Search for Sterile Neutrino Oscillations with MiniBooNE Robert Cooper

3-Flavor Neutrino Mixing Model Mass splittings Dm212 ≅ 7.6 × 10-5 eV2 Dm312 ≅ 2.4 × 10-3 eV2 Mixing angles sin2 2q13 ≅ 0.1 sin2 2q23 ≅ 0.97 sin2 2q12 ≅ 0.86 Hierarchy, CP d, mass scale? m12 m22 m32 m2 solar atm ? normal inverted ne nm nt R.L. Cooper

3-Flavor Anomalies Radioactive source disappearance (SAGE/GALLEX) Short baseline reactor disappearance, “Reactor Anomaly” Sterile neutrinos Dm2 ~ 1 eV2 ? 3 n oscillations (new flux) 3+1-n oscillations R.L. Cooper

LSND LSND searched for oscillations Decay At Rest source Excess of oscillation events that are inconsistent solar and atmospheric oscillations Excess = 87.9 ± 22.4 (sys) ± 6.0 (stat)  (3.8s) Sterile neutrino(s) ? … Enter MiniBooNE R.L. Cooper

LSND LSND searched for oscillations Decay At Rest source m2 ? LSND searched for oscillations Decay At Rest source Excess of oscillation events that are inconsistent solar and atmospheric oscillations Excess = 87.9 ± 22.4 (sys) ± 6.0 (stat)  (3.8s) Sterile neutrino(s) ? … Enter MiniBooNE R.L. Cooper

MiniBooNE Experiment, Neutrinos Designed to look for and oscillations 8 GeV protons strike Be target Magnetic horn selects charged mesons, leptons absorbed <En> ~ 800 MeV 2002-2005, 2007  6.7×1020 POT R.L. Cooper

MiniBooNE Experiment, Antineutrinos Designed to look for and oscillations 8 GeV protons strike Be target Magnetic horn selects charged mesons, leptons absorbed <En> ~ 800 MeV 2005-2006, 2008-2012  11.3×1020 POT R.L. Cooper

MiniBooNE Detector 800 tons very pure mineral oil (CnH2n+2) Cherenkov detector Small amount of natural scintillation 12 m diameter sphere 541 m from BNB target Inner signal region 1280× 8” PMTs (10% coverage) Outer veto region 240× 8” PMTs R.L. Cooper

MiniBooNE Event Reconstruction Oscillation signal is Charged Current Quasi-Elastic (CCQE)  e- final state CCQE is kinematically reconstructed from lepton energy and angle Lepton reconstruction (type, energy, direction) with PMT time and charge likelihood p0  gg can be poorly reconstructed as a single electron R.L. Cooper

Neutrino Results 6.7×1020 POT Excess (En > 200 MeV) 146.3 ± 28.4 ± 40.2 (3.8s) NCg & NCp0 are biggest at low En c2 probabilities for (null) hypothesis, best fit (bf) 2n oscillation hypothesis R.L. Cooper

Antineutrino Results 11.3×1020 POT Excess (En > 200 MeV) 77.8 ± 20.0 ± 23.4  (3.8s) NCg & NCp0 are biggest at low En c2 probabilities for (null) hypothesis, best fit (bf) 2n oscillation hypothesis R.L. Cooper

Combined Fit Excess (En > 200 MeV) 240.3 ± 34.5 ± 52.6  (3.8s) Consistent with LSND 3+1 n fits relatively poor 3+2 n fits better Is a low En background likely? NCp0 is directly measured NCg is constrained by NCp0 (due to D  Ng) Theory corroborates MiniBooNE estimates (e.g. Zhang & Serot) R.L. Cooper

Combined Fit Excess (En > 200 MeV) 240.3 ± 34.5 ± 52.6  (3.8s) Consistent with LSND 3+1 n fits relatively poor 3+2 n fits better Is a low En background likely? NCp0 is directly measured NCg is constrained by NCp0 (due to D  Ng) Theory corroborates MiniBooNE estimates (e.g. Zhang & Serot) R.L. Cooper

Discriminating NC & CC with Neutrons Excellent CCQE En Recon. “Clean” Expect ~1% (200 MeV) rising to ~10% (1 GeV) neutron production NC Poor CCQE En Recon. More energy to hadrons Expect ~50% neutron production Tagging neutrons can discriminate between NC backgrounds and CC oscillation signal R.L. Cooper

Future: MiniBooNE+ Neutrons thermalize, n(p,d)g capture, release 2.2 MeV g Need more light! 300 kg PPO will allow 2.2 MeV g to be detected Measure neutron fraction Use nm events to calibrate 3 years (6×1020 POT) neutrino mode run If excess remains, could be combined with previous runs for 5s rejection of null R.L. Cooper

Future: MiniBooNE+ Neutrons thermalize, n(p,d)g capture, release 2.2 MeV g Need more light! 300 kg PPO will allow 2.2 MeV g to be detected Measure neutron fraction Use nm events to calibrate 3 years (6×1020 POT) neutrino mode run If excess remains, could be combined with previous runs for 5s rejection of null R.L. Cooper

Future: Low-Mass Dark Matter Search Direct production of dark matter through SM-Dark portal vectors Phys. Rev. D86 (2012) 035022 Beam off-target to reduce n signal Elastic forward-scattering and beam timing sensitive to mc ~ 200 MeV Currently collecting off-target data in test beam run Full proposal soon R.L. Cooper

Summary MiniBooNE completed running April 2012 Currently collecting off-target test beam data Low-mass dark matter run See a 3.8s excess in combined and oscillations MiniBooNE+ will add scintillator to tag neutrons Neutrons discriminate NC backgrounds from CC signal R.L. Cooper

Summary MiniBooNE completed running April 2012 Currently collecting off-target test beam data Low-mass dark matter run See a 3.8s excess in combined and oscillations MiniBooNE+ will add scintillator to tag neutrons Neutrons discriminate NC backgrounds from CC signal R.L. Cooper