νμ Results from the MINOS experiment

νμ Results from the MINOS experiment

Nicholas DevenishRecontres de Blois 2010

The MINOS Experiment

Antineutrino Disappearance

Recent Results

➤

Summary

Nicholas Devenish, Recontres de Blois 2010, 17th July 2010, for the MINOS collaboration / 19

Main Injector Neutrino Oscillation Search

735 km

The oscillated neutrino beam is measured by the Far Detector, at a mine in Minnesota.

Neutrinos are produced by the NuMI beam. The beams composition and energy are measured by the Near Detector

31 Institutions, 140 Physicists

Measurements and limits include:

Δm232, sin22θ32, Δm232, sin22θ32, θ13, sterile neutrinos, CPT

conservation, cross-sections...

3


Physics Goals

‣ With three active neutrinos there are two independent mass splittings

‣ MINOS is most sensitive to the larger of these and θ23 through νμ disappearance

€

Δmatm2

€

Δmsol2€

Δmatm2 ≈ Δm32

2 ≈ 2.4 ×10−3 eV2

€

Δmsol2 ≈ Δm21

2 ≈ 8.0 ×10−5 eV2

€

P νµ →νµ( ) =1− sin2 2θ23( )sin2 1.27Δmatm2 LE

⎛

⎝ ⎜

⎞

⎠ ⎟

(Monte Carlosin22θ = 1.0,

Δm2 = 3.35x10-3 eV2)

Unoscillated

Oscillated

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Near Detector‣At Fermilab, IL‣282 Planes‣980 Ton

MINOS Detectors

B

Far Detector

Near DetectorPlanes of 2.54cm Steel and 1cm Scintillator

Alternating scintillator planes in perpendicular directions

for 3D event reconstruction

Toroidal magnetic field allows charge sign determination

Both detectors are functionally equivalent, in order to reduce systematics.

Far Detector‣At Soudan, MN‣486 Planes‣5400 Ton

5

Recent Results➤

Summary

Antineutrino Disappearance



νe Appearance Results

for δCP = 0, sin2 2θ23( ) = 1,

Δm322 = 2.43×10−3 eV2

sin2 (2θ13) < 0.12 normal hierarchysin2 (2θ13) < 0.20 inverted hierarchyat 90% C.L.

arXiv:1006.0996v1 [hep-ex]

‣ Looking for appearance of νe in the νμ beam

‣ Discriminate against NC events using 11 shape variables in an Artificial Neural Network

‣ Find Limits:

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Neutral Current Results‣ Neutral Current event rate

should not change in standard 3 flavour oscillations

‣ A deficit in the Far event rate could indicate mixing to sterile neutrinos

‣ νe CC events would be included with the selected NC sample, so result depends on the possibility of νe appearance

Expect:Observe:

757 Events802 Events

No deficit of NC Events

fs ≡Pνµ→νs

1− Pνµ→νµ

< 0.22 (0.40) at 90% C.L.no (with) νe appearance

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νμ Disappearance Results

‣ Last published results 2008 (PRL 101:131802,2008)

‣ Additional data 3.4×1020→7.2×1020 POT

‣ Many analysis improvements including:

• Updated simulation and reconstruction• New selection with improved efficiency• Improved shower energy resolution• Separate data into bins of energy

resolution• Smaller systematic uncertainties

† Super-Kamiokande Collaboration (preliminary)

Δm2 = 2.35−0.08+0.11 ×10−3eV2

sin2 (2θ) > 0.91 (90%C.L.)

Best fit to oscillations at:

†

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Antineutrino Disappearance➤

Summary


Recent Results


Antineutrinos - Motivation

‣ Previously we presented an antineutrino analysis based on 3.2×1020 of neutrino mode data

‣World measurements of antineutrino disappearance are still limited

‣ MINOS magnetised detectors allow direct measurement of the charge sign of the muon

