## Single pion production in electron-nucleon interactions

PHYSICAL REVIEW D 102 (2020) ARTN 053009

## Search for neutral-current induced single photon production at the ND280 near detector in T2K

Journal of Physics G: Nuclear and Particle Physics IOP Publishing 46 (2019) 08LT01

K Abe, G Barr, M Batkiewicz-Kwasniak, FD Lodovico, N Dokania, S Dolan, O Drapier, KE Duffy, S Emery-Schrenk, P Hamacher-Baumann, M Hartz, A Hiramoto, NTH Van, T Lindner, RP Litchfield, X Li, A Longhin, JP Lopez, T Lou, L Ludovici, X Lu, T Lux, L Magaletti, K Mahn, JF Martin

All rights reserved. Neutrino neutral-current (NC) induced single photon production is a subleading order process for accelerator-based neutrino beam experiments including T2K. It is, however, an important process to understand because it is a background for electron (anti)neutrino appearance oscillation experiments. Here, we performed the first search of this process below 1 GeV using the finegrained detector at the T2K ND280 off-axis near detector. By reconstructing single photon kinematics from electron positron pairs, we achieved 95% pure gamma ray sample from 5.738 1020 protons-on-targets neutrino mode data. We do not find positive evidence of NC induced single photon production in this sample. We set the model-dependent upper limit on the cross-section for this process, at 0.114 10-38 cm2 (90% C.L.) per nucleon, using the J-PARC off-axis neutrino beam with an average energy of .En. ~ 0.6 GeV. This is the first limit on this process below 1.GeV which is important for current and future oscillation experiments looking for electron neutrino appearance oscillation signals.

## Search for light sterile neutrinos with the T2K far detector Super-Kamiokande at a baseline of 295km

Physical Review D American Physical Society 99 (2019) 071103

P Dunne, S Emery-Schrenk, A Ereditato, P Fernandez, T Feusels, AJ Finch, GA Fiorentini, G Fiorillo, C Francois, M Friend, Y Fujii, A Knight, A Knox, T Kobayashi, L Koch, T Koga, A Konaka, LL Kormos, Y Koshio, K Kowalik, H Kubo, Y Kudenko, R Kurjata, T Kutter, M Kuze

We perform a search for light sterile neutrinos using the data from the T2K far detector at a baseline of 295 km, with an exposure of 14.7(7.6)×10^20 protons on target in neutrino (antineutrino) mode. A selection of neutral-current interaction samples is also used to enhance the sensitivity to sterile mixing. No evidence of sterile neutrino mixing in the 3+1 model was found from a simultaneous fit to the charged-current muon, electron and neutral-current neutrino samples. We set the most stringent limit on the sterile oscillation amplitude sin^2θ24 for the sterile neutrino mass splitting Δm^2v41&lt;3×10^−3eV^2/c^4.

## Search for heavy neutrinos with the T2K near detector ND280

Physical Review D American Physical Society 100 (2019) 052006

K Abe, R Akutsu, A Ali, C Andreopoulos, L Anthony, M Antonova, S Aoki, A Ariga, Y Ashida, Y Awataguchi, Y Azuma, S Ban, M Barbi, GJ Barker, G Barr, C Barry, M Batkiewicz-Kwasniak, F Bench, V Berardi, S Berkman, RM Berner, L Berns, S Bhadra, S Bienstock, S Bolognesi

This paper reports on the search for heavy neutrinos with masses in the range $140 &lt; M_N &lt; 493$ MeV/c$^2$ using the off-axis near detector ND280 of the T2K experiment. These particles can be produced from kaon decays in the standard neutrino beam and then subsequently decay in ND280. The decay modes under consideration are $N \to \ell^{\pm}_{\alpha} \pi^{\mp}$ and $N \to \ell^+_{\alpha} \ell^-_{\beta} \nu (\bar\nu)$ ($\alpha,\beta=e,\mu$). A search for such events has been made using the Time Projection Chambers of ND280, where the background has been reduced to less than two events in the current dataset in all channels. No excess has been observed in the signal region. A combined Bayesian statistical approach has been applied to extract upper limits on the mixing elements of heavy neutrinos to electron-, muon- and tau- flavoured currents ($U_e^2$, $U_{\mu}^2$, $U_{\tau}^2$) as a function of the heavy neutrino mass, e.g. $U_e^2 &lt; 10^{-9}$ at $90\%$ C.L. for a mass of $390$ MeV/c$^2$. These constraints are competitive with previous experiments.

