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Recent Results from the MINOS Neutrino Oscillation Experiment

Neutrino Oscillations The MINOS experiment Recent Results Summary. Physics at the Terascale, Bad Honnef 29 th April 2008. Recent Results from the MINOS Neutrino Oscillation Experiment. Neutrinos mix. Neutrino Oscillations The MINOS experiment Recent Results Summary.

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Recent Results from the MINOS Neutrino Oscillation Experiment

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  1. Neutrino Oscillations The MINOS experiment Recent Results Summary Physics at the Terascale, Bad Honnef 29th April 2008 Recent Results from the MINOS Neutrino Oscillation Experiment Tobias Raufer

  2. Neutrinos mix Neutrino Oscillations The MINOS experiment Recent Results Summary Two conditions necessary for neutrino oscillations: • Neutrinos are massive • Neutrinos mix • flavour eigenstates govern interactions • mass eigenstates propagate Flavour eigenstates Mass eigenstates Tobias Raufer

  3. Neutrinos are massive Neutrino Oscillations The MINOS experiment Recent Results Summary What does the neutrino mass spectrum look like? There are only 3 light neutrinos coupling to the Z0 … Tobias Raufer

  4. Neutrinos are massive Neutrino Oscillations The MINOS experiment Recent Results Summary There are only 3 light neutrinos coupling to the Z0 … Tobias Raufer

  5. Neutrinos are massive Neutrino Oscillations The MINOS experiment Recent Results Summary There are only 3 light neutrinos coupling to the Z0 … … but there could be sterile neutrinos! Tobias Raufer

  6. Neutrinos oscillate Neutrino Oscillations The MINOS experiment Recent Results Summary If mass and weak eigenstates are different: • Neutrino is produced in weak eigenstate. • It travels a distance L as a (superposition of) mass eigenstate(s). • It is detected as a (possibly different) weak eigenstate. Tobias Raufer

  7. Neutrino Oscillations The MINOS experiment Recent Results Summary 735 km The MINOS experiment • MINOS (Main Injector Neutrino Oscillation Search) • Long-baseline neutrino oscillation experiment • Neutrino beam provided by 120 GeV protons from the Fermilab Main Injector • Basic concept • Measure energy spectrum at the Near Detector, at Fermilab • Measure energy spectrum at the Far Detector, 735 km away, deep underground in the Soudan Mine • Compare Near and Far measurements to study neutrino oscillations Tobias Raufer

  8. Neutrino Oscillations The MINOS experiment Recent Results Summary Producing Neutrinos • Neutrinos from the Main Injector (NuMI) • 10 μs spill of 120 GeV protons every 2.4 s • 180 kW typical beam power • 2.5 1013 protons per pulse • Neutrino spectrum changes with target position Tobias Raufer 8

  9. Neutrino Oscillations The MINOS experiment Recent Results Summary MINOS Detectors Veto Shield Far Near Plane installation fully completed on Aug 11, 2004 Coil 5.4 kt mass, 8830m 484 steel/scintillator planes Divided into 2 super modules M64 multi-anode PMTs 1 kt mass, 3.84.815m282 steel and 153 scintillator planes Front 120 planes  Calorimeter Remaining planes  Spectrometer M16 multi-anode PMTs Detectors magnetised to ~1.3 TGPS time-stamping to synch FD data to ND/Beam Flexible software triggering in DAQ PCs: FD triggers from FNAL over IP Tobias Raufer 9

  10. Neutrino Oscillations The MINOS experiment Recent Results Summary Event Topologies Monte Carlo νμ CC Event νeCC Event NC Event 3.5m 1.8m 2.3m long μ track & hadronic activity at vertex short event, often diffuse short, with typical EM shower profile • Energy resolution • π±: 55%/E(GeV) • μ±: 6% range, 10% curvature Tobias Raufer

  11. CC disappearance Neutrino Oscillations The MINOS experiment Recent Results Summary Selecting charged-current events: • Vertex in fiducial volume • In time with beam spill • Reconstructed track with θ<53° w.r.t. beam direction • Reject NC background using a likelihood ratio discriminant constructed from 6 variables, e.g. Tobias Raufer

  12. CC disappearance Result Neutrino Oscillations The MINOS experiment Recent Results Summary Tobias Raufer

  13. Neutral Current Analysis Neutrino Oscillations The MINOS experiment Recent Results Summary No νs With νs mixing Toy Simulation Why look at NC events? • If oscillations only involve active neutrinos, NC events are unaffected. • Oscillations into sterile neutrinos cause energy dependent deficit in neutral current energy spectrum Tobias Raufer

  14. Neutrino Oscillations The MINOS experiment Recent Results Summary NC Event selection Neutral current event selection proceeds via cuts on three variables: • Event classified as NC-like if: • event length < 60 planes • has no reconstructed track or • has one reconstructed track that does not protrude more than 5 planes beyond the shower Excluded Excluded Excluded Tobias Raufer

