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New Results from MINOS. Patricia Vahle, for the MINOS collaboration College of William and Mary. The MINOS Experiment. Long base-line neutrino oscillation experiment Neutrinos from NuMI beam line L/E ~ 500 km/ GeV atmospheric Δm 2. Far Detector 735 km from Source.

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new results from minos

New Results from MINOS

Patricia Vahle, for the MINOS collaboration

College of William and Mary

the minos experiment
The MINOS Experiment
  • Long base-line neutrino oscillation experiment
  • Neutrinos from NuMI beam line
  • L/E ~ 500 km/GeV
    • atmospheric Δm2

Far Detector

735 km from Source

  • Two detectors mitigate
  • systematic effects
      • beam flux mis-
      • modeling
      • neutrino interaction
      • uncertainties

Near Detector

1 km from Source

minos physics goals
MINOS Physics Goals
  • Measure νμ disappearance as a function of energy
    • Δm232and sin2(2θ23)
    • test oscillations vs. decay/decoherence

Δm232

Δm221

minos physics goals1
MINOS Physics Goals
  • Measure νμ disappearance as a function of energy
    • Δm232and sin2(2θ23)
    • test oscillations vs. decay/decoherence
  • Mixing to sterile neutrinos?

Δm232

Δm221

Δm214

minos physics goals2
MINOS Physics Goals
  • Measure νμ disappearance as a function of energy
    • Δm232and sin2(2θ23)
    • test oscillations vs. decay/decoherence
  • Mixing to sterile neutrinos?
  • Study νμ→νemixing
    • measure θ13

Δm232

Δm221

minos physics goals3
MINOS Physics Goals
  • Measure νμ disappearance as a function of energy
    • Δm232and sin2(2θ23)
    • look for differences between neutrino and anti-neutrinos

Δm232

Δm221

minos physics goals4
MINOS Physics Goals
  • Measure νμ disappearance as a function of energy
    • Δm232and sin2(2θ23)
    • look for differences between neutrino and anti-neutrinos
  • More MINOS analyses:
    • atmospheric neutrinos

(See A. Blake poster)

    • cross section measurements
    • Lorentz invariance tests
    • cosmic rays

Δm232

Δm221

the detectors
The Detectors

Magnetized, tracking calorimeters

5.4 ktFar Detector—

look for changes in the beam relative to the Near Detector

1 ktNear Detector—

measure beam

before

oscillations

735 km from source

1 km from source

detector technology
Detector Technology

2.54 cm Fe

  • Tracking sampling calorimeters
    • steel absorber 2.54 cm thick (1.4 X0)
    • scintillator strips 4.1 cm wide

(1.1 Moliere radii)

    • 1 GeVmuons penetrate 28 layers
  • Magnetized
    • muon energy from range/curvature
    • distinguish μ+ fromμ-
  • Functionally equivalent
    • same segmentation
    • same materials
    • same mean B field (1.3 T)

Extruded

PS scint.

4.1 x 1 cm2

U V planes

+/- 450

WLS fiber

Clear

Fiber cables

Multi-anode PMT

making a neutrino beam1
Making a neutrino beam
  • Production
    • bombard graphite target with 120 GeVp+ from Main Injector
      • 2 interaction lengths
      • 310 kW typical power
    • produce hadrons, mostly π and K
making a neutrino beam2
Making a neutrino beam
  • Focusing
    • hadrons focused by 2 magnetic focusing horns
    • sign selected hadrons
      • forward current, (+) for standard neutrino beam runs
      • reverse current, (–) for anti-neutrino beam
making a neutrino beam3
Making a neutrino beam
  • Decay
    • 2 m diameter decay pipe
    • result: wide band beam, peak determined by target/horn separation
    • secondary beam monitored (see L. Loiacono poster)
beam performance
Beam Performance

Total Protons (x1020)

Protons per week (x1018)

Date

beam performance1
Beam Performance

1021 POT!

Total Protons (x1020)

Protons per week (x1018)

Date

beam performance2
Beam Performance

Previously published analyses

Total Protons (x1020)

Protons per week (x1018)

Date

beam performance3
Beam Performance

Data set for today’s report

Total Protons (x1020)

Protons per week (x1018)

Anti-

neutrino running

Date

High energy running

events in minos
Events in MINOS
  • νμCharged Current events:
    • long μtrack, with hadronic activity at vertex
    • neutrino energy from sum of muon energy (range or curvature) and shower energy

Simulated Events

CC νe Event

e-

Transverse position (m)

Depth (m)

CC νμ Event

NC Event

ν

μ-

events in minos1
Events in MINOS
  • Neutral Current events:
    • short, diffuse shower event
    • shower energy from calorimetric response

