Baseline Neutrino Experiment Research Articles

Synergy between DUNE and T2HKK to probe invisible neutrino decay

We address the consequence of invisible neutrino decay within the framework of two long base-line neutrino experiments: T2HKK (Tokai-to-Hyper-Kamiokande-to-Korea) and DUNE (Deep Underground Neutrino experiment). Our primary objective is to bring out the aspects of CC (charged current) and NC (neutral current) measurements at DUNE in the context of invisible neutrino decay. We find that the inclusion of NC measurements with the CC measurements enhances its ability to constrain invisible neutrino decay. Further, the synergy between DUNE and T2HKK improves the constraints on invisible neutrino decay. At 3σ C.L. (confidence level) the derived constraint is τ3/m3 ≥ 6.21 × 10−11 s/eV. Additionally, if nature prefers ν3 to be unstable and the decay width is τ3/m3 = 2.2 × 10−11 s/eV, this combination can exclude the no-decay scenario at more than 5σ C.L. Although the CP sensitivity is not much hindered in the presence of invisible neutrino decay, the measurements of θ23 and the ability to resolve octant of θ23 is significantly influenced in these individual experiments. In the presence of invisible neutrino decay, the synergy between DUNE and T2HKK can exclude the wrong octant somewhat more effectively than either experiment alone.

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New neutrino–nucleus interaction cross-section measurements are required to improve nuclear models sufficiently for future long baseline neutrino experiments to meet their sensitivity goals. A time projection chamber (TPC) filled with a high-pressure gas is a promising detector to characterise the neutrino sources used for such experiments. A gas-filled TPC is ideal for measuring low-energy particles, which travel further in gas than in solid or liquid detectors and using high-pressure increases the target density, resulting in more neutrino interactions. We examine the suitability of multiwire proportional chambers (MWPCs) from the ALICE TPC for use as the readout chambers of a high-pressure gas TPC. These chambers were previously operated at atmospheric pressure. 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Significance of classically forbidden regions for short baseline neutrino experiments

Classically forbidden regions (CFRs) are common to both non-relativistic quantum mechanics, and to relativistic quantum field theory. It is known since 2001 that CFR contributes roughly sixteen percent of energy to the ground state of a simple harmonic oscillator (Adunas G. Z. et al., Gen. Relativ. Gravit., 33 (2001) 183). Similarly, quantum field theoretic arguments yield a non-zero amplitude for a massive particle to cross the light cone (that is, into the CFR). The signs of these amplitudes are opposite for fermions and antifermions. This has given rise to an erroneous conclusion that amplitude to cross the light cone is identically zero. This is true as long as a measurement does not reveal the considered object to be a particle or antiparticle. However, neutrino oscillation experiments do measure a neutrino ν, or an antineutrino . Here we show that in the context of neutrino oscillations these observations have the potential to resolve various short baseline anomalies for a sufficiently light lowest mass eigenstate. In addition, we make a concrete prediction for the upcoming results to be announced later this year by JSNS2.

Impact of nuclear effects in energy reconstruction methods on sensitivity of neutrino oscillation parameters at NOνA experiment

Long baseline (LBL) neutrino experiments aim to measure the neutrino oscillation parameters to high precision. These experiments use nuclear targets for neutrino scattering and hence are inflicted with complexities of nuclear effects. Nuclear effects and their percolation into sensitivity measurement of neutrino oscillations parameters are not yet fully understood and therefore need to be dealt with carefully. In a recent work [1], we reported some results on this for NOνA experiment using the kinematic method of neutrino energy reconstruction, where it was observed that the nuclear effects are important in sensitivity analysis, and inclusion of realistic detector set up specifications increases uncertainty in this analysis as compared to ideal detector case. Precise reconstruction of neutrino energy is an important component in the extraction of oscillation parameters, and it is required that the neutrino energy is reconstructed with very high precision. With this motivation, in this work, we use two methods of neutrino energy reconstruction - kinematic and calorimetric, including the nuclear effects, and study their impact on sensitivity analysis. We consider nuclear interactions such as RPA and 2p2h and compare two energy reconstruction methods with reference to events generation, measurement of neutrino oscillation parameters Δm322 and θ23 for (νμ→νμ) disappearance channel, mass hierarchy sensitivity, and CP-violation sensitivity for (νμ→νe) appearance channel of the NOνA experiment. It is observed that with an ideal detector setup, the kinematic method shows significant dependence on nuclear effects, as compared to the calorimetric method. We also investigate the impact of realistic detector setup for NOνA in these two methods (with nuclear effects) and find that the calorimetric method shows more bias (uncertainty increases) in sensitivity contours, as compared to the kinematic method. This is found to be true for both the mass hierarchies and for both neutrino and antineutrino incoming beams. The results of this study can offer useful insights into future neutrino oscillation analysis at LBL experiments (including leptonic CP phase measurement), especially when we are in the precision measurement era for the same, particularly in the context of some nuclear effects and energy reconstruction methods.

