Searching for Sterile Neutrinos with MINOS 51th Rencontres de Moriond EW2016 Ashley Timmons on behalf of the MINOS/MINOS+ collaboration 1
Intro - Neutrino Oscillations Neutrino oscillations arise from mixture of mass and flavour eigenstates X | ν α i = U ∗ α i | ν i i ( α = e, µ, τ ) flavour state mass state i Many neutrino experiments observe data consistent with three-flavour model θ 12 , θ 23 , θ 13 , δ 13 , Δ m 232 (~10 -3 eV 2 ) and Δ m 221 (~10 -4 eV 2 ) LSND, MiniBooNE at L/E ~ 1 km/GeV, interpret as oscillations if Δ m 2 ~ 1eV 2 we consider the model 3(active)+1(sterile) Introduces: θ 14 , θ 24 , θ 34, δ 24, δ 14 and Δ m 241 U e 1 U e 2 U e 3 U e 4 U µ 1 U µ 2 U µ 3 U µ 4 U = U τ 1 U τ 2 U τ 3 U τ 4 U s 1 U s 2 U s 3 U s 4 2
MINOS/MINOS+ Data Set Low Energy antineutrinos 22 14 Low Energy neutrinos Higher Energies 20 NOvA neutrinos ) 12 18 18 ) 20 10 10 16 10 × Protons per week ( × 14 Total Protons ( 8 12 10 6 8 4 6 4 2 2 0 0 2005/05/02 2006/08/03 2007/11/05 2009/02/05 2010/05/10 2011/08/11 2012/11/12 2014/02/13 2015/05/18 Date MINOS MINOS+ MINOS+ is the continuation of MINOS with the NuMI beam in the medium energy configuration. 3
The NuMI Beam This analysis uses this beam mode 0.06 0.06 (Arbitary Units) (Arbitary Units) CC CC ν ν µ µ CC CC ν ν µ µ Near Detector 0.04 0.04 Near Detector Simulated Simulated Low Energy Beam CC Low Energy Beam CC σ Reverse Horn Current σ Forward Horn Current 0.02 0.02 Flux x Flux x 0 0 0 5 10 15 20 25 30 0 5 10 15 20 25 30 True Neutrino Energy (GeV) True Neutrino Energy (GeV) 4
Detectors Near Far • 4.2 kiloton fiducial mass • 23.7 ton fiducial mass • Veto shield for cosmic suppression • 1.04 km downstream from target • 705m underground • Both detectors are magnetised tracking/sampling calorimeters, segmented into planes composed of 2.54 cm-thick steel planes and 1 cm-thick scintillator strips • Detectors designed to be functionality equivalent, cancels systematics uncertainties in flux modelling and cross section to first order. 5
Long-Baseline Sterile Search MINOS was built for measurement of Δ m 232 by looking for ν μ disappearance optimised for L/E = 500km/GeV Looking for perturbations from three-flavour This is at FD baseline disappearance (sensitive to θ 24, θ 23 ) of 735km Neutral current interaction rate is the same for the three active flavours P( ν μ -> ν s ) depends on θ 24, θ 34, θ 23, 6
Event Topologies CC NC 7
FD Spectra - Data FD spectra three-flavour oscillated with MINOS 2012 CC-analysis fit values This is NOT a fit 200 MINOS Preliminary MINOS Preliminary 20 20 10.56x10 POT 10.56x10 POT 400 running running ν MINOS NC-like Far Detector data ν MINOS CC-like Far Detector data µ µ Three-flavour simulation 150 Systematic uncertainty NC Three-flavour simulation CC ν CC background 300 Events Events µ Beam background Systematic uncertainty ν e appearance ν e 100 NC background ν appearance τ 200 2 -3 2 m = 2.37 x10 eV 2 -3 2 ∆ ∆ m = 2.37 x10 eV 32 32 2 sin ( ) = 0.41 2 θ sin ( ) = 0.41 θ 50 23 23 100 -5 2 2 m = 7.54 x10 eV 2 -5 2 ∆ m = 7.54 x10 eV ∆ 21 21 2 sin ( θ ) = 0.022 2 sin ( ) = 0.022 θ 13 13 0 0 0 10 20 30 40 0 10 20 30 40 Reconstructed Visible Energy (GeV) Reconstructed Neutrino Energy (GeV) 1211 NC-like events 2563 CC-like events R [0-3 GeV] = 1.10 +/- 0.06 +/- 0.07 R [0-40 GeV] = 1.05 +/- 0.04 +/- 0.10 If no NC disappearance R = 1 8
Oscillations This is assuming a three-flavour model - no sterile neutrinos 9
Oscillations Sterile oscillations in the FD only. 10
Oscillations Fast oscillations in the FD, counting experiment 11
Oscillations oscillations now occur at the ND. Typical extrapolation using ND data is no longer possible! 12
Far Over Near Ratio New analysis technique to probe many magnitudes of Δ m 241 0 1 2 3 4 5 5 10 15 20 20 30 30 40 MINOS Preliminary 0.8 0.8 -3 2 2 m = 2.37 x10 eV Direct fit to F/N ratio ∆ 32 2 sin ( ) = 0.41 θ 23 0.6 0.6 for CC and NC events ) -5 2 2 m = 7.54 x10 eV -3 ∆ 21 Far / Near Ratio (x10 2 sin ( ) = 0.022 θ 13 0.4 0.4 Assume 3+1 sterile model 0.2 0.2 CC selection Set δ 13 , δ 14 , δ 24 and θ 14 to zero 0 1 2 3 4 5 5 10 15 20 20 30 30 40 0 1 2 3 4 5 5 10 15 20 20 30 30 40 0.5 0.5 MINOS data Three-flavour simulation 0.4 0.4 Systematic uncertainty we assume no ν e -> ν s 0.3 0.3 0.2 0.2 Parameters fit are: 0.1 0.1 Δ m 232 , Δ m 241 , θ 24, θ 23, and θ 34 NC selection 0 1 2 3 4 5 5 10 15 20 20 30 30 40 Reconstructed Energy (GeV) Moved from likelihood method towards χ 2 fit, containing covariance matrix with systematics 13