Simulated Events

CC νe Event

e-

Transverse position (m)

Depth (m)

CC νμ Event

NC Event

ν

μ-

events in minos2
Events in MINOS
  • νeCharged Current events:
    • compact shower event with an EM core
    • neutrino energy from calorimetric response

Simulated Events

CC νe Event

e-

Transverse position (m)

Depth (m)

CC νμ Event

NC Event

ν

μ-

near to far

π+

Target

p

FD

Decay Pipe

ND

Near to Far
  • Neutrino energy depends on angle wrt original pion direction and parent energy
    • higher energy pions decay further along decay pipe
    • angular distributions different between Near and Far

Far spectrum without oscillations is similar, but not identical to the Near spectrum!

extrapolation
Extrapolation

Muon-neutrino and anti-neutrino analyses: beam matrix for FD prediction of track events

NC and electron-neutrino analyses: Far to Near spectrum ratio for FD prediction of shower events

disappearance
νμ Disappearance

Monte Carlo

(Input parameters: sin22θ = 1.0, Δm2 = 3.35x10-3 eV2 )

νμ spectrum

spectrum ratio

Unoscillated

Characteristic Shape

Oscillated

Monte Carlo

disappearance1
νμ Disappearance

Monte Carlo

(Input parameters: sin22θ = 1.0, Δm2 = 3.35x10-3 eV2 )

νμ spectrum

spectrum ratio

Unoscillated

sin2(2θ)

Oscillated

Monte Carlo

disappearance2
νμ Disappearance

Monte Carlo

(Input parameters: sin22θ = 1.0, Δm2 = 3.35x10-3 eV2 )

νμ spectrum

spectrum ratio

Unoscillated

Δm2

Oscillated

Monte Carlo

cc events in the near detector
CC events in the Near Detector

Show ND energy spectrum

  • Majority of data from low energy beam
  • High energy beam improves statistics in energy range above oscillation dip
  • Additionalexposure in other configurations for commissioning and systematics studies
analysis improvements
Analysis Improvements
  • Since PRL 101:131802, 2008
  • Additional data
    • 3.4x1020 → 7.2x1020 POT
  • Analysis improvements
    • updated reconstruction and simulation
    • new selection with increased efficiency
    • no charge sign cut
    • improved shower energy resolution
    • separate fits in bins of energy resolution
    • smaller systematic uncertainties

See C. Backhouse, J. Mitchell, and J. Ratchford, M. Strait posters

far detector energy spectrum1
Far Detector Energy Spectrum
  • Oscillations fit the data well, 66% of experiments have worse χ2
  • Pure decoherence† disfavored: > 8σ
  • Pure decay‡ disfavored: > 6σ
  • (7.8σif NC events included)

†G.L. Fogliet al., PRD 67:093006 (2003) ‡V. Barger et al.,PRL 82:2640 (1999)

contours
Contours
  • Contour includes effects of dominant systematic uncertainties
    • normalization
    • NC background
    • shower energy
    • track energy
contours1
Contours
  • Contour includes effects of dominant systematic uncertainties
    • normalization
    • NC background
    • shower energy
    • track energy

†Super-Kamiokande Collaboration (preliminary)

neutral current near event rates
Neutral Current Near Event Rates
  • Neutral Current event rate should not change in standard 3 flavor oscillations
  • A deficit in the Far event rate could indicate mixing to sterile neutrinos
    • νeCC events would be included in NC sample, results depend on the possibility of νe appearance

See P. Rodrigues and A. Sousa poster

neutral currents in the far detector
Neutral Currents in the Far Detector
  • Expect: 757 events
  • Observe: 802 events
  • No deficit of NC events

no (with) νeappearance

e appearance
νe Appearance
  • A few percent of the missing νμ could change into νedepending on value ofθ13
  • Appearance probability additionally depends onδCPand mass hierarchy

Normal Hierarchy

Inverted Hierarchy

?

looking for electron neutrinos
Looking for electron-neutrinos
  • 11 shape variables in a Neural Net (ANN)
    • characterize longitudinal and transverse energy deposition
  • Apply selection to ND data to predict background level in FD
    • NC, CC, beam νeeach extrapolates differently
    • take advantage of NuMI flexibility to separate background components

νe

selected region

BG Region

See R. Toner, L. Whitehead, G. Pawloski poster

  • Data
  • MC
e appearance results
νe Appearance Results

Based on ND data, expect: 49.1±7.0(stat.)±2.7(syst.)

e appearance results1
νe Appearance Results

Based on ND data, expect: 49.1±7.0(stat.)±2.7(syst.)

