Accelerator Neutrino Experiments Research Articles

Probing CP Violation with Neutrino Disappearance Alone.

The best way to probe CP violation in the lepton sector is with long-baseline accelerator neutrino experiments in the appearance mode: the appearance of ν_{e} in predominantly ν_{μ} beams. Here we show that it is possible to discover CP violation with disappearance experiments only, by combining JUNO for electron neutrinos and DUNE or Hyper-Kamiokande for muon neutrinos. While the maximum sensitivity to discover CP is quite modest (1.6σ with 6years of JUNO and 13years of DUNE), some values of δ may be disfavored by >3σ depending on the true value of δ.

Majorana CP-violating phases and NSI effects in neutrino decay

In this work, we investigate the impact of neutrino decay in the presence of non-standard interactions (NSI) along with the effects of the Majorana phase on neutrino decay in matter in the context of two-flavor neutrino oscillations. These effects are studied on neutrino oscillation probabilities P α β ≡ P(ν α → ν β ), and the difference ΔPαβ≡P(να→νβ)−P(ν¯α→ν¯β) for several accelerator and reactor neutrino experiments. We find that for P α β , the influence of the Majorana phase on decay in matter can be replicated by the simultaneous presence of both decay and NSI. However, precise measurements of the P α β and ΔP α β observables have the potential to unequivocally identify the presence of the Majorana phase by discerning its effects from the concurrent presence of both decay and NSI.

First Measurement of η Meson Production in Neutrino Interactions on Argon with MicroBooNE.

We present a measurement of η production from neutrino interactions on argon with the MicroBooNE detector. The modeling of resonant neutrino interactions on argon is a critical aspect of the neutrino oscillation physics program being carried out by the DUNE and Short Baseline Neutrino programs. η production in neutrino interactions provides a powerful new probe of resonant interactions, complementary to pion channels, and is particularly suited to the study of higher-order resonances beyond the Δ(1232). We measure a flux-integrated cross section for neutrino-induced η production on argon of 3.22±0.84(stat)±0.86(syst) 10^{-41} cm^{2}/nucleon. By demonstrating the successful reconstruction of the two photons resulting from η production, this analysis enables a novel calibration technique for electromagnetic showers in GeV accelerator neutrino experiments.

DarkNews: A Python-based event generator for heavy neutral lepton production in neutrino-nucleus scattering

We introduce DarkNews, a lightweight Python -based Monte-Carlo generator for beyond-the-Standard-Model neutrino-nucleus scattering. The generator handles the production and decay of heavy neutral leptons via additional vector or scalar mediators, as well as through transition magnetic moments. DarkNews samples pre-computed neutrino-nucleus upscattering cross sections and heavy neutrino decay rates to produce dilepton and single-photon events in accelerator neutrino experiments. We present two case studies with differential distributions for models that can explain the MiniBooNE excess. The aim of this code is to aid the neutrino theory and experimental communities in performing searches and sensitivity studies for new particles produced in neutrino upscattering. Program summaryProgram Title: DarkNewsCPC Library link to program files:https://doi.org/10.17632/k9nh5fn4pw.1Developer's repository link:https://github.com/mhostert/DarkNews-generatorLicensing provisions: MITProgramming language: PythonNature of problem: In many theories beyond the Standard Model of particle physics, new light particles are introduced with masses below the 100 GeV scale. These can be produced by neutrino-nucleus interactions inside neutrino detectors, leaving a visible signature through their decay. To search for these signatures, experiments have to simulate the underlying physical processes, which requires detailed knowledge of the cross sections and decay rates in the model, as well as the ability to generate Monte Carlo events.Solution method: DarkNews provides the necessary tools to simulate the production of heavy neutral leptons in accelerator neutrino experiments, focusing on neutrino-nucleus scattering processes. The program's scope includes models with new mediators and three heavy neutral leptons, parameterizing a large class of theories through generic neutrino, quark, and lepton interactions. It generates weighted Monte-Carlo events using vegas and its pre-calculated differential rates.

