MINOS Oscillation Results from The First Year of NuMI Beam Operation

Transcription

1 1 MINOS Oscillation Results from The First Year of NuMI Beam Operation Masaki Ishitsuka, Indiana University For the MINOS Collaboration Kyoto University, July 3 rd, 006

2 Overview of the talk Introduction to the MINOS experiment MINOS Physics Goals The NuMI facility and the MINOS detectors Beam and detector performance Near detector distributions and comparison with Monte Carlo Beam measurements by the near detector data Far detector analysis Near-Far extrapolation of the neutrino flux Oscillation Analysis with NuMI 1.7x10 0 pot beam data

3 Neutrino oscillation 3 Weak eigenstates Mixing parameters ν e ν1 ν μ = U ν ντ ν 3 Mass eigenstates 3 mass states ( mass differences) Δm 1 : solar+reactor Δm 3 : Atm-ν+LBL MINOS 3 mixing angles & 1 CPV phase U PMNS = Atm-ν+LBL MINOS c ij =cosθ ij s ij =sinθ ij iδ 0 0 c 13 0 s13e c1 s c3 s s1 c iδ s 3 c3 s13e 0 c LBL+reactor Solar+reactor

4 Current knowledge of -3 sector of mixing parameters and previous MINOS results 4 Allowed regions from Super-K, KK and previous MINOS (9.3x10 0 POT) Current measurements of Δm 3 and sin θ 3 from Super-Kamiokande and KK (9x10 19 pot) sin θ> <Δm < ev at 90%CL from SK L/E analysis The MINOS first result for 9.3x10 19 pot provided a competitive measurement of the mixing parameters. Oscillation results from 1.7x10 0 pot data is reported in this talk.

5 The MINOS Collaboration scientists 3 institutions 6 countries Argonne Athens Benedictine Brookhaven Caltech Cambridge Campinas Fermilab College de France Harvard IIT Indiana ITEP-Moscow Lebedev Livermore Minnesota-Twin Cities Minnesota-Duluth Oxford Pittsburgh Protvino Rutherford Sao Paulo South Carolina Stanford Sussex Texas A&M Texas-Austin Tufts UCL Western Washington William & Mary Wisconsin

6 The Concept of MINOS 6 MINOS (Main Injector Neutrino Oscillation Search) is a long-baseline neutrino oscillation experiment: High intensity muon neutrino beam produced from Main Injector 10GeV proton beam at Fermilab Near detector at Fermilab measure the un-oscillated energy spectrum 735 km Search for evidence for oscillations at Far detector deep underground in the Soudan Mine, Minnesota

7 7 Example of ν μ disappearance measurement Survival probability of muon neutrinos: P( ν ν ) = 1 sin θ sin (1.67Δm μ μ L / E) ν μ spectrum spectrum ratio Monte Carlo Unoscillated Monte Carlo (NC subtracted) Oscillated sin θ Δm

8 8 MINOS Physics Goals Demonstrate ν μ ν τ oscillation behavior Precise (<10%) measurement of oscillation parameters: Δm and sin θ. Search for/rule out exotic phenomena: Sterile neutrinos Neutrino decay Search for sub-dominant ν μ ν e oscillations Use magnetized MINOS Far detector to study neutrino and anti-neutrino oscillations Test of CPT violation Atmospheric neutrino oscillations in the MINOS far detector: First MINOS paper: Phys. Rev. D73 (006) 0700 [hep-ex/051036]

9 9 The NUMI facility Design parameters: 10 GeV protons from the Main Injector Main Injector can accept up to 6 Booster batches/cycle 1.9 second cycle time 4x10 13 protons/pulse 0.4 MW Single turn extraction (10μs) Average from 10/5 to 1/6:. second cycle time.3x10 13 protons/pulse 0.17 MW

10 Producing the neutrino beam segments of graphite of 0 mm length and mm cross section (total length 95.4 cm) Two parabolic focussing horns (3.0 Tesla peak field) Moveable target relative to horn 1 continuously variable neutrino spectrum

11 The NuMI neutrino beam 11 Currently running in the LE-10 configuration - Beam composition : 98.7% ν μ +ν μ (5.8% ν μ ), 1.3% ν e +ν e We have already accumulated data in 5 other beam configurations for systematics studies (~5% of total exposure). LE pme phe Expected no of events (no osc.) in Far Detector Beam Target z position (cm) FD Events per 1e0 pot LE pme phe Events in fiducial volume Position of osc. minimum for Δm =0.005 ev

