Results and Implications from MiniBooNE

1. Results and Implications from MiniBooNE LLWI, 25 Feb 2011 Warren Huelsnitz, LANL whuelsn@fnal.gov

2. Outline • 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

3. Motivation for MiniBooNE: The LSND Evidence for Oscillations LSND Saw an excess ofe:87.9 ± 22.4 ± 6.0 events. With an oscillation probability of (0.264 ± 0.067 ± 0.045)%. 3.8 s evidence for oscillation. The three oscillation signals cannot be reconciled without introducing Beyond Standard Model Physics!

4. P(nm ne)= sin22q sin2(1.27Dm2L/E) target and horn decay region absorber dirt detector nm ne??? K+ p+ Booster primary beam secondary beam tertiary beam (protons) (mesons) (neutrinos) MiniBooNE was designed to test the LSND signal Keep L/E same as LSND while changing systematics, energy & event signature  Two neutrino fits LSND: E ~ 30 MeV MiniBooNE: E ~ 500 MeV L ~ 30 m L/E ~ 1 L ~ 500 m L/E ~ 1 FNAL 818 ton mineral oil 1280 PMTs inner region 240 PMTs veto region Neutrino mode: search for νμ -> νe appearance with 6.5E20 POT  assumes CP/CPT conservation Antineutrino mode: search for νμ -> νe appearance with 5.66E20 POT  direct test of LSND FNAL has done a great job delivering beam!

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

6. Combined fit of νμ and νe CCQE spectra • Maximum likelihood fit: • Simultaneously fit (FC-corrected) • νe CCQE signal + high E νe sample • High statistics νμ CCQE sample • νμ CCQE sample acts like a near detector, i.e. same flux as oscillation νe by definition, lepton universality + muon mass corrections fix relative cross-section • Low E νμ's constrain signal rate • Low E νμ's constrain νe from muons • High E νμ's constrain νe from kaons M = Mom + Mxsec + Mflux + Mπ0 + Mdirt + MK0+... + stat. 1000's of MC universes go into forming M Feldman-Cousins method with fake data studies to determine probabilities

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 475-1250 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 Below 475 MeV... Find 544 events, expect 415 ± 20(stat) ± 39(syst) Excess is 128 ± 20(stat) ± 39(syst) events 6σ statistical excess, but reduced to 3σ due to falling in region where backgrounds are rising Shape not consistent with simple 2 ν oscillations Low E Bkgds and errors in 200-475 MeV region *not rigorously correct but within 5%

11. First Antineutrino mode MB results (2009) Anti-Neutrino Exclusion Limits: 3.4E20 POT 90% CL limit 90% CL sensitivity E>475 MeV • 3.4E20 POT collected in anti-neutrino mode • From 200-3000 MeV excess is 4.8 +/- 17.6 (stat+sys) events. • Statistically small excess (more of a wiggle) in 475-1250 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 103,111801 (2009)

12. Above 475 MeV... In 475-1250 MeV, excess 20.9 ± 14 events (1.4σ) In 475-675 MeV, excess is 25.7 ± 7.2 events (3.6σ) True significance comes from fit over entire > 475 MeV energy region + numu constraint Best fit preferred over null at 99.4% CL (2.7σ) Probability of null hypothesis (no model dep.) is 0.5% in 475-1250 MeV signal region New Antineutrino Results (above 475 MeV) Dc2vsDm2 anti- results

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

15. New Antineutrino Results (below 475 MeV) 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 anti- results Reminder:  results

16. What does MiniBooNE claim? In a νμ beam above 475 MeV, we see no evidence for an excess of νe-like events. (This is the region of maximal sensitivity if the LSND signal is L/E and CP invariant.) In a νμ beam below 475 MeV, we see a 3σ excess (128 ± 43) of νe signal candidates that don't fit well to a 2ν mixing hypothesis. In a anti-νμ beam below 475 MeV, we see a small excess (18 ± 14). It rules out some explanations of the νμ beam low-E excess. In a anti-νμ beam above 475 MeV, we see an excess of events. The null hypothesis in the 475-1250 MeV region is only 0.5% probable. A 2ν fit prefers an LSND-like signal at 99.4% CL.

17. LSND=3.8σ, MBν=3.0σ, MBν=2.7σ...What now? 2011-2012 2013-2015

18. Sterile Neutrinos Cosmology Data Consistent with Extra Sterile Neutrinos (J. Hamann, et. al. PRL 105 (2010) 181301) Reactor Neutrino Anomaly (G. Mention, et. al., arXiv:1101.2755) “The no-oscillation hypothesis is disfavored at 99.86% CL” 3 + Ns mv = 0 3 + Ns ms = 0 (Y. Izotov and T. Thuan, ApJL 710 (2010) L67)

19. MiniBooNE Neutrino & Antineutrino Disappearance Limits A.A. Aguilar-Arevalo et al.,PRL 103, 061802 (2009) Improved results soon from MiniBooNE/SciBooNE Joint Analysis!

20. BooNE: Near Detector at ~200 m (LOI arXiv:0910.2698) • 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 nm->ne & nm->ne oscillations and CP violation 6.5e20 Far + 1e20 Near POT 10e20 Far + 1e20 Near POT Sensitivity (Neutrinos) Sensitivity (Antineutrinos)

21. BooNE: Near Detector at ~200 m • Much better sensitivity for nm & nm disappearance • Look for CPT violation 10e20 Far/1e20 Near POT 6.5e20 Far/1e20 Near POT

22. Sterile Neutrinos in IceCube ATMOSPHERIC NEUTRINO ENERGY SPECTRUM 100 GEV TO 400 TEV in IceCube (Phys. Rev. D 83, 012001) Estimated neutrino energy resolution (from simulation) Matter effects should produce unique signature in IceCube: vacuum

23. QE 8  cross section publications in the period from 2008-2010 Neutrino Cross Sections at MiniBooNE PRD 82, 092005 (2010) PRL 103, 081802 (2009) arXiv:1011.3572, submitted to PRD PRD 81, 092005 (2010) PRL 100, 032301 (2008) have measured cross sections for 90% of  interactions in MB additional  and analyses in progress now arXiv:1010.3264, submitted to PRD PRD 81, 013005 (2010) PL B664, 41 (2008)

24. QE Neutrino Cross Sections at MiniBooNE also the 1st time full kinematics have been reported for many of these reaction channels

25. nmCCQE Scattering A.A. Aguilar-Arevalo, Phys. Rev. D81, 092005 (2010). 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, 024002 (2002) & Gerry Garvey.

26. Summary Low energy excess in neutrino mode is not yet resolved. It does not fit a simple 2ν 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.