Neutrino physics: Experimental and theoretical challenges

The existence of massive neutrinos is the first solid evidence of physics beyond the standard model of particle physics. A remarkable progress has been achieved in solar, atmospheric, reactor, and accelerator neutrino experiments during the last decades. On the theoretical side, several questions are being addressed, namely the Dirac or Majorana nature of neutrinos, the mechanisms for neutrino mass generation, and the relation between neutrinos and the matter–antimatter asymmetry observed in the Universe, among others. This article provides a brief overview on some of the current experimental and theoretical aspects in neutrino physics.

Determining neutrino mass ordering with ICAL, JUNO and T2HK

In this paper we study the synergy among the future accelerator (T2HK), future atmospheric (ICAL) and future reactor (JUNO) neutrino experiments to determine the neutrino mass ordering. T2HK can measure the mass ordering only for favorable values of $\delta_{\rm CP}$, whereas the mass ordering sensitivity of JUNO is dependent on the energy resolution. Our results show that with a combination of T2HK, ICAL and JUNO one can have a mass ordering sensitivity of 7.2 $\sigma$ even for the unfavorable value of $\delta_{\rm CP} = 0^\circ$ for T2HK and most conservative value of JUNO energy resolution of 5$\%/\sqrt{E(MeV)}$. The synergy mainly comes because different oscillation channels prefer different values of $|\Delta m_{31}^2|$ in the fit when the mass-ordering $\chi^2$ is minimized. In this context we also study: (i) effect of varying energy resolution of JUNO, (ii) the effect of longer run-time of ICAL, (iii) effect of different true values of $\theta_{23}$ and (iv) effect of octant degeneracy in the determination of neutrino mass ordering.

A substandard candle: the low-nu method at few-GeV neutrino energies

As accelerator-based neutrino oscillation experiments improve oscillation parameter constraints with more data, control over systematic uncertainties on the incoming neutrino flux and interaction models is increasingly important. The intense beams offered by modern experiments permit a variety of options to constrain the flux using in situ “standard candle” measurements. These standard candles must use very well understood interaction processes to avoid introducing additional interaction model dependence. One option often discussed in this context is the “low-nu ” method, which is designed to isolate neutrino interactions where there is low energy-transfer to the nucleus, such that the interaction cross section is expected to be approximately constant as a function of neutrino energy. The shape of the low-energy transfer event sample can then be used to extract the flux shape. Applications of the method at high neutrino energies (many tens of GeV) are well understood. However, the applicability of the method at the lower energies of current and future few-GeV accelerator neutrino experiments remains unclear due to the presence of nuclear and form-factor effects inherent in the interaction models.In this analysis we examine the prospects for improving constraints on the accelerator neutrino fluxes in situ with the low-nu method in an experiment-independent way, using (anti)neutrino interactions on argon and hydrocarbon targets from the GENIE, NEUT, NuWro and GiBUU event generators. We begin by investigating the extent to which deviations from the constant cross-section assumption are dependent on poorly understood aspects of the neutrino interaction model. We then assess whether a low energy-transfer event sample can be confidently identified using experimentally accessible observables. We finally consider how the practicalities of reconstructing the energy spectrum of interacting neutrinos in realistic detectors might further limit the utility of low-nu flux constraints. The results show that flux constraints from the low-nu method would be severely dependent on the interaction model assumptions used in an analysis of neutrinos with energies below 5 GeV, and anti-neutrinos below at least 15 GeV. The spread of model predictions show that a low-nu analysis is unlikely to offer much improvement on typical neutrino flux uncertainties, even with a perfect detector. Notably—running counter to the assumption inherent to the low-nu method—the model-dependence increases with decreasing energy transfer for experiments in the few-GeV region.

