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Recent Results from the MINOS Experiment

Recent Results from the MINOS Experiment. Robert Pittam University of Oxford (for the MINOS collaboration). Physics of Massive Neutrinos, Milos. 20-22 May 2008. The MINOS Experiment. M ain I njector N eutrino O scillation S earch

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Recent Results from the MINOS Experiment

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  1. Recent Results from the MINOS Experiment Robert Pittam University of Oxford (for the MINOS collaboration) Physics of Massive Neutrinos, Milos 20-22 May 2008

  2. The MINOS Experiment • Main Injector Neutrino Oscillation Search • Long baseline Experiment to measure Neutrino oscillations. • 2 Functionally identical detectors • Near Detector at Fermilab • Far Detector at Soudan Mine Robert Pittam, University of Oxford

  3. Precise measurements of |Dm232| and sin22q23 via nm disappearance Search for or constrain exotic physics such as sterile n Search for sub-dominant nm→ne oscillations via ne appearance Compare n, n oscillations Atmospheric neutrino and cosmic ray physics Study n interactions and cross sections using high statistics Near Detector data set Physics Goals of MINOS Robert Pittam, University of Oxford

  4. MINOS Methodology Measure energy spectrum at the Near Detector at Fermilab Measure energy spectrum at the Far Detector, 735km away in the Soudan Mine Look for νμ deficit at Far Detector νμ spectrum Spectrum ratio Monte Carlo Monte Carlo Unoscillated Oscillated Robert Pittam, University of Oxford

  5. Exp. Decay Pipe m+ Hadron n p+ p Absorber Rock Target Horns Making the Neutrino Beam • Neutrinos from the Main Injector • 10 μs spill of 120 GeV protons every 2.4 s • Typical beam power 180kW • 2.5x1013 Protons Per Pulse • Neutrino energy spectrum changes with target and horns position 675m 290m Robert Pittam, University of Oxford

  6. MINOS Detectors Far Near 5.4 kt mass, 8830m 484 steel/scintillator planes Divided into 2 super modules M16 multi-anode PMTs 1 kt mass, 3.84.815m282 steel and 153 scintillator plane Front 120 planes  Calorimeter Remaining planes  Spectrometer M64 multi-anode PMTs Detectors magnetised to 1.2 TGPS time-stamping to synch FD data to ND/Beam Robert Pittam, University of Oxford

  7. 2.54 cm Fe Extruded PS scint. 4.1 x 1 cm WLS fiber U V planes +/- 450 U V U V U V U V Clear Fiber cables Multi-anode PMT Detector Technology • Detectors are Functionally identical • 2.54 cm thick steel planes • Planes of 4.1cm wide strips of co-extruded polystyrene scintillator • Alternating orthogonal Orientation between consecutive planes – U,V • Signal read out by embedded Wavelength Shifting Fibres into multi-anode PMTs Orthogonal orientations of strips Steel Scintillator Robert Pittam, University of Oxford

  8. νμ CC Event νeCC Event NC Event 1.8m 3.5m Event Topologies νμ CC Event νeCC Event NC Event 2.3m Long μ track and hadronic activity at vertex short, with typical EM shower profile Short event often diffuse Monte Carlo Robert Pittam, University of Oxford

  9. Charged Current Selection • Selecting Charged Current Events • Require event vertex in fiducial volume • Reconstructed track with θ<53° w.r.t. beam • In time with beam spill • Reject NC Background based on a likelihood ratio discriminant made from 6 variables eg. NC Like Robert Pittam, University of Oxford

  10. + - D = ´ 2 0 . 20 3 2 m 2 . 38 10 eV - 32 0 . 16 = 2 sin 2 1 . 00 Q - 23 0 . 08 Charged Current Results Stat+syst errors Robert Pittam, University of Oxford

  11. Measurements of Z0 width at LEP exclude more than 3 light active neutrinos A 4th neutrino cannot couple to Z0 Cannot participate in weak interactions – sterile neutrino LSND results suggested the existence of a fourth neutrino with large mass splitting Earlier findings (Bugey, Karmen) combined with recent results from MiniBooNE strongly disfavour sterile neutrinos as an explanation for LSND If they exist, sterile neutrinos would be possible dark matter candidates Indicate existence of additional mass eigenstate Sterile neutrinos => new physics! NC Motivation Robert Pittam, University of Oxford

  12. Both Detectors Beam quality and detector quality cuts Far Detector: Remove Cosmics, detector noise and split events Use fiducial volume and cuts Near Detector: Many interactions in one spill within detector and surrounding rock Separate events with timing and topology cuts Use tight fiducial volume to control leakage Neutral Current Pre-selection Calorimeter Spectrometer n Robert Pittam, University of Oxford

  13. Neutral Current Separation • Cut Based Method Used • Event < 60 planes • Event < 2 tracks • If 0 tracks = NC • If 1 track & track extension < 5 = NC Excluded Error envelopes shown reflect systematic uncertainties due to cross-section and beam modeling Excluded Excluded Robert Pittam, University of Oxford