## Characterization of nuclear effects in muon-neutrino scattering on hydrocarbon with a measurement of final-state kinematics and correlations in charged-current pionless interactions at T2K

Physical Review D American Physical Society 98 (2018) 032003-

K Abe, J Amey, C Andreopoulos, L Anthony, M Antonova, S Aoki, A Ariga, Y Ashida, Y Azuma, S Ban, M Barbi, GJ Barker, G Barr, C Barry, M Batkiewicz, V Berardi, S Berkman, RM Berner, L Berns, S Bhadra, S Bienstock, A Blondel, S Bolognesi, S Bordoni, B Bourguille

This paper reports measurements of final-state proton multiplicity, muon and proton kinematics, and their correlations in charged-current pionless neutrino interactions, measured by the T2K ND280 near detector in its plastic scintillator (C8H8) target. The data were taken between years 2010 and 2013, corresponding to approximately 6×1020 protons on target. Thanks to their exploration of the proton kinematics and of imbalances between the proton and muon kinematics, the results offer a novel probe of the nuclear-medium effects most pertinent to the (sub-)GeV neutrino-nucleus interactions that are used in accelerator-based long-baseline neutrino oscillation measurements. These 3 results are compared to many neutrino-nucleus interaction models which all fail to describe at least part of the observed phase space. In case of events without a proton above a detection threshold in the final state, a fully consistent implementation of the local Fermi gas model with multinucleon interactions gives the best description of the data. In the case of at least one proton in the final state the spectral function model agrees well with the data, most notably when measuring the kinematic imbalance between the muon and the proton in the plane transverse to the incoming neutrino. Within the models considered, only the existence of multinucleon interactions are able to describe the extracted cross-section within regions of high transverse kinematic imbalance. The effect of final-state interactions is also discussed.

## The status of neutrino interaction theory and its impact on future neutrino oscillation experiments.

Proceedings of Science 337 (2018)

© Copyright owned by the author(s) under the terms of the Creative Commons. Over the last decade, there has been enormous effort to measure neutrino interaction cross sections important to oscillation experiments. However, a number of results from modern experiments appear to be in tension with our model predictions. It also has been known that our models are outdated and with assumptions for simplicity, therefore, many efforts have been devoted to the quasielastic peak and dip region to improve them but very little attention has been given to the resonance and higher regions. The MK model provides a full kinematic description of single pion production in the neutrino-nucleon interactions, including resonant and nonresonant interactions in the helicity basis, in order to study the interference effect. The MK model shows better agreements with data compare to the exciting (RS) model in NEUT. The effects of new (MK) model on T2K oscillation measurements shows bias on ∆223 and θ23. Although bias is small with respect to the uncertainty right now, clearly mis-modelling can produce biased oscillation parameters, and this will be a serious problem for next generation experiments.

## Single pion production in neutrino-nucleon interactions

Physical Review D 97 (2018)

© 2018 authors. Published by the American Physical Society. This work represents an extension of the single pion production model proposed by Rein [Z. Phys. C 35, 43 (1987).ZPCFD20170-973910.1007/BF01561054]. The model consists of resonant pion production and nonresonant background contributions coming from three Born diagrams in the helicity basis. The new work includes lepton mass effects, and nonresonance interaction is described by five diagrams based on a nonlinear σ model. This work provides a full kinematic description of single pion production in the neutrino-nucleon interactions, including resonant and nonresonant interactions in the helicity basis, in order to study the interference effect.

## First measurement of the nu(mu) charged-current cross section on a water target without pions in the final state

Physical Review D American Physical Society 97 (2018) 012001-

K Abe, J Amey, C Andreopoulos, GD Barr, D Coplowe, S Dolan, X Lu, R Shah, T Vladisavljevic, DL Wark, AJG Weber

This paper reports the first differential measurement of the charged-current interaction cross section of νμ on water with no pions in the final state. This flux-averaged measurement has been made using the T2K experiment’s off-axis near detector, and is reported in doubly differential bins of muon momentum and angle. The flux-averaged total cross section in a restricted region of phase space was found to be σ=(0.95±0.08(stat)±0.06(det syst)±0.04(model syst)±0.08(flux))×10^−38 cm^2/n.

