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First MINOS Results from the NuMI Beam

Marvin L. Marshak University of Minnesota

for the MINOS collaboration

SLAC, May 16, 2006

Introduction to the MINOS experiment• Overview of MINOS Physics Goals• The NuMI facility and the MINOS detectorsNear Detector and beam measurements• Selecting cc muon neutrino events• Near detector distributions and comparison with

Monte Carlo Far detector analysis• Selecting Beam neutrino candidates• Near-Far extrapolation of the neutrino flux• Oscillation Analysis with 0.931020 POT

Overview

3

735 km

(12 km)

The MINOS Experiment

• MINOS (Main Injector Neutrino Oscillation Search)– a long-baseline neutrino

oscillation experiment:– Neutrino beam provided

by 120 GeV protons from the Fermilab Main Injector.

– Near Detector at Fermilab to measure the beam composition and energy spectrum

– Far Detector deep underground in the Soudan Mine, Minnesota, to search for evidence of oscillations

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The MINOS Collaboration

Argonne • Athens • Benedictine • Brookhaven • Caltech • Cambridge • Campinas College de France • Fermilab • Harvard • IIT • Indiana • ITEP-Moscow • Lebedev • Livermore

Minnesota-Duluth • Minnesota-Twin Cities • Oxford • Pittsburgh • Protvino • Rutherford Sao Paulo • South Carolina • Stanford • Sussex • Texas A&M • Texas-Austin

Tufts • UCL • Western Washington • William & Mary • Wisconsin

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MINOS Physics Goals

• Verify mixing hypothesis and make a precise (<10%) measurement of the oscillation parameters m2 and sin2 2

• Search for sub-dominant e oscillations

• Rule out exotic phenomena (e.g. neutrino decay)

• Use magnetized MINOS Far Detector to study neutrino and anti-neutrino oscillations– Test of CPT violation

• Atmospheric neutrino oscillations– First MINOS paper:

hep-ex/0512036, forthcoming in Phys. Rev D

eν µν τ

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

=

Ue1 Ue2 Ue3

Uµ1 Uµ2 Uµ3

Uτ 1 Uτ 2 Uτ 3

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

ν 1

ν 2

ν 3

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

sin2 2θ23 = 4Uµ32 1 −Uµ3

2( )

ifΔm232 >> Δm12

2

ν e  appearance

ν µ  disappearance

3

Δm232

ν 2

ν 1

6

Current knowledge of atmospheric neutrino

oscillationsCurrent best measurements of

Δm2 and sin22θ fromSuper-Kamiokande (atmospheric neutrinos) andK2K (0.9 x 1020 POT)

The limits (at 90% C.L.) are:• sin22θ > 0.9• (1.9 < Δm2 < 3.0)  10-3 eV2

MINOS analysis is for 0.93  1020 POT, and should provide a competitive measurement of the mixing parameters

) / 267 . 1( sin 2 sin 1 ) (2 2 2

E L m P − = →

Allowed regions from Super-K and K2K

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Look for a deficit of νμ events at Soudan

Unoscillated

Oscillated

νμ spectrum

Monte Carlo

Monte Carlo

Spectrum ratio

MINOS Methodology

P µ → µ( ) =1−sin2 223 sin2 1.267m232 L / E( )

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• To perform the oscillation analysis, we need to predict the neutrino spectrum seen by the Far Detector in the absence of oscillations.

• Want to minimize uncertainties related to beam modeling and cross-sections (nominal values are built-in to our Monte Carlo.)

• Use the Near Detector data to correct the nominal Monte Carlo– beam spectrum– neutrino cross-sections

Overview of the Oscillation Measurement

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The NUMI facility

• Design parameters:

– 120 GeV protons from the Main Injector

– Main Injector can accept up to 6 Booster batches/cycle,

– Either 5 or 6 batches for NuMI

– 1.867 second cycle time

– 4 x 1013 protons/pulse

– 0.4 MW

– Single turn extraction (~10ms)

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The NuMI beamline

Primary proton line

Target hall Decay pipe

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Producing the neutrino beam

• Single turn extraction• ~10 μs spill of 120 GeV protons every ~2 s• 0.25 MW average beam power• 2.5 1013 protons per pulse (ppp)

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BeamTarget z

position (cm)FD Events per

1e20 pot

LE-10 -10 390

pME -100 970

pHE -250 1340

LE

pME

pHE

Events expected in fiducial volume

The NuMI neutrino beam

• Currently running in the LE-10 configuration• ~1.5 1019 POT in pME and pHE configurations early in the

run for commissioning and systematics studies

µ  92%

ν µ   6.5%

ν e + ν e  1.5%

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Dataset used for the oscillation analysis

Observation of

neutrinos in Near

Detector! Start of LE running

1020 pot!

