1MINOS Oscillation Resultsfrom The First Year of NuMI Beam Operation

Masaki Ishitsuka, Indiana University
For the MINOS Collaboration
Kyoto University, July 3rd, 2006

2Overview of the talk• Introduction to the MINOS experiment– MINOS Physics Goals– The NuMI facility and the MINOS detectors• Beam and detector performance– Near detector distributions and comparison with Monte Carlo– Beam measurements by the near detector data

• Far detector analysis– Near-Far extrapolation of the neutrino flux
– Oscillation Analysis with NuMI 1.27x1020 pot beam data

3Neutrino oscillation⎛ν e ⎞⎛ν 1 ⎞⎜ ⎟⎜ ⎟Weak⎜ν μ ⎟ = U ⎜ν 2 ⎟eigenstates ⎜ ⎟⎜ν ⎟⎝ν τ ⎠⎝ 3⎠Mixing parameters

3 mass states (2 mass differences)Δm212 : solar+reactor
Δm322 : Atm-ν+LBL Å MINOS
3 mixing angles & 1 CPV phase
cij=cosθij sij=sinθij

Atm-ν+LBL Å MINOS0⎛1⎜
U PMNS = ⎜ 0 c23⎜0 − s23⎝Masseigenstates

0 ⎞⎛ c13⎟⎜s23 ⎟⎜ 0c23 ⎟⎠⎜⎝ − s13e −iδ

0 s13e iδ ⎞⎛ c12⎟⎜
10 ⎟⎜ − s120 c13 ⎟⎠⎜⎝ 0LBL+reactor

s12c1200⎞⎟0⎟1 ⎟⎠Solar+reactor

4

Current knowledge of 2-3 sector of mixing parametersand previous MINOS results
Allowed regions from Super-K, K2K
and previous MINOS (9.3x1020POT)

Current measurements of Δm232 andsin22θ23 from Super-Kamiokande and K2K(9x1019 pot)
sin22θ>0.9
1.9<Δm2<3.0 × 10-3 eV2
at 90%CL from SK L/E analysis

The MINOS first result for 9.3x1019 pot
provided a competitive measurement of themixing parameters.

Oscillation results from 1.27x1020 pot data is reported in this talk.

5The MINOS Collaboration

175 scientists
32 institutions
6 countries
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

6The Concept of MINOSMINOS (Main Injector Neutrino Oscillation Search)
is a long-baseline neutrino oscillation experiment:
High intensity muon neutrino beam
produced from Main Injector 120GeV
proton beam at Fermilab

735km

Near detector at Fermilab
measure the un-oscillated
energy spectrum
Search for evidence for oscillations at
Far detector deep underground in theSoudan Mine, Minnesota

7

Example of νμ disappearance measurement
Survival probability of muon neutrinos:P(ν μ → ν μ ) = 1 − sin 2 2θ sin 2 (1.267 Δm 2 L / E )νμ spectrum

spectrum ratio
Monte Carlo(NC subtracted)

Monte Carlo
Unoscillated
Oscillatedsin22θ

Δm2

8MINOS Physics Goals• Demonstrate νμ→ντ oscillation behavior• Precise (<10%) measurement of oscillation
parameters: Δm2 and sin22θ.
•Search for/rule out exotic phenomena:– Sterile neutrinos– Neutrino decay•••

Search for sub-dominant νμ→νe oscillations
Use magnetized MINOS Far detector to study neutrino and anti-neutrino
oscillations– Test of CPT violation
Atmospheric neutrino oscillations in the MINOS far detector:– First MINOS paper: Phys. Rev. D73 (2006) 072002 [hep-ex/0512036]

9The NUMI facility
Design parameters:¾ 120 GeV protons from the Main Injector¾ Main Injector can accept up to 6 Booster
batches/cycle¾ 1.9 second cycle time
¾ 4x1013 protons/pulse¾ 0.4 MW
¾ Single turn extraction (10μs)

