SHORT-BASELINE NEUTRINO PHYSICS AT MiniBooNE E. D. Zimmerman - PowerPoint PPT Presentation

SHORT-BASELINE NEUTRINO PHYSICS AT MiniBooNE E. D. Zimmerman University of Colorado PANIC 2011 Cambridge, Mass. 25 July 2011

Short-Baseline Neutrino Physics at MiniBooNE • MiniBooNE • Neutrino cross-sections • Hadron production channels • Oscillation physics • Antineutrino Oscillations • MiniBooNE-SciBooNE joint result

Motivating MiniBooNE: LSND Liquid Scintillator Neutrino Detector • Stopped π + beam at Los Alamos LAMPF produces ν e , ν μ , ν ̅ μ but no ν ̅ e (due to π － capture). Search for ν ̅ e appearance via reaction: ν e + p → e + + n ¯ Look for delayed coincidence of positron and neutron capture. • • Major background non-beam (measured, subtracted) • 3.8 standard dev. excess above background. • Oscillation probability: ν e ) = (2 . 5 ± 0 . 6 stat ± 0 . 4 syst ) × 10 − 3 P (¯ ν µ → ¯

LSND oscillation signal 90% CL 99% CL • LSND “allowed region” shown as band • KARMEN2 is a similar experiment with a slightly smaller L/E; they see no evidence for oscillations. Excluded region is to right of curve.

The Overall Picture ∆ m 2 > 0 . 1eV 2 LSND ν µ ↔ ¯ ¯ ν e ∆ m 2 ≈ 2 × 10 − 3 eV 2 Atmos . ν µ ↔ ν ? ∆ m 2 ≈ 10 − 4 eV 2 Solar ν e ↔ ν ? • With only 3 masses, can’t construct 3 Δ m 2 values of different orders of magnitude! • Current ideas out there: • An experiment or two is wrong • Sterile neutrino sector: extra masses and mixing angles

MiniBooNE: E898 at Fermilab • Purpose is to test LSND with: • Higher energy • Different beam • Different oscillation signature • Different systematic effects • L=500 meters, E=0.5 − 1 GeV: same L/E as LSND.

Oscillation Signature at MiniBooNE • Oscillation signature is charged-current quasielastic scattering: ν e + n → e − + p • Dominant backgrounds to oscillation: Intrinsic ν e in the beam • π → µ → ν e in beam K + → π 0 e − ν e , K 0 L → π 0 e ± ν e in beam • Particle misidentification in detector Neutral current resonance: ∆ → π 0 → γγ or ∆ → n γ , mis-ID as e

MiniBooNE Beamline • 8 GeV primary protons come from Booster accelerator at Fermilab • Booster provides about 5 pulses per second, 5 × 10 12 protons per 1.6 μ s pulse under optimum conditions • Beryllium target, single 174 kA horn • 50 m decay pipe, 91 cm radius, filled with stagnant air

MiniBooNE neutrino detector • Pure mineral oil • 800 tons; 40 ft diameter • Inner volume: 1280 8” PMTs • Outer veto volume: 240 PMTs

MiniBooNE’s track-based reconstruction • A detailed analytic model of extended-track light production and propagation in the tank predicts the probability distribution for charge and time on each PMT for individual muon or electron/photon tracks. • Prediction based on seven track parameters: vertex (x,y,z) , time, energy, and direction ( θ , φ ) ⇔ (U x , U y , U z ) . • Fitting routine varies parameters to determine 7-vector that best predicts the actual hits in a data event • Particle identification comes from ratios of likelihoods from fits to different parent particle hypotheses

Beam/Detector Operation • Fall 2002 - Jan 2006: Neutrino mode (first oscillation analysis). • Jan 2006 - 201?: Antineutrino mode • (Interrupted by short Fall 2007 - April 2008 neutrino running for SciBooNE) • Present analyses use: • ≥ 5.7E20 protons on target for neutrino analyses • 5.66 ⇒ 8.58 E20 protons on target for antineutrino analyses (Updated on data collected up to May 2011) • Over one million neutrino interactions recorded: by far the largest data set in this energy range

Neutrino scattering cross- sections • To understand the flavor physics of neutrinos ( i.e. oscillations), it is critical to understand the physics of neutrino interactions • This is a real challenge for most neutrino experiments: • Broadband beams • Large backgrounds to most interaction channels • Nuclear effects (which complicate even the definition of the scattering processes!)