Study of final-state interactions of protons in neutrino-nucleus scattering with INCL and NuWro cascade models

The modeling of neutrino-nucleus interactions constitutes a challenging source of systematic uncertainty for the extraction of precise values of neutrino oscillation parameters in long-baseline accelerator neutrino experiments. To improve such modeling and minimize the corresponding uncertainties, a new generation of detectors is being developed, which aim to measure the complete final state of particles resulting from neutrino interactions. In order to fully benefit from the improved detector capabilities, precise simulations of the nuclear effects on the final-state nucleons are needed. This article presents the study of the in-medium propagation of knocked-out protons, i.e., final-state interactions (FSI), comparing the NuWro and INCL cascade models. The INCL model is used here for the first time to predict exclusive final states in measured neutrino interaction cross sections. This study of INCL in the framework of neutrino interactions features various novelties, including the production of nuclear clusters (e.g., deuterons, $\ensuremath{\alpha}$ particles) in the final state. The paper includes a complete characterization of the final state after FSI, comparisons to available measurements of single transverse variables, and an assessment of the observability of nuclear clusters.

A Review of the Tension between the T2K and NOνA Appearance Data and Hints to New Physics

In this article, we review the status of the tension between the long-baseline accelerator neutrino experiments T2K and NOνA. The tension arises mostly due to the mismatch in the apappearance data of the two experiments. We explain how this tension arises based on νμ→νe and ν¯μ→ν¯e oscillation probabilities. We define the reference point of vacuum oscillation, maximal θ23 and δCP and compute the νe/ν¯e appearance events for each experiment. We then study the effects of deviating the unknown parameters from the reference point and the compatibility of any given set of values of unknown parameters with the data from T2K and NOνA. T2K observes a large excess in the νe appearance event sample compared to the expected νe events at the reference point, whereas NOνA observes a moderate excess. The large excess in T2K dictates that δCP be anchored at −90° and that θ23 > π/4 with a preference for normal hierarchy. The moderate excess at NOνA leads to two degenerate solutions: (a) NH, 0 < δCP < 180°, and θ23 > π/4; (b) IH, −180° < δCP < 0, and θ23 > π/4. This is the main cause of tension between the two experiments. We review the status of three beyond standard model (BSM) physics scenarios, (a) non-unitary mixing, (b) Lorentz invariance violation, and (c) non-standard neutrino interactions, to resolve the tension.

Search for sterile neutrinos by shower events at a future neutrino telescope

Abstract It is pointed out that searching for sterile neutrinos in high energy regions at a future IceCube-like facility has advantages compared with reactor or short baseline accelerator neutrino experiments, in which the size of the detector and energy resolution make it difficult to gain good sensitivity for a large mass-squared difference. In this study we show that it is possible to improve constraints on sterile neutrino mixing θ14 for 1 eV$^2 \lesssim \Delta m_{41}^2\lesssim$ 100 eV2 by looking for a dip in the shower events at an IceCube-like neutrino telescope whose volume is at least 10 times as large as that of IceCube and whose duration is 10 years. We also give an analytic expression for the oscillation probabilities in two cases where the condition of one mass scale dominance is satisfied.

NuFIT: Three-Flavour Global Analyses of Neutrino Oscillation Experiments

In this contribution, we summarise the determination of neutrino masses and mixing arising from global analysis of data from atmospheric, solar, reactor, and accelerator neutrino experiments performed in the framework of three-neutrino mixing and obtained in the context of the NuFIT collaboration. Apart from presenting the latest status as of autumn 2021, we discuss the evolution of global-fit results over the last 10 years, and mention various pending issues (and their resolution) that occurred during that period in the global analyses.