Average from 10/5 to 1/6:
9 2.2 second cycle time
9 2.3x1013 protons/pulse
9 0.17 MW

10Producing the neutrino beam
47 segments of graphite of 20 mm length and6.4×15 mm2 cross section (total length 95.4 cm)• Two parabolic focussing horns (3.0 Tesla peak field)• Moveable target relative to horn 1 – continuously
variable neutrino spectrum

11The NuMI neutrino beam••

Currently running in the LE-10 configuration- Beam composition : 98.7% νμ+νμ (5.8% νμ), 1.3% νe+νe
We have already accumulated data in 5 other beam configurations
for systematics studies (~5% of total exposure).

LEpME
pHE

Expected no of events (no osc.) in Far Detector

BeamTarget z
FD Events perposition (cm)1e20 pot

LE-10-10390

pME

-100

970

pHE-2501340

Events in fiducial volume

Position of osc. minimum for Δm2=0.0025 eV2

12The MINOS detectors
Near Detector

Far Detector
Veto Shield

5.4 kton mass, 8×8×30m

1 kton mass 3.8×4.8×15m

484 steel/scintillator planes

282 steel and 153 scintillator planes(x 8 multiplexing)(x 4 multiplexing after plane 120)

VA electronics

Fast QIE electronics
B ~1.2T
Multi-pixel (M16,M64) PMTs

GPS time-stamping to synch FD data to ND/BeamContinuous untriggered readout of whole detector (only during spill for the ND)
Interspersed light injection (LI) for calibration
Spill times from FNAL to FD trigger farm

13Detector technology
Near and Far Detectors: Identical target components and detection technology
2.54 cm thick magnetized steel plates
4.1x1cm co-extruded scintillator strips (MINOS-developed technology)
orthogonal orientation on alternate planes – U,Voptical fibre readout to multi-anode PMTsUVUVUVUV
steel

Scintillator stripscintillator

orthogonalorientationsof strips

M16 PMTFar Detector

14MINOS Calibration system••

Calibration of ND andFD response using:– Light Injection
system (PMT gain)– Cosmic ray muons(strip to strip anddetector todetector)– Calibration detector(overall energyscale)
Energy scale calibration:– 5.7% absolute error– 2% relative

15

First year of NuMI beam operation
1e20 pot!

Observationof neutrinos
in NearDetector!
Start of LE running

Dataset used for theoscillation analysis

16

Near detector events
One near detector spill•

Intense neutrino beam makes
multiple neutrino interactions per
spill in the near detector•

Events are separated by topology
and timing

IndividualeventsMINOS PreliminaryTime (us)Batch structure clearly seen!17Event topologies
Sensitive toνμ – ντ oscillation

Monte Carloνμ CC Event

NC Eventνe CC Event

1.8m

2.3m

3.5m

long μ track+ hadronic
activity at vertex

short event, often
diffuseEν = Eshower+Pμ55%/√E

6% range, 10% curvature

short, with typical
EM shower profile

18Selecting CC events
CC events are selected using a likelihood-based procedure

MINOS Preliminary

ND

MINOS Preliminary

ND

ND

MINOS Preliminary– Event length in planes (related to muon momentum)– Fraction of event pulse height in the reconstructed track (related to theinelasticity of CC events)– Average track pulse height per plane (related to dE/dX of the reconstructed track)19

CC selection efficiencies•The Particle ID (PID) parameter is defined as:

PID = −( − log( Pμ ) − − log( PNC ) )•CC-like events are defined by the cut PID>-0.2 in the FD (>-0.1 in the ND)– NC contamination is limited to the lowest visible energy bins (below 1.5 GeV)
– Selection efficiency is quite flat as a function of visible energy
MINOS Preliminary

ND

Monte Carlo(87%)(97%)
PID parameter

20

Event selection cuts – Near and Far
1. Event must contain at least one good reconstructed track
2. The reconstructed track vertex should be within thefiducial volume of the detector:––ND: 1m < z < 5m (z measured from the front face of the detector),
R< 1m from beam centre.
FD: z>50cm from front face, z>2m from rear face, R< 3.7m fromcentre of detector.
FAR DETECTOR

NEAR DETECTOR

νCalorimeter

Spectrometer

Fiducial Volume

3. The fitted track should have negative charge (selects νμ)
4. Cut on likelihood-based Particle ID parameter which isused to separate CC and NC events.

