1. First MINOS Results from the NuMI Beam
Simona Murgia
Stanford University
PHENO 2006
Madison, WI, May
for the MINOS Collaboration
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
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2. Outline Neutrino oscillations
Oscillations at Dm2atm: Super-K, K2K, MINOS
MINOS
NuMI/MINOS overview
Start-up and running
Oscillation analysis
Results
Summary
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3. Oscillation Physics → L/E determines what Dm2 is probed
There is experimental evidence that neutrino flavor is not conserved and thus neutrinos have non-zero masses.
A neutrino of flavor a=e,m,t is a superposition of mass eigenstates described by the lepton mixing matrix U:
sij=sinqij, cij=cosqij
|Uai|2: probability that ni interaction will produce n of flavor a
In the two-flavor approximation:
→ L/E determines what Dm2 is probed
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4. Neutrino Mass Spectrum
(3 mass eigenstates - assume no nsterile) n 3 e m t
Normal Hierarchy
Inverted Hierarchy 1 2
|Umi|2
|Uti|2
|Uei|2
Dm2atm
Dm2sol
Two mass splittings:
Large (Dm2atm ):
Atmospheric (up-down asymmetry)
Long baseline
Small (Dm2sol ):
Solar + reactor
|Ue3|2 is not known (bounded by reactor expts) and neither is the mass hierarchy.
Solar data suggests |Ue2|2~1/3, and thus |Ue1|2~2/3 (unitarity and small |Ue3|2 ).
Also, data suggests nm  nt dominant at Dm2atm and maximal mixing angle,
|Umi|2 ~|Uti|2
With L/E~103 MINOS is sensitive to Dm2atm
This scale will be the focus of this talk
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5. 50 kT water Cherenkov detector
Super-Kamiokande
Ref. hep-ex/ , T. Kajita WHEPP9
Neutrinos produced by the interaction of primary cosmic rays in the Earth’s atmosphere. Wide range of energies and travel distances.
Measurement relies on knowledge of flux w/o oscillations
2,700 m.w.e. overburden
50 kT water Cherenkov detector
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6. Super-K (I+II) – Zenith
Down
90% CL:
2.1 < Dm223< 3.0×10-3eV2
sin22q > 0.93
(preliminary)
Unoscillated MC
Best fit: Dm223 = 2.5x10-3 eV2, sin22q23=1
Data
(preliminary)
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7. Super-K (I+II) – L/E SK-I+II SK-I+II (preliminary) (preliminary)
Consistent with Zenith angle analysis results.
At 90% CL: 2.0 < Dm223 < 2.9 ×10-3 eV2 , sin22q23> 0.92
(preliminary)
SK-I+II
Osc.
Decay
Decoh.
(preliminary)
SK-I+II
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8. K2K First long baseline accelerator neutrino experiment.
Ref. hep-ex/ , hep-ex/
First long baseline accelerator neutrino experiment.
Accelerator produced nm beam (1.3 GeV mean energy) travels 250 km toward Super-K. The near detector is located 300 m from the production target.
Observe energy dependent nm disappearance.
Super-K
Δm2=0.003eV2 , L=250km
En (GeV)
Near Detectors (SciBar,
1 kton water Cherenkov)
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9. K2K - Results
Observe deficit of nm at SK and distortion in the energy spectrum:
Well described by nm  nt oscillation
112 events at SK, expect
0.922x1020 POT
MC normalization:
number of events
(preliminary)
En (GeV)
Best fit: Dm223 = 2.76 x 10-3 eV2, sin22q23= 1
For sin22q23= 1: 90% CL 1.9 < Dm223<3.5 x10-3 eV2
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10. MINOS Main Injector Neutrino Oscillation Search
MINOS is a long baseline neutrino experiment
n produced at Fermilab travel in the direction of Soudan, MN, 735 km away.
Measure the neutrino energy spectrum at Soudan, MN, site of the MINOS far detector and compare it to the unoscillated spectrum prediction from the near detector, 1km from the target.
735 km 1 2
Monte Carlo 2 1
spectrum ratio
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11. NuMI Beamline 120 GeV protons from the Fermilab Main Injector
Up to 4x1013 protons every 1.9 sec
0.4 MW average beam power
Single turn extraction (10 ms)
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12. NuMI Target and Horns Target: 6.4x15 mm2 graphite segments.