Sensitivity of a search for eV-scale sterile neutrinos with 8 years of IceCube DeepCore data

Several anomalies in reactor and accelerator neutrino experiments motivate the search for sterile neutrinos with squared mass splittings at the eV-scale. We present an analysis that probes the elements Uμ4 and Uτ4 of the extended (3+1) neutrino mixing matrix using an 8 year data sample from IceCube's DeepCore sub-array containing atmospheric neutrinos between 5 and 300 GeV. We show the expected sensitivities of the analysis to |Uμ4|2 and |Uτ4|2 under the assumption of mass splittings between 1 and 100 eV2, and to |Uμ4|2 for mass splittings below 1 eV2. We specifically discuss how we overcame the challenges of efficiently calculating neutrino oscillation probabilities in the presence of very fast neutrino oscillations involving large Δ m2.

Probing source and detector nonstandard interaction parameters at the DUNE near detector

We investigate the capability of the DUNE near detector (ND) to constrain nonstandard interaction parameters (NSIs) describing the production of neutrinos $({ϵ}_{\ensuremath{\alpha}\ensuremath{\beta}}^{s})$ and their detection $({ϵ}_{\ensuremath{\alpha}\ensuremath{\beta}}^{d})$. We show that the DUNE ND is able to reject a large portion of the parameter space allowed by DUNE far detector analyses and to set the most stringent bounds from accelerator neutrino experiments on $|{ϵ}_{\ensuremath{\mu}e}^{s,d}|$ for wide intervals of the related phases. We also provide simple analytic understanding of our results as well as a numerical study of their dependence on the systematic errors, showing that the DUNE ND offers a clean environment to study source and detector NSIs.

Matter versus vacuum oscillations at long-baseline accelerator neutrino experiments

The neutrino oscillation probabilities at the long-baseline accelerator neutrino experiments are expected to be modified by matter effects. We search for evidence of such modification in the data of T2K and NO[Formula: see text]A, by fitting the data to the hypothesis of (a) matter modified oscillations and (b) vacuum oscillations. We find that vacuum oscillations provide as good a fit to the data as matter modified oscillations. Even extended runs of T2K and NO[Formula: see text]A, with five years in neutrino mode [Formula: see text] and five years in anti-neutrino mode [Formula: see text], cannot make a [Formula: see text] distinction between vacuum and matter modified oscillations. The future experiment DUNE, with neutrino and anti-neutrino runs of five years each [Formula: see text], can rule out vacuum oscillations by itself at [Formula: see text] if the hierarchy is normal. If the hierarchy is inverted, a [Formula: see text] discrimination against vacuum oscillations requires the combination of [Formula: see text] runs of T2K, NO[Formula: see text]A and DUNE.

Non-standard interactions in SMEFT confronted with terrestrial neutrino experiments

The Standard Model Effective Field Theory (SMEFT) provides a systematic and model-independent framework to study neutrino non-standard interactions (NSIs). We study the constraining power of the on-going neutrino oscillation experiments T2K, NOνA, Daya Bay, Double Chooz and RENO in the SMEFT framework. A full consideration of matching is provided between different effective field theories and the renormalization group running at different scales, filling the gap between the low-energy neutrino oscillation experiments and SMEFT at the UV scale. We first illustrate our method with a top- down approach in a simplified scalar leptoquark model, showing more stringent constraints from the neutrino oscillation experiments compared to collider studies. We then provide a bottom-up study on individual dimension-6 SMEFT operators and find NSIs in neutrino experiments already sensitive to new physics at ∼20 TeV when the Wilson coefficients are fixed at unity. We also investigate the correlation among multiple operators at the UV scale and find it could change the constraints on SMEFT operators by several orders of magnitude compared with when only one operator is considered. Furthermore, we find that accelerator and reactor neutrino experiments are sensitive to different SMEFT operators, which highlights the complementarity of the two experiment types.