## Measurement of inclusive double-differential νμ charged-current cross section with improved acceptance in the T2K off-axis near detector

Physical Review D American Physical Society 98 (2018) 012004

K Abe, J Amey, C Andreopoulos, L Anthony, M Antonova, S Aoki, A Ariga, Y Ashida, Y Azuma, S Ban, M Barbi, GJ Barker, G Barr, C Barry, M Batkiewicz, V Berardi, S Berkman, RM Berner, S Bhadra, S Bienstock, A Blondel, S Bolognesi, S Bordoni, B Bourguille, SB Boyd

We report a measurement of the flux-integrated cross section for inclusive muon neutrino chargedcurrent interactions on carbon. The double-differential measurements are given as a function of the muon momentum and angle. Relative to our previous publication on this topic, these results have an increased angular acceptance and higher statistics. The data sample presented here corresponds to 5.7 × 1020 protons on target. The total flux-integrated cross section is measured to be ð6.950 0.662Þ × 10−39 cm2 nucleon−1 and is consistent with our simulation.

## Measurement of the single pi(0) production rate in neutral current neutrino interactions on water

Physical Review D American Physical Society 97 (2018) 032002

J Morrison, TA Mueller, S Murphy, J Myslik, T Nakadaira, M Nakahata, KG Nakamura, K Nakamura, KD Nakamura, Y Nakanishi, S Nakayama, T Nakaya, K Nakayoshi, C Nantais, C Nielsen, M Nirkko, K Nishikawa, Y Nishimura, P Novella, J Nowak, HM O'Keeffe, R Ohta, K Okumura, T Okusawa, W Oryszczak

The single π0 production rate in neutral current neutrino interactions on water in a neutrino beam with a peak neutrino energy of 0.6 GeV has been measured using the PØD, one of the subdetectors of the T2K near detector. The production rate was measured for data taking periods when the PØD contained water (2.64×1020 protons-on-target) and also periods without water (3.49×1020 protons-on-target). A measurement of the neutral current single π0 production rate on water is made using appropriate subtraction of the production rate with water in from the rate with water out of the target region. The subtraction analysis yields 106±41±69 signal events where the uncertainties are statistical (stat.) and systematic (sys.) respectively. This is consistent with the prediction of 157 events from the nominal simulation. The measured to expected ratio is 0.68±0.26(stat)±0.44(sys)±0.12(flux). The nominal simulation uses a flux integrated cross section of 7.63×10-39 cm2 per nucleon with an average neutrino interaction energy of 1.3 GeV.

## First measurement of the muon neutrino charged current single pion production cross section on water with the T2K near detector

Physical Review D American Physical Society 95 (2017)

A Ariga, S Assylbekov, D Autiero, S Ban, M Barbi, GJ Barker, G Barr, P Bartet-Friburg, M Batkiewicz, F Bay, V Berardi, S Berkman, S Bhadra, S Bienstock, A Blondel, S Bolognesi, S Bordoni, SB Boyd, D Brailsford, A Bravar, C Bronner, M Buizza Avanzini, RG Calland, T Campbell, S Cao

The T2K off-axis near detector, ND280, is used to make the first differential cross section measurements of muon neutrino charged current single positive pion production on a water target at energies ∼0.8 GeV. The differential measurements are presented as a function of the muon and pion kinematics, in the restricted phase space defined by pπ+&gt;200 MeV/c, pμ&gt;200 MeV/c, cos(θπ+)&gt;0.3 and cos(θμ)&gt;0.3. The total flux integrated νμ charged current single positive pion production cross section on water in the restricted phase space is measured to be σ

## Single Pion Production in Neutrino Reactions

XXVII INTERNATIONAL CONFERENCE ON NEUTRINO PHYSICS AND ASTROPHYSICS (NEUTRINO2016) 888 (2017)

## Search for Lorentz and violation using sidereal time dependence of neutrino flavor transitions over a short baseline

Physical Review D American Physical Society 95 (2017)

K Abe, J Amey, C Andreopoulos, M Antonova, S Aoki, A Ariga, D Autiero, PF Denner, C Densham, D Dewhurst, F Di Lodovico, S Di Luise, S Dolan, O Drapier, KE Duffy, J Dumarchez, M Dunkman, M Hierholzer, A Hillairet, A Himmel, T Hiraki, F Hosomi, K Huang, AK Ichikawa

A class of extensions of the Standard Model allows Lorentz and CPT violations, which can be identified by the observation of sidereal modulations in the neutrino interaction rate. A search for such modulations was performed using the T2K on-axis near detector. Two complementary methods were used in this study, both of which resulted in no evidence of a signal. Limits on associated Lorentz and CPT-violating terms from the Standard Model extension have been derived by taking into account their correlations in this model for the first time. These results imply such symmetry violations are suppressed by a factor of more than 1020 at the GeV scale.