ASSEMBLED
HORN #1
TARGET
HORN #2
Target: 6.4x15 mm2 graphite segments.
Two parabolic focusing horns (3T at 200kA).
The relative position of the target and the focusing horns allows running in different energy configurations
sensitive to different values of the oscillation parameters and non-oscillation models
study systematics and tune simulation
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13. Hadron and Muon Monitors
DECAY PIPE
Parallel plate ionization chambers monitor
hadron and muon content of secondary beam
BEAM MONITORING
HADRON MONITOR
MUON MONITOR
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14. The MINOS Detectors n beam n beam
Near and Far detectors have same basic design, with alternating layers of 2.54 cm thick steel and 1 cm thick solid scintillator (extruded polystyrene)
Magnetized to 1.2 T
Far Detector, Soudan, MN
980 tons, 105 m underground
282 steel and 153 scintillator planes
Near Detector at Fermilab, IL
n beam
735 km
5400 tons, 710 m underground
486 steel and 484 scintillator planes
n beam
Scintillator planes segmented in 4.1 cm wide strips embedded with WLS fibers.
The orientation of the strips in adjacent planes is orthogonal
Multi-anode Hamamatsu PMT (64-channel at near det and 16-channel at far det) optical readout.
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15. Calibration 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:
1.9% absolute error in ND
3.5% absolute error in FD
3% relative
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16. Start-Up and Running NuMI operations underway in December 2004
First neutrinos recorded in early 2005:
Near Detector, Jan Far Detector, Mar 2005
Average intensity (15 Oct to 31 Jan): 2.3 x 1013 protons every 2.2 sec
Integrated POT in 1 year running 1.39 x 1020 POT
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17. Neutrino Energy Spectrum
Running in different energy configurations has been achieved by moving the target.
1.5 x 1018 POT in pME and pHE configurations early in the run.
Target in LE-10 configuration (sensitive to favored Dm223 )
Beam composition: 98.5% nm+nm (6.5% nm), 1.5% ne+ne LE
pME
pHE
Beam
Target z position (cm)
FD Events (no osc) per 1 x 1020 POT
LE-10
-10
390
pME
-100
970
pHE
-250
1340
Events in fiducial volume
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18. Oscillation Analysis
The beam nm disappearance analysis was performed using data collected between May and Dec 2005.
The data sample corresponds to 0.93 x 1020 POT.
The analysis was performed by blinding an unknown fraction of far detector events (based on event length and total energy deposition)
The near detector data remained unblinded.
Extensive quality checks of the near and far (open) data were performed.
The data selection and analysis procedure were finalized before unblinding the far detector data in early March, 2006.
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19. Event Topologies nm ne En = Eshower+Pm Monte Carlo CC Event CC EventUZ VZ
Long m track + hadronic activity at vertex
3.5m ne
CC Event
Short, with typical EM shower profile
2.3m
NC Event
Short event, often diffuse
1.8m
En = Eshower+Pm
55%/E % range, 10% curvature
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20. Data Selection nm CC-like selection:
Events with at least one good reconstructed track.
Track vertex within the fiducial volume of the detector:
NEAR: 1m < z < 5m (z from front face) FAR: z>50cm from front face
R< 1m from beam center z>2m from rear face
R< 3.7m from center of detector
3. Fitted track should have negative charge (selects nm)
4. Discriminate NC background based on Particle ID parameter
(next two slides).
Calorimeter
Spectrometer
NEAR DETECTOR n
FAR DETECTOR
Fiducial Volume
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21. Selecting CC events
Further NC background reduction is achieved by assigning to each event CC-like and NC-like probabilities.
Pm and PNC are based on three input Probability Density Functions (PDFs) that differ for True CC and NC interactions:
Event length in planes
Fraction of event pulse height in the reconstructed track
Average track pulse height per plane
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22. CC Selection Efficiencies
The Particle ID (PID) parameter is defined as:
Optimized CC-like cuts: PID>-0.2 at FD, PID>-0.1 at ND
NC contamination limited to Evisible<1.5 GeV
Selection efficiency is quite flat as a function Evisible. MC MC
CC-like
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23. Near Detector Distributions
Very large near detector data sample (~107 events in the fiducial volume for 1020 pot) allows detailed Data/MC comparison and better understanding of detector performance.
