New Results from the MiniBooNE Booster Neutrino Experiment Mike - PowerPoint PPT Presentation

1 New Results from the MiniBooNE Booster Neutrino Experiment Mike Shaevitz Columbia University for the MiniBooNE Collaboration

2 Outline • Overview of MiniBooNE Beam and Detector • Brief Presentation of New Cross Section Results • Recent Oscillation Results – ν e and ⎯ν e appearance – ν µ and ⎯ν µ disappearance – Offaxis results from NuMI beam • Future Plans and Prospects

3 MiniBooNE was Prompted by the Positive LSND Result LSND observed a (~3.8 σ ) excess of ⎯ν e events in a pure ⎯ν µ beam: 87.9 ± 22.4 ± 6.0 events ν → ν = ± ± Oscillation Probability: ( ) (0.264 0.067 0.045)% P µ e The Karmen Exp. did not confirm the LSND oscillations but had a smaller distance 3+2 models LSND in conjunction with the atmospheric m 5 (Sorel, Conrad, and and solar oscillation results needs more Shaevitz, PRD than 3 ν ’s 70(2004)073004 (hep-ph/0305255) ⇒ Models developed with 2 sterile ν ’s Karagiorgi et al., or PRD75(2007)013011 ⇒ Other new physics models (hep-ph/0609177)

4 The MiniBooNE Experiment at Fermilab LMC ? µ + K + ν µ →ν e 8GeV π + ν µ Booster magnetic horn decay pipe absorber 450 m dirt detector and target 25 or 50 m • Proposed in summer 1997 ， operating since 2002 • Goal to confirm or exclude the LSND result - Similar L/E as LSND – Different systematics: event signatures and backgrounds different from LSND – High statistics: ~ x5 LSND • Since August 2002 have collected data: – 6.9 × 10 20 POT ν – 5.1 × 10 20 POT ⎯ν • Recently approved for an additional 5 × 10 20 POT in ⎯ ν mode

5 The MiniBooNE Collaboration Alabama, Bucknell, Cincinnati, Colorado, Columbia, Embry- Riddle, Fermilab, Florida, Illinois, Indiana, Los Alamos, LSU, MIT, Michigan, Princeton, Saint Mary’s, Virginia Tech, Yale

6 Neutrino Flux • Well understood ν µ neutrino flux using HARP pion production data • Wrong-sign contamination small due to sign selection of focusing horn • ν e flux from µ -decay constrained by observed ν µ events • Contribution to ν e flux from K-decay small at 8 GeV Flux Publication: primary proton energy PRD 79, 072002 (2009) Neutrino-Mode Flux Antineutrino-Mode Flux ⎯ν µ ν µ ν µ ⎯ν µ ⎯ν e ν e ν e ⎯ν e Wrong-sign background: ~6% Wrong-sign background: ~18% Intrinsic ν e background: ~0.5% Intrinsic ν e background: ~0.5%

7 MiniBooNE Detector • 12m diameter tank • Filled with 900 tons of pure mineral oil • Optically isolated inner region with 1280 PMTs • Outer veto region with 240 PMTs. • Detector Requirements: – Detect and Measure Events: Vertex, E ν … Separate ν µ events from ν e events – γ ’s from π 0 ’s µ -decay electrons Detector Publication: Muon Energy NIM A599, 28 (2009) vs Range Very good ν µ versus ν e event identification using: • Cherenkov ring topology • Scint to Cherenkov light ratio • µ -decay Michel tag

8 MiniBooNE Cross Section Measurements • Cross section measurements are important for the future neutrino oscillation program – Quasi-Elastic events used for ν µ and ν e signal – Backgrounds: ⇒ For ν e appearance is NC single π 0 production ⇒ For ν µ disappearance is CC single π ± ,0 production • MiniBooNE can measure a wide range of NC & CC processes by identifying outgoing π ’s and µ ’s using Michel electron tags • Past measurements have limited accuracy and coverage for the energy range of T2K, NOvA, and DUSEL ⇒ MiniBooNE better match ν µ CC Cross Section ⎯ν µ CC Cross Section MiniBooNE MiniBooNE NOvA T2K DUSEL

9 Recent MiniBooNE Xsec Measurements ν µ NC Elastic n,p n,p π 0 ν µ NC π 0 Extended n,p n,p range and precision with respect to previous BNL E734 (1987) CC π + /QE σ ratio ν µ CC π + arXiv:0904.3159 µ − W + π + n,p n,p First measurement of absolute NC π 0 differential cross section Also, first measurement of absolute CC π + diff’l cross sections

