direct measurement of the numi flux with neutrino-electron scattering in minerva jaewon park...
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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
2
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
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
3
Oscillation Experiment Strategy
• 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
1111 AN 2222 PANbeam-
Near Detector (ND)Far Detector (FD)
2
1
2
1
2
1
1
2
222
2
A
A
N
N
A
NP
or ?
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
Isn’t this just 1/L2?
N: events in dataB: Background: EfficiencyA: Acceptance: Cross section
4
Needs of Precision Oscillation Experiments
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
• 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
5
Neutrinos from an Accelerator
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
NearDetector
FarDetector
proton
K,Horn 1
Horn 2Target
Decay pipe Rock
• 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
6
Neutrinos from an Accelerator
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
NearDetector
FarDetector
proton
K,Horn 1
Horn 2Target
Decay pipe Rock
• Kaon and muon decays are main source of electron neutrinos
K
e
e0
e
e
7
Constraining flux with Hadron Production Data
p πn
target
ν
decay pipe
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
• 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
Particle production xF Reference
NA49 pC
@158 GeV
π± <0.5 Eur.Phys.J. C49 (2007) 897
K± <0.2 G. Tinti Ph.D. thesis
p <0.9 Eur.Phys.J. C73 (2013) 2364
MIPP pC @
120 GeV K/π ratio A. Lebedev Ph.D. thesis
8
NA49: pC → π,K,p @ 158 GeV
NA49 datavs. GEANT4
Uncertainties7.5% systematic2-10% statistical
π+ which makea νμ in MINERvA
focusingpeak
f(xF,p
T) = E d3σ/dp3 = invariant production cross-section
high energytail
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
9
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, , KL,S)
• Beamline geometry and focusing elements contribute uncertainties
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
10
Special Runs to Understand Flux• 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 xF pT space, but same horn geometry and current
• MINERvA does this by using low hadron energy charged current events, where energy dependence of cross section is very well understood
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
Normal Running
Target Moved
upstream
Pion Phase Space
Neu
trin
os a
t M
INE
RvA
xF
xF
Pt (
GeV
/c)
Pt (
GeV
/c)
Inclusive Event
Spectra
11
Flux constraint using Near Detector
Cross-section uncertainty goes intoflux uncertainty
MINERvA
Flux uncertainty goes intocross-section uncertainty
Neutrino Flux and Cross-section Measurement
A
N
AN
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
• Flux and cross-section are anti-correlated with given Near Detector constraint
σ (Cross Section)
Φ (
Flu
x)
1111 AN
N: Events: Efficiency
A: Acceptance: signal cross section
Measurement uncertainty
12
Known Interaction (Standard Candle)
• ν-e scattering is well known interaction we can use to constrain the neutrino flux
AN
Flux constraint using ND
Cross-section uncertainty goes intoflux uncertainty
ν-e Scattering20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
e e
0Z 1111 AN
σ (Cross Section)
Φ (
Flu
x)
13
Outline
• Neutrino experiments and their fluxes• ν-e scattering: signal• Event reconstruction• Event selection• Background Prediction• Systematic uncertainty• Result and Conclusions
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
14
ν-e Scattering History
e
First unambiguousneutral current(Gargamelle)
Solar ν oscillation measurementusing ν-e scattering (SNO)
e
e
e
e
x
epn ,, epn ,,
x
,,ex
ZW
Coherent forward scatterings
Additional interaction for e
All flavor
Matter effect is due tocharged current νe scattering
on electrons, only for νe
Electroweaktheory
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
15
Neutrino Scattering on Nucleon
• 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
ee ee
e e
0Z
e
Very forward single electron final state
νe→ νe candidate event
ElectronElectron
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
16
ν-e Scattering
• 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
Ee )( dyd
energy) (neutrino
KE)(electron y
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
FLUX e Scattering Events
e Scattering Events
24
22
2
)1(sinsin2
1
2
)(y
EmG
dy
eedWW
veF
GF and θW: well-known electroweak parameters
17
Signal Events
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
• 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
eeee ee and ,,,
%9: and
%91: and
ee
ee
ee
E>0.8 GeV
E<0.8 GeV is not used•Large background•Tough reconstruction
For remainder of talk, means and
18
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
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
19
Data and Simulation Samples
• 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
MINERvA ran in three kinds of beam:
Low Energy neutrino
Low energy anti-neutrino
