neutrino Beamline H. Ray, University of Florida Spallation Neutron Source at J-PARC Muons DAR to produce neutrinos Primarily μ +  e + anti-ν μ ν e 50 ton fiducial mass liquid scintillator detector at 17 m Use CCQE appearance analysis (anti-ν μ  anti-ν e ) Use ν e CC disappearance Above ground, may have issues with neutron backgrounds 4 years operation Blue = 5σ CL Green = 3σ CL T. Maruyama et al., arXiv:

Sensitivities H. Ray, University of Florida40 ν μ  ν e, ν e  ν μ appearance searches neutrino and anti-neutrino modes App only fit + LBL reactors, Kopp, Machado, Maltoni, Schwetz, arXiv: Global fit, Giunti, Laveder, Li, Long, arXiv: ICARUS curve is for CERN, not FNAL Difference in opinion of how to do fits de Gouvea et al, arXiv: Abazajiana, et al. arXiv:

Event Rates LAr1-ND 100 m ICARUS 150 m, E < 5 GeV ICARUS 700 m, E < 5 GeV MiniBooNE 200 to 1250 MeV OscSNSJ-PARC ν μ CC Inclusive (anti-ν μ ) 2,500,000 (291,000) 387,000 (56,900) ν e CC Inclusive (anti-ν e ) 26,200 (1,780) 4,460 (312) ν μ  ν e app (1.15 eV 2, 1.5e-3) 310 signal 322 bgd 400, 380 signal 2,520, 1860 bgd (E < 5 GeV, 2 GeV) 233 sig (expect) 162 sig (obs) 790 bgd anti-ν e p  e + n app (1.2 eV 2, 3e-3) 100 sig (expect) 78 sig (obs) 400 bgd 480 signal 168 bgd 337 signal 494 bgd ν e + 12 C  e - 12 N gs dis 9412 signal 96 bgd 22,934 H. Ray, University of Florida41 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

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

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 43H. Ray, University of Florida