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Impact of neutrino interaction uncertainties in T2K
Kei Ieki for the T2K collaboration 'Toward unified description of lepton-nucleus reactions from MeV to GeV region' 2014/2/9
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Contents of this talk Results from T2K π-N interaction: How is it related to π π βπ π measurement? How big is the effect of the uncertainty in π-N interaction?
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1. Results from T2K
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The T2K experiment p Discovery of Ξ½ΞΌ ο Ξ½e ΞΈ13, Ξ΄CP Main goals
We observed Ξ½ΞΌ ο Ξ½e with 7.3Ο significance in 2013! Precise measurement of Ξ½ΞΌ ο Ξ½ΞΌ ΞΈ23, Ξm232 Main goals J-PARC ΞΌ 295km Ο+ p Ξ½ΞΌ Ξ½e,ΞΌ,Ο ~40m Near Detector (ND280) Far Detector (Super-Kamiokande) High intensity Ξ½ΞΌ beam & Giant water Cherenkov detector SK
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Analyzed data Latest Ξ½ΞΌβΞ½e result Latest Ξ½ΞΌβΞ½ΞΌ result
(will be updated soon) Latest Ξ½ΞΌβΞ½e result 1.2Γ1014 protons per pulse (world record)
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Latest result (Ξ½ΞΌο Ξ½ΞΌ, 3.01Γ1020 POT)
Observed 58 Ξ½ΞΌ candidate events. Expected Ξ½ΞΌ events (no osc.): 205Β±17 events Ξ½ΞΌ energy spectrum |Ξ π 32 2 | vs. sin22ΞΈ23 contour Best fit: |Ξ π 32 2 | = 2.4 β Γ 10 β3 eV2/c4 sin2ΞΈ23 = 0.514Β±0.082
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Latest result (Ξ½ΞΌο Ξ½e, 6.57Γ1020 POT)
Observed 28 Ξ½e candidate events. Expected backgrounds: 4.9Β±0.6 events Electron momentum and angular distribution Best fit for normal (inv.) hierarchy: sin22ΞΈ13 = β ( β ) (sin2ΞΈ23 and Ξ π constrained by T2K Ξ½ΞΌο Ξ½ΞΌ, Ξ΄CP=0) Significance: 7.3Ο βDiscoveryβ of Ξ½ΞΌο Ξ½e
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Latest result (Ξ½ΞΌο Ξ½e, 6.57Γ1020 POT)
Combined with reactor measurement (sin22ΞΈ13=0.098Β±0.013 from PDG2012) Ξ΄CP negative log likelihood curve 90% CL excluded region Normal hierarchy: γγγ0.604ο½2.509 Inverted hierarchy: γ ο½-3.043, ο½3.142 Precision Ξ½ΞΌο Ξ½e measurement is required for the observation of CP violation. 90% excluded regions
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2. π-N interaction: How is it related to π π βπ π measurement?
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Ξ½ΞΌο Ξ½e measurement Ξ½e event selection: 1-ring e-like event Signal π π
β π π CCQE ( π π + n β e- + p) π β Signal π π π π π π π π Main interaction mode in T2K EΞ½~0.6 GeV) EΞ½ can be reconstructed from pe and ΞΈe e- β π π CC1Ο ( π π + N β e- + N + Ο) π β π π π π π π π Backgrounds β Ξ½ΞΌ NC Ο0 events β Contamination of π π π π π β π π π π π πΎ π π π π π π πΎ Ο 0
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Fraction of events after Ξ½e event selection
Ξ½ΞΌο Ξ½e measurement Ξ½e event selection: 1-ring e-like ring β π π CCQE ( π π + n β e- + p) π β 68% π π π π π π Fraction of events after Ξ½e event selection (assuming sin 2 2 π 13 =0.1) Main interaction mode in T2K EΞ½~0.6 GeV) EΞ½ can be reconstructed from pe and ΞΈe β π π CC1Ο ( π π + N β e- + N + Ο) π β π π π π π 12% π π 4% 14% β Ξ½ΞΌ NC Ο0 events β Contamination of π π π π π β π π π π π π π πΎ π π π π πΎ Ο 0
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Oscillation analysis (Ξ½ΞΌο Ξ½e)
In the analysis, we compare: Number of Ξ½e events NΞ½e Electron momentum and angular distribution (pe,ΞΈe) between data and MC prediction. e- ΞΈe Ξ½e ββsinΞ΄CP P(Ξ½ΞΌο Ξ½e) = sin22ΞΈ13sin2ΞΈ23sin2 Ξ m πΈ +(CPV term)+β¦ Leading term sin22ΞΈ13=0.1 ( π π CCQE dominated) π π (MeV/c) 400 800 1200 Expected NΞ½e π π , π π distribution Total sin22ΞΈ13=0.0, Ξ΄CP=0 sin22ΞΈ13=0.1, Ξ΄CP=0 sin22ΞΈ13=0.1, Ξ΄CP=+Ο/2 17.2 sin22ΞΈ13=0.1, Ξ΄CP=βΟ/2 25.7 4.9 π π (MeV/c) 400 800 1200 60 120 π π (degrees) 180 Β±0.6(syst) sin22ΞΈ13=0.0 (BG only) 21.6 Β±1.9(syst) (sin2ΞΈ23=0.5, normal hierarchy, 6.57Γ1020 POT) The uncertainty in Ξ½-N interaction affects the prediction of NΞ½e and (pe,ΞΈe).
