recent results from the minos neutrino oscillation experiment

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


Neutrinos mix

Two conditions necessary for neutrino oscillations:– Neutrinos are massive

– Neutrinos mix


Flavour eigenstates

Mass eigenstates

flavour eigenstates govern interactions

mass eigenstates propagate

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Neutrinos are massive

What does the neutrino mass spectrum look like?


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There are only 3 light neutrinos coupling to the Z0 …


Neutrinos are massiveNeutrino OscillationsThe MINOS experimentRecent ResultsSummary

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Neutrinos are massiveNeutrino OscillationsThe MINOS experimentRecent ResultsSummary

… but there could be sterile neutrinos!

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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.


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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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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


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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


MINOS Detectors

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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


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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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CC disappearance Result

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m322 2.38 0.16

0.20(stat syst)10 3eV2

sin2(223)1.00 0.08(stat syst)


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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Toy Simulation

No νs

With νs mixing


• 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

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NC Energy Spectrum

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• 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.


Is there a deficit?

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• 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.


4-flavour Model

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• 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)


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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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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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)


Backup Slides

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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)

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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


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


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

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FDipredicted

FDiMC

NDiMCNDi

Data


• 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

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• 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


Systematic Errors

Tobias Raufer

recent results from the minos neutrino oscillation experiment

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