First Year of Running

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The MINOS Detectors

Detectors magnetised to 1.2 TGPS 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

M16 multi-anode PMTs, VA chips

1 kt mass, 3.84.815m282 steel and 153 scintillator

planeFront 120 planes Calorimeter

Remaining planes SpectrometerM64 multi-anode PMTs, QIE chips

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Scintillator strip

M64

M16

Detector Technology

MINOS Near and Far Detectors are functionally identical:

• 2.54 cm thick magnetized steel plates

• co-extruded scintillator strips

• orthogonal orientation on alternate planes – U,V

• optical fibre readout to multi-anode PMTs

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Reconstruction of a MINOS event

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Reconstruction of a MINOS event

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νμ CC Event NC Event νe CC EventUZ

VZ

long μ track & hadronic activity at

vertex

short, with typical EM shower profile

short event, often diffuse

3.5m 1.8m 2.3m

Monte Carlo

Eμ = Eshower + pμ

55%/E/GeV 6% range, 10% curvature

Event topologies

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Event selection cuts

CC-like events are selected in the following way:

1. Event must contain at least one good reconstructed track2. The reconstructed track vertex should be within the fiducial

volume of the detector:

3. The fitted track should have negative charge (selects ) [for now]4. Cut on likelihood-based Particle ID parameter which is used to

separate CC and NC events.

νCalorimeter SpectrometerNEAR:

1m < z < 5m (from detector front),R < 1m from beam centre.

FAR:z > 50 cm from front face, z > 2 m from rear face,z not in supermodule gap, R2 < 14 m2 from detector center.

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• Help understand energy response to reconstruct Eν

Eν = pµ + Ehad

• Measured in a CERN test beam with a “mini-Minos”

• operated in both Near and Far configurations

• Study e/µ/hadron response of detector

• Test MC simulation of low energy interactions

• Provides absolute energy scale for calibration

E/%55

E/%23

Single particle energy resolution

beam

The MINOS Calibration Detector

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• Calibration of ND and FD response using:

– Light Injection system (PMT gain)

– Cosmic ray muons (strip to strip and detector to detector)

– Calibration detector (overall energy scale)

• Energy scale calibration:

– 1.9% absolute error in ND

– 3.5% absolute error in FD

– 3% relative

MINOS Calibration system

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Selecting CC events

Input variables for PDF based event selectionMonte Carlo

Events selected by likelihood-based procedure, with 3 input Probability Density Functions (PDFs)• event length in planes• fraction of event pulse height in the reconstructed track• average track pulse height per plane

Define Pμ (PNC) as the product of the three CC (NC) PDFs, at the values of these variables taken by the event

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CC selection efficiencies

• Particle ID (PID) parameter is defined:

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

CC-like (87%)

(97%)

Monte

Carlo

( ) ( )NClog logPID P Pì=− − + −

PDF PID parameter distribution PDF PID parameter distribution

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Near Detector distributions

• We observe very large event rates in the Near detector (~107 events in the fiducial volume for 1020 POT)

• This provides a high statistics dataset with which we can study how well we understand the performance of the Near Detector and check the level to which our data agrees with our Monte Carlo predictions

Reconstructed x vertex (m)

Rec

on

stru

cted

y v

erte

x (m

)

Coil hole

Detector outline

Fiducial region

Partially instrumented planes

Area

normalised

Beam points down 3 degrees to reach Soudan

Reconstructed track angle with respect to verticalDistribution of reconstructed event vertices in the

x-y plane

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Calorimeter/ spectrometer boundary

Event length Track PH per plane

Track PH fraction

Particle ID variables (LE-10 Beam)

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PID parameter

PID cut to select CC-like events is at –0.1

LE-10 pME

pHE

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• Overall agreement between data and MC• Data showers tend to be slightly shorter and more “dense”

than MC showers

Shower profiles – LE-10 beam

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These distributions shown after xF, pT reweighting

Reconstructed Neutrino Energy (GeV)

Reconstructed Y =Eshw/(Eshw+Em)

LE-10 pME pHE

LE-10 pME pHE

Energy spectra & Y (CC-like events)

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Agreement between data and Fluka05 Beam MC is mostly good, but by tuning the MC by fitting to hadronic xF and pT, improved agreement can be obtained.

