Charged Current Cross SectionMeasurements at T2K
David Hadley on behalf of the T2K collaborationNuFact 2013
The T2K Experiment
Goals
I discover νe appearance in aνµ beam
I make precise measurements ofνµ disappearance
I study neutrino-nucleusinteractions at Eν ∼ 1GeV
I A high intensity proton beam at J-PARC produces anarrow-band νµ beam with a peak energy of0.6GeVat the far detector,
I The Far detector is Super-Kamiokande, a 50ktonwater Cherenkov detector, located 2.5◦ off-axis and295km from the production point.
I Detectors in the ND280 complex at 280m are used todirectly measure the neutrino beam properties andneutrino-nucleus interaction cross sections.
The T2K Beam
I T2K has collected 6.6 × 1020 POT to date (Run 1-4).
I The analyses presented here are based on 2.7 × 1020 POT (Run 1-3@ ND280).
I Improved analyses under development will include Run 4.
The T2K Beam
I Narrow-band beam at off axis angle.
I Mostly νµ from pion decay.
I Beam has a peak energy ∼ 0.6GeV.
I Close to the quasi-elastic peak.I On-axis near detector INGRID monitors the neutrino beam.
I INGRID will also make measurements of neutrino cross sections.
(GeV)νE0 1 2 3 4 5 6 7 8 9 10
PO
T)
21
/50
MeV
/10
2F
lux
(/c
m
710
810
910
1010
1110
1210 at ND280µν
at ND280µ
ν
at ND280eν
at ND280eν
Off-axis Near Detector (ND280)
DownstreamECal
FGDsTPCs
PØD
UA1 Magnet YokeSMRD
PØD ECal
Barrel ECal
Solenoid Coil
Neutrino beam
x
y
z
TPC2 TPC3
Scintillator
µ-
p
TPC1
FGD1
TPC2 TPC3
Scintillator
TPC1
FGD1
Run #: 4200 Evt #: 24083 Time: Sun 2010-03-21 22:33:25 JST
µ-
FGD2
Scintillator
ND280 Tracking Detector
I The Fine Grained Detector(FGD1) consists of layers of10 × 10mm plastic scintillator barsreadout with Multi-Pixel PhotonCounters (MPPCs).
I FGDs provide target mass andvertex reconstruction.
I The Time Projection Chambers(TPCs) provided PID based ondE/dx in the Argon based gasand momentum measurementfrom track curvature in themagnetic field.
π0Detector
I see NCE talk by D. Ruterbories.T2K, Nucl. Instrum. Meth. A 659, 106 (2011)FGD, Nucl. Instrum. Meth. A 696, 1 (2012)TPC Nucl. Instrum. Meth. A 637, 25 (2011)
ND280 Event Selection
2 samples selected: a QE enhanced,and an non-QE sample.CC Inclusive Selection (µ+ X )
I 1 good-quality negative trackstarting within the FGD fiducialvolume.
ND280 Event Selection
dz
Muon candidate
2 samples selected: a QE enhanced,and an non-QE sample.CC Inclusive Selection (µ+ X )
I 1 good-quality negative trackstarting within the FGD fiducialvolume.
I Upstream veto
ND280 Event Selection
2 samples selected: a QE enhanced,and an non-QE sample.CC Inclusive Selection (µ+ X )
I 1 good-quality negative trackstarting within the FGD fiducialvolume.
I Upstream veto
I Muon PID
ND280 Event Selection
2 samples selected: a QE enhanced,and an non-QE sample.CC Inclusive Selection (µ+ X )
I 1 good-quality negative trackstarting within the FGD fiducialvolume.
I Upstream veto
I Muon PID
µ
e
π
ND280 Event Selection
2 samples selected: a QE enhanced,and an non-QE sample.CC Inclusive Selection (µ+ X )
I 1 good-quality negative trackstarting within the FGD fiducialvolume.
I Upstream veto
I Muon PID
CC QE Selection (µ+ 0π)
I TPC track veto
ND280 Event Selection
2 samples selected: a QE enhanced,and an non-QE sample.CC Inclusive Selection (µ+ X )
I 1 good-quality negative trackstarting within the FGD fiducialvolume.
I Upstream veto
I Muon PID
CC QE Selection (µ+ 0π)
I TPC track veto
I Michel electron veto
ND280 Event Selection
2 samples selected: a QE enhanced,and an non-QE sample.CC Inclusive Selection (µ+ X )
I 1 good-quality negative trackstarting within the FGD fiducialvolume.
