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Direct Measurement of the NuMI Flux with Neutrino-Electron Scattering in MINERvA. Jaewon Park University of Rochester On behalf of MINERvA Collaboration December 20, 2013 Fermilab Joint Experimental-Theoretical Seminar. Outline. Neutrino experiments and their fluxes

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Direct Measurement of the NuMI Flux with Neutrino-Electron Scattering in MINERvA

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Direct measurement of the numi flux with neutrino electron scattering in minerva

Direct Measurement of the NuMI Flux with Neutrino-Electron Scattering in MINERvA

Jaewon Park

University of Rochester

On behalf of MINERvA Collaboration

December 20, 2013

Fermilab Joint Experimental-Theoretical Seminar


Outline

Outline

  • Neutrino experiments and their fluxes

  • ν-e scattering: signal

  • Event reconstruction

  • Backgrounds and how to remove them

  • Background Prediction

  • Systematic uncertainty

  • Result and Conclusions

Jaewon Park, U. of Rochester FNAL JETP


Oscillation experiment strategy

Oscillation Experiment Strategy

N: events in data

B: Background

e: Efficiency

A: Acceptance

s: Cross section

or ?

Near Detector (ND)

  • In fact the flux doesn’t just decrease like 1/L2

    • Oscillations

    • Near detector sees line source, far detector sees point source

  • Far detector sample is always very different from near detector sample

Far Detector (FD)

Isn’t this just 1/L2?

Jaewon Park, U. of Rochester FNAL JETP


Needs of precision oscillation experiments

Needs of Precision Oscillation Experiments

  • Precise measurement of oscillation parameters is the key to answer important questions like neutrino mass hierarchy and CP violation

  • To achieve the highest precision, we need:

    • (High intensity beam) × (big detector) × (long operation)

    • Low uncertainties on flux prediction

    • Better understanding of neutrino interactions

      • More accurate cross-section (May 10 JETP by MINERvA)

      • Understanding nuclear effects (October 11 JETP by MINERvA)

      • Detailed understanding of background interactions

  • This talk is about a method to constrain or measure the neutrino flux using neutrino-electron scattering

    • This helps to reduce flux normalization uncertainties on MINERvA’s absolute cross-section measurements

    • This technique can be used in future high intensity beam experiments to measure the flux

Jaewon Park, U. of Rochester FNAL JETP


Neutrinos from an accelerator

Neutrinos from an Accelerator

Decay pipe

Rock

Near

Detector

Far

Detector

Horn 2

Target

Horn 1

proton

  • Neutrino beam is generated from a decay of secondary or tertiary particles  Hard to control beam itself, too hot to measure in situ

  • Flux has large uncertainties due to poor knowledge of hadron production

  • Non-perturbative QCD governs it  Difficult to calculate from basic principles

  • ~15-30% normalization uncertainties on flux

Jaewon Park, U. of Rochester FNAL JETP


Neutrinos from an accelerator1

Neutrinos from an Accelerator

Decay pipe

Rock

Near

Detector

Far

Detector

Horn 2

Target

Horn 1

proton

  • Kaon and muon decays are main source of electron neutrinos

Jaewon Park, U. of Rochester FNAL JETP


Constraining flux with hadron production data

decay pipe

n

ν

π

p

target

Constraining flux with Hadron Production Data

  • Hadron production primarily function of xF=pion/proton momentum ratio and ptransverse

    • Use NA49 measurements

    • Scale to 120 GeV using FLUKA (simulation)

    • Check by comparing to NA61 data at 31 GeV/c [Phys.Rev. C84 (2011)034604]

