Latest Results from the MINOS Experiment Justin Evans, University College London for the MINOS Collaboration NOW th September 2008

2Justin Evans The MINOS Experiment Two detectors to mitigate systematics  e.g. neutrino flux or cross section mismodellings  Use measured near detector data to predict what should be observed at the far detector  An observed ν μ deficit at the far detector tells us about the oscillation parameters Measuring ν μ disappearance Near detector, 1.0 ktonne, 1km from source Far detector, 5.4 ktonne, 735 km from source Tracking, sampling calorimeters  Alternate steel and scintillator planes  Magnetised to 1.3 T Near detector Far detector

9th September 20083Justin Evans Use the measured ND energy spectrum to predict the FD spectrum: Spread of pion decay directions smears neutrino energies  Different energy spectra at the two detectors Encode the pion decay kinematics into a beam transfer matrix  Convert ND to FD spectrum FD Decay Pipe π+π+ Target ND p MC CC ν μ Beam Extrapolation

9th September 20084Justin Evans Effect of uncertainties estimated by fitting systematically shifted MC in place of data Analysis is still statistically limited Three largest uncertainties included as penalty terms in fit to data  Relative (ND to FD) normalisation (4%)  Absolute hadronic energy scale (10%)  NC background (50%) Systematic Uncertainties Relative normalisation Absolute hadronic energy NC background

9th September 20085Justin Evans FD data not looked at until the analysis was finalised Expected 1065 ± 60 with no oscillations Observed 848 events Energy spectrum fit with the oscillation hypothesis Far Detector Data Best Fit: |  m 2 | = 2.43x10 -3 eV 2 sin 2 (2  ) =1.00  2 /N DoF = 90/97

9th September 20086Justin Evans Constrained fit  |  m 2 | =(2.43±0.13)x10 -3 eV 2 (68% C.L.)  sin 2 (2  23 ) > 0.90 (90% C.L.)   2 /N DoF = 90/97 Unconstrained fit  |  m 2 | = 2.33 x eV 2  sin 2 (2  23 ) = 1.07  Δ  2 = -0.6 Allowed Region

9th September 20087Justin Evans Alternative Models Two alternative disappearance models are disfavoured Decay: V. Barger et al., PRL82:2640(1999)  2 /ndof = 104/97  2 = 14 disfavored at 3.7  Decoherence: G.L. Fogli et al., PRD67: (2003)  2 /ndof = 123/97  2 = 33 disfavored at 5.7 

9th September 20088Justin Evans NC Event Selection Excluded

9th September 20089Justin Evans NC Energy Spectrum Far detector NC energy spectrum Shown at θ 13 = 0 and θ 13 at Chooz limit Fraction of ν μ which oscillate to sterile neutrinos No ν e appearance  f s = (stat.+sys.)  f s < 0.68 (90% c.l.)  With ν e appearance  f s = (stat.+sys.)  f s < 0.80 (90% c.l.)

9th September Justin Evans ν e spectrum is heavily background dominated  Dominant backgrounds: NC and CC ν μ events Near detector shows a large discrepancy between selected and expected ν e energy spectrum Using data-driven methods to correct the data/MC differences ν e Appearance Analysis

9th September Justin Evans With 3.25x10 20 protons, at the Chooz limit, we expect 12 signal and 42 background events At current exposure MINOS will reach the Chooz limit In the future MINOS can improve on the Chooz limit by a factor of ~2 (normal hierarchy) ν e Appearance Sensitivity

9th September Justin Evans MINOS has made a new measurement of the atmospheric oscillation parameters  |  m 2 | =(2.43 ± 0.13) x eV 2 (68% C.L.)  sin 2 (2  23 ) > 0.90 (90% c.l.) Alternative models disfavoured  Decay at 3.7 σ, decoherence at 5.7 σ Measurement of the NC event spectrum places a limit on oscillations to sterile neutrinos  f s < 0.68 (90% c.l.) Work is ongoing towards a ν e appearance measurement  At the current exposure, MINOS’s sensitivity will rival the Chooz limit Summary

9th September Justin Evans

9th September Justin Evans Backup Slides

9th September Justin Evans CC ν μ Event Selection Aim to separate charged and neutral current ν μ interactions Four variables combined using a k-nearest-neighbour algorithm  Track length  Mean signal in track planes  Transverse track profile  Signal fluctuation along the track

9th September Justin Evans NC Energy Spectrum Far detector NC energy spectrum Shown at θ 13 = 0 and θ 13 at Chooz limit Energy Range (GeV) 0—30—120 Data events MC events ( θ 13 = 0) ± ± Significance1.15 σ 0.10 σ

9th September Justin Evans ν e spectrum is heavily background dominated  Dominant backgrounds: NC and CC ν μ events Near detector shows a large discrepancy between selected and expected ν e energy spectrum Using data-driven methods to correct the data/MC differences ν e Appearance Analysis

9th September Justin Evans Event Topologies ν μ CC Event NC Event ν e CC Event UZ VZ long μ track & hadronic activity at vertex short, with typical EM shower profile short event, often diffuse 3.5m 1.8m 2.3m Monte Carlo E ν = E shower + p μ