1 Mike Kordosky – NuFact 06 - Aug 27, 2006 Neutrino Interactions in the MINOS Near Detector Mike...

1Mike Kordosky – NuFact 06 - Aug 27, 2006

Neutrino Interactions in the MINOS Near Detector

Mike KordoskyUniversity College London

on behalf of the

MINOS Collaboration


Plan for this talk● Introduction & CC sample:

– NuMI beam, energy and kinematics coverage

– MINOS Near Detector, data collection and reconstruction

– Selection of -CC events, energy spectra, kinematics distributions

● Flux extraction strategies:

– Low- method

– QE selection and method

● DIS measurements:

– Projected cross section and structure function measurements

– Prospects for a di-muon measurement


Introductionand CC sample


The NuMI neutrino beam

● Variable target position = variable beam energy!● Two magnetic focusing horns● Sign selected beam: neutrino or anti-neutrino

enriched

to Near Detector


The NuMI neutrino beam

= 92.9% = 5.8%ee = 1.3%

Beam POT / 1e18

LE 125.1 106.7

ME 1.1 1.9

HE 1.6 3.7

Selected CC Events / 1e4

Exposure (to March 3, 2006)

Beam Composition (LE)


Kinematic CoverageKinematic Coverage

of the LE Beam

A

B

C D

A) Safe-DIS: 24.2%● |Q| > 1 GeV/c

● |W| > 2 GeV

B) Low Q2 DIS: 8.5%● |Q| < 1 GeV/c

● |W| > 2 GeV

C) RES ⇔ DIS: 32.4%● 2.0<W<1.3 GeV

D) QEL + : 34.8%● W<1.3 GeV

Kinematic Regions

QE/RES/DIS: 19/23/57%


Kinematic CoverageKinematic Coverage

of the LE Beam

A

B

C D

A) Safe-DIS: 24.2%● |Q| > 1 GeV/c

● |W| > 2 GeV

B) Low Q2 DIS: 8.5%● |Q| < 1 GeV/c

● |W| > 2 GeV

C) RES ⇔ DIS: 32.4%● 2.0<W<1.3 GeV

D) QEL + : 34.8%● W<1.3 GeV

Kinematic Regions

QE/RES/DIS: 19/23/57%


Near Detector● 1km from Target● 0.98 kton● 282 steel planes

– 0-120 = calorimeter

– 120+ = spectrometer

● B=1.2 T● 64-anode PMTs● High Rates● QIE electronics

– no deadtime!

Near detector during installation

Partial Plane

PMTs, QIE electronics

Beam

Full Plane

Coil Hole

To Far detector


Detector

Technology

2.54cm Steel absorber

● Tracking-Sampling calorimeter

● Segmentation:

– 5.94cm longitudinal

– 4.1cm transverse

● Planes rotated +/- 90 deg

● WLS collects/routes light to PMTs

Scint. 1cm thick, 4.1 cm

wide WLS Fibers

Multi-anodePMT

Fiber ''cookie''

Scint. Plane

Readout Cable

PMT DarkBox

M64 PMT M16 PMT


Event Reconstruction

● High rate in Near detector results in multiple neutrino interactions per MI spill

● Events are separated by topology and timing (19ns resolution)

Batch structure clearly seen!

One near detector spill

7.1 mbeam direction


CC event topology

E = Eshower+P

Shower Energy Resolution: ~56%/E

Muon Energy Resolution

6% range, 13% curvature

-CC event


● 1 good track– Stopping = prange

– Exiting = pcurvature

● Vertex in fiducial volume– Centered on beam

spot

● Negative charge (for )

● Topological PID to discriminate CC/NC

-CC event selection

Calorimeter Spectrometer

-


CC/NC classification

event lengthfraction of signal

in track

PID efficiency

average track signal/plane

~dE/dx

RequirePID > -0.1


Energy Spectra

Reweight pion xF and pT to improve data/MC agreement

Include horn focusing, NC normalization, energy scale as nuisance parameters

lowenergybeam

mediumenergybeam

highenergybeam


● NEUGEN3 generator (H.Gallagher, Nucl.Phys.Proc.Suppl. 112, 188-194, 2002)

● QEL: dipole parameterisation with mA = 1.032 GeV/c2

● Resonance production: Rein-Seghal for W<1.7 GeV/c2

● DIS: Bodek-Yang modified LO model, tuned to e and data in resonance/DIS overlap region

● Coherent production

● Nuclear model: Fermi Gas model, Pauli blocking of QEL scattering

● Final state interactions for pions

Event Generation


Kinematic Distributions

x=Q2

2MEHAD

y=EHAD

EE

HAD

Q2=2EE

E

HAD1−cos

W 2=M 22MEHAD

−Q 2

High Energy Tail 10 < E < 30 GeV

Best understood flux

“Safe DIS” W>2 GeV, Q>1 GeV/c

Best understood cross-section

MINOSpreliminary

MINOSpreliminary


Neutrino Flux Measurements


Low- approach


Low- approach

● Require, in lieu of PID: p > 2 GeV/c, Eshw < 1 GeV● Acceptance correction from MC to give N(E)● Correction for energy

dependent QEL (35-45% QE)

