Neutrino Oscillation Results from MINOS and MiniBooNE

1. Neutrino Oscillation Results from MINOS and MiniBooNE Tobias Raufer Rutherford Appleton Laboratory for the MINOS collaboration FPCP08, Taipei, 5-9 May, 2008

2. Overview Introduction to Neutrino Oscillations Neutrino masses and mixing Sterile neutrinos Current world knowledge on neutrino oscillation parameters Results from MINOS The NuMI beam and MINOS detectors Charged-current disappearance analysis Neutral current analysis νe appearance status Results from MiniBooNE The MiniBooNE Beam and Detector Results Outlook

3. Introduction to Neutrino Oscillations

4. Neutrinos mix • flavour eigenstates govern interactions • mass eigenstates propagate Flavour eigenstates Mass eigenstates Talk by Reyco Henning • Atmospheric+LBL ChoozSolar+KamLAND Majorana Two conditions necessary for neutrino oscillations: • Neutrinos mix • Neutrinos are massive

5. Neutrinos are massive There are only 3 light neutrinos coupling to the Z0 …

6. Neutrinos are massive There are only 3 light neutrinos coupling to the Z0 …

7. Neutrinos are massive There are only 3 light neutrinos coupling to the Z0 … … but there could be sterile neutrinos!

8. Neutrinos oscillate 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.

9. Neutrino oscillations: disappearance • Experiments in Homestake, Kamioka and Sudbury established deficit of νe from the sun • Total solar flux measured by SNO agrees with prediction • Super-K, K2K and MINOS have measured L/E form of νμ disappearance rate • KamLAND have measured L/E form of reactor anti-νe disapperance rate • CHOOZ have placed a limit on θ13 using non-disappearance of reactor anti-νe arXiv:0801.4589 [hep-ex]

10. Super-K Zenith Angle Best fit Honda Sub GeV 1ring e-like Sub GeV 1ring m-like Sub GeV Multi ring (m) Upward stopping m Upward through going m Multi GeV 1ring e-like Multi-GeV 1ring m-like + Partially Contained Multi GeV Multi ring (m)

11. νe νe νe νe νe νe sin22θ13 2 2 2 P ( ) 1 sin 2 sin ( 1 . 27 m L / E ) n  n = - q D e e 13 13 n Reactor Experiments Well understood, isotropic source of electron anti-neutrinos Oscillations observed as disappearance of νe 1.0 Probability νe Survival Probability + O(Dm122 / Dm132) Distance

12. Neutrino oscillations: appearance • Another signature of neutrino oscillation is appearance of ''wrong'' flavour neutrinos • LNSD observes excess ofanti-νein anti-νμ beam: 87.9 ± 22.4 ± 6.0 (3.8σ) LSND signal

13. Neutrino oscillation parameters MINOS result later in the talk!

14. The MINOS experiment

15. 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

16. 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 Producing Neutrinos Tobias Raufer 16

17. 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 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 Tobias Raufer 17

18. νμ CC Event νeCC Event NC Event Event Topologies νμ CC Event νeCC Event NC Event

19. νμ CC Event νeCC Event NC Event Event Topologies Monte Carlo νμ CC Event νeCC Event NC Event UZ VZ 3.5m long μ track & hadronic activity at vertex

20. νμ CC Event νeCC Event NC Event Event Topologies Monte Carlo νμ CC Event νeCC Event NC Event UZ VZ 3.5m 1.8m long μ track & hadronic activity at vertex short event, often diffuse

21. νμ CC Event νeCC Event NC Event Event Topologies Monte Carlo νμ CC Event νeCC Event NC Event UZ VZ 3.5m 1.8m 2.3m long μ track & hadronic activity at vertex short event, often diffuse short, with typical EM shower profile

22. νμ CC Event νeCC Event NC Event Event Topologies Monte Carlo νμ CC Event νeCC Event NC Event UZ VZ 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

23. CC disappearance measurement

24. CC disappearance Selecting charged-current events: • Reconstructed track with θ<53° w.r.t. beam direction • Vertex in fiducial volume • In time with beam spill • Reject NC background using a likelihood ratio discriminant constructed from 6 variables, e.g.

