Results and Implications from MiniBooNE

LLWI, 25 Feb 2011Warren Huelsnitz, LANL

whuelsn@fnal.gov

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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

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.

Motivation for MiniBooNE: The LSND Evidence for Oscillations

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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(nm ne)= sin22 q sin2(1.27Dm2L/ ) E

Booster

K+

target and horn detectordirt decay region absorber

primary beam tertiary beamsecondary beam

(protons) (mesons) (neutrinos)

p+ n m n e ???

LSND: E ~ 30 MeVMiniBooNE: 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 νμ -> νe appearance with 6.5E20 POT assumes CP/CPT conservationAntineutrino mode: search for νμ -> νe appearance with 5.66E20 POT direct test of LSND

Two neutrino fits

FNAL

FNAL has done a great job delivering beam!

818 ton mineral oil1280 PMTs inner region240 PMTs veto region

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Events in MB Identify events using timing and hit topology Use primarily Cherenkov light Can’t distinguish electron from photon

Cha

rge

Cur

rent

Q

uasi

Ela

stic

Neu

tral

Cur

rent

Interactions in MiniBooNE(neutrino mode):

(similar mix for antineutrino mode, except rate down by factor of 5)

QE

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Combined fit of νμ and νe CCQE spectra

M = Mom + Mxsec + Mflux + Mπ0 + Mdirt + MK

0+...1000's of MC universes go into forming M

flux through the detector ( mode)

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

+ stat.

Feldman-Cousins method with fake data studies to determine probabilities

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Reminder: Neutrino Oscillation SearchAbove 475 MeV...

After unblinding, we see amazing agreement with our background predictionsFind 408 events, expect 386 ± 20(stat) ± 30(syst)Chi-square probability of 40% in 475-1250 MeVSince 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

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Reminder: Neutrino Oscillation SearchLow E 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 risingShape not consistent with simple 2 ν oscillations

Bkg Source Bkg Counts Inc. Needed Syst Error*

νμ CCQE 26.4 487% ~30%

NC π0 181.3 71% ~20%

Rad. Δ 67.0 192% ~25%

νe from μ 58.1 222% ~25%

νe from K 17.4 740% ~40%

dirt 23.8 544% ~15%

Bkgds and errors in 200-475 MeV region

*not rigorously correct but within 5%

First Antineutrino mode MB results (2009)

• 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)

E>475 MeV

90% CL limit

90% CL sensitivity

Anti-Neutrino Exclusion Limits: 3.4E20 POT

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anti- results 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 constraintBest 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)

Dc2 vs Dm2

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Comparing MiniBooNE anti-ν to LSND

Fit to 2ν mixing model

Model-independent plot of inferred oscillation probability:

Obs Pred

Full Osc

e e

e

N NP

N

MiniBooNE antineutrino oscillation result is consistent with LSND

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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 Source Nubar Prediction

CC bkgs 38.6

NC π0 31

Rad Δ 24.9

K0 114.3

charged K 38

WS neutrinos 12

same xsec 68

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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.

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LSND=3.8σ, MBν=3.0σ, MBν=2.7σ...What now?

2011-2012

2013-2015

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Sterile Neutrinos

3 + Ns

mv = 0

3 + Ns

ms = 0

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”

(Y. Izotov and T. Thuan, ApJL 710 (2010) L67)

MiniBooNE Neutrino & Antineutrino Disappearance Limits

Improved results soon from MiniBooNE/SciBooNE Joint Analysis!

A.A. Aguilar-Arevalo et al., PRL 103, 061802 (2009)

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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

Sensitivity(Neutrinos)

Sensitivity(Antineutrinos)

10e20 Far + 1e20 Near POT

BooNE: Near Detector at ~200 m(LOI arXiv:0910.2698)

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Much better sensitivity for nm & nm disappearance

Look for CPT violation6.5e20 Far/1e20 Near POT10e20 Far/1e20 Near POT

BooNE: Near Detector at ~200 m

Sterile Neutrinos in IceCube

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vacuum in Earths

ATMOSPHERIC NEUTRINO ENERGYSPECTRUM 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:

QEPRD 81,092005 (2010)

PRL 100, 032301 (2008)

PRD 81, 013005 (2010)

PL B664, 41 (2008)

PRD 82, 092005 (2010)

Neutrino Cross Sections at MiniBooNE

arXiv:1010.3264,

submitted to PRD

PRL 103,081802 (2009)

arXiv:1011.3572,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 2008-2010

QE

Neutrino Cross Sections at MiniBooNE

also the 1st 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, 024002 (2002) & Gerry Garvey.

nm CCQE Scattering

A.A. Aguilar-Arevalo, Phys. Rev. D81, 092005 (2010).

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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.