New Observations from the MiniBooNE Experiment Motivation 1. - PowerPoint PPT Presentation

New Observations from the MiniBooNE Experiment Motivation 1. MiniBooNE Appearance Results 2. Geoffrey Mills Comparison of LSND and MiniBooNE 3. Los Alamos National Laboratory For the MiniBooNE Collaboration Future Possibilities 4. Conclusions 5. ICHEP Paris, France XXV Juillet, MMX

Motivation…. Neutrino Oscillations The oscillation patterns between the 3 known active neutrino species have been demonstrated by a number of experiments over the last two decades: SNO, Kamland Super-K, K2K, MINOS Armed with that knowledge, measurements of neutrino behavior outside the standard 3 generations of active neutrinos indicate new physics: LSND indicates that new physics may be operating Interpretations of such a non-standard result probe some deep theoretical issues, for example: Light sterile neutrinos, neutrino decays, CP and/or CPT violation, Lorentz invariance, Extra dimensions The investigation of neutrino oscillations at the <1% level is unique in its physics reach 3

Motivation…. Excess Events from LSND still remain: — — LSND found an excess of ν e in ν μ beam Signature: Cerenkov light from e + with delayed n-capture (2.2 MeV) Excess: 87.9 ± 22.4 ± 6.0 (3.8 σ ) The data was analysed under a two neutrino mixing hypothesis* KARMEN at a distance of 17 meters saw no evidence for oscillations → low Δ m 2 *3 active + ≥ 2 sterile ν s needed to fit all appearance and disappearance 5

MiniBooNE looks for an excess of electron neutrino events in a predominantly muon neutrino beam ν mode flux ν mode flux π − → µ − ν µ π + → µ + ν µ ~6% ν ~18% ν K + → µ + ν µ K + → µ + ν µ neutrino mode: ν µ → ν e oscillation search _ _ antineutrino mode: ν µ → ν e oscillation search

Data stability  Very stable throughout the run 25m absorber 5

MiniBooNE Detects Cherenkov Light Pattern of Cerenkov Light Gives Event Type The most important types of neutrino events in the oscillation search: Background Muons (or charged pions): Produced in most CC events. Usually 2 or more subevents or exiting through veto. Signal and Background Electrons (or single photon): Tag for : ν µ → ν e CCQE signal. 1 subevent Background π 0 s: Can form a background if one photon is weak or exits tank. In NC case, 1 subevent.

Benchmark Reaction: Charged Current Quasi Elastic (CCQE) Normalizes our (flux x cross section ) Neutrino mode events Antineutrino mode events We adjust the parameters of a Fermi Gas model to match our observed Q 2 ν Fit Reproduces ν Data Distribution. Fermi Gas Model describes CCQE ν µ data well M A,eff = 1.23+-0.20 GeV κ = 1.019+-0.011 Also used to model ν e and ν e interactions

Reconstruction of NC π 0 events Separating electrons from neutral current π 0 s by using a likelihood ratio combined with the γγ invariant mass Monte Carlo π 0 only Signal region invariant mass BLIND e π 0 BLIND log(L e /L π ) e π 0 Invariant Mass

MiniBooNE Oscillation Searches ν µ → ν e Neutrino mode ν e appearance: • Seach for excess ν e events above expected background • Pure sample of neutrinos ν µ → ν e Antineutrino mode ν e appearance: • Search for excess ν e events above expected background • Contamination from large amount of in ν e antineutrino mode which creates ambiguities in the analysis, e.g. how does one treat the observed low energy excess seen in neutrino mode?

MiniBooNE ν e and ν e Data ν Mode New! 5.66E20 POT ν Mode

ν e Background Uncertainties Uncertainty (%) 200-475MeV 475-1100MeV  Unconstrained π + 0.4 0.9 ν e background 3 2.3 π - uncertainties K + 2.2 4.7 K - 0.5 1.2  Propagate K 0 1.7 5.4 input Target and beam models 1.7 3 uncertainties Cross sections 6.5 13 NC π 0 yield 1.5 1.3 from either Hadronic interactions 0.4 0.2 MiniBooNE Dirt 1.6 0.7 measurement Electronics & DAQ model 7 2 or external Optical Model 8 3.7 data ( ν µ constrained error ~10%) Total 13.4% 16.0%

Model Independent Views of Oscillations Why L/E? • Neutrino oscillations usually appear as simple trigonometric functions of L/E, e.g.: N N 2 L 2 L * U β i U α j U β j * U β i U α j U β j ( ) = δ αβ − 4 ( ) sin 2 ( Δ m ij ( ) sin(2 Δ m ij ∑ * ∑ * P ν α → ν β ℜ U α i E ) + 2 ℑ U α i E ) i > j i > j (antineutrinos : U → U * ) Δ m 2 L    is just the phase difference of the two states  E ν   • Experiments can be compared directly to each other in L/E to look for the interference of mass states and oscillation effects • The next graphs show P(osc) vs L/E: observed event excess ( ) ≡ P α → β number expected for full transmutation of ν µ or ν µ