  14. Discrepancies much smaller than systematic uncertainties NC events are selected with 90% efficiency and 60% purity ND NC Energy Spectrum • NC selected Data and MC energy spectra for Near Detector Robert Pittam, University of Oxford

  15. NC Extrapolation • Far detector energy spectrum without oscillations is not the same as the Near detector spectrum • Decay angles for neutrinos to reach detector are different for ND and FD • different energy spectrum • We use the measured ND energy spectrum to predict the unoscillated FD energy spectrum • Near to Far extrapolation makes use of Monte Carlo to correct for energy smearing and acceptance differences π+ p Target FD Decay Pipe ND En ~ 0.43Eπ/ (1+gπ2θn2) Robert Pittam, University of Oxford

  16. Far Over Near 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 NDiData/NDiMC • Simple, makes no assumptions about ND Data parameterization, robust to systematic errors Robert Pittam, University of Oxford

  17. NC 3-Flavour Analysis • Compare the NC energy spectrum with the expectation of standard 3-flavor oscillation physics • Chosen oscillation parameter values: • sin22Θ23 = 1 • Δm232= 2.38x10-3 eV2 • Δm221 = 7.59x10-5 eV2, Θ12 = 0.61 from KamLAND+SNO • Θ13 = 0 or 0.21 (normal MH, δ=3π/2) from CHOOZ Limit • Note that CC ne are classified as NC by the analysis • Make comparison in terms of number of events in different energy ranges • 0-3 GeV • All events (0-120 GeV) • Result is #σ (dis-)agreement From MINOS CC measurement Robert Pittam, University of Oxford

  18. NC 3-Flavour - Energy Spectrum Robert Pittam, University of Oxford

  19. Comparisons between observed Data and MC Prediction Significance is given by NC 3-Flavour - Significances • For the 0-3 GeV reconstructed energy range, a 1.15σ difference between Data and Osc. Monte Carlo is observed in the case where Θ13 = 0. Robert Pittam, University of Oxford

  20. NC 4-Flavour Model • Assume there is an additional sterile neutrino and an additional mass scale • Mixing matrix is extended to: • Parameters (Δm221 ~ 0) • |Us3|2,|Us4|2,|Uμ4|2, Δm241 and φ43 Robert Pittam, University of Oxford

  21. NC 4-Flavour Model • 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) Robert Pittam, University of Oxford

  22. 4-Flavour Model Spectrum • Best fit energy spectrum for 2.461020 POT. • Largest systematic uncertainties included in the fit. Penalty terms for systematic uncertainties Robert Pittam, University of Oxford

  23. 90% C.L. contour for the fits to |Us3|2 and |Um3|2 Showing both cases:|Ue3|2 = 0 and |Ue3|2 = 0.04 (CHOOZ limit) 4-Flavour Model Contour Robert Pittam, University of Oxford

  24. Projected limits shown with current and expected MINOS exposure At CHOOZ limit expected 12 νesignal events and 42 background events with 3.25x1020 protons. MINOS νe Sensitivity • Use sidebands to study predicted far detector backgrounds • Expect first result later this year. Robert Pittam, University of Oxford

  25. = 2 + - D = ´ 2 0 . 20 3 2 sin 2 1 . 00 Q m 2 . 38 10 eV - 23 0 . 08 - 32 0 . 16 Summary Slide • MINOS still taking data • CC disappearance result for 2.5x1020 POT • Updated result public very soon • NC Result for 2.5x1020 POT • 3-Flavour analysis 1.15σ deficit for E < 3GeV • Consistent with no sterile admixture • 4-Flavour analysis • Electron Neutrino Appearance Result expected later this year Robert Pittam, University of Oxford

  26. Back-up Slides Robert Pittam, University of Oxford

  27. MINOS Near Detector • Partially instrumented (282 steel, 153 scintillator planes) • Uses both partial and full scintillator planes • Fast QIE readout electronics, continuous sampling during beam spill • Located 1km downstream of the target • ~1kt (980t) total mass • Shaped as squashed octagon (4.83.815m3) Beam center 4.8m Partial Plane Coil 3.8m Full Plane Robert Pittam, University of Oxford

  28. Veto shield 8m Coil MINOS Far Detector • Located 735km away at the Soudan mine, Minnesota, USA • 5.4kt, 2 supermodules • Shaped as octagonal prism (8830m3) • 486 steel planes, 484 scintillator planes • Veto shield (scintillator modules) • Spill times from Fermilab for beam trigger Robert Pittam, University of Oxford

  29. Extrapolating CC Near to Far • Pion/Kaon decay kinematics are encapsulated in matrix • Measured ND spectrum is transported to FD • Largely reduce systematics • hadron production • cross section Robert Pittam, University of Oxford

  30. 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 Robert Pittam, University of Oxford

  31. Systematic shifts in the fitted parameters are computed using MC simulated data histograms oscillated with |Um3|2= 0.5, |Us3|2= 0.2 4-Flavor Systematic Shifts Robert Pittam, University of Oxford

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