Scattering cross-sections The state of knowledge of ν μ interactions before the current generation of experiments: for ν μ • Lowest energy ( E < 500 MeV ) is dominated by CCQE. • Moderate energies ( 500 MeV < E < 5 GeV ) have lots of single pion production. • High energies ( E > 5 GeV ) are completely dominated by deep inelastic scattering (DIS). • Most data over 20 years old, 300 GeV and on light targets (deuterium). 100 MeV • Current and future experiments NuMI, BooNEs NO ν A use nuclear targets from C to CNGS MINOS, LBNE Miner ν a Pb; almost no data available. T2K

Dominant interaction channels at MiniBooNE ν μ - W π 0 Δ n p ν μ - Charged-current CCQE (44%) W π 0 production n p 0 CC (4%) � Charged-current DIS (0.4%) CC multi- (3%) � quasielastic 0 NC (5%) � ν ν + NC (2%) � + CC (19%) � Others (4.1%) NC multi- (1%) � Z π 0 - CC � (0.5%) NCEL (17%) Charged-current Δ π + production n,p n,p + coherent ν μ - Neutral-current ν ν π 0 production π + W Z Δ n,p n,p Neutral-current + coherent n,p n,p elastic

Dominant interaction channels at MiniBooNE ν μ - W π 0 Δ n p ν μ - Charged-current CCQE (44%) W π 0 production n p 0 CC (4%) � Charged-current MiniBooNE has measured cross- DIS (0.4%) CC multi- (3%) � quasielastic 0 NC (5%) sections for all of these exclusive � ν ν + NC (2%) � + CC (19%) � Others (4.1%) channels, which add up to 89% of the NC multi- (1%) � Z π 0 - CC � (0.5%) NCEL (17%) Charged-current total event rate Δ π + production n,p n,p + coherent ν μ - Neutral-current ν ν π 0 production π + W Z Δ n,p n,p Neutral-current + coherent n,p n,p elastic

MiniBooNE cross-section measurements Due to limited time, only discussing a few topics here. • NC π 0 • CC π 0 • CC π + See plenary talk by G. Zeller • CC Quasielastic • NC Elastic • CC Inclusive

Measured observable CC π 0 cross-section -39 -39 10 × 10 × 18 ] ] 2 2 / CH / CH Statistical error Additionally, we 16 25 statistical 2 0 2 � � � + � absorption X) [cm + + / GeV Systematic error beam unisims 14 measure beam � + cross-sections NUANCE 20 2 0 DISC X) [cm 12 differential cross- � optical model - µ � � 10 sections vs: X 15 � 0 µ � � 8 • θ μ ( - � µ � � � 10 6 X • θ π QTcorr µ + beam K � ( CC + production � 4 2 • E μ � Q - beam � � 5 � hadronic 2 0 • E π beam K MC prediction 0 0 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 600 0.6 800 0.8 1000 1200 1400 1600 1800 2000 1 1.2 1.4 1.6 1.8 2 2 2 Q [GeV ] E E [MeV] [GeV] � � • The dominant error is π + charge exchange and absorption in the detector. • First-ever differential cross-sections on a nuclear target. • The cross-section is larger than expectation for all energies. • Phys.Rev.D83:052009,2011

Measured observable charged- current π + cross-sections -36 # 10 Error Bands ) 2 ) (cm MiniBooNE Measurement 0.12 Total Uncertainty ! • Differential cross sections (flux (E MC Prediction " 0.1 averaged): 0.08 0.06 d σ / dQ 2 , d σ / dE μ , d σ / d cos θ μ , • 0.04 d σ / d ( E π ), d σ / d cos θ π : 0.02 0 600 800 1000 1200 1400 1600 1800 2000 • Double Differential Cross Sections Neutrino Energy (MeV) -45 # 10 Error Bands ) 2 /MeV d 2 σ / dE μ d cos θ μ , d 2 σ / dE π d cos θ π MiniBooNE Measurement • 60 Total Uncertainty 4 c 2 MC Prediction (cm 50 ) 2 • Data Q 2 shape differs from the " (Q $ 40 $ model 30 20 • Phys.Rev.D83:052007,2011. 10 3 10 # 0 0 200 400 600 800 1000 1200 1400 2 2 4 Q (MeV /c )

Neutrino Oscillations: 2007 result Search for ν e appearance in • the detector using quasielastic scattering candidates • Sensitivity to LSND-type oscillations is strongest in 475 MeV < E < 1250 MeV range Oscillation • Data consistent with analysis region background in oscillation fit range • Significant excess at lower energies: source unknown, Oscillation search: Phys.Rev.Lett . 98 :231801 (2007) consistent experimentally with Low-E excess: Phys.Rev.Lett . 102 :101802 (2009) either ν e or single photon production

Antineutrino Oscillations • LSND was primarily an antineutrino oscillation search; need to verify with antineutrinos as well due to potential CP - violating explanations • Published analysis has same number of protons on target in antineutrino vs. neutrino mode, but... • Antineutrino oscillation search suffers from lower statistics than in neutrino mode due to lower production and interaction cross-sections • Also, considerable neutrino contamination (22±5)% in antineutrino event sample (e-print 1102.1964 [hep-ex])

Oscillation Fit Method • Simultaneous maximum likelihood fit to • ν̅ e CCQE sample • High-statistics ν̅ μ CCQE sample • ν̅ μ CCQE sample constrains many of the uncertainties: • ν̅ e and ν̅ μ flux uncertainties: ν e μ π ν μ • Cross section uncertainties (assume lepton universality) • Background modes -- estimate before constraint from ν̅ μ data (constraint changes background by about 1%) • Systematic error on background ≈ 10% (energy dependent)