  15. NC Energy Spectrum Neutrino Oscillations The MINOS experiment Recent Results Summary • Far Detector reconstructed energy spectrum for NC-like events. • Oscillation parameters are fixed. MC predictions with Θ13=0 and Θ13 at the CHOOZ limit are shown. Tobias Raufer

  16. Is there a deficit? Neutrino Oscillations The MINOS experiment Recent Results Summary • Comparisons between observed Data and MC Prediction • Significance is given by • For the 0-3 GeV reconstructed energy range, a 1.15σ • difference between Data and Monte Carlo is observed in the case where Θ13 = 0. Tobias Raufer

  17. 4-flavour Model Neutrino Oscillations The MINOS experiment Recent Results Summary • Introduce one additional, sterile neutrino • Assume Δm241=0 • Oscillation at single mass scale • Oscillation probabilities simplify to: • Fit for Δm231, |Uμ3|2 and |Us3|2 • Joint fit of NC and CC spectra • Fix |Ue3|2 = 0 and 0.04 (CHOOZ limit) Tobias Raufer

  18. 4-flavour Result Neutrino Oscillations The MINOS experiment Recent Results Summary • 90% C.L. contour for the fit to |Us3|2 and |Uμ3|2 • Showing the limiting cases: |Ue3|2=0 and |Ue3|2=0.04 Tobias Raufer

  19. Summary & Outlook Neutrino Oscillations The MINOS experiment Recent Results Summary • MINOS is steadily accumulating data • CC disappearance result for 2.5 x 1020 POT: • Neutral Current analysis result: • 3-flavour analysis: 1.15σ deficit for E < 3GeVconsistent with no sterile admixture • 4-flavour analysis: In the near future: • Updated CC result with more data and an improved analysis • Electron-neutrino appearance result Tobias Raufer

  20. Neutrino Oscillations The MINOS experiment Recent Results Summary Backup Slides Tobias Raufer

  21. Accumulated Beam Data Higher energy beam RUN III>0.9x1020 POT(current) RUN IIb~0.75x1020 POT(not included) RUN IIa1.22x1020 (LE) POT(new) RUN I - 1.24x1020 POT (LE)(PRL Publication nm disappearance) This Analysis: Run I + Run IIa => 2.46x1020 POT (LE Beam only) Tobias Raufer

  22. NC Event pre-selection • FD: remove cosmics, detector noise and split events • Fiducial volume and cleaning cuts • ND: many interactions in one beam spill, both inside the detector and in the surrounding rock • Separate events based on topology and timing • Tight fiducial volume Calorimeter Spectrometer n Tobias Raufer

  23. Hadron Production Tuning LE-10/170kA LE-10/185kA LE-10/200kA pME/200kA Horn off pHE/200kA Use tuning of hadron production in CC events to provide flux corrections for Monte Carlo Parameterize Fluka2005 prediction as a function of xF and pT Perform fit which reweights neutrino parent pion xF and pT to improve data/MC agreement Tobias Raufer

  24. Far/Near Ratio Method • An approach that uses the ND data in a non-parameterized way is provided by the F/N ratio method: • For every event that passes FD NC selection, a reconstructed energy vs true energy 2D histogram is created • Oscillation weights are calculated for bins of true Energy • For each bin of true energy, the reconstructed energy projection is multiplied by the corresponding oscillation weight • Prediction is obtained by multiplying each bin by NiData/NiMC • Simple, makes no assumptions about ND Data parameterization, robust to systematic errors Tobias Raufer

  25. Systematic Errors • Normalization: 4% • POT counting, Near/Far reconstruction efficiency, fiducial mass • Relative Hadronic Calibration:3% • Inter-Detector calibration uncertainty • Absolute Hadronic Calibration: 11% • Hadronic Shower Energy Scale(6%), Intranuclear rescattering(10%) • Muon energy scale:2% • Uncertainty in dE/dX in MC • CC Contamination of NC-like sample: 15% • NC contamination of CC-like sample: 25% • Cross-section uncertainties: • mA (qe) and mA (res): 15% • KNO scaling: 33% • Poorly reconstructed events: 10% • Near Detector NC Selection: 8% in 0-1 GeV bin • Far Detector NC Selection: 4% if E < 1 GeV, <1.6% if E > 1 GeV • Beam uncertainty: 1s error band around beam fit results Tobias Raufer

  26. Systematic Errors Simulated Data • Systematic errors studied using simulated Far Detector data histograms with oscillation parameters Dm2= 2.38 x10-3 eV2, sin22q23=1 • Left plot displays magnitude of shift in FD simulated data compared to nominal • Ratio plots show shifted/nominal ratio for FD simulated data, overlaid with shifted/nominal MC FD prediction • Displays ability of F/N extrapolation method to reproduce systematic shift • relative, where shifts only applied to one detector Tobias Raufer

  27. Systematic Errors Tobias Raufer

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