  • Use MIPP (120GeV protons) for K/π ratio

Jaewon Park, U. of Rochester FNAL JETP


Na49 pc k p @ 158 gev

NA49: pC → π,K,p @ 158 GeV

f(xF,pT) = E d3σ/dp3 = invariant production cross-section

π+ which makea νμ in MINERvA

NA49 data

vs. GEANT4

focusing

peak

high

energy

tail

Uncertainties

7.5% systematic

2-10% statistical

Jaewon Park, U. of Rochester FNAL JETP


Need more than hadron production measurements

Need more than Hadron Production Measurements

  • Hadron Production measurements don’t tell the whole story, only 70%

    • Some pion production is out of range of Hadron Production data

    • Tertiary production of neutrinos also important (n, h, KL,S)

  • Beamline geometry and focusing elements contribute uncertainties

Jaewon Park, U. of Rochester FNAL JETP


Special runs to understand flux

Special Runs to Understand Flux

Normal Running

Pt (GeV/c)

xF

Neutrinos at MINERvA

Target Moved upstream

Pt (GeV/c)

Inclusive Event Spectra

xF

  • MINERvA integrated 10% of our total neutrino beam exposure in alternate focusing geometries:

    • Changed horn current

    • Changed Target Position

  • Purpose is to disentangle focusing uncertainties from hadron production uncertainties

    • Different geometry focuses different parts of xFpT space, but same horn geometry and current

  • MINERvA does this by using low hadron energy nm charged current events, where energy dependence of cross section is very well understood

Jaewon Park, U. of Rochester FNAL JETP

Pion Phase Space


Neutrino flux and cross section measurement

Neutrino Flux and Cross-section Measurement

Flux and cross-section are anti-correlated with given Near Detector constraint

MINERvA

Flux uncertainty goes into

cross-section uncertainty

Measurement uncertainty

Φ (Flux)

Flux constraint using

Near Detector

Cross-section uncertainty goes into

flux uncertainty

σ (Cross Section)

N: Events

e: Efficiency

A: Acceptance

s: signal cross section

20 December 2013

Jaewon Park, U. of Rochester FNAL JETP


Known interaction standard candle

Known Interaction (Standard Candle)

  • ν-e scattering is well known interaction we can use to constrain the neutrino flux

Φ (Flux)

Flux constraint using ND

Cross-section uncertainty goes into

flux uncertainty

σ (Cross Section)

ν-e Scattering

Jaewon Park, U. of Rochester FNAL JETP


Outline1

Outline

  • Neutrino experiments and their fluxes

  • ν-e scattering: signal

  • Event reconstruction

  • Event selection

  • Background Prediction

  • Systematic uncertainty

  • Result and Conclusions

Jaewon Park, U. of Rochester FNAL JETP


E scattering history

ν-e Scattering History

First unambiguous

neutral current

(Gargamelle)

Electroweak

theory

Solar ν oscillation measurement

using ν-e scattering (SNO)

Additional interaction

for

All flavor

Matter effect is due to

charged current νe scattering

on electrons, only for νe

Coherent forward scatterings

Jaewon Park, U. of Rochester FNAL JETP


Neutrino scattering on nucleon

Neutrino Scattering on Nucleon

Electron

Very forward single electron final state

  • Let’s use well-known reaction to measure the flux

  • Standard electroweak theory predicts it precisely

    • Point-like scattering

  • Very small cross section (~1/2000 of ν-nucleon scattering)

    • Low center of mass energy due to light electron

  • Very forward electron final state (Experimental signature)

  • Good angular resolution is important to isolate the signal

νe→ νe candidate event

Jaewon Park, U. of Rochester FNAL JETP


E scattering

ν-e Scattering

GF and θW: well-known electroweak parameters

  • E > 0.8 GeV

    • High background rate and tough reconstruction at low energy

  • Predict 147 signal events for 3.43×1020 Protons On Target (POT)

    • ~100 events when you fold in (reconstruction + selection) efficiency of ~ 70%

  • Not a large sample in low energy run but still useful to constrain absolute flux

ne Scattering Events

ne Scattering Events

FLUX

Jaewon Park, U. of Rochester FNAL JETP


Signal events

Signal Events

E<0.8 GeV is not used

  • Large background

  • Tough reconstruction

E>0.8 GeV

  • Signal is mixture of in LE-FHC (neutrino beam)