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How we constrain the model
β π-N interaction, π flux simulation β‘ Constraints from external data β’ Constraints from ND280 β£ SK π π event selection MC Data Comparison of SK π π events β€ Oscillation analysis
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β Ξ½-N interaction simulation in T2K
NEUT event generator - CCQE: Llewellyn-Smith base model Smith-Moniz fermi gas model for nucleus - Single pion resonance production (CC/NC1Ο): Rein-Sehgal model - Deep Inelastic Scattering (DIS) and CC multi-Ο: γ γ GRV98 PDF, Bodek-Yang correction - Final state interactions (FSI): Cascade model
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β‘ Constraints from external data
We use effective parameters (MAQE, normalization parameters etc.) with uncertainties that span the base model and data, and allow the ND280 to constrain the model. Past measurements of MAQE CCQE MAQE (axial mass) 1.21Β±0.45 GeV/c2 CCQE norm 1Β±0.11
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β‘ Constraints from external data
CC1Ο+ Resonant Ο production We use MiniBooNE 1Ο data (CC and NC) and fit to NEUT predictions. MARES (axial mass) 1.41Β±0.22 GeV/c2 CC1Ο norm 1.15Β±0.32 NC1Ο0 norm 0.96Β±0.33 NC1Ο0
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β’ Constraints from ND280 Measure the CC interactions to constrain the fluxΓcross section Fine Grained Detectors (FGD) Ξ½ interaction target Tracking & PID Finely segmented scintillator bars (CH) Time Projection Chambers (TPC) Gas 3D tracker Momentum measurement & PID 0.2T magnet
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β’ Constraints from ND280 ΞΌ + hadrons ΞΌ ΞΌ + Ο+ CC other CC0Ο CC1Ο+
We measure the muon momentum and angular distributions in three samples. CC other CC0Ο CC1Ο+ ΞΌ + hadrons ΞΌ ΞΌ + Ο+ TPC2 TPC1 TPC3 FGD1 FGD2 CC0Ο ΞΌ momentum CC other ΞΌ momentum CC1Ο+ ΞΌ momentum DIS RES CCQE DIS
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CC0Ο ΞΌ momentum distribution
β’ Constraints from ND280 The cross section parameters are constrained by fitting the muon momentum and angular distributions. CC0Ο ΞΌ momentum distribution After ND280 constraint MAQE 1.24Β±0.072 GeV/c2 MARES 0.96Β±0.068 GeV/c2 CCQE norm 0.97Β±0.076 CC1Ο norm 1.26Β±0.16 NC1Ο0 norm 1.14Β±0.25
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3. How big is the effect of the uncertainty in π-N interaction?
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Systematic errors in Ξ½ΞΌο Ξ½e analysis
Systematic error on predicted number of Ξ½e (sin22ΞΈ13=0.1, Ξ΄CP=0, normal hierarchy) Error sources Error Neutrino flux & cross section (constrained by ND280) 2.9% Neutrino cross section (not constrained by ND280) 7.5% SK detector & Final state interaction & Ξ³-N interaction 3.5% Total 8.8% 25.9% if there are no ND280 constraint Cross section systematic errors are important! Part of the errors are largely reduced thanks to ND280 constraint.
