Results and Implications from MiniBooNE LLWI, 25 Feb 2011 Warren Huelsnitz, LANL

2 Neutrino and Antineutrino Oscillation Results from MiniBooNE Where are we today? How did we get there? Where are we going? Neutrino Cross Section Measurements from MiniBooNE

LSND Saw an excess of e : 87.9 ± 22.4 ± 6.0 events. With an oscillation probability of (0.264 ± ± 0.045)%. 3.8  evidence for oscillation. 3 The three oscillation signals cannot be reconciled without introducing Beyond Standard Model Physics!

Keep L/E same as LSND while changing systematics, energy & event signature P    e  sin   sin   m  L  Booster K+K+ target and horndetectordirtdecay regionabsorber primary beamtertiary beamsecondary beam (protons)(mesons)(neutrinos)    e   LSND: E ~ 30 MeV MiniBooNE: E ~ 500 MeV L ~ 30 m L/E ~ 1 L ~ 500 m L/E ~ 1 MiniBooNE was designed to test the LSND signal Neutrino mode: search for ν μ -> ν e appearance with 6.5E20 POT  assumes CP/CPT conservation Antineutrino mode: search for ν μ -> ν e appearance with 5.66E20 POT  direct test of LSND  Two neutrino fits FNAL FNAL has done a great job delivering beam! 818 ton mineral oil 1280 PMTs inner region 240 PMTs veto region 4

5 Identify events using timing and hit topology Use primarily Cherenkov light Can’t distinguish electron from photon Charge Current Quasi Elastic Neutral Current Interactions in MiniBooNE (neutrino mode): (similar mix for antineutrino mode, except rate down by factor of 5) QE

6 Combined fit of ν μ and ν e CCQE spectra M = M om + M xsec + M flux + M π 0 + M dirt + M K 's of MC universes go into forming M Maximum likelihood fit: Simultaneously fit (FC-corrected) ν e CCQE signal + high E ν e sample High statistics ν μ CCQE sample ν μ CCQE sample acts like a near detector, i.e. same flux as oscillation ν e by definition, lepton universality + muon mass corrections fix relative cross-section Low E ν μ 's constrain signal rate Low E ν μ 's constrain ν e from muons High E ν μ 's constrain ν e from kaons + stat. Feldman-Cousins method with fake data studies to determine probabilities

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9 Reminder: Neutrino Oscillation Search Above 475 MeV... After unblinding, we see amazing agreement with our background predictions Find 408 events, expect 386 ± 20(stat) ± 30(syst) Chi-square probability of 40% in MeV Since this is the region of highest sensitivity to LSND-like 2 neutrino mixing hypothesis, can use it to exclude that model (assuming CP cons) Low E

10 Reminder: Neutrino Oscillation Search Low E Below 475 MeV... Find 544 events, expect 415 ± 20(stat) ± 39(syst) Excess is 128 ± 20(stat) ± 39(syst) events 6 σ statistical excess, but reduced to 3 σ due to falling in region where backgrounds are rising Shape not consistent with simple 2 ν oscillations Bkg SourceBkg CountsInc. NeededSyst Error* ν μ CCQE %~30% NC π %~20% Rad. Δ %~25% ν e from μ %~25% ν e from K %~40% dirt %~15% Bkgds and errors in MeV region *not rigorously correct but within 5%

First Antineutrino mode MB results (2009) 3.4E20 POT collected in anti-neutrino mode From MeV excess is 4.8 +/ (stat+sys) events. Statistically small excess (more of a wiggle) in MeV region Only antineutrino’s allowed to oscillate in fit Limit from two neutrino fit excludes less area than sensitivity due to fit adding a LSND-like signal to account for wiggle Stat error too large to distinguish LSND-like from null No significant excess E < 475 MeV. Published PRL 103, (2009) E>475 MeV 90% CL limit 90% CL sensitivity Anti-Neutrino Exclusion Limits: 3.4E20 POT

12 anti- results Above 475 MeV... In MeV, excess 20.9 ± 14 events (1.4 σ ) In MeV, excess is 25.7 ± 7.2 events (3.6 σ ) True significance comes from fit over entire > 475 MeV energy region + numu constraint Best fit preferred over null at 99.4% CL (2.7 σ ) Probability of null hypothesis (no model dep.) is 0.5% in MeV signal region New Antineutrino Results (above 475 MeV)

