recent results from the minos neutrino oscillation experiment
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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. - PowerPoint PPT PresentationTRANSCRIPT
Recent Results from MINOS
Dr Tobias Raufer
Recent Results from the MINOS Neutrino Oscillation Experiment
Physics at the Terascale, Bad Honnef
29th April 2008
Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
Tobias Raufer
Recent Results from MINOS
Neutrinos mix
Two conditions necessary for neutrino oscillations:– Neutrinos are massive
– Neutrinos mix
Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
Flavour eigenstates
Mass eigenstates
flavour eigenstates govern interactions
mass eigenstates propagate
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Recent Results from MINOS
Neutrinos are massive
What does the neutrino mass spectrum look like?
Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
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There are only 3 light neutrinos coupling to the Z0 …
Recent Results from MINOS
Neutrinos are massiveNeutrino OscillationsThe MINOS experimentRecent ResultsSummary
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There are only 3 light neutrinos coupling to the Z0 …
Tobias Raufer
Recent Results from MINOS
Neutrinos are massiveNeutrino OscillationsThe MINOS experimentRecent ResultsSummary
… but there could be sterile neutrinos!
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There are only 3 light neutrinos coupling to the Z0 …
Tobias Raufer
Recent Results from MINOS
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.
Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
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Recent Results from MINOS
735 km
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
The MINOS experimentNeutrino OscillationsThe MINOS experimentRecent ResultsSummary
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Recent Results from MINOS
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
Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
Tobias Raufer 8
Recent Results from MINOS
Detectors magnetised to ~1.3 T
GPS time-stamping to synch FD data to ND/Beam
Flexible software triggering in DAQ PCs: FD triggers from FNAL over IP
Coil
Veto Shield Far
Near
Plane installation fully completed on Aug 11, 2004
5.4 kt mass, 8830m
484 steel/scintillator planes
Divided into 2 super modules
M64 multi-anode PMTs
1 kt mass, 3.84.815m
282 steel and 153 scintillator planes
Front 120 planes Calorimeter
Remaining planes Spectrometer
M16 multi-anode PMTs
Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
MINOS Detectors
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Recent Results from MINOS
Event Topologies
νμ CC Event νe CC EventNC Event
3.5m 1.8m 2.3m
long μ track & hadronic activity at vertex
Monte Carlo
short event, often diffuse
short, with typical EM shower profile
Energy resolution
π±: 55%/E(GeV)
μ±: 6% range, 10% curvature
Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
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Recent Results from MINOS
CC disappearance
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.
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Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
Recent Results from MINOS
CC disappearance Result
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Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
Tobias Raufer
m322 2.38 0.16
0.20(stat syst)10 3eV2
sin2(223)1.00 0.08(stat syst)
Recent Results from MINOS
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
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Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
Toy Simulation
No νs
With νs mixing
Recent Results from MINOS
• 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
Neutral current event selection proceeds via cuts on three variables:
Excluded Excluded
Excluded
NC Event selectionNeutrino OscillationsThe MINOS experimentRecent ResultsSummary
Tobias Raufer 14
Recent Results from MINOS
NC Energy Spectrum
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Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
Tobias Raufer
• 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.
Recent Results from MINOS
Is there a deficit?
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Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
Tobias Raufer
• 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.
Recent Results from MINOS
4-flavour Model
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Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
Tobias Raufer
• 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)
Recent Results from MINOS
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
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Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
Recent Results from MINOS
Summary & Outlook
• 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 < 3GeV
consistent 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
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Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
m322 2.38 0.16
0.20(stat syst)10 3eV2, sin2(223)1.00 0.08(stat syst)
Us3
2 0.14 0.130.18, for Ue3
2 0 (no e admixture)
Us3
2 0.21 0.120.20, for Ue3
2 0.04 ( e admixture)
Recent Results from MINOS
Backup Slides
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Neutrino OscillationsThe MINOS experimentRecent ResultsSummary
Recent Results from MINOS 21
Accumulated Beam Data
RUN I - 1.24x1020 POT (LE)(PRL Publication
disappearance)
Higher energy beam
RUN IIa1.22x1020 (LE) POT(new)
RUN IIb~0.75x1020 POT(not included)
This Analysis: Run I + Run IIa => 2.46x1020 POT (LE Beam only)
RUN III>0.9x1020 POT(current)
Tobias Raufer
Recent Results from MINOS
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
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Calorimeter Spectrometer
Recent Results from MINOS 23
LE-10/170kA LE-10/185kA
pME/200kA
Horn off
LE-10/200kA
pHE/200kA
Hadron Production Tuning
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
Recent Results from MINOS 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 N iData/Ni
MC
• Simple, makes no assumptions about ND Data parameterization, robust to
systematic errors
Tobias Raufer
FDipredicted
FDiMC
NDiMCNDi
Data
Recent Results from MINOS 25
• 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: 1 error band around beam fit results
Systematic Errors
Tobias Raufer
Recent Results from MINOS 26
• Systematic errors studied using simulated Far Detector data histograms with oscillation
parameters m2 = 2.38 x10-3 eV2, sin2223=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
Systematic Errors
Simulated Data
Tobias Raufer