Form factors of the nucleon axial current

A symmetry-preserving Poincaré-covariant quark+diquark Faddeev equation treatment of the nucleon is used to deliver parameter-free predictions for the nucleon's axial and induced pseudoscalar form factors, GA and GP, respectively. The result for GA can reliably be represented by a dipole form factor characterised by an axial charge gA=GA(0)=1.25(3) and a mass-scale MA=1.23(3)mN, where mN is the nucleon mass; and regarding GP, the induced pseudoscalar charge gp⁎=8.80(23), the ratio gp⁎/gA=7.04(22), and the pion pole dominance Ansatz is found to provide a reliable estimate of the directly computed result. The ratio of flavour-separated quark axial charges is also calculated: gAd/gAu=−0.16(2). This value expresses a marked suppression of the size of the d-quark component relative to that found in nonrelativistic quark models and owes to the presence of strong diquark correlations in the nucleon Faddeev wave function – both scalar and axial-vector, with the scalar diquark being dominant. The predicted form for GA should provide a sound foundation for analyses of the neutrino-nucleus and antineutrino-nucleus cross-sections that are relevant to modern accelerator neutrino experiments.

T2K Experiment: Latest Results and Prospects

The international accelerator neutrino experiment T2K (Tokai-to-Kamioka) began accumulating data in 2010 and has since then accomplished 10 runs in the neutrino and antineutrino modes. The present article reports on the latest results following from the analysis of these data and including the first ever 3 $$\sigma$$ constraints on the CP-violating phase $$\delta_{CP}$$ . Also, the plans for an upgrade of the near detector ND280 are surveyed.

Augmented signal processing in Liquid Argon Time Projection Chambers with a deep neural network

The Liquid Argon Time Projection Chamber (LArTPC) is an advanced neutrino detector technology widely used in recent and upcoming accelerator neutrino experiments. It features a low energy threshold and high spatial resolution that allow for comprehensive reconstruction of event topologies. In current-generation LArTPCs, the recorded data consist of digitized waveforms on wires produced by induced signal on wires of drifting ionization electrons, which can also be viewed as two-dimensional (2D) (time versus wire) projection images of charged-particle trajectories. For such an imaging detector, one critical step is the signal processing that reconstructs the original charge projections from the recorded 2D images. For the first time, we introduce a deep neural network in LArTPC signal processing to improve the signal region of interest detection. By combining domain knowledge (e.g., matching information from multiple wire planes) and deep learning, this method shows significant improvements over traditional methods. This work details the method, software tools, and performance evaluated with realistic detector simulations.

Matter vs vacuum oscillations in atmospheric neutrinos

At present, both vacuum oscillations as well as matter modified oscillations can explain the data of atmospheric neutrino experiments and the long baseline accelerator neutrino experiments equally well. Given the important role the matter effects play in the determination of CP violation in neutrino oscillations, it is imperative to establish the signal for matter effects unambiguously. In this work, we study the ability of ICAL at INO to make a distinction between vacuum oscillations and matter modified oscillations. We find that it is possible to make a 3σ discrimination in ten years, whether the atmospheric mass-squared difference is positive or negative.

Prospects and requirements of opaque detectors in accelerator neutrino experiments

Opaque detectors are a recently proposed novel detector concept where an opaque scintillator aligned with wavelength-shifting fibers is used to enable the discrimination of electron neutrinos and antineutrinos with a rather low energy threshold. In this work, we investigate the potential effects of the enhanced detection capabilities of the opaque detectors in accelerator neutrino experiments. Focusing on the energy threshold, energy resolution, detection efficiency and background suppression in the analysis of electron-like events, we determine whether using opaque detectors could lead to improvements in the CP violation and light sterile neutrino searches in the future accelerator neutrino experiments. We also identify the minimum requirements for the opaque detectors to reach the designated physics goals in the simulated experiments. We find that a 75.6% fraction of $\delta_{CP}$ values could be reached for CP violation discovery by 3$\sigma$ confidence level or better when opaque detectors of 120 kton and 130 kton fiducial masses are used together with neutrino beams from J-PARC and MOMENT, respectively, whereas near detectors placed about 250 m from sources are sufficient to exclude the gallium anomaly at 2$\sigma$ confidence level.