Analytic treatment of 3-flavor neutrino oscillation and decay in matter

We present compact analytic expressions for 3-flavor neutrino oscillation probabilities with invisible neutrino decay, where matter effects have been explicitly included. We take into account the possibility that the oscillation and decay components of the effective Hamiltonian do not commute. This is achieved by employing the techniques of inverse Baker-Campbell-Hausdorff (BCH) expansion and the Cayley-Hamilton theorem applied in the 3-flavor framework. If only the vacuum mass eigenstate ν3 decays, we show that the treatment of neutrino propagation may be reduced to an effective 2-flavor analysis in the One Mass Scale Dominance (OMSD) approximation. The oscillation probabilities for Pμμ, Pee, Peμ and Pμe — relevant for reactor, long baseline and atmospheric neutrino experiments — are obtained as perturbative expansions for the case of only ν3 decay, as well as for the more general scenario where all components of the decay matrix are non-zero. The analytic results thus obtained match the exact numerical results for constant density matter to a high precision and provide physical insights into possible effects of the decay of neutrinos as they propagate through Earth matter. We find that the effects of neutrino decay are most likely to be observable in Pμμ. We also point out that at any long baseline, the oscillation dips in Pμμ can show higher survival probabilities in the case with decay than without decay, and explain this feature using our analytic approximations.

ENUBET: A monitored neutrino beam for high precision cross section measurements

The main source of systematic uncertainty on neutrino cross section measurements at the GeV scale is represented by the poor knowledge of the initial flux. The goal of cutting down this uncertainty to 1% can be achieved through the monitoring of charged leptons produced in association with neutrinos, by properly instrumenting the decay region of a conventional narrow-band neutrino beam. Large angle muons and positrons from kaons are measured by a sampling calorimeter on the decay tunnel walls (tagger), while muon stations after the hadron dump can be used to monitor the neutrino component from pion decays. This instrumentation can provide a full control on both the muon and electron neutrino fluxes at all energies. Furthermore, the narrow momentum width (<10%) of the beam provides a O(10%) measurement of the neutrino energy on an event by event basis, thanks to its correlation with the radial position of the interaction at the neutrino detector. The ENUBET project has been funded by the ERC in 2016 to prove the feasibility of such a monitored neutrino beam and is cast in the framework of the CERN neutrino platform (NP06) and the Physics Beyond Colliders initiative. In our contribution, we summarize the ENUBET design, physics performance and opportunities for its implementation in a timescale comparable with next long baseline neutrino experiments.

Uncertainties in neutrino oscillation parameter sensitivity due to resonance processes at NOνA

The long baseline (LBL) neutrino experiments use heavy nuclear targets for neutrino scattering in which nuclear effects give rise to complications in measuring the neutrino oscillation parameters up to high precision. These nuclear effects are not yet fully understood and therefore need to be quantified as they contribute to the systematic uncertainties. Precision reconstruction of neutrino energy is one of the main components in measuring the oscillation parameters, and it is required that the neutrino energy is reconstructed with very high precision. In this work, we investigate the effects of the resonance (RES) interaction process using two models for carbon target for [Formula: see text] disappearance channel of the NO[Formula: see text]A experiment, on neutrino-nucleus scattering cross-section, events, and neutrino oscillation parameter sensitivity. We also incorporate the realistic detector specifications of NO[Formula: see text]A. To quantify the systematic uncertainties due to RES interactions, we compare the cross-sections, events, and sensitivity analysis for two models of RES processes—Rein–Sehgal (RS) and Berger–Sehgal (BS), and comment on which model produces more precision. We observe that RES processes contribute significantly, and should be included carefully in models while extracting neutrino oscillation parameters.

The Q-Pix pixelated readout concept for future Liquid Argon Time Projection Chambers: status and prospects.

Future long baseline neutrino experiments such as the Deep Underground Neutrino Experiment (DUNE) pose challenges for development of readout techniques for multi-kiloton LAr Time Projection Chambers (TPCs). In contrast to wire/strip anode readout, a pixelated readout eliminates disadvantages such as disambiguation in 2D track reconstruction. The Q-Pix Consortium, established in 2019, is developing a pixelated readout technique for LAr TPCs based on charge-integrate/reset (CIR) circuits. The CIR blocks generate a sequence of reset pulses with time intervals corresponding to fixed charge integrals, allowing signal reconstruction without continuous digitization. The Q-Pix ASIC, intended for reading out pixel arrays, comprises CIR blocks along with digital components responsible for communication and reconfigurable data routing. This work is devoted to give an overview of the Q-Pix project, its status, and prospects, with emphasis on the development and prototyping of the Q-Pix readout ASICs.