25. LE-10/170kA LE-10/185kA LE-10/200kA pME/200kA Horn off pHE/200kA Hadron Production Tuning Hadron production in the NuMI target has large uncertainties!  uncertain beam flux 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

26. π+ Target p FD Decay Pipe ND Predicting the FD spectrum • directly use Near Detector data to perform extrapolation between Near and Far • use Monte Carlo to provide necessary corrections due to energy smearing and acceptance. • use our knowledge of pion decay kinematics and the geometry of our beamline to predict the FD energy spectrum from the measured ND spectrum

27. CC disappearance Result

28. NC measurement

29. No νs With νs mixing Toy Simulation Neutral Current Analysis 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.

30. NC Event pre-selection Calorimeter Spectrometer n • 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

31. NC Event selection • Final neutral current event selection proceeds via cuts on three variables • Error envelopes shown reflect systematic uncertainties due to cross-section modeling and beam modeling Excluded Excluded Excluded • 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

32. NC Energy Spectrum • 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.

33. Is there a deficit? • 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.

34. 4-flavour Model • 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)

35. 4-flavour Result 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

36. Outlook • 90% C.L. sensitivity curves for different NuMI beam exposures • Input values of oscillation parameters • |Um3|2 = 0.5, |Us3|2 = 0.1, Δm232 = 2.38 x 10-3 eV2,|Ue3|2 = 0 • Only MC events are used

37. νe appearance search

38. MINOS νe appearance search • Search for far detector νe appearance in initially 99% νμ beam • Select νe with neural net based algorithm • Selected near detector events are mostly CCνμ and NC • Selection depends on details of hadronic simulation • Solution: use two independent data driven methods to estimate NC and CCνμ backgrounds selected νe sample

39. MINOS νe sensitivity • Projected limits shown with current and expected MINOS exposure • At CHOOZ limit expect 12 νe signal events and 42 background events with 3.25x1020 protons • Use sidebands to study predicted far detector backgrounds • Expect first result later this year

40. The MiniBooNE experiment

41. MiniBooNE searches for νμ→νe • 8GeV/c protons hit beryllium target • 4x1012 protons/spill with up to 4Hz rate • 174kA pulsed magnetic horn focuses positively charged hadrons: x6 flux gain • Detector is 800 tons of mineral oil placed with L/E similar to LSND:LSND: 0.03km/0.05GeV ~ 0.60 km/GeVMiniBooNE: 0.50km/0.80GeV ~ 0.63 km/GeV

42. MiniBooNE flux prediction  • HARP pion data were fit with Sanford-Wang parametrization: ~17% uncertainty • Fit world kaon data in 10-24GeV using Feynman scaling: ~30% uncertainty • Kaon flux is checked with off-axis ''Little Muon Counter'' and high energy events • Geant4 simulation of beamline: target, horn, decay volume and absorber e/= 0.5% K ee Kee

43. MiniBooNE beam events veto hits<6 tank hits>200 veto hits<6 veto cut removes cosmic μ removes electrons from cosmic μ decays CC1π 3 subevents • PMTs collect scintillation and Cherenkov light • Subvent is set of PMT hits close in time • Select subevents within beam spill window • Number of veto hits < 6 • Number of tank hits > 200 • Fiducial R < 500cm • Only 1 subevent in spill window - removes CC1π and CCQE events CCQE 2 subevents

44. Background θ,Φ E light t,x,y,z Signal Background MiniBooNE νe selection: step 1 • Maximize likelihood of observed hits under 2 hypotheses: 1) track is an electron 2) track is a muon • Vary 7 parameters Select electron tracks using likelihood ratio

45. E1,θ1,Φ1 light s1 t,x,y,z E2,θ2Φ2 s2 MiniBooNE νe selection: step 2 • Maximize likelihood of observed hits under 2 hypotheses with 10 parameters: 1) event is electron 2) event is π0→γγ • Select electron events using likelihood ratios blind π0 mass≈135Mev

46. MiniBooNE νe signal prediction • Blind analysis: signal box was opened in steps by gradually revealing more details about data events • Event selection tuning and background estimation used events outside signal region • ''Bad'' initial χ2 for data and predicted visible energy (null and best fit): move energy threshold to 475MeV

47. MiniBooNE Result • No excess of νe events in expected signal region from LSND • Significance (stat + syst error): • 475-1250 MeV: 22 ± 40 • 300- 475 MeV: 95 ± 28 • 200- 300 MeV: 91 ± 31 • What does it all mean? • LSND was wrong? • Difference between νe and anti-νe? • New physics that doesn't scale with L/E? • Detector or flux effects?

48. Summary & Outlook • MINOS • MINOS is steadily accumulating data • CC disappearance result for 2.5 x 1020 POT: • NC result for 2.5 x 1020 POT: • 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 • First MINOS electron-neutrino appearance result • MiniBooNE • No excess observed • Incompatible with LSND at 98% C.L. (two-flavour approx.)

49. Back-up slides

50. CC future sensitivity