I Upstream veto
I Muon PID
CC QE Selection (µ+ 0π)
I TPC track veto
I Michel electron veto
Non-QE selection
I any event that fails either ofthe final 2 cuts
Flux Integrated CC Inclusive Cross Section Measurement
(MeV/c)µ
p0 500 1000 1500 2000
nucl
eon M
eV/c
2cm
θ
dp d
cos
σ 2
d
0
5
10
15
4210×
Data
Systematic Error
Statistical Error
NEUT
GENIE
< 0.84 µθ 0.00 < cos
(MeV/c)µ
p0 500 1000 1500 2000
nucl
eon M
eV/c
2cm
θ
dp d
cos
σ 2
d
0
5
10
15
4210×
Data
Systematic Error
Statistical Error
NEUT
GENIE
< 0.90 µθ 0.84 < cos
(MeV/c)µ
p0 500 1000 1500 2000
nucl
eon M
eV/c
2cm
θ
dp d
cos
σ 2
d
0
5
10
15
4210×
Data
Systematic Error
Statistical Error
NEUT
GENIE
< 0.94 µθ 0.90 < cos
(MeV/c)µ
p0 500 1000 1500 2000
nucl
eon M
eV/c
2cm
θ
dp d
cos
σ 2
d
0
5
10
15
4210×
Data
Systematic Error
Statistical Error
NEUT
GENIE
< 1.00 µθ 0.94 < cos
I Combine the QE and non-QE samples.
I Unfold the reconstructed pµ − cos(θµ) distributions to estimate the truemuon kinematics.
I Measure double differential pµ − cos(θµ) distribution and total fluxintegrated cross section.
Phys. Rev. D 87, 092003 (2013)
Reconstructed Kinematics
)µθcos(0 0.2 0.4 0.6 0.8 1
even
ts /
0.1
0
500
1000
1500
2000
2500
3000
Nominal NEUT
background
data
[GeV]QE
ν
reconstructed E0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
even
ts /
0.2
GeV
0
200
400
600
800
1000
1200
1400
1600 Nominal NEUT
background
data
[MeV]µ
p0 500 1000 1500 2000
even
ts /
100 M
eV
0
200
400
600
800
1000 Nominal NEUT
background
data
]2 [GeVQE
2reconstructed Q0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
2ev
ents
/ 0
.2 G
eV0
1000
2000
3000
4000
5000Nominal NEUT
background
data
I CCQE efficiency=40%, purity=72%.
I Dominant background from CC resonant pion production.
I Eν and Q2 calculated from muon momentum assuming QE kinematics.
NEUT CCQE Model
I Smith-Moniz implementation CCQEI Dipole form factor (MQE
A = 1.2GeV)I Initial Nucleon state given by relativistic Fermi gas model
I FSI with semi-classical cascade model
I No additional contribution from multi-nucleon effects
Measurement of the CCQE Cross Section
=0.0
0θ
p=
0M
eV,
=0.8
4θ
p=
0M
eV,
=0.9
0θ
p=
0M
eV,
=0.9
4θ
p=
0M
eV,
=0.0
0θ
p=
40
0M
eV,
=0.8
4θ
p=
40
0M
eV,
=0.9
0θ
p=
40
0M
eV,
=0.9
4θ
p=
40
0M
eV,
=0.0
0θ
p=
50
0M
eV,
=0.8
4θ
p=
50
0M
eV,
=0.9
0θ
p=
50
0M
eV,
=0.9
4θ
p=
50
0M
eV,
=0.0
0θ
p=
70
0M
eV,
=0.8
4θ
p=
70
0M
eV,
=0.9
0θ
p=
70
0M
eV,
=0.9
4θ
p=
70
0M
eV,
=0.0
0θ
p=
90
0M
eV,
=0.8
4θ
p=
90
0M
eV,
=0.9
0θ
p=
90
0M
eV,
=0.9
4θ
p=
90
0M
eV,
even
ts
0
200
400
600
800
1000
1200
1400
1600 Nominal NEUT
Background
Data
The Log Likelihood Ratio is minimised,
−2lnλ(θ) = 2
pµ−cos(θµ)bins∑i=1
[Npredictedi (θ) − Nobserved
i
+Nobservedi ln
Nobservedi
Npredictedi (θ)
+ln
πd (d)πd (dnominal)
+lnπf (f)
πf (fnominal)
+lnπx (x)
πx (xnominal)
(1)which includes,
I standard Poisson statistical terms
I penalty terms for the systematics
Analysis Method
I Simulated template histograms were fit to the observed pµ − cos(θµ)distribution.
I The CCQE cross section was extracted by weighting 5 template histogramsin bins of Eν .
I Systematic uncertainties were accounted for by varying bin contents withnuisance parameters.
I A maximum likelihood fit was used to find the best fit parameters.
Systematic Uncertainties and Implementation
Flux
I Flux prediction based onmeasurements at NA61/SHINEand T2K proton beammeasurements.
I ∼ 10 − 15% uncertainty on νµflux.
Implementation
I MC prediction binned in pµ,cos(θµ), Eν and interactiontype.
I Reweight bin contents based onvalue of nuisance parameters.
I Multi-variate Gaussian priors onnuisance parameters.