13 Comparing MiniBooNE anti- ν to LSND Fit to 2 ν mixing model Model-independent plot of inferred oscillation probability: MiniBooNE antineutrino oscillation result is consistent with LSND

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15 New Antineutrino Results (below 475 MeV) anti- results Reminder: results Below 475 MeV... Find 119 events, expect 100 ± 10(stat) ± 10(syst) Excess is 18.5 ± 10(stat) ± 10(syst) events Starting to become inconsistent with many hypotheses explaining the nu mode low E excess Bkg SourceNubar Prediction CC bkgs38.6 NC π 0 31 Rad Δ 24.9 K0K charged K38 WS neutrinos12 same xsec68

16 What does MiniBooNE claim? In a ν μ beam above 475 MeV, we see no evidence for an excess of ν e -like events. (This is the region of maximal sensitivity if the LSND signal is L/E and CP invariant.) In a ν μ beam below 475 MeV, we see a 3 σ excess (128 ± 43) of ν e signal candidates that don't fit well to a 2 ν mixing hypothesis. In a anti- ν μ beam below 475 MeV, we see a small excess (18 ± 14). It rules out some explanations of the ν μ beam low-E excess. In a anti- ν μ beam above 475 MeV, we see an excess of events. The null hypothesis in the MeV region is only 0.5% probable. A 2 ν fit prefers an LSND-like signal at 99.4% CL.

17 LSND=3.8 σ, MB ν =3.0 σ, MB ν =2.7 σ...What now?

N s m v = N s m s = 0

MiniBooNE Neutrino & Antineutrino Disappearance Limits Improved results soon from MiniBooNE/SciBooNE Joint Analysis! A.A. Aguilar-Arevalo et al., PRL 103, (2009) 19

20 MiniBooNE like detector at 200m Flux, cross section and optical model errors cancel in 200m/500m ratio analysis Gain statistics quickly, already have far detector data Measure   e &   e oscillations and CP violation 6.5e20 Far + 1e20 Near POT Sensitivity (Neutrinos) Sensitivity (Antineutrinos) 10e20 Far + 1e20 Near POT (LOI arXiv: )

21 Much better sensitivity for  &  disappearance Look for CPT violation 6.5e20 Far/1e20 Near POT 10e20 Far/1e20 Near POT

22 vacuum ATMOSPHERIC NEUTRINO ENERGY SPECTRUM 100 GEV TO 400 TEV in IceCube (Phys. Rev. D 83, ) Estimated neutrino energy resolution (from simulation) Matter effects should produce unique signature in IceCube:

QE PRD 81, (2010) PRL 100, (2008) PRD 81, (2010) PL B664, 41 (2008) PRD 82, (2010) arXiv: , submitted to PRD PRL 103, (2009) arXiv: , submitted to PRD have measured cross sections for 90% of interactions in MB additional and analyses in progress now 8 cross section publications in the period from

QE also the 1 st time full kinematics have been reported for many of these reaction channels

Extremely surprising result - CCQE     C)>6    n) How can this be? Not seen before, requires correlations. Fermi Gas has no correlations. A possible explanation involves short-range correlations & 2-body pion- exchange currents: Joe Carlson et al., Phys.Rev.C65, (2002) & Gerry Garvey.  CCQE Scattering A.A. Aguilar-Arevalo, Phys. Rev. D81, (2010). 25

26 Summary Low energy excess in neutrino mode is not yet resolved. It does not fit a simple 2 ν mixing hypothesis, although some recent theoretical explanations (i.e. neutrino decay, 3+N, etc.) have not been ruled out. MicroBooNE should be able to weigh in. In a muon antineutrino beam, we see an excess of electron antineutrino events above 475 MeV. This is consistent with the LSND result. MB is continuing to take data in antineutrino mode. Additional analyses are underway to improve sensitivity to muon neutrino and antineutrino disappearance, including joint MB/SciBooNE analyses. Recent cross section results have identified difficulties in characterizing and calculating neutrino-nucleon cross sections.