Observe: 54 events in the FD, a 0.7σ excess

e appearance results2
νe Appearance Results

arXiv:1006.0996v1 [hep-ex]

making an anti neutrino beam
Making an anti-neutrino beam

Neutrino mode

Horns focus π+,K+

Events

νμ: 91.7%

νμ: 7.0%

νe+νe: 1.3%

Focusing Horns

Target

2 m

π-

νμ

120 GeVp’s from MI

νμ

π+

30 m

15 m

675 m

making an anti neutrino beam1
Making an anti-neutrino beam

Neutrino mode

Horns focus π+,K+

Anti-neutrino Mode

Horns focus π-,K-enhancing theνμflux

Events

Events

νμ: 91.7%

νμ: 7.0%

νe+νe: 1.3%

νμ: 39.9%

νμ: 58.1%

νe+νe: 2.0%

Focusing Horns

Target

2 m

π+

νμ

120 GeVp’s from MI

νμ

π-

30 m

15 m

675 m

nd anti neutrino data
ND Anti-neutrino Data
  • Focus and select positive muons
    • purity 94.3% after charge sign cut
    • purity 98% < 6GeV
  • Analysis proceeds as (2008) neutrino analysis
  • Data/MC agreement comparable to neutrino running
    • different average kinematic distributions
    • more forward muons

See J. Evans, N. Devenish poster

Also A. Blake poster on atmospheric neutrinos

nd data
ND Data
  • Data/MC agreement comparable to neutrino running
fd data
FD Data
  • No oscillation Prediction: 155
  • Observe: 97
  • No oscillations disfavored at 6.3σ
fd data1
FD Data
  • No oscillation Prediction: 155
  • Observe: 97
  • No oscillations disfavored at 6.3σ
summary
Summary
  • With 7x1020 POT of neutrino beam, MINOS finds
    • muon-neutrinos disappear
    • NC event rate is not diminished
    • electron-neutrino appearance is limited
  • With 1.71x1020 POT of anti-neutrino beam
    • muon anti-neutrinos also disappear with
    • we look forward to more anti-neutrino beam!
neutrino spectrum

HE

ME

LE 10

Neutrino Spectrum

Use flexibility of beam line to constrain hadron production, reduce uncertainties due to neutrino flux

near to far1
Near to Far

Far spectrum without oscillations is similar, but not identical to the Near spectrum!

far near differences
Far/Near differences
  • νμCC events oscillate away
  • Event topology
    • Light level differences (differences in fiber lengths)
    • Multiplexing in Far (8 fibers per PMT pixel)
    • Single ended readout in Near
  • PMTs (M64 in Near Detector, M16 in Far):
    • Different gains/front end electronics
    • Different crosstalk patterns
  • Neutrino intensity
  • Relative energy calibration/energy resolution

Account for these lower order effects using detailed detector simulation

cc systematic uncertainties
CC Systematic Uncertainties
  • Dominant systematic uncertainties:
    • hadronic energy calibration
    • track energy calibration
    • NC background
    • relative Near to Far normalization
rock and anti fiducial events
Rock and Anti-fiducial Events

Neutrinos interact in rock around detector and outside of Fiducial Region

These events double sample size, events have poorer energy resolution

Combined fit coming soon

fits to nc
Fits to NC
  • Fit CC/NC spectra simultaneously with a 4th (sterile) neutrino
  • 2 choices for 4th mass eigenvalue
    • m4>>m3
    • m4=m1
mrcc background rejection check
MRCC Background Rejection Check

Neutrino Energy: 5.3 GeV

MuonEnergy: 3.2 GeV

Remnant Energy: 2.1 GeV

ANN PID: 0.86

R

Remove muons, test BG rejection on shower remnants

  • Mis-id rate:
    • pred (6.42±0.05)%
    • data (7.2±0.9)%
  • (stats error only)
  • Compatible at 0.86σ
checking signal efficiency
Checking Signal Efficiency

Test beam measurements demonstrate electrons are well simulated

checking signal efficiency1
Checking Signal Efficiency

Check electron neutrino selection efficiency by removing muons, add a simulated electron

slide66

Making an antineutrino beam

Hadron production and cross sections conspire to change the shape and normalization of energy spectrum

~3x fewer antineutrinos for the same exposure

anti neutrino selection
Anti-neutrino Selection

Coil Hole

μ+ Focused

Coil Hole

μ- Not Focused

fd anti neutrino data
FD Anti-neutrino Data

Vertices uniformly distributed

Track ends clustered around coil hole

previous anti neutrino results
Previous Anti-neutrino Results
  • Results consistent with (less sensitive) analysis of anti-neutrinos in the neutrino beam
    • anti-neutrinos from unfocused beam component
    • mostly high energy antineutrinos
  • Analysis of larger exposure on going
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