Total Uncertainties MINOS Preliminary F/N Fractional Error MINOS Preliminary F/N Fractional Error 0.2 0.2 CC total systematic NC total systematic 0.1 0.1 0 0 -0.1 -0.1 -0.2 -0.2 0 10 20 30 40 0 10 20 30 40 Reconstructed Energy (GeV) Reconstructed Energy (GeV) Including 26 systematics into the fit via covariance matrix, accounting for: Normalisation, Detector acceptance, NC selection, Hadron production, Beam focusing, Cross sections, Energy scale and background 14
Total Uncertainties 2 10 MINOS Preliminary 10 20 10.56x10 POT ) 2 MINOS simulation, running ν (eV µ 1 Statistics + Normalization 41 2 + Acceptance -1 10 m + NC selection ∆ Total Systematics -2 10 -3 10 0.02 0.04 0.06 0.08 0.1 0.12 2 sin ( ) θ 24 E fg ect on the sensitivity when including largest systematics added incrementally. 15
Disappearance Limit 2 10 MINOS Preliminary 10 20 10.56x10 POT running ν µ ) 2 1 (eV MINOS data -1 10 41 MINOS data 90% C.L. 2 m MINOS data 95% C.L. -2 10 ∆ Super-K 90% C.L. CDHS 90% C.L. -3 10 CCFR 90% C.L. SciBooNE + MiniBooNE 90% C.L. -4 10 -3 -4 -2 -1 10 10 10 10 1 2 sin ( ) θ 24 Feldman-Cousins procedure used for confidence limit 16
Combination with Bugey MINOS disappearance search sensitive mainly to θ 24 Bugey reactor experiment - electron anti-neutrino disappearance, θ 14 Accelerator and reactor - largely uncorrelated systematic uncertainties 2 10 MINOS Preliminary 20 MINOS data: 10.56 10 POT × 10 mode ν µ ) LSND 90% CL 2 1 (eV ICARUS 90% CL 1 − OPERA 90% CL 10 2 NOMAD 90% CL m 2 − 10 MiniBooNE 90% CL ∆ MINOS/Bugey* 90% CL 3 − 10 * GLoBES 2012 fit with new reactor fluxes, courtesy of P. Huber 4 − 10 6 5 3 7 4 2 1 − − − − − − − 10 10 10 10 10 10 10 1 2 2 2 sin 2 = 4|U | |U | θ e µ 17 e4 4 µ
The Future 18
Summary MINOS uses CC+NC sample to look for sterile neutrinos via deviations from the three-flavour model using a 3+1 model on the F/N Ratio Use of covariance matrices for systematics, show power of two detector experiment with cancellation of large systematics Combination with reactor experiment Bugey allows for limit on same parameter space as LSND etc Future with additional data from MINOS+ with higher stats at higher energies. 19
BACK UP 20
Sterile Neutrinos? Looking for ν e appearance in a ν μ beam anti-neutrinos 3.4 σ 3.8 σ LSND 2.8 σ MiniBooNE Blue histogram includes E ~ 0.2 - 3 GeV oscillations E ~ 20-200 MeV L ~ 540m for Δ m 2 ~ 1eV 2 L ~ 30m L/E ~ 1 km/GeV 21
Sterile Neutrinos An experiment with L/E ~ 1 km/GeV could only observe oscillations if Δ m 2 ~ 1eV 2 LEP measurements of the Z width show three active neutrinos. Therefore any additional ones must be sterile experimentally we consider the model 3(active)+1(sterile) Introduces: θ 14 , θ 24 , θ 34, and Δ m 241 U e 1 U e 2 U e 3 U e 4 energy dependence U µ 1 U µ 2 U µ 3 U µ 4 of oscillations U = amplitude U τ 1 U τ 2 U τ 3 U τ 4 ∆ 41 = ∆ m 2 41 L of oscillations 4 E ν U s 1 U s 2 U s 3 U s 4 | Δ m 241 | >> | Δ m 232 |, | Δ m 221 | L/E ~ 1 km/GeV 22
Sterile Neutrinos 2 10 mode ν µ LSND 90% CL LSND 99% CL 10 ) KARMEN2 90% CL 2 (eV ICARUS 90% CL MiniBooNE 90% CL 1 2 MiniBooNE 99% CL m ∆ 1 − 10 2 − 10 6 5 3 7 − − 4 − 2 1 − − − − 10 10 10 10 10 10 10 1 2 2 2 sin 2 = 4|U | |U | θ e µ e4 4 µ 23
The NuMI Beam 7 7 10 10 MINOS ND Simulation MINOS ND Simulation - + π π ν 6 ν 10 Forward Horn Current 6 µ Forward Horn Current 10 µ # Events (A.U) # Events (A.U) - + K K 5 10 5 ν 10 ν e - e + µ µ 4 10 4 10 3 10 3 10 2 10 2 10 10 10 1 0 20 40 60 80 100 120 0 20 40 60 80 100 120 True Neutrino Energy (GeV) True Neutrino Energy (GeV) • Anti-neutrino background, high • Neutrino parents energies, hard to defocus • Mainly pions, significant koan • Intrinsic electron neutrino component at higher energies component. 24
Experimental Setup Near Far 25
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