12 The MINOS detectors Far Detector Veto Shield Near Detector kton mass, m 1 kton mass m 484 steel/scintillator planes 8 steel and 153 scintillator planes (x 8 multiplexing) (x 4 multiplexing after plane 10) VA electronics Fast QIE electronics B ~1.T Multi-pixel (M16,M64) PMTs GPS time-stamping to synch FD data to ND/Beam Continuous untriggered readout of whole detector (only during spill for the ND) Interspersed light injection (LI) for calibration Spill times from FNAL to FD trigger farm

13 Detector technology 13 Near and Far Detectors: Identical target components and detection technology.54 cm thick magnetized steel plates 4.1x1cm co-extruded scintillator strips (MINOS-developed technology) orthogonal orientation on alternate planes U,V optical fibre readout to multi-anode PMTs steel U V U V U V U V Scintillator strip scintillator orthogonal orientations of strips M16 PMT Far Detector

14 14 MINOS Calibration system Calibration of ND and FD response using: Light Injection system (PMT gain) Cosmic ray muons (strip to strip and detector to detector) Calibration detector (overall energy scale) Energy scale calibration: 5.7% absolute error % relative

15 15 First year of NuMI beam operation 1e0 pot! Observation of neutrinos in Near Detector! Start of LE running Dataset used for the oscillation analysis

16 Near detector events 16 One near detector spill Intense neutrino beam makes multiple neutrino interactions per spill in the near detector Events are separated by topology and timing Individual events MINOS Preliminary Batch structure clearly seen! Time (us)

17 Sensitive to ν μ ν τ oscillation ν μ CC Event Event topologies Monte Carlo NC Event ν e CC Event m 1.8m.3m long μ track+ hadronic activity at vertex short event, often diffuse short, with typical EM shower profile E ν = E shower +P μ 55%/ E 6% range, 10% curvature

18 18 Selecting CC events CC events are selected using a likelihood-based procedure MINOS Preliminary ND MINOS Preliminary ND ND MINOS Preliminary Event length in planes (related to muon momentum) Fraction of event pulse height in the reconstructed track (related to the inelasticity of CC events) Average track pulse height per plane (related to de/dx of the reconstructed track)

19 CC selection efficiencies The Particle ID (PID) parameter is defined as: 19 PID = μ ( log( P ) log( PNC )) CC-like events are defined by the cut PID>-0. in the FD (>-0.1 in the ND) NC contamination is limited to the lowest visible energy bins (below 1.5 GeV) Selection efficiency is quite flat as a function of visible energy MINOS Preliminary ND Monte Carlo (87%) (97%) PID parameter

20 0 Event selection cuts Near and Far 1. Event must contain at least one good reconstructed track. The reconstructed track vertex should be within the fiducial volume of the detector: ND: 1m < z < 5m (z measured from the front face of the detector), R< 1m from beam centre. FD: z>50cm from front face, z>m from rear face, R< 3.7m from centre of detector. ν NEAR DETECTOR FAR DETECTOR Calorimeter Spectrometer Fiducial Volume 3. The fitted track should have negative charge (selects ν μ ) 4. Cut on likelihood-based Particle ID parameter which is used to separate CC and NC events.

21 Near detector data distributions 1 Event rate MINOS Preliminary Near detector event raye LE POT Horn current test runs Different tunes in Feb. X Event vertices in the ND MINOS Preliminary MINOS Preliminary MINOS Preliminary Y Z

22 Energy spectra in the ND and hadron production tuning Agreement between data and Fluka05 Beam MC is within the systematic errors Further improvement by hadron production tuning as a funtion of x F and p T MINOS Preliminary Weights applied as a function of hadronic x F and p T. LE-10/170kA Data Fluka05 MC Tuned Had. Prod. LE-10/185kA LE-10/00kA pme/00ka phe/00ka Horns off LE-10/185kA MC π distributions for MINOS neutrino events

23 Stability of the energy spectrum & reconstruction 3 Energy spectrum by Month Energy spectrum by batch June July August September October November MINOS Preliminary MINOS Preliminary Reconstructed energy distributions agree to within statistical uncertainties (~1-3%) beam is stable for long period There is no significant intensity-dependent biases in event reconstruction MINOS Preliminary

24 4 Performing a blind analysis Far detector blinding Unknown fraction of FD events were hidden Blinded as a function of event length and energy The Open FD data used to check data quality Near detector data was open Used to study beam properties, cross sections, and detector systematics Analysis procedures were defined prior to box opening

25 Selecting beam induced events 5 Time stamping of the neutrino events is provided by two GPS units located at Near and Far detector sites. FD Spill Trigger reads out 100us of activity around beam spills MINOS Preliminary POT Neutrino events have distinctive topology and are easily separated from cosmic muons Backgrounds were estimated by fake triggers: 0 events in.6 million fake trrigers survived cuts upper limit of 0.5 background events Time of neutrino interactions from beam spill (µs)