‣We recently took 1.71×1020 of data with NuMI in antineutrino mode

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Making Antineutrinos

120 GeV protons from MI

Focusing Horns2 m

675 m15 m 30 m

€

νµ = 91.7%ν µ = 7.0%

νe +ν e =1.3%

Target

Neutrino modeHorns focus π+, K+

Decay Pipe

π-

π+

νµνµ

Monte Carlo ‣With NuMI in neutrino mode only 7% of the beam is antineutrino

‣ These are of a higher average energy, making it harder to measure oscillations

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Antineutrino Mode

π+

π-

Target Focusing Horns Decay Pipe

2 m

675 m

νµ

15 m 30 m

νµ120 GeV protons from MI

Monte CarloNeutrino modeHorns focus π+, K+

€

νµ = 91.7%ν µ = 7.0%

νe +ν e =1.3%

Monte CarloAntineutrino modeHorns focus π-, K-

€

ν µ = 39.9%νµ = 58.1%

νe +ν e = 2.0%

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Track Charge Sign / Momentum (c/GeV)1 0.5 0 0.5 1

pot

1810×

Even

ts /

ton

/ 1

0

10

20

30

40

DataMC Expectation

Near Detector PoT19 10×8.65

Antineutrino Running

MINOS Preliminary

CC/NC Separation Parameter0 0.2 0.4 0.6 0.8 1

pot

1810×

Even

ts /

ton

/ 1

110

1

10

0 0.2 0.4 0.6 0.8 1

110

1

10 DataMC ExpectationTotal Background

Near Detector PoT19 10×8.65


MINOS Preliminary

Selecting Antineutrinos

‣ Events in-time with the spill‣ In the fiducial volume‣ At least one reconstructed track‣ Positive reconstructed charge

Basic Selection

CC/NC SeparationUsing a k-Nearest-Neighbour algorithm - data is compared to monte-carlo events in four parameters:

‣ Track Length‣ Mean energy of track hits‣ Energy fluctuations along the track‣ Transverse track profile

Accept

Accept

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Reconstructed Energy (GeV)0 5 10 15 20 25Se

lect

or P

erfo

rman

ce (%

)

0

20

40

60

80

100

MINOS PreliminarySimulated Far Detector

NC Contamination Contaminationµ

Selection Efficiency

Selection Efficiency and Contamination

‣ High energy νμ contamination does not affect the oscillation result

‣ Highest purity is in the oscillation region

Signal Bkgd.

0-6 GeV 106 1.9

6-20 GeV 38 4.3

> 20 GeV 8 3.0Monte Carlo

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Results: Far Detector

‣ No Oscillation Prediction: 155 Events

‣Observe: 97 Events

‣ Disfavour no-oscillations at 6.3σ

‣ Best fit to oscillations:

Δm2 = 3.36−0.40+0.45 ×10−3eV2

sin2 (2θ) = 0.86 ± 0.11Reco. Energy (GeV)

FD E

vent

s/G

eV0

10

20

30

0 5 10 20 30 40 50

MINOS Preliminary

running, Far Detectorµ POT MINOS 20 10×1.71

MINOS dataNo oscillationsBest oscillation fitBackground

16


Comparison with νμ Result

‣ Contours include the effects of systematic errors

)(22) and sin(22sin0.5 0.6 0.7 0.8 0.9 1

)2 e

V-3

| (10

2m

| and

|2

m|

2

3

4

5

6-310×

MINOS Preliminary

-modeµ POT 20 10×1.71

runningµMINOS 90%µMINOS 68%µMINOS

FitµBest POT20 10×1.71

90%µMINOS 68%µMINOS

FitµBest POT20 10×7.24

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The Future‣With more antineutrino running, MINOS can quickly improve

the precision by a significant amount

‣ Doubling out current six-month data set would decrease the error by ~30%

18

)(22) and sin(22sin0.5 0.6 0.7 0.8 0.9 1

)2 e

V-3

| (10

2m

| and

|2

m|

234567

-310×

MINOS Preliminary90% MC Sensitivity

POT20 10×1.7 POT20 10×3.5

POT20 10×5 POT20 10×7

Data 90% C.L.µ


Summary

‣With 7×1020 POT of neutrino beam, MINOS finds:

‣With 1.71×1020 POT of antineutrino beam, MINOS finds:

• Muon neutrinos disappear:

• NC event rate is not diminished:

• Electron-neutrino appearance is limited:

Δm2 = 2.35−0.08+0.11 ×10−3eV2,

sin2 (2θ) > 0.91 (90%C.L.)

fs < 0.22(0.40) at 90% C.L.

sin2 (2θ13) < 0.12 (0.20) at 90% C.L.