21

Near detector data distributions
Event rate

MINOS Preliminary

1.27×1020 POT

Near detector event raye – LE-10

Horn current test runs

Different tunes in Feb.

Event vertices in the NDMINOS PreliminaryX

MINOS PreliminaryY

MINOS PreliminaryZ

22

Energy spectra in the ND and hadron production tuning
Agreement between data and Fluka05 Beam MC is within the systematic errors
Æ Further improvement by hadron production tuning as a funtion of xF and pTWeights applied as afunction of hadronic
xF and pT.

MINOS Preliminary
LE-10/170kA

LE-10/185kA

LE-10/200kA

pHE/200kA

Horns off

Data
Fluka05 MC
Tuned Had. Prod.

pME/200kA

LE-10/185kA MCπ distributionsfor MINOS
neutrino events

23

Stability of the energy spectrum & reconstruction
Energy spectrum by Month
•

June•

July

•

August•September•

October•November

Energy spectrum by batchMINOS Preliminary

MINOS Preliminary•

Reconstructed energy distributions agree
to within statistical uncertainties (~1-3%)– beam is stable for long period•There is no significant intensity-dependent
biases in event reconstruction
MINOS Preliminary24

Performing a blind analysis
Far detector blinding– Unknown fraction of FD events were hidden• Blinded as a function of event length and energy– The “Open” FD data used to check data quality

Near detector data was open
– Used to study beam properties, cross sections,and detector systematics

Analysis procedures were defined prior to box opening

25

Selecting beam induced events• Time stamping of the neutrino events is provided by two GPSunits located at Near and Far detector sites.
– FD Spill Trigger reads out 100us of activity around beam spills

MINOS Preliminary
1.27×1020 POT• Neutrino events have distinctive topology andare easily separated from cosmic muons– Backgrounds were estimated by fake triggers:
0 events in 2.6 million fake trrigers survived
cuts Æ upper limit of 0.5 background events

Time of neutrino interactions
from beam spill (µs)

26

Far detector beam data analysis
Oscillation analysis was performed using data taken in theLE configuration from May 20th 2005 – March 3rd 2006
– Total integrated POT: 1.27x1020
MINOS Preliminary

1.27×1020
POT27

Far detector distributions
PID parameter
MINOS Preliminary

Muon energy
MINOS Preliminary

Data
Predicted no oscillations
Best-fitShower Energy
MINOS Preliminary

28

Near to Far extrapolation: “Beam Matrix” method• Directly use the Near detector data to perform the extrapolation
between Near and Far, using our Monte Carlo to provide
necessary corrections due to energy smearing and acceptance.
• Predict the Far detector energy distribution from the measured
Near detector distribution using pion decay kinematics and thegeometry of beamline.

π+(stiff)targetπ(soft)+1 ⎛1 ⎞⎟
Flux ∝ 2 ⎜⎜L ⎝ 1 + γ 2θ 2 ⎟⎠to farDetector

θfθn2 Decay Pipe0.43Eπ
Eν =1 + γ 2θ 2ND

29

Procedure of predicting the FD spectrumA)

E

Reconstructed
Near CC -like

⇒E

True
Near CC

Correction for purity, Reconstructed =>True, Correction for efficiency

EB)

True
Near CC⇒E

True
Far CC

BEAM MATRIXC)

E

True
Far CC⇒E

Reconstructed
Far CC -likei) Oscillation, True => Reconstructed, Correction for efficiency to obtain CC
oscillated spectrumii) Unoscillated True => Reconstructed, Use purity to obtain NC background30“Beam Matrix” : Near to Far extrapolation
CC true spectrumin FD (un-oscillated)