“Special Runs”: higher energy runs to constrain flux model
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
Thank you!for the excellent ν beam
20
MINERvA Detector
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
Inner Detector
5m
3.5m
4m
Outer Detector(steel + scintillator)
Nuclear Targets(C, Pb, Fe, H2O)
Tracker(Active target)
Electromagnetic Calorimetry
Hadronic Calorimetry
21
MINOSNear Detector
(muon spectrometer)
Inside the Detector
−60°
+60°
xvxu
Nuclear Target
Tracker
EcalHcal
Number of channels: ~31kNumber of scintillator plane: 128
Scintillator plane
(X, U, V stereo angle)
Tracking Ecal (lead absorber + tracking plane)Tracking Hcal (steel absorber + tracking plane)
22
Detector Technology
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
• Extruded plastic scintillator with wavelength shifting fiber readout• 64 channel multi-anode PMT for photo-sensor
Wavelength shifting fiber
8×8 pixels
64 channel multi-anode PMT
Scintillator strip
17 mm
16 mm
Position resolution: ~3mm
2.1m127 strips into a plane
2.5 m
23
ν + e- → ν + e- candidate event
X-View U-View V-View
Data run: 2157/12/1270/2
ee
0Z
e
Fiducial volume
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
24
Single Electron ReconstructionNuclear Target Region
(He,C/H2O/Pb/Fe)HCALECAL
Track-like
Shower-like
Track-like part (beginning of electron shower) gives good direction
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
25
Single Electron ReconstructionNuclear Target Region
(He,C/H2O/Pb/Fe)HCALECAL
Track-like part (beginning of electron shower) gives good direction
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
Shower cone
26
Critical Variables for Signal
• Electron Identification– Must discriminate from photons
• Electron Energy Measurement
• Electron Angular Measurement
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
27Electron Photon Discrimination using dE/dx
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
• 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
γe
ee
e
e e
γ
γγ
e
γe
γe
e
e
e
e
e
Electron-induced electromagnetic shower
Photon -induced electromagnetic shower
MINERvA Preliminary
28
Energy and Angle Reconstruction
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
• Energy resolution ~ 5%• Projected angle resolution ~ 0.3 degree (2 sigma truncated RMS)• Precise angle reconstruction is critical to separate ν e elastic scattering
from background– Lower energy angular resolution is worse due to multiple scattering
Using simulated signal
Using simulated signal
3.6% %2.5)(
EE
E
MINERvA PreliminaryMINERvA Preliminary
29
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
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
30
Initial Background Rejection• -e scattering is very rare, even for 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
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
e e
n p
W
N N
Z
0
e Quasi-elastic (CCQE) Coherent 0
,
N X
ZW ,
Most Events
( Charged or neutral Current)
Rare but hard to reject:
31
Background Events
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
Use Eθ2 to selectvery forward signal
pene
nepe
e e
p n
WElectron neutrino fraction in flux is small ~ 1%.
electron
proton
z
x
0
2
4
6
8
MeVMCMC
•If recoil nucleon is not observed, it looks similar to signal•Angles of electron have wide spread while signal is very forward
0
0
NN
AA
NC-coherent π0
NC-resonant π0
Neutral current single π0
1. Small opening angle between two gammas
π0 (1.1 GeV)
γ (67 MeV )π0 (7.5 GeV)
0
0
2. One of gammas is not observed in the detector
Simulated event Simulated event
Also, photon has wide spread of angleIn addition, use dE/dx to reject
32Example: Neighborhood Energy
• Neighborhood energy = energy around shower cone• Small neighborhood energy means isolated shower
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
Signal × 200 Not Full Sample
MINERvA Preliminary
MINERvA Preliminary
5 cm
Neighborhood
Shower cone
33
Event Selection
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
Shower coneReconstruction
• Electron Energy>0.8GeV• Fiducial cut
Otherreconstruction quality cuts
Signalsample
• Eθ2
• dE/dx
Kinematic constraint on e scattering, using Mandelstam variables:
ee *cos12
s
t *cos12
1 y syt
)cos1(2 eEEu
2)1(2
)cos1(2)1(
ee
e
Eym
EEys
uts
ee mEy 2 ,10 Since 2
in CM frame
in lab frame
34
dE/dx Cut
• 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
tunedtuned
dE/dx<4.5MeV/1.7cm
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
MINERvA Preliminary
MINERvA Preliminary
35 Eθ2 Cut
• All cuts but E2 cut• Kinematic limit for signal
– Eθ2 < 2me
• Clean separation of signal
22 radGeV 0032.0 E
tuned tuned
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
MINERvA PreliminaryMINERvA Preliminary
36
Electron Spectrum after all cuts
tuned
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
True electron energy(signal only)
Reconstructed electron energy
MINERvA Preliminary
MINERvA Preliminary
37
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
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
38
Backgrounds after all Cuts