26 Far detector beam data analysis 6 Oscillation analysis was performed using data taken in the LE configuration from May 0th 005 March 3rd 006 Total integrated POT: 1.7x10 0 MINOS Preliminary POT

27 7 Far detector distributions PID parameter MINOS Preliminary Muon energy MINOS Preliminary Shower Energy MINOS Preliminary Data Predicted no oscillations Best-fit

28 8 Near to Far extrapolation: Beam Matrix method Directly use the Near detector data to perform the extrapolation between Near and Far, using our Monte Carlo to provide necessary corrections due to energy smearing and acceptance. Predict the Far detector energy distribution from the measured Near detector distribution using pion decay kinematics and the geometry of beamline. target π + (stiff) to far Detector π + (soft) θ n θ f Decay Pipe E Flux π Eν = L 1+ γ θ 1+ γ θ ND

29 Procedure of predicting the FD spectrum 9 A) Reconstructed True E E Near CC-like Near CC Correction for purity, Reconstructed =>True, Correction for efficiency B) E True Near CC E BEAM MATRIX True Far CC C) E True Far CC E Reconstructed Far CC-like i) Oscillation, True => Reconstructed, Correction for efficiency to obtain CC oscillated spectrum ii) Unoscillated True => Reconstructed, Use purity to obtain NC background

30 Beam Matrix : Near to Far extrapolation 30 CC true spectrum in FD (un-oscillated) CC true spectrum in ND Beam Matrix provides relations between the FD and ND spectrum determined by pion -body decay kinematics and geometry of beamline

31 31 Different methods for predicting the FD spectrum Three alternative ND to FD extrapolation methods: ND fit : Reweight the FD MC using systematic parameters obtained by the ND fit D Grid fit : Reweight the FD MC using E ν x y correction matrix and systematic parameters obtained by the ND fit F/N ratio : Extrapolation using the Far/Near spectrum ratio from MC Predicted FD unoscillated spectra POT MINOS Preliminary The methods are robust to different categories of systematics

32 Numbers of observed and expected events POT MINOS Preliminary Numbers Data sample Observed Expected (matrix, no osc.) Ratio (matrix, no-osc.) Expected (ND fit, no osc.) ν μ (<30 GeV) ±1 0.64± ν μ (<10 GeV) 1 39± ± ν μ (<5 GeV) ±1 0.45± Energy dependent deficit is observed Significance of the deficit below 10 GeV is 5.9 σ (stat+syst)

33 MINOS observed spectrum and the best-fit for 1.7x10 0 POT 33 χ ( Δm,sin θ ) = nbins i= 1 ( e i o ) + o i i ln( o i / e i ) + (1 N) 0.04 o i : observed # events e i : expected # events N : absolute normalization MINOS Preliminary MINOS Preliminary Neutral Current subtracted Δm sin 3 θ =.7 3 = 1.00 Normalization (stat) = 0.98 (stat) -3 ev

34 34 Allowed regions Projected onto axis Δm 3 Δm sin 3 θ = = 1.00 (stat) (stat) Constrained to sin θ 3 1 Statistical errors -3 ev

35 Systematic errors 35 MINOS Preliminary Numbers Uncertainty Δm (x10-3 ev ) sin θ Near/Far normalisation +/- 4% Muon energy scale +/- % Relative Shower energy scale +/- % NC contamination +/- 50% CC cross-section uncertainties Intranuclear re-scattering / absolute energy scale (+/- 6%) Reconstruction Beam uncertainty Fit bias Total (sum in quadrature) Statistical sensitivity

36 Projected sensitivity of MINOS 36 ν μ disappearance Input parameters: Δm 3 =.7x10-3 ev sin θ 3 = %CL, statistical error only

37 Projected sensitivity of MINOS 37 Search for sub-dominant ν μ ν e 4X10 0 pot 16X10 0 pot MINOS Preliminary MINOS sensitivity as a function of CP violating phase and mass hierarchy Reasonable chance of making the first measurement of non-zero θ 13!

38 38 Summary and conclusions Preliminary MINOS oscillation results from the first year of NuMI beam operation was presented. Our exposure to data is pot. Deficit of ν μ events below 10GeV disfavors no oscillation at 5.9 σ (rate only). FD spectrum distortion is consistent with ν μ disappearance with the following parameters: Δm sin 3 θ =.7 3 = (stat) ± 0.13(syst) (stat) ± 0.04(syst) MINOS is taking data from the nd year of NuMI beam operation. Significant improvement in precision of oscillation parameters should be made with a larger dataset. -3 ev