## Combined analysis of neutrino and antineutrino oscillations at T2K

Physical Review Letters American Physical Society 118 (2017) 151801-

K Abe, J Amey, C Andreopoulos, GD Barr, D Coplowe, S Dolan, X Lu, R Shah, T Vladisavljevic, DL Wark, AJG Weber

T2K reports its first results in the search for CP violation in neutrino oscillations using appearance and disappearance channels for neutrino- and antineutrino-mode beams. The data include all runs from January 2010 to May 2016 and comprise 7.482×10^{20} protons on target in neutrino mode, which yielded in the far detector 32 e-like and 135  μ-like events, and 7.471×10^{20} protons on target in antineutrino mode, which yielded 4 e-like and 66  μ-like events. Reactor measurements of sin^{2}2θ_{13} have been used as an additional constraint. The one-dimensional confidence interval at 90% for the phase δ_{CP} spans the range (-3.13, -0.39) for normal mass ordering. The CP conservation hypothesis (δ_{CP}=0, π) is excluded at 90% C.L.

## Measurement of (nu)over-bar(mu) and nu(mu) charged current inclusive cross sections and their ratio with the T2K off-axis near detector

Physical Review D American Physical Society 96 (2017) 052001-

K Abe, J Amey, C Andreopoulos, GD Barr, D Coplowe, S Dolan, X Lu, R Shah, T Vladisavljevic, DL Wark, AJG Weber

We report a measurement of cross section σ(νμ+nucleus→μ-+X) and the first measurements of the cross section σ(ν-μ+nucleus→μ++X) and their ratio R(σ(ν-)σ(ν)) at (anti) neutrino energies below 1.5 GeV. We determine the single momentum bin cross section measurements, averaged over the T2K ν-/ν-flux, for the detector target material (mainly carbon, oxygen, hydrogen and copper) with phase space restricted laboratory frame kinematics of θμ &lt; 32° and pμ &gt; 500 MeV/c. The results are σ(ν-)=(0.900±0.029(stat)±0.088(syst))×10-39 and σ(ν)=(2.41±0.022(stat)±0.231(syst))×10-39 in units of cm2/nucleon and R(σ(ν-)σ(ν))=0.373±0.012(stat)±0.015(syst).

## Updated T2K measurements of muon neutrino and antineutrino disappearance using 1.5 × 10^21 protons on target

Physical Review D American Physical Society 96 (2017) 011102-

K Abe, J Amey, C Andreopoulos, GD Barr, D Coplowe, S Dolan, X Lu, R Shah, T Vladisavljevic, DL Wark, AJG Weber

We report measurements by the T2K experiment of the parameters θ23 and Δm322 governing the disappearance of muon neutrinos and antineutrinos in the three-flavor neutrino oscillation model. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, the parameters are measured separately for neutrinos and antineutrinos. Using 7.482×1020 POT in neutrino running mode and 7.471×1020 POT in antineutrino mode, T2K obtained sin2(θ23)=0.51-0.07+0.08 and Δm322=2.53-0.13+0.15×10-3 eV2/c4 for neutrinos, and sin2(θ-23)=0.42-0.07+0.25 and Δm-232=2.55-0.27+0.33×10-3 eV2/c4 for antineutrinos (assuming normal mass ordering). No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed.

## Measurement of neutrino and antineutrino oscillations by the T2K experiment including a new additional sample of nu(e) interactions at the far detector

Physical Review D American Physical Society 96 (2017) 092006-

K Abe, J Amey, C Andreopoulos, G Barr, D Coplowe, S Dolan, X Lu, R Shah, T Vladisavljevic, DL Wark, AJG Weber