Area normalised
Beam points down 3 degrees to reach Soudan
Reconstructed track angle with respect to vertical
Reconstructed x vertex (m)
Reconstructed y vertex (m)
Detector outline
Fiducial region
Partially instrumented planes
Distribution of reconstructed event vertices in the x-y plane
Vertex Z
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24. Near Detector - PID Distributions
Calorimeter/ spectrometer boundary
Event length
Track PH per plane
Track PH fraction
LE-10
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25. Hadron Production Tuning
Good agreement between data and Fluka05 Beam MC Better agreement obtained by tuning the MC by fitting to hadronic xF and pT.
LE-10/185kA
pME/200kA
pHE/200kA
LE-10/Horns off
LE-10 events
Weights applied as a function of hadronic xF and pT.
Not used in the fit
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26. Far Detector Data
The far detector n events used for the oscillation analysis have timing consistent with the spill. Event time-stamping provided by GPS units.
Easily separated from cosmic muons (0.5 Hz) using topology (upper limit on cosmics background in open sample: 1.7 events 90% C.L.)
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27. Observed/Expected Rates
33% deficit of events between 0 and 30 GeV with respect to the no oscillation expectation is observed.
Numbers are consistent for nm+nm sample and for the nm-only sample
The statistical significance of this effect is 5 standard deviations
Data sample
observed
expected
ratio
significance
All CC-like events (nm+nm)
204
29815
0.69
4.1s
nm only (<30 GeV)
166
24914
0.67
4.0s
nm only (<10 GeV) 92
17711
0.52
5.0s
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28. Far Detector - PID Distributions
Track Length
Track Pulse Height per Plane
Particle Identification Parameter
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29. Far Detector -Physics Distributions
Muon Momentum (GeV/c)
Shower Energy (GeV)
y = Eshw/(Eshw+Pm)
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30. Predicting the Far Detector Spectrum
Use the Near detector data to perform the extrapolation between Near and Far.
Monte Carlo provides necessary corrections for energy smearing and acceptance.
Use our knowledge of pion decay kinematics and the geometry of our beamline (extended neutrino source, seen as point-like from the Far Detector) to predict the Far detector energy distribution from the measured Near detector distribution
This method is known as the “Beam Matrix” method. p+
to far
Detector
target
(stiff) qf p+ qn
(soft)
Decay Pipe ND
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31. Beam Matrix Method FAR NEAR
Beam Matrix encapsulates the knowledge of pion 2-body decay kinematics & geometry.
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32. Predicted Spectrum Predicted FD unoscillated spectra
Nominal MC
0.93e20 pot
The Far Detector, unoscillated spectrum as predicted by the beam matrix method.
Excess in the high energy tail carried over from the near detector true spectrum.
Predicted FD unoscillated spectra
Three alternative methods were used
to predict the far det spectrum.
Different sensitivities to systematics.
Very good agreement.
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33. Oscillation Parameters
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34. Ratio Data/MC and Allowed Regions
The results of the four different extrapolation methods are in excellent agreement with each other.
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35. Total (sum in quadrature) Statistical error (data)
Systematic Errors
Systematic shifts in the fitted parameters have been computed with MC “fake data” samples for Dm2=0.003 eV2, sin22q=0.9 for the following uncertainties
Uncertainty
Dm2 shift (eV2)
Sin22q shift
Normalisation +/- 4%
0.63e-4
0.025
Muon energy scale +/- 2%
0.14e-4
0.020
Relative Shower energy scale +/- 3%
0.27e-4
NC contamination +/- 30%
0.77e-4
0.035
CC cross-section uncertainties
0.50e-4
0.016
Beam uncertainty
0.13e-4
0.012
Intranuclear re-scattering
0.030
Total (sum in quadrature)
1.19e-4
0.063
Statistical error (data)
6.4e-4
0.15
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36. Outlook nm disappearance nmne
Perform precise (<10%) measurements of Dm223 and sin22q23.
Search for sub-dominant nmne oscillations well below the current exclusion limit.
Test/rule out alternate models such as neutrino decay, sterile neutrinos.
nm disappearance nmne
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37. Summary
The first MINOS accelerator-based neutrino oscillation analysis from a 0.931020 POT exposure has been performed.
5 s evidence of nm disappearance has been observed.
The result is well described by nm oscillations with:
If sin22q23 is fixed to one, the best fit result is:
Systematic uncertainties are well under control.
Increasing POT will greatly improve the accuracy.
Total exposure to date is 1.4 1020 POT.
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