● B/A correction to inelastic cross section

Bands computed from physical limits

Neutrino: -0.24 < B/A < 0.0Anti-neutrino: -2.0 < B/A < -1.7


Measured Flux LE Beam

Data v. MC flux for LE-10 beam.Normalization is to POT exposure.

flux

data/MC

MINOSpreliminary

dataMC


Low- ApproachPrognosis

● Current uncertainties dominated by MC statistics for acceptance correction

● B/A corrections have large uncertainty for E< 5 GeV

● Evaluation of systematic errors● Improve purity of anti-neutrino

sample (now 91.4%)● Investigating radiative

corrections● “unfolding” rather than binned

acceptance correction?

muon energy scale +/- 2%

shower energy scale +/- 2%


Quasi-elastic approach● QEL reasonably well

constrained, and ~flat● select QE enriched

sample 0.5-30 GeV● flux shape

● Inclusive CC well

measured above 30 GeV on Fe

● inclusive CC sample 10-30 GeV

● flux normalization


Quasi-elastic flux extraction

E =n E −n

NCE

QEL

E QEL

E RES

E RES

EDIS

EDIS

E

Selected Events NC background (MC)

Extracted Flux

Cross Sections (MC) Selection Efficiencies (MC)

i=

events selected in reco bin i

events generated in true bin iNormalization fixed

according to inclusive sample 10-30 GeV


Quasi-elastic selection

efficiency ~ 40%purity ~ 70%

Monte Carlo Monte Carlo

● PDF based selection procedure, using shower topology, expected proton direction, reco-W.

● 40% efficiency, 70% purity (MC), energy independent


Quasi-elastic prognosis● Basic method works when

applied to fake data● Selection procedure based

on low-energy shower topology. Uncertainties in:– single particle response

(have test beam data)– final state interactions

(difficult to quantify and model)

● cross-section uncertainties less serious

– RES also flat w/energy


Cross Section Measurements


Total cross section

● Event selection, as before but:

– p> 2 GeV/c , separate by muon charge

● purity: =99.4% , anti-= 91.4%

● Cross section simply:● Energy dependence only: norm. to world average at high energy

“Mock Data”

Extracted Cross Section

CC

Ei=−1E

iN

CCE

i f

accE

i


Cross Section Systematics

● Very large (0.8e5 /1e20 POT) event sample, measurement will be systematics limited, even for anti-

shower energy scale

muon energy scale


Structure Functions

MINOS: Statistics only, 7.4e20 POT

Systematics due to energy scale

+/- 2% E scale+/- 5% Ehad scale

Q2 = 2 (GeV/c)2

X

F 2(x

)

F 2(x

,Q2)

Q2(GeV/c)2

Q2=2 (GeV/c)2

Projected F2 reach (MC study)

MINOS(MC)NuTeVCCFRCDHSWGRV98o+HT


Di-muon prospectsRev.Mod.Phys. v70, n4 (1998)

neutrino energy (GeV)

ReconstructedEnergy Spectrum

LE Beam (MC)

arbitrarynormalization

Di- rate & shape sensitive to charm production mechanism, charm mass

MINOS event sample concentrated in interesting low energy region (few 10s of GeV)


Di-muon prospects

>0.5 ~16800

>1.5 ~7200

>2.5 ~3900

mu1, mu2 momentum (GeV/c)

di-muon events / 1e21 POT / 40 ton

Estimated Sample Size

A fully reconstructed di- event

A work in progress, main challenges:Efficient 2 track reconstruction

Background rejection: ~1e4 needed for ~10% background


Summary● Intense NuMI beam and highly efficient MINOS Near

Detector offer excellent opportunities for cross-section measurements at low energy and low-Q2

● Data collection/ reconstruction well understood● Several analyses nearing maturity

– Flux extraction

– Total -CC cross section

● Much to do in the future– Differential cross sections, structure functions– di-muon analysis

– mQEL, coherent production, NC


Backup Slides


CC efficiency

PID cut only

all cuts


Energy Spectrum

Tuning

peak

HE tail

PT v Pz weights


Oscillation Result

∣ m23

2 ∣=2.74−0.26

0.44eV 2 /c4

sin2 2230.871


Muon Range v. Curvature


● Calibration Detector = mini-MINOS

● Ran @ CERN PS

● Sixty 1-m2 planes

● Near and Far Electronics

● , e, p and response at few GeV/c

CalDet in T7

1 m

Optical Cables

PMTs

Beam

Energy Scale


ND Track angle

Area

normalized

Beam points down

3 degrees to reach

SoudanTrack angle w.r.t. vertical


ND event rate and vertex dist.

X ZY

• Event rate is flat as a function of time

• Horn current scans – July 29 – Aug 3

LE-10 Beam


Energy spectrum & reconstruction stability

● 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

proton intensity ranges from 1e13 ppp - 2.8e13 ppp

Energy spectrum by batchEnergy spectrum by Month


Kinematic Distributions

x=Q2

2MEHAD

y=EHAD

EE

HAD

Q2=2EE

E

HAD1−cos

W 2=M 22MEHAD

−Q 2

High Energy Tail 10 < E < 30 GeV

Best understood flux

“Low-Q2 DIS” W>2 GeV, Q<1 GeV/c

Few cross-sectionmeasurements

MINOSpreliminary

MINOSpreliminary

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