Δm2 = 3.36−0.40+0.45 ×10−3eV2,

sin2 (2θ) = 0.86 ± 0.11

• Muon antineutrinos also disappear with:

‣We look forward to taking more anti-neutrino data!

19

Backup Slides➤


The NuMI Beam‣ Neutrinos at the Main Injector

‣ 120 GeV Protons incident on a thick, segmented graphite target produces a spray of hadrons

‣ Magnetic horns can focus either sign by reversing the direction of current

‣ Can enhance the νμ flux by focusing π+, K+ (or vice versa)

‣ Adjustable energy by moving the target relative to the horns

π-

π+120 GeV p’s from MI

Target Focusing Horns

Evacuated Decay Pipe

2 m

675 m

νµνµ

1.5 m 3 m

Low EnergyMedium Energy

Monte Carlo

21


Beam Performance

Run I Run II Run IIIHigh

Ene

rgy

Antin

eutrino

s

Run IV

€

3.21×1020 POT νµ modePrevious Analyses

22


Beam Performance

Run I Run II Run IIIHigh

Ene

rgy

Antin

eutrino

s

Run IV

€

7.24 ×1020 POT νµ modeCurrent νµ Analysis

€

1.71×1020 POTν µ mode

23


Previous Antineutrino Results

‣ Analysed 3.2×1020 POT of neutrino-mode running

‣ Antineutrinos are on average of higher energy, moving the spectrum peak out of the expected region of oscillations

‣ Very poor sensitivity to oscillations

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νμ Near Detector Data Spectrum

‣ Selected Antineutrino data energy spectrum

‣ Good Data/MC agreement at the Near detector

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‣ Flux and cross-section uncertainties cancel when we extrapolate from Near to Far detectors

‣ Near and Far detector energy spectra are not identical

• Due to π/K decay kinematics, neutrino energy varies with angle - the Near detector covers a wider solid angle

• Higher energy π travel further and decay closer to the Near detector

Extrapolation

Monte Carlo

‣ A beam matrix encapsulates our knowledge of decay kinematics, and transports the measured Near detector spectrum to the Far detector

26


Systematics

‣ The antineutrino analysis is statistically limited

‣ Studies were done to assess the effect of systematics on the fitted result

‣ Results contours were produced with systematic uncertainties included

Monte Carlo

27


Reco. Energy (GeV)

FD E

vent

s/G

eV

0

10

20

30

0 5 10 20 30 40 50

MINOS Preliminary


MINOS dataNo oscillations

)=1(22, sin2eV-310×=2.352mBest oscillation fitBackground

Comparison with νμ Result

Reco. Energy (GeV)R

atio

to N

o O

scilla

tions

-0.5

0

0.5

1

1.5

0 5 10 20 30 40 50

MINOS Preliminary BackgroundSubtracted


MINOS dataBest oscillation fit

)=1(22, sin2eV-310×=2.352m

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The Future - At νμ Best Fit

‣ This shows the sensitivity to future antineutrino running, in the scenario where the new data matches the νμ disappearance best fit value

)(22sin0.5 0.6 0.7 0.8 0.9 1

)2 e

V-3

| (10

2m

|

2

3

4

5

6-310×

MINOS Preliminary

90% MC Sensitivity

POT20 10×1.7 POT20 10×3.5

POT20 10×5 POT20 10×7

Dataµ POT MINOS 20 10×1.7 with additional MC oscillated at

)=1(22, sin2 eV-3 10×=2.35 2m

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Q/P1 0.5 0 0.5 1

Even

ts

0

20

40

60

80

DataOscillated MCNo Oscillations

Far Detector POT20 10×1.71


MINOS Preliminary

Data/MC Agreement - Far Detector

Reconstructed Shower Energy (GeV)0 5 10 15 20

Even

ts

0

20

40

60

80DataOscillated MCNo Oscillations



MINOS Preliminary

CC/NC Separation Parameter0 0.2 0.4 0.6 0.8 1

Even

ts

0

10

20

30

40

50

60




MINOS Preliminary

Energy (GeV)+µReconstructed 0 5 10 15 20

Even

ts

0

10

20

30

40




MINOS Preliminary

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νμ Results from the MINOS experiment

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