LE-10/185kA

pME/200kA

pHE/200kA

Weights applied as a function of hadronic xF and pT.

LE-10/Horns off

LE-10 eventsNot used in the fit

Hadron production tuning

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• Reconstructed energy distributions agree to within statistical uncertainties (~1-3%)

• Beam is very stable and there are no significant intensity dependent biases in event reconstruction.

• June

• July

• August

• September

• October

• November

Typical proton intensity ranges from 1013 ppp - 2.8times1013 ppp Energy spectrum by

batchEnergy spectrum by Month

Stability of the energy spectrum & reconstruction

with intensity

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• The agreement between low level quantities indicates that there are no obvious pathologies introduced by detector modeling and/or reconstruction.

• Agreement between high level quantities is within the expected systematic uncertainties from cross-section modeling, beam modeling and calibration uncertainties (initial agreement improved after applying beam reweighting on the xF and pT of parent hadrons in the Monte Carlo)

Summary of ND Data/MC agreement

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Far Detector Beam Analysis

Oscillation analysis performed using data taken in the LE-10 configuration from May 20th 2005 – December 6th 2005

• Total integrated POT: 0.931020

• Excluded periods of “bad data” – coil and HV trips, periods without accurate GPS timestamps. The effect of these cuts are small (~0.7% of our total POT)

• POT-weighted live-time of the Far detector: 98.9%

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Performing a blind analysis

• The MINOS collaboration decided to pursue a blind analysis policy for the first accelerator neutrino results– The blinding procedure hides an unknown fraction of

FarDet events based on their length and total energy deposition.

• No blinding was applied to NearDet data• Unknown fraction of Far Detector data was open

– performed extensive data quality checks.

• Unblinding criteria were:

– no problems with the FarDet beam dataset (missing events, reconstruction problems, etc.)

– Oscillation analysis (cuts and fitting procedures) pre-defined and validated on MC; no re-tuning of cuts allowed after box opening

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Selecting beam induced events

• Time stamping of the neutrino events is provided by two GPS units (located at Near and Far detector sites).

– FD Spill Trigger reads out 100μs of activity around beam spills

• Far detector neutrino events easily separated from cosmic muons (0.5 Hz) using topology

Backgrounds estimated by applying selection algorithm on “fake” triggers taken in anti-coincidence with beam spills

In 2.6 million “fake” triggers, 0 events survived the selection cuts (upper limit on background in open sample is 1.7 events at 90% C.L. )

Neutrino candidates are in 10μs window

Time difference of neutrino interactions from beam spill

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Predicting the unoscillated FD spectrum

• Directly use Near Detector data to perform extrapolation between Near and Far

• Use Monte Carlo to provide necessary corrections due to energy smearing and acceptance.

• Use our knowledge of pion decay kinematics and the geometry of our beamline to predict the FD energy spectrum from the measured ND spectrum

• This method is known as the Beam Matrix method.

f

to FarDetector

Decay Pipe

(soft)

(stiff)

n

target

ND

Flux ∝1L2

11+ γ2 2

⎛

⎝⎜⎞

⎠⎟E =

0.43E

1+ γ2 2

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The “Beam Matrix” Method

Step 1: ENear  CC−likeReconstructed ⇒ ENearCC

True

Correctionforpurity,Reconstructed⇒ True,Correctionforefficiency( )

Step2:ENearCCTrue ⇒ EFarCC

True

BeamMatrix( )

Step3:EFarCCTrue ⇒ EFarCC−like

Reconstructedi)Oscillation,True⇒ Reconstructed,correctionforefficiencytoobtain

ccoscillatedspectrum

ii)Unoscillated,True⇒ Reconstucted,UsepuritytoobtainNCbackground

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)()( binNCtrueCCtrue

CCtruebinPurity

+=

)()( binCCallCCtrue

binEfficiency =

1

2

Correction for purity

Step A, Beam Matrix Method

Reconstructed =>True and Correction for efficiency

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• Beam Matrix encapsulates the knowledge of pion 2-body decay kinematics & geometry.

• Beam Matrix provides a very good representation of how the Far Detector spectrum relates to the near one.

Beam Matrix Method : Near to Far extrapolation

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Predicted true FD spectrum

• higher than nominal FD MC in high energy tail

• expected, given that the ND visible energy spectrum is also higher than the nominal MC in this region

Predicted spectrum

Nominal MC

0.931020 POT

Predicted FD true spectrum from the Matrix

Method

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Vertex distributions of selected events

• 296 selected events with a track – no evidence of background contamination.