  • ~100 signal events for 3.43E20 POT

  • Can’t distinguish neutrino type

  • Still useful to constrain the flux

    • Total events: Constraint for integrated flux

    • Electron spectrum: Constraint for flux shape

For remainder of talk,

means and

Jaewon Park, U. of Rochester FNAL JETP


Outline2

Outline

  • Neutrino experiments and their fluxes

  • ν-e scattering: signal

  • Event reconstruction

  • Backgrounds and how to remove them

  • Background Prediction

  • Systematic uncertainty

  • Result and Conclusions

Jaewon Park, U. of Rochester FNAL JETP


Direct measurement of the numi flux with neutrino electron scattering in minerva

Thank you!

for the excellent ν beam

Data and Simulation Samples

MINERvA ran in three kinds of beam:

Low Energy neutrino

Low energy anti-neutrino

“Special Runs”: higher energy runs to constrain flux model

  • All Low Energy neutrino data is used for the analysis: more than previous analyses shown to date (3.43 × 1020 Protons on Target)

  • Time-dependent effects (calibrations, accidental activity) included in the simulation

Jaewon Park, U. of Rochester FNAL JETP


Minerva detector

Outer Detector

(steel + scintillator)

4m

5m

3.5m

Hadronic Calorimetry

Electromagnetic Calorimetry

Nuclear Targets

(C, Pb, Fe, H2O)

Tracker

(Active target)

MINERvA Detector

Inner Detector

Jaewon Park, U. of Rochester FNAL JETP


Inside the detector

Inside the Detector

MINOS

Near Detector

(muon spectrometer)

Scintillator plane

(X, U, V stereo angle)

Hcal

Ecal

Tracker

Nuclear Target

−60°

+60°

Number of channels: ~31k

Number of scintillator plane: 128

u

x

Pb

Fe

v

x

Tracking Ecal (lead absorber + tracking plane)

Tracking Hcal (steel absorber + tracking plane)


Detector technology

127 strips into a plane

17 mm

2.1m

16 mm

Position resolution: ~3mm

2.5 m

Detector Technology

64 channel multi-anode PMT

8×8 pixels

Scintillator strip

Wavelength shifting fiber

  • Extruded plastic scintillator with wavelength shifting fiber readout

  • 64 channel multi-anode PMT for photo-sensor

Jaewon Park, U. of Rochester FNAL JETP


E e candidate event

Fiducial volume

ν + e- → ν + e- candidate event

X-View

U-View

V-View

Data run: 2157/12/1270/2

Jaewon Park, U. of Rochester FNAL JETP


Single electron reconstruction

Single Electron Reconstruction

Nuclear Target Region

(He,C/H2O/Pb/Fe)

HCAL

ECAL

Shower-like

Track-like

Track-like part (beginning of electron shower) gives good direction

Jaewon Park, U. of Rochester FNAL JETP


Single electron reconstruction1

Single Electron Reconstruction

Nuclear Target Region

(He,C/H2O/Pb/Fe)

HCAL

ECAL

Shower cone

Track-like part (beginning of electron shower) gives good direction

Jaewon Park, U. of Rochester FNAL JETP


Critical variables for signal

Critical Variables for Signal

  • Electron Identification

    • Must discriminate from photons

  • Electron Energy Measurement

  • Electron Angular Measurement

Jaewon Park, U. of Rochester FNAL JETP


Electron photon discrimination using de dx

Electron Photon Discrimination using dE/dx

Electron-induced electromagnetic shower

Photon -induced electromagnetic shower

MINERvA Preliminary

  • Electromagnetic shower process is stochastic

    • Electron and photon showers look very similar

  • Photon shower has twice energy loss per length (dE/dx) at the beginning of shower than electron shower