Interaction Model Uncertainties
I Vary model parameters egMRES
A , pF etc
I Empirical parameters eg pionbackground normalisationuncertainties.
I Uncertainties from comparisonof NEUT generator with externaldata
Detector Uncertainties
I Estimate uncertainty on rate ofselection in pµ − cos(θµ) bins.
I Dominant uncertainties are fromuncertainties on the TPCmomentum measurement andout of FV backgrounds.
I ∼ 5 − 10% overall detectoruncertainty.
Measurement of the CCQE Cross Section
[GeV]ν
E
0 0.5 1 1.5 2 2.5
]2
cm3
8(E
) [1
0σ
0.5
1
1.5
2
2.5 ND280 stat
ND280 stat+syst
NEUT MC
NEUT (binned)
A χ2 test comparing the fitted result with the nominal NEUT model,with MQE
A = 1.2GeV, gives a p-value of 17% indicating agreementbetween the data and the cross section model.
T2K Preliminary
Measurement of the CCQE Cross Section
[GeV]ν
E
0 0.5 1 1.5 2 2.5
]2
cm3
8(E
) [1
0σ
0.5
1
1.5
2
2.5 ND280 stat+syst
NEUT MC
MiniBoone
NEUT (binned)
A χ2 test comparing the fitted result with the nominal NEUT model,with MQE
A = 1.2GeV, gives a p-value of 17% indicating agreementbetween the data and the cross section model.
T2K Preliminary
Measurement of the CCQE Cross Section
[GeV]ν
E
110 1 10 210
]2
cm3
8(E
) [1
0σ
0.5
1
1.5
2
2.5ND280 stat+syst
NEUT MC
MiniBoone
NOMAD
NEUT (binned)
A χ2 test comparing the fitted result with the nominal NEUT model,with MQE
A = 1.2GeV, gives a p-value of 17% indicating agreementbetween the data and the cross section model.
T2K Preliminary
MQEA -effective extraction
Fit pµ-cos(θµ)distribution with MQE
Aas a free parameter.Fit with 2 settings,
I MQEA shape-only
I MQEA normalisa-
tion+shapenorm RFG
QE effective
AM shape RFGQE effective
AM
Fit
val
ue
[GeV
]
0.6
0.8
1
1.2
1.4
1.6
1.8
2
stats only
stats+syst
GeV0.18
+0.211.26 GeV
0.22
+0.281.43
I Previous experiments have observed a discrepancy in the fittedvalues of MQE
A between Deuterium and heavier nuclei.
I A large effective MQEA is believed to account for nuclear effects not
included in the model.
I Both fit results are consistent with the value used in NEUT,MQE
A = 1.2GeV.
T2K Preliminary
New CC Analysis
Additional TPC+FGD Tracks
I Highest momentum negative track is selected as the muon candidate.
I Tag pion/electrons/protons by applying PID to additional tracks.
FGD only tracks
I Use FGD only tracks to tag stopping particles.
I Tag pion from Michel tag or dE/dx in FGD.
New CC Analysis
I Cleaner sample of CC1π to better constrain the π background inCCQE cross section analysis.
T2K PreliminaryT2K Preliminary
T2K Preliminary
New CC Analysis
I Some example results from the fit to these samples for the oscillationanalysis.
I Significant improvement on the uncertainty on these modelparameters.
I Primarily from analysis improvements, not from increased statistics.
I We should expect similar improvements when these samples are usedfor cross section measurements.
I See Oscillation Systematics talk by A. Kaboth
Summary
I T2K’s first CC inclusive cross section publication was publishedearlier this year (Phys. Rev. D 87, 092003 (2013)).
I First Preliminary T2K CCQE Cross Section measurement presentedin this talk.
I Extraction of CCQE energy dependent cross section and modelparameters from fit to ND280 pµ − cos(θµ).
I Expect better performance in future cross section analysesI at least double statistics (current analysis only uses data up to
summer 2012)I new improved reconstructionI selection and analysis
Backup
ND280 CC Selection Efficiency and Purity
The T2K Beam
ND280 TPC PID
Flux Integrated CC Inclusive Cross Section Measurement
(GeV)νE0 0.5 1 1.5 2 2.5 3 3.5
/nucl
eon)
2 (
cmσ
0
0.5
1
1.5
2
2.5
3
3.5
PO
T)
21
/50M
eV/1
02
Flu
x (
/cm
0
0.5
1
1.5
2
2.5
3
3.5
SciBooNE data based on NEUT
BNL 7ft
NEUT prediction for SciBooNE
NEUT prediction for T2K
GENIE prediction for T2K
φ⟩ σ ⟨T2K
12 10×38
10×
data
NEUT prediction
GENIE prediction
flux µν
I Combine the QE and non-QE samples.
I Unfold the reconstructed pµ − cos(θµ) distributions to estimate the truemuon kinematics.
I Measure double differential pµ − cos(θµ) distribution and total fluxintegrated cross section.