Data plotted vs L/E 0.020 ( ) ν mode MiniBooNE Measured � stat error � 0.015 Background � sys error � P � Ν Μ �Ν e � New! 0.010 5.66E20 POT 0.005 0.000 � 0.005 0.020 0.5 1.0 1.5 2.0 2.5 ( ) L m ν LSND 0.015 E Ν � MeV � P � Ν Μ �Ν e � • MiniBooNE L/E bins match 0.010 the standard MB energy bins, 0.005 just recast in L/E 0.000 0.020 � 0.005 ( ) MiniBooNE ν mode � Measured � stat error � 0.015 Background � sys error � P � Ν Μ �Ν e � 0.010 0.005 0.000 � 0.005 0.5 1.0 1.5 2.0 2.5 L m E Ν � MeV � observed event excess ( ) ≡ P α → β number expected for full transmutation of ν µ or ν µ

Direct MiniBooNE-LSND Comparison of ν Data 0.020 LSND 0.015 MB ν mode ) New! P � µ � � e 0.010 ( 0.005 0.000 � 0.005 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 ( ) L / E ν m / MeV

Oscillation Fit Method  Maximum likelihood fit:  Simultaneously fit  ν e CCQE sample  High statistics ν µ CCQE sample  ν µ CCQE sample constrains many of the uncertainties:  Flux uncertainties ν e µ π ν µ  Cross section uncertainties 15

Testing the Null Hypothesis in ν -mode Model independent, uses only the background estimate and  constrains ν e backgrounds to ν μ event rate. Generate the χ 2 distribution of fake experiments thrown from  background-only error matrix (null) P null (MB excess) ~ 1.6% (full energy range) P null (MB excess) ~ 3.0% (E>475) (signal ν e bins only) P null (MB excess) ~ 0.5% (signal bins only) 16

Antineutrino mode MB results Full Energy Range • Results for 5.66E20 POT • Maximum likelihood fit in simple 2 neutrino model • Null excluded at 99.5% with respect to the two neutrino oscillation fit • P χ 2 (best fit)= 17.1% E>475 MeV 17

2 neutrino fit excluding low energy region (E>475 avoids question of low energy excess in nu-mode)

Antineutrino mode MB results for E>475 MeV ( E>475 avoids question of low energy excess in nu-mode) • Results for 5.66E20 POT • Maximum likelihood fit for simple two neutrino model • Null excluded at 99.4% with respect to the two neutrino oscillation fit. • P χ 2 (best fit)= 20.5% E>475 MeV • Signal ν e bins only: • P χ 2 (null)= 0.5% • P χ 2 (best fit)= ~10% Submitted to PRL arXiv: 1007.5510

Conclusions Significant ν e (~3 σ ) and ν e (~2.5 σ ) excesses above background are emerging in both neutrino mode and antineutrino mode in MiniBooNE The two modes do not appear to be consistent with a simple two flavor neutrino model Neutrino mode systematic errors dominate (near detector?) Antineutrino mode statistical errors dominate (more data?) MiniBooNE plans to accumulate more data until the goal of 10 21 protons on target is reached

Long-Baseline News, May 2010: “ *** LSND effect rises from the dead… “ !"#$

BACKUP

Future sensitivity in ν Data E>475MeV fit  MiniBooNE approved for a total of 1x10 21 POT  Potential 3 σ exclusion of null point assuming best fit signal  Combined analysis of ν e and ν e Protons on Target 23

Outlook Additional experiments under consideration or design: Moving MiniBooNE to a near position following the ν run • High statistics in a 1 year run MicroBooNE • 70 ton Liquid Argon TPC • Good electron-gamma separation ICARUS @PS • 600 ton Liquid Argon TPC running at Grand Sasso • Move to CERN PS beam and augment with small near detector (~<100 tons) • Good electron-photon separation Repeat LSND: • SNS (OscSNS) is running now at 1 MW (neutrinos are going to waste as we speak!!)

Motivation…. Cosmology Fits for the Number of Sterile Neutrinos (J. Hamann, et. al. arXiv:1006.5276) 3 + N s m v = 0 3 + N s m s = 0 N s + 3 m s = 0 4

Meson production at the Proton Target Kaons: Pions(+/-): HARP collaboration, hep-ex/0702024 MiniBooNE members joined the HARP collaboration 8 GeV proton beam Kaon data taken on multiple targets in 5% Beryllium target 10-24 GeV range Fit to world data using Feynman scaling Spline fits were used to parameterize the data. 30% overall uncertainty assessed

Backgrounds: Order( α QED x NC) , single photon FS N’ N Radiative Delta Decay Δ (constrained by NC π 0 ) (G 2 α / α S ) γ ν Other PCAC (small) Axial Anomaly (small) N’ N N’ N γ γ ω ν ν N’ N ν – ν comparison disfavors neutral current hypothesis γ All order (G 2 α s ) 0 since radiative Δ is Z A constrained by NC π 0 ν

MINOS Antineutrino Disappearance Low statistics but results hint at possible new effect in ν µ