• Distribution of selected events consistent with neutrino interactions

Full dataset

Area normalised

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Track Length Track Pulse Height per Plane

Particle IdentificationParameter

Track quantities & PID parameter

CC-like

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Notice that beam is pointing 3 degrees up at Soudan!

X Y

Z

Track angles

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y = Eshw/(Eshw+Pµ)

Muon Momentum (GeV/c) Shower Energy (GeV)

Physics distributions

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• We observe a 33% deficit of events between 0 and 30 GeV with respect to the no oscillations expectation.

– Numbers are consistent for sample and for the -only sample

• The statistical significance of this effect is 5 standard deviations

Data sample observed expected ratio significance

All CC-like events ( 204 29815 0.69 4.1

only (<30 GeV) 166 24914 0.67 4.0

only (<10 GeV) 92 17711 0.52 5.0

Numbers of observed and expected events

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Cut Events efficiency

All events in fiducial volume 331 -

Events with a track 296 89.1%

Track quality cuts 281 95.3%

PID cut (CC-like) 204 72.9%

Track charge sign cut (negative muons only)

186 91.2%

Reconstructed energy < 30 GeV 166 89.2%

Breakdown of selected events

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Best-fit spectrum

χ 2 Δm232 ,sin2 2θ23( ) = 2 ei − oi( ) + 2oi ln oi / ei( ) ei  exp ected

oi  observed

i=1

nbins

∑

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Data

Best-fit

Ratio of Data/MC

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Allowed regions

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Systematic errors

Systematic shifts in the fitted parameters have been computed with MC “fake data” samples for Δm2=0.003 eV2, sin22θ=0.9 for the following uncertainties:

Uncertainty m2 shift (eV2) Sin22 shift

Normalization +/- 4% 0.63e-4 0.025

Muon energy scale +/- 2% 0.14e-4 0.020

Relative Shower energy scale +/- 3% 0.27e-4 0.020

NC contamination +/- 30% 0.77e-4 0.035

CC cross-section uncertainties 0.50e-4 0.016

Beam uncertainty 0.13e-4 0.012

Intranuclear re-scattering 0.27e-4 0.030

Total (sum in quadrature) 1.19e-4 0.063

Statistical error (data) 6.4e-4 0.15

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Summary and Conclusions

• In this talk we have presented the first accelerator neutrino oscillation results from a 0.931020 pot exposure of the MINOS far detector.

• Our result disfavors no disappearance at 5 and is consistent with oscillations with the following parameters:

• The systematic uncertainties on this measurement are well under control and we should be able to make significant improvements in precision with a larger dataset.

– Our total exposure to date is 1.41020 pot.

m232 = 3.05−0.55

+0.60 stat( ) ± 0.12 syst( )⎡⎣ ⎤⎦×10−3eV 2

sin2 2θ23 = 0.88−0.15+0.12 stat( ) ± 0.06 syst( )

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Next Steps

• Continue to study other Near/Far extrapolation methods

• Analyze additional data already collected (~40% more data)

• Relax fiducial and other cuts to achieve greater efficiency in analysis of events

• Collect new data beginning in June with continued increases in beam intensity

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Δm2 = 0.003 eV2

Outlook

• Study neutrino/anti-neutrino oscillations • Search for/rule out exotic phenomena:

– Sterile neutrinos, Neutrino decay

Improve this measurement:Sensitivity at 16 x 1020 POT

Search for sub-dominant

νμ νe oscillations

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Future of NuMI Beam

• NOA Detector to observe e appearance

• Continued intensity upgrades; possible Proton Driver(?)

• Second Maximum Detector(?), Megaton Neutrino and Proton Decay Detector [Liquid Argon]?

• Interaction with possible Deep Underground Laboratory

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Canada

United States

Duluth

International Falls Ash River

Orr-Buyck

Soudan-Lake Vermilion

Mine Centre

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Summary and Conclusions

• In this talk we have presented the first accelerator neutrino oscillation results from a 0.931020 pot exposure of the MINOS far detector.

• Our result disfavors no disappearance at 5 and is consistent with oscillations with the following parameters:

• The systematic uncertainties on this measurement are well under control and we should be able to make significant improvements in precision with a larger dataset.

– Our total exposure to date is 1.41020 pot.

m232 = 3.05−0.55

+0.60 stat( ) ± 0.12 syst( )⎡⎣ ⎤⎦×10−3eV 2

sin2 2θ23 = 0.88−0.15+0.12 stat( ) ± 0.06 syst( )