    • Photon shower starts with electron and positron

Jaewon Park, U. of Rochester FNAL JETP


Energy and angle reconstruction

Energy and Angle Reconstruction

Using simulated signal

Using simulated signal

MINERvA Preliminary

MINERvA Preliminary

  • Energy resolution ~ 5%

  • Projected angle resolution ~ 0.3 degree (2 sigma truncated RMS)

  • Precise angle reconstruction is critical to separate νe elastic scattering from background

    • Lower energy angular resolution is worse due to multiple scattering

Jaewon Park, U. of Rochester FNAL JETP


Outline3

Outline

  • Neutrino experiments and their fluxes

  • ν-e scattering: signal and backgrounds

  • Event reconstruction

  • Backgrounds and how to remove them

  • Background Prediction

  • Systematic uncertainty

  • Result and Conclusions

Jaewon Park, U. of Rochester FNAL JETP


Initial background rejection

Initial Background Rejection

Rare but hard to reject:

  • n-e scattering is very rare, even for n interactions:

  • Simple cuts can eliminate most background events while keeping high fraction of signal events

    • Obvious muon-like event rejection

    • Upstream energy rejection

      • Removes neutrino interactions upstream of detector that make m

Most Events

(nm Charged or neutral Current)

Coherent p0

ne Quasi-elastic (CCQE)

Jaewon Park, U. of Rochester FNAL JETP


Background events

8

6

4

2

0

x

z

Background Events

MeV

proton

MC

Electron neutrino fraction in flux is small ~ 1%.

electron

  • If recoil nucleon is not observed, it looks similar to signal

  • Angles of electron have wide spread while signal is very forward

Use Eθ2to select

very forward signal

Neutral current single π0

Also, photon has wide spread of angle

In addition, use dE/dx to reject

NC-coherent π0

2. One of gammas is not observed in the detector

NC-resonant π0

1. Small opening angle between two gammas

γ (67 MeV )

π0 (7.5 GeV)

π0 (1.1 GeV)

Simulated event

Simulated event

Jaewon Park, U. of Rochester FNAL JETP


Example neighborhood energy

Example: Neighborhood Energy

MINERvA Preliminary

  • Neighborhood energy = energy around shower cone

  • Small neighborhood energy means isolated shower

Not Full Sample

Signal × 200

MINERvA Preliminary

5 cm

Shower cone

Neighborhood

Jaewon Park, U. of Rochester FNAL JETP


Event selection

Event Selection

Other

reconstruction quality cuts

  • Electron Energy>0.8GeV

  • Fiducial cut

Shower cone

Reconstruction

  • Eθ2

  • dE/dx

Signal

sample

Kinematic constraint on ne scattering, using Mandelstam variables:

in CM frame

in lab frame

Jaewon Park, U. of Rochester FNAL JETP


De dx cut

dE/dx<4.5MeV/1.7cm

dE/dx Cut

MINERvA Preliminary

  • All cuts made on this sample except for the dE/dx cut

  • Neutrino interaction doesn’t always produce only single electron or single photon (from π0)

  • Non-single particle activity affects dE/dx

MINERvA Preliminary

tuned

tuned

Jaewon Park, U. of Rochester FNAL JETP


E 2 cut

Eθ2 Cut

  • All cuts but Eq2 cut

  • Kinematic limit for signal

    • Eθ2 < 2me

  • Clean separation of signal

tuned

tuned

MINERvA Preliminary

MINERvA Preliminary

Jaewon Park, U. of Rochester FNAL JETP


Electron spectrum after all cuts

Electron Spectrum after all cuts

tuned

MINERvA Preliminary

MINERvA Preliminary

True electron energy

(signal only)

Reconstructed electron energy

Jaewon Park, U. of Rochester FNAL JETP


Outline4

Outline

  • Neutrino experiments and their fluxes

  • ν-e scattering: signal and backgrounds

  • Event reconstruction

  • Backgrounds and how to remove them

  • Background Prediction

  • Systematic uncertainty

  • Result and Conclusions

Jaewon Park, U. of Rochester FNAL JETP


Backgrounds after all cuts

Backgrounds after all Cuts

MINERvA Preliminary

MINERvA Preliminary

Signal

Need to know energy spectrum of background

Sideband

  • Background prediction is affected by the flux and physics model

  • Cross-section of various neutrino reactions are uncertain

    • That’s what MINERvA is trying to measure

  • Data-driven background prediction tuning is used to handle the uncertainty of predicted background