CC true spectrum
in ND

Beam Matrix
provides relations between the FD and ND
spectrum determined by pion 2-body decay
kinematics and geometry of beamline

31

Different methods for predicting the FD spectrum
Three alternative ND to FD extrapolation methods:
ND fit :Reweight the FD MC using
systematic parameters obtainedby the ND fit2D Grid fit :Reweight the FD MC using Eν x ycorrection matrix and systematicparameters obtained by the ND fit
F/N ratio :Extrapolation using the Far/Nearspectrum ratio from MC

Predicted FD unoscillated spectra

1.27×1020 POT
MINOS Preliminary

The methods are robust to different categories of systematics

32

Numbers of observed and expected events
1.27×1020 POT MINOS Preliminary Numbers

ExpectedRatio

Expected(matrix, no osc.)(matrix, no-osc.)(ND fit, no osc.)215

336±210.64±0.08333

νμ (<10 GeV)

122

239±170.51±0.08

238νμ (<5 GeV)67

168±120.45±0.09

169

Data sampleObservedνμ (<30 GeV)

• Energy dependent deficit is observed• Significance of the deficit below 10 GeV is 5.9 σ (stat+syst)

33

MINOS observed spectrum and the best-fit
for 1.27x1020POT(1 − N ) 2
χ (Δm , sin 2θ ) = ∑ 2(ei − oi ) + 2oi ln(oi / ei ) +0.04 2i =1222nbins

MINOS Preliminary

2-32Δm 32= 2.72 +0.38- 0.25 (stat) × 10 eVsin 2 2θ 23 = 1.00 - 0.13 (stat)
Normalizat ion = 0.98

oi : observed # events
ei : expected # events
N : absolute normalization

MINOS Preliminary Neutral Current subtracted

34

Allowed regions

Projected onto
2Δm32
axis

2-32Δm 32= 2.72 -+0.38
0.25 (stat) × 10 eV

sin 2 2θ 23 = 1.00 - 0.13 (stat)

Constrained to sin22θ23 ≤ 1
Statistical errors

35

Systematic errors
MINOS Preliminary Numbers

Uncertainty

Δm2 (x10-3 eV2)

sin22θ

Near/Far normalisation +/- 4%

0.003

0.000

Muon energy scale +/- 2%
Relative Shower energy scale +/- 2%

0.035
0.010

0.003
0.003

NC contamination +/- 50%
CC cross-section uncertainties
Intranuclear re-scattering /absolute energy scale (+/- 6%)

0.088
0.016
0.083

0.038
0.004
0.018

Reconstruction

0.013

0.005

Beam uncertainty

0.025

0.005

Fit bias

0.010

0.010

Total (sum in quadrature)

0.131

0.044

Statistical sensitivity

0.36

0.12

36

Projected sensitivity of MINOSνμ disappearance

Input parameters: |Δm232| = 2.72x10-3eV2
sin22θ23 = 1.00

90%CL, statistical error only

37

Projected sensitivity of MINOS
Search for sub-dominant νμ→νe4X1020pot

16X1020pot

MINOS Preliminary• MINOS sensitivity as a function of CPviolating phase and mass hierarchy• Reasonable chance of making the firstmeasurement of non-zero θ13!

38

Summary and conclusions••

Preliminary MINOS oscillation results from the first year of NuMI
beam operation was presented.
Our exposure to data is 1.27×1020 pot.

•Deficit of νμ events below 10GeV disfavors no oscillation at 5.9 σ(rate only) .

•FD spectrum distortion is consistent with νμ disappearance withthe following parameters:
2-32Δm 32= 2.72 +0.38(stat)±0.13(syst)
×10eV- 0.25

sin 2 2θ 23 = 1.00 - 0.13 (stat) ± 0.04(syst )•MINOS is taking data from the 2nd year of NuMI beam operation.

•Significant improvement in precision of oscillation parameters
should be made with a larger dataset.