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Systematic errors in Ξ½ΞΌο Ξ½e analysis
Systematic error on predicted number of Ξ½e (sin22ΞΈ13=0.1, Ξ΄CP=0, normal hierarchy) Error sources Error Neutrino flux & cross section (constrained by ND280) 2.9% Neutrino cross section (not constrained by ND280) 7.5% SK detector & Final state interaction & Ξ³-N interaction 3.5% Total 8.8% Error sources Error MAQE 3.1% MARES 1.0% CCQE norm 6.2% CC1Ο norm 2.0% NC1Ο0 norm 0.4% Anti-correlated with Ξ½ flux. Flux + cross section error is small.
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Systematic errors in Ξ½ΞΌο Ξ½e analysis
Systematic error on predicted number of Ξ½e (sin22ΞΈ13=0.1, Ξ΄CP=0, normal hierarchy) Error sources Error Neutrino flux & cross section (constrained by ND280) 2.9% Neutrino cross section (not constrained by ND280) 7.5% SK detector & Final state interaction & Ξ³-N interaction 3.5% Total 8.8% Error sources Error CC other norm. 0.1% Spectral function 5.9% Fermi momentum CC coh. norm. 0.2% NC coh. norm. NC other norm. 0.5% ΟΞ½e/ΟΞ½ΞΌ 2.8% W-shape Ο-less Ξ decay 3.6% Explained in the next page Ξ½ΞΌ/Ξ½e cross section difference 3% uncertainty applied according to Phys. Rev., D86, p , 2012. Disappearance of the resonance state without Ο emission 20% uncertainty applied according to Phys. Lett., Vol. B416, pp , 1998
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Systematic errors in Ξ½ΞΌο Ξ½e analysis
Systematic error on predicted number of Ξ½e (sin22ΞΈ13=0.1, Ξ΄CP=0, normal hierarchy) Error sources Error Neutrino flux & cross section (constrained by ND280) 2.9% Neutrino cross section (not constrained by ND280) 7.5% SK detector & Final state interaction & Ξ³-N interaction 3.5% Total 8.8%
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Spectral function Spectral function (SF) is a sophisticated model which is known as better representation of the nuclear model compared to Fermi Gas model. Nucleon momentum distribution (Relativistic Fermi Gas) Electron scattering data SF shows better agreement with electron scattering data. SF defines the probability distribution of nuclear momenta and energies required to remove a nucleon. Currently we use RFG because SF is not implemented in NEUT yet. We apply the difference between RFG and SF as the error. SF will be implemented in NEUT soon.
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Final state interaction (FSI)
Pions are often absorbed by the nuclei before being detected. ο CC1Ο events are misidentified as CCQE. Roughly half of the pions in the CC1Ο interaction are absorbed (ABS) or charge exchanged (CX, Ο++NβΟ0+Nβ) at EΞ½ ~ 0.6 GeV. ΞΌ ABS, CX cross section Ξ½ΞΌ Ο ? p FSI is constrained by the Ο-N cross section measurements in the past. However, the cross section uncertainties are large. ΞΟABS~25%, ΞΟCX~50%
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Ο-C ABS+CX cross section
Constraint on FSI We measured the Ο-C cross section at TRIUMF Ο beamline to constrain the FSI uncertainty. ~5cm, 32 layers ~5cm, 32 fibers Ο+ Ο-C ABS+CX cross section Finely segmented scintillator fiber tracker is constructed for this measurement. ABS+CX cross section measured with the uncertainty improved by a factor of 2. FSI error will be improved by using this result.
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Summary Ξ½-N interaction systematic errors are important in the precision neutrino oscillation measurement. The dominant systematic errors in the oscillation measurement are the cross section parameters which are not constrained by ND280. Future improvements: Implementation of the models in the simulation (Spectral function etc.) Improved inputs from internal/external cross section measurements (Ξ½-N cross section in T2K, Ο-N cross section)
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Backup slides
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Multi nucleon process There are some indications that multi nucleon interactions can consistently describe multiple datasets. Multi nucleon effects are often identified as CCQE ο Introduce a bias to the neutrino energy reconstruction.
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MiniBooNE data
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