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
• 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
0032.02 E SidebandSignal
22 radGeV 005.0 E
Need to know energy spectrum of background
MINERvA Preliminary
MINERvA Preliminary
39 4 Background Processes, 4 Sidebands
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
• 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
dE/dx(MeV/1.7cm)
0.00320.005
4.5
(a) Sideband
signal
20
(b) Unused
Eθ2 (GeV∙rad 2)
3 Min dE/dx
Energy
1.2
0.8
Sideband 1Sideband 3
Sideband 2
Sideband 4
Sideband 1, 2, 3(not sideband 4)
(Coherent π0 rich region)
• No side-exiting muon• Narrow shower at beginning• Eθ2<0.1
40
Sideband Populations
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
e e
n p
W
N N
Z
0
Coherent 0
,
N X
ZW ,
Most Events
( Charged or Neutral Current )
Rare but hard to reject:
e Charged Current
41
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
After tuning
Before tuning
Events with tracks in downstream Hadron Calorimeter are mostly νμ CC
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
Track Length in HCAL (modules)
Track Length in HCAL (modules)
Parameter Tuned value
0.83 ± 0.04
0.81 ± 0.03
0.94 ± 0.01
0.90 ± 0.08
νe
νμ NC
νμ CC
COH π0
MINERvA Preliminary
MINERvA Preliminary
42
dE/dx and in Sidebands after tuning
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
4.5dE/dx (MeV/1.7cm)
0.00320.005
Sideband
Signal
Eθ2
(GeV∙rad 2)
(a)
(b)
(c) Unused
• Both dE/dx and Eθ2 are well simulated in the sideband region after fitting
dE/dx (MeV/1.7cm)
Eθ2 (GeV∙radians 2)
# Events (Eθ2 < 0.2)
MINERvA Preliminary
MINERvA Preliminary
43
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
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
44
Systematic Uncertainties
• Error in background contribution– Flux uncertainties– Cross Section Uncertainties
• Error in efficiency and Acceptance
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
ABN
N: events in dataB: Background: Efficiency
A: Acceptance: signal cross section
45 Uncertainty in eCCQE extrapolation from sideband
• Previous MINERvA results on Quasi-elastic process shows that momentum transfer squared (Q2
QE) 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 ebackground prediction E2 extrapolation with two different models: one is GENIE, the other is one inspired by MINERvA data: systematic uncertainty: 3.3%
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
46 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
Uncertainty SourcesMC background uncertainty [events]
Before tuning After tuning
MC background events 38.9 32.9
MC bkg statistical 6.2 5.3
Total systematic 10.3 5.7
Flux_BeamFocus 1.1 0.2
Flux_NA49 1.8 0.3
Flux_Tertiary 7.0 1.1
GENIE 6.3 4.5
CCQE Shape 3.7 3.3
Total 12.1 7.8
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
47
Reconstruction Systematic Uncertainties
• Electromagnetic Energy Scale: look at electrons from stoppeddecays (Michel): see agreement at 4.2% level, add as systematic uncertainty
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
• Angular Alignment: look at data-simulation differences in angles for CC events with low hadron energy
– 3 (1) mrad correction in y (x)
– uncertainty is ±1mrad
MINERvA Preliminary
MINERvA Preliminary
Charged Current Events
with hadron energy<100MeV
48
Reconstruction Uncertainties
SourceUncertainty on Source
Systematic Uncertainty
Beam angle uncertainty x and y : ± 1 mrad 1.1% and 1.3%
Energy scale 4.2% 1.9%
EM calorimeter energy smearing
Additional energy smearing 0.0%
Absolute Electron Reconstruction Efficiency
2% based on muon studies 2.8%
All Reconstruction Uncertainties 5.4%
Simulation statistics (Bckgd) 6.0%
Flux (Bkgd) Beam focusing, Beam tuning 1.3%
Cross Section (Bkgd) GENIE, CCQE Shape 6.3%
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
49
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
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
50
Result• Found: 121 events before
background subtraction
• -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%
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
Observed ν-e scattering events give a constraint on flux with similar uncertainty as current flux
uncertainty, consistent with prediction
51 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%
Medium Energy Flux: Now being produced in the NuMI Beamline, as of September 2013
~20 times thelow energy signal sample
MINERvA Preliminary
MINERvA Preliminary
52
Conclusions• -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
20 December 2013 Jaewon Park, U. of Rochester FNAL JETP
53
(Backup)
54
Neutrino Beam Spread
• Diameter of decay pipe: ~ 2m• 0.5 m transverse position at 500 m distance 1 mrad angle
MINERvA Preliminary MINERvA Preliminary
55
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
56 Sideband 4 (After Tuning)
MINERvA Preliminary
MINERvA Preliminary
MINERvA Preliminary
MINERvA Preliminary
57
Background Subtraction
MINERvA Preliminary
MINERvA Preliminary
58
Comparing Observed and Predicted Spectra
MINERvA Preliminary
MINERvA Preliminary