The T2K experiment reports an updated analysis of neutrino and antineutrino oscillations in appearance and disappearance channels. Asample of electron neutrino candidates at Super-Kamiokande in which a pion decay has been tagged is added to the four single-ring samples used in previous T2K oscillation analyses. Through combined analyses of these five samples, simultaneous measurements of four oscillation parameters, |Δm2/32|, sin2 θ23, sin2 θ13, and δCP and of the mass ordering are made. A set of studies of simulated data indicates that the sensitivity to the oscillation parameters is not limited by neutrino interaction model uncertainty. Multiple oscillation analyses are performed, and frequentist and Bayesian intervals are presented for combinations of the oscillation parameters with and without the inclusion of reactor constraints on sin2 θ13.When combined with reactor measurements, the hypothesis of CP conservation (δCP = 0 or π) is excluded at 90% confidence level. The 90% confidence region for δCP is [−2.95;−0.44] ([−1.47;−1.27]) for normal (inverted) ordering. The central values and 68% confidence intervals for the other oscillation parameters for normal (inverted) ordering are Δm2/32 = 2.54 ± 0.08(2.51 ± 0.08) × 10^−3 eV^2/c^4 and sin2θ23 = 0.55+0.05/−0.09 (0.55+0.05/−0.08 ), compatible with maximal mixing. In the Bayesian analysis, the data weakly prefer normal ordering (Bayes factor 3.7) and the upper octant for sin2 θ23 (Bayes factor 2.4).

## Measurement of double-differential muon neutrino charged-current interactions on C8H8 without pions in the final state using the T2K off-axis beam

Physical Review D American Physical Society 93 (2016) 112012-

GD Barr, D Dewhurst, S Dolan, KE Duffy, A Jacob, X Lu, R Shah, A Vacheret, DL Wark, A Weber

We report the measurement of muon neutrino charged-current interactions on carbon without pions in the final state at the T2K beam energy using 5.734×1020 protons on target. For the first time the measurement is reported as a flux-integrated, double-differential cross section in muon kinematic variables (cosθμ, pμ), without correcting for events where a pion is produced and then absorbed by final state interactions. Two analyses are performed with different selections, background evaluations and cross-section extraction methods to demonstrate the robustness of the results against biases due to model-dependent assumptions. The measurements compare favorably with recent models which include nucleon-nucleon correlations but, given the present precision, the measurement does not distinguish among the available models. The data also agree with Monte Carlo simulations which use effective parameters that are tuned to external data to describe the nuclear effects. The total cross section in the full phase space is σ=(0.417±0.047(syst)±0.005(stat))×10-38 cm2 nucleon-1 and the cross section integrated in the region of phase space with largest efficiency and best signal-over-background ratio (cosθμ&gt;0.6 and pμ&gt;200 MeV) is σ=(0.202±0.036(syst)±0.003(stat))×10-38 cm2 nucleon-1.

## Measurement of muon antineutrino oscillations with an accelerator-produced off-axis beam.

Physical Review Letters American Physical Society 116 (2016) 181801-

GD Barr, D Dewhurst, S Dolan, KE Duffy, A Jacob, X Lu, R Shah, A Vacheret, DL Wark, A Weber

T2K reports its first measurements of the parameters governing the disappearance of ν¯μ in an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic ν¯μ beam, produced with a peak energy of 0.6 GeV at J-PARC, is observed at the far detector Super-Kamiokande, 295 km away, where the ν¯μ survival probability is expected to be minimal. Using a data set corresponding to 4.01×1020 protons on target, 34 fully contained μ-like events were observed. The best-fit oscillation parameters are sin2(θ¯23)=0.45 and |Δm¯232|=2.51×10−3  eV2 with 68% confidence intervals of 0.38–0.64 and 2.26–2.80×10−3  eV2, respectively. These results are in agreement with existing antineutrino parameter measurements and also with the νμ disappearance parameters measured by T2K.

## Measurement of coherent π^{+} production in low energy neutrino-carbon scattering

Physical Review Letters American Physical Society 117 (2016) 192501

K Abe, C Andreopoulos, M Antonova, G Barr, D Coplowe, D Dewhurst, S Dolan, K Duffy, A Jacob, X Lu, R Shah, A Vacheret, D Wark, A Weber, E Et al.

We report the first measurement of the flux-averaged cross section for charged current coherent πþ production on carbon for neutrino energies less than 1.5 GeV, and with a restriction on the final state phase space volume in the T2K near detector, ND280. Comparisons are made with predictions from the ReinSehgal coherent production model and the model by Alvarez-Ruso et al., the latter representing the first implementation of an instance of the new class of microscopic coherent models in a neutrino interaction Monte Carlo event generator. We observe a clear event excess above background, disagreeing with the null results reported by K2K and SciBooNE in a similar neutrino energy region. The measured flux-averaged cross sections are below those predicted by both the Rein-Sehgal and Alvarez-Ruso et al. models.