Jaewon Park, U. of Rochester FNAL JETP


4 background processes 4 sidebands

4 Background Processes, 4 Sidebands

Eθ2(GeV∙rad 2)

  • No side-exiting muon

  • Narrow shower at beginning

  • Eθ2<0.1

Sideband 4

(Coherent π0

rich region)

(a) Sideband

Energy

0.005

Sideband 1, 2, 3

(not sideband 4)

0.0032

(b) Unused

Sideband 3

signal

Sideband 1

1.2

4.5

20

Sideband 2

0.8

dE/dx

(MeV/1.7cm)

3

Min dE/dx

  • Sideband = Outside of major Eθ2 and dE/dx cuts

  • (b) region is not used because there are not many events for tuning

  • Further, cut is slightly loosened on sideband so it gets some νμ CC for tuning purpose

Jaewon Park, U. of Rochester FNAL JETP


Sideband populations

Sideband Populations

Most Events

(nmCharged or Neutral Current )

Rare but hard to reject:

ne Charged Current

Coherent p0

Jaewon Park, U. of Rochester FNAL JETP


Sideband tuning

Sideband Tuning

Scale three MC components to match to data

Minimize χ2 across 7 histograms 3 parameters tuned in this step

Minimize χ2 across 2 histograms 1 parameter tuned in this step

Before tuning

MINERvA Preliminary

After tuning

Track Length in HCAL (modules)

MINERvA Preliminary

Events with tracks in downstream Hadron Calorimeter are mostly νμ CC

Track Length in HCAL (modules)

νe

νμ NC

νμ CC

COH π0

20 December 2013

Jaewon Park, U. of Rochester FNAL JETP


De dx and eq 2 in sidebands after tuning

dE/dx and Eq2 in Sidebands after tuning

Eθ2

(GeV∙rad 2)

# Events (Eθ2 < 0.2)

Sideband

(b)

0.005

0.0032

Signal

(c) Unused

(a)

MINERvA Preliminary

4.5

dE/dx (MeV/1.7cm)

Eθ2 (GeV∙radians 2)

  • Both dE/dx and Eθ2 are well simulated in the sideband region after fitting

MINERvA Preliminary

dE/dx (MeV/1.7cm)

Jaewon Park, U. of Rochester FNAL JETP


Outline5

Outline

  • Neutrino experiments and their fluxes

  • ν-e scattering: signal and backgrounds

  • Event reconstruction

  • Backgrounds and how to remove them

  • Background Prediction

  • Systematic uncertainty

  • Result and Conclusions

Jaewon Park, U. of Rochester FNAL JETP


Systematic uncertainties

Systematic Uncertainties

N: events in data

B: Background

e: Efficiency

A: Acceptance

s: signal cross section

  • Error in background contribution

    • Flux uncertainties

    • Cross Section Uncertainties

  • Error in efficiency and Acceptance

Jaewon Park, U. of Rochester FNAL JETP


Uncertainty in n e ccqe extrapolation from sideband

Uncertainty in neCCQE extrapolation from sideband

Previous MINERvA results on nm Quasi-elastic process shows that momentum transfer squared (Q2QE) distribution is not what GENIE predicts Phys. Rev. Lett. 111, 022502 (2013), Phys. Rev. Lett. 111, 022501 (2013).