10 Quasi-Elastic Cross Section Mystery • MiniBooNE provides the most complete information on ν µ QE scattering to date for E ν < 2 GeV – 146,070 ν µ QE events (76% purity, 27% ε ) • One main physics parameter – Axial Vector Mass M A ⇒ Use Q 2 shape fit to extract M A (No normalization) – MiniBooNE Q 2 shape fit result: M A =1.35 ± 0.17 GeV ⇒ Consistent with K2K and MINOS – Much larger than NOMAD: M A = 1.06 ± 0.06 GeV • Also measure total cross section versus E ν (Depends on normalization) – MiniBooNE and recent SciBooNE in good agreement – Both higher than recent σ QE from NOMAD ?! (all three on 12 C) ⇒ Future MINOS and Minerva data in missing energy region µ − W + preliminary n Higher value of M A also consistent with σ total vs E ν

11 MiniBooNE Neutrino Oscillation Results (In the ∆ m 2 > 0.1 eV 2 Region) • Search for ν e Appearance – Original 2007 result excludes LSND 2 ν osc hypothesis but sees “Low energy excess” – Updated results with improved analysis • Search for ⎯ν e Appearance – New results from antineutrino running • Search for ν µ and ⎯ν µ Disappearance – New results for both neutrino and antineutrinos • Measurements of events in MiniBooNE from NuMI offaxis neutrinos.

Original ν µ → ν e Appearance Search in LSND Region 12 Method: Search for an excess of “ ν e ” • events over expectation ⇒ Knowing expectation is key Use observed ν µ events to constrain ν e physics and background 1. Cross section π 0 and ∆ Rad backgrounds 2. ν e from µ -decay 3. 4. Bkgnds from external interactions • In analysis region between 475 < E ν < 3000 MeV, no evidence for oscillation in LSND region Simple 2 ν osc excluded at 98% CL – • Unexpected excess of events at low energy < 475 MeV Phys. Rev. Lett. 98, 231801 (2007), arXiv:0704.1500 [hep-ex]

Updated ν µ → ν e Appearance Results 13 Many improvements and cross checks of analysis Backgrounds: 1. Improved π 0 production data and ∆ Rad modeling 2. Inclusion of missing “Photo-nuclear absorption” backgrounds 3. Improved cuts to reduce external interaction background Excess over Background • Systematic errors rechecked, and some improvements made • Analysis threshold lowered to 200 MeV with reliable syst. errors. • Increased statistics 5.6 × 10 20 pot ⇒ 6.5 × 10 20 pot Published: “Unexplained Excess of Electron-Like Events from a 1 GeV ν For 200-475 MeV: Beam”, PRL 102 , 101802 (2009) Excess =128.8+-20.4+-38.3 (3.0 σ )

New ⎯ν µ →⎯ν e Appearance Results 14 • The antineutrino search important because Provides direct tests of LSND ⎯ν appearance – – More information on low-energy excess • The backgrounds at low-energy are almost the same for the neutrino and antineutrino data samples. • Antineutrino analysis is the same as the neutrino analysis. • First antineutrino result has low statistics 3.4 × 10 20 POT giving about 100K event – – Inconclusive wrt LSND No indication of ⎯ν data-MC excess: 200-475 MeV: -0.5 ± 11.7 events 475-1250 MeV: 3.2 ± 10.0 events (arXiv:0904.1958)

ν µ and ⎯ν µ Disappearance Search 15 Method: Identify CCQE events and compare to expectation µ 12 C e ν µ n p Identification: Tag single muon events and their decay electron 74% CCQE purity 70% CCQE purity 190,454 events 27,053 events CCQE ν µ µ - CCQE ⎯ν µ ν µ µ + ⎯ν µ W − W + p n n p ν µ CC π + CC π +/- E ν QE (GeV) Similar CC π +/- background, and CCQE Background is CC π + where the pion is purity as in neutrino mode absorbed in the nucleus or detector Also, substantial neutrino events in the antineutrino sample (~25%)

16 MiniBooNE ν µ and ⎯ν µ Disappearance Limits MiniBooNE observes no neutrino or antineutrino Neutrino: disappearance at 90%CL Purple: Data ⇒ Excludes some 3+2 model possibilities Red: Monte Carlo CCFR CDHS χ 2 (no osc) = 17.8 / 16 dof AntiNeutrino: CCFR Purple: Data Red: Monte Carlo (arXiv:0903.2465) χ 2 (no osc) = 10.3 / 16 dof In future, plan to incorporate data from a second detector, SciBooNE, as a near detector for osc search

17 Events from NuMI Directed at MiniBooNE “1st Measurement of ν µ , ν e Events in MiniBooNE N E o B o Off-Axis Horn-Focused ν Beam”, n i M i o m t a Detector B e I u M N i s a x O f f PRL 102 , 211801 (2009) N u M I B e a m t o S o u d a n ν e / ⎯ν e • MiniBooNE detector sees neutrinos from MINOS NuMI beam at a 110 mrad off-axis angle • NuMI offaxis neutrinos have different composition wrt BNB: ν µ 81% ν e 5% ⎯ν µ 13% ⎯ν e 1% • Almost all ν e / ⎯ν e from K ± ,0 decay • L/E similar to MiniBooNE beam For current data, observe small ν µ / ⎯ν µ 1- σ ν e excess at low energy ⇒ Can reduce syst. errors in the future.