Q2QE and Eθ2 are highly correlated

Compare nebackground prediction Eq2 extrapolation with two different models: one is GENIE, the other is one inspired by MINERvA nm data: systematic uncertainty: 3.3%

Jaewon Park, U. of Rochester FNAL JETP


Flux and cross section systematic uncertainties on mc background

Flux and Cross Section Systematic Uncertainties on MC Background

Sideband tuning reduced systematic uncertainty on predicted background

Predicted background (before tuning): 38.9 ± 6.2 (stat) ± 10.3 (sys)

Predicted background (after tuning): 32.9 ± 5.3 (stat) ± 5.7 (sys)

The tuning didn’t eliminate systematic uncertainty but it gives confidence on background prediction

20 December 2013

Jaewon Park, U. of Rochester FNAL JETP


Reconstruction systematic uncertainties

Reconstruction Systematic Uncertainties

  • Angular Alignment: look at data-simulation differences in m angles for nm CC events with low hadron energy

    • 3 (1) mrad correction in y (x)

    • uncertainty is ±1mrad

MINERvA Preliminary

MINERvA Preliminary

nmCharged Current Events with hadron energy<100MeV

Electromagnetic Energy Scale: look at electrons from stopped m decays (Michel): see agreement at 4.2% level, add as systematic uncertainty

Jaewon Park, U. of Rochester FNAL JETP


Reconstruction uncertainties

Reconstruction Uncertainties

Jaewon Park, U. of Rochester FNAL JETP


Outline6

Outline

  • Neutrino experiments and their fluxes

  • ν-e scattering: signal and backgrounds

  • Event reconstruction

  • Backgrounds and how to remove them

  • Background Prediction

  • Systematic uncertainty

  • Result and Conclusions

Jaewon Park, U. of Rochester FNAL JETP


Result

Result

  • Found: 121 events before background subtraction

  • n-e scattering events after background subtraction and efficiency correction:

    123.8 ± 17.0 (stat) ± 9.1 (sys)total uncertainty: 15%

  • Prediction from Simulation: 147.5 ± 22.9 (flux)

    • Flux uncertainty: 15.5%

Observed ν-e scattering events give a constraint on flux with similar uncertainty as current flux uncertainty, consistent with prediction

Jaewon Park, U. of Rochester FNAL JETP


Future flux measurement at numi

Future Flux Measurement at NuMI

Assuming similar signal/background ratio as in Low Energy Run:

Can expect statistical uncertainty = ~2%

Total systematic uncertainty on this measurement: 7%

Total uncertainty = ~7.3%

MINERvA Preliminary

~20 times thelow energy signal sample

MINERvA Preliminary

Medium Energy Flux:

Now being produced in the NuMI Beamline, as of September 2013


Conclusions

Conclusions

  • n-e scattering provides an independent flux measurement for ν-nucleon cross-section normalization

  • Uncertainty on ν-e based flux measurement in Low Energy beam is 15%

    • It is similar size as current flux prediction uncertainty

    • Will be used as constraint in future MINERvA cross section measurements

  • In Medium Energy run, estimate a 7% uncertainty on total flux

    • Currently dominant uncertainty is statistical uncertainty

  • This technique could be used in future higher intensity experiments like NOvA and LBNE to provide a precise flux measurement

Jaewon Park, U. of Rochester FNAL JETP


Backup

(Backup)


Neutrino beam spread

Neutrino Beam Spread

Diameter of decay pipe: ~ 2m

0.5 m transverse position at 500 m distance  1 mrad angle

MINERvA Preliminary

MINERvA Preliminary


Data energy stability michel electron

Data Energy Stability (Michel Electron)

Some odd behavior is found between minerva1 and rest of playlists

1 or 2% energy variation

Use 4.2% as the systematic uncertainty on energy scale

MINERvA Preliminary

MINERvA Preliminary


Sideband 4 after tuning

Sideband 4 (After Tuning)

MINERvA Preliminary

MINERvA Preliminary

MINERvA Preliminary

MINERvA Preliminary


Background subtraction

Background Subtraction

MINERvA Preliminary

MINERvA Preliminary


Comparing observed and predicted spectra

Comparing Observed and Predicted Spectra

MINERvA Preliminary

MINERvA Preliminary


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