Exploring the effects of scalar non standard interactions on the CP violation sensitivity at DUNE

The Neutrino oscillations have provided an excellent opportunity to study new-physics beyond the Standard Model, popularly known as BSM. The unknown couplings involving neutrinos, termed non-standard interactions (NSI), may appear as ‘new-physics’ in different neutrino experiments. The neutrino NSI offers significant effects on neutrino oscillations and CP-sensitivity, which may be probed in various neutrino experiments. The idea of neutrinos coupling with a scalar has evolved recently and looks promising. The effects of scalar NSI may appear as a perturbation to the neutrino mass matrix in the neutrino Hamiltonian. It modifies the neutrino mass matrix and may provide a direct possibility of probing neutrino mass models. As the scalar NSI affects the neutrino mass matrix in the Hamiltonian, its effect is energy independent. Moreover, the matter effects due to scalar NSI scales linearly with the matter density.In this work, we have performed a model-independent study of the effects of scalar NSI at long baseline neutrino experiments, taking DUNE as a case study. We have performed such a thorough study for DUNE for the first time. Various neutrino parameters may get affected due to the inclusion of scalar NSI as it modifies the effective mass matrix of neutrinos. We have explored the impact of scalar NSI in neutrino oscillations and its impact on the measurements of various mixing parameters. We have probed the effects of scalar NSI on different oscillation channels relevant to the experiment. We have also explored the impact of various possible elements in the scalar NSI term on the CP-violation sensitivity at DUNE.

A gas monitoring chamber for high pressure applications

Time Projection Chambers (TPCs) operated at high pressure have become a topic of interest for future long baseline neutrino experiments. Pressurized gas retains the low momentum threshold for particle detection of atmospheric TPCs, but offers a larger target mass for neutrino interactions at the same volume. Operation at high pressure poses several new challenges in safety aspects regarding overpressure and high voltage safety. The presented High Pressure Gas Monitoring Chamber (HPGMC) can be used to study the suitability of various drift gas mixtures up to 10 bar and a maximum field of ∼ 3000 V/cm. A flexible construction makes it possible to exchange parts of the inner detector and to test new technologies. In this work, the construction of a HPGMC and its commissioning using the P10 gas mixture (90 % Ar + 10 % CH4) are presented.

Study of Using Machine Learning for Level 1 Trigger Decision in JUNO Experiment

A study on the use of a machine learning algorithm for the level 1 trigger decision in the JUNO experiment ispresented. JUNO is a medium baseline neutrino experiment in construction in China, with the main goal of determining the neutrino mass hierarchy. A large liquid scintillator (LS)volume will detect the electron antineutrinos issued from nuclear reactors. The LS detector is instrumented by around 20000 large photomultiplier tubes. The hit information from each PMT will be collected into a center trigger unit for the level 1 trigger decision. The current trigger algorithm used to select a neutrino signal event is based on a fast vertex reconstruction. We propose to study an alternative level 1 (L1) trigger in order to achieve a similar performance as the vertex fitting trigger but with less logic resources by using firmware implemented machine learning model at the L1 trigger level. We treat the trigger decision as a classification problem and train a Multi-Layer Perceptron (MLP)model to distinguish the signal events with an energy higher than a certain threshold from noise events. We use JUNO software to generate datasets which include 100K physics events with noise and 100K pure noise events coming from PMT dark noise.For events with energy higher than 100 keV, the L1 trigger based on the converged MLP model can achieve an efficiency higher than 99%. After the training performed on simulations,we successfully implemented the trained model into a Kintex 7FPGA. We present the technical details of the neural network development and training, as well as its implementation in the hardware with the FPGA programming. Finally the performance of the L1 trigger MLP implementation is discussed.

The SuperFGD for the T2K near detector upgrade

Tokai-to-Kamioka (T2K) experiment is a long baseline neutrino experiment in Japan. T2K started data taking in 2010 and obtained a hint on matter-antimatter asymmetry in neutrino oscillations. To provide better sensitivity, T2K plans to have a run extension with higher intensity beam and an upgrade of the T2K near detector. We adopted a novel detector called SuperFGD as an upgraded fully-active target tracker. It consists of about two millions of plastic scintillator cubes and about sixty-thousand readouts through WLS fibers and MPPCs. It provides fine granularity and larger acceptance to suppress systematic error. The new detector will be ready to accept the beam in 2022. Here we report the current status of the new detector.

Performances of two resistive MicroMegas prototypes for the Time Projection Chambers of the T2K Near Detector upgrade

T2K is a long baseline neutrino experiment that has been operating since 2009 providing some of the world-wide leading measurements for neutrino oscillation parameters. An upgrade for the Near Detector, ND280, of T2K has been proposed. It includes the installation of two new Time Projection Chambers (TPC) based on a new read-out technology: the resistive anode MicroMegas (RMM). This technology is expected to reduce the number of electronic channels while maintaining or improving the current ND280 TPCs' bulk MicroMegas perfomance. A series of tests have been performed and further studies are ongoing to validate this approach. Two RMM prototypes were studied in dedicated beamtests. All results so far, some of them still preliminary, indicate that a better performance can be achieved, even with larger pads, thanks to the advantages of RMM.

The shielding design concept for the ISODAR neutrino target

The IsoDAR sterile-neutrino search requires a very high intensity neutrino source. For IsoDAR, this high intensity is produced using the high neutron flux from a 60 MeV, 10 mA proton beam striking a beryllium target that floods a sleeve of highly-enriched Li-7. Through neutron capture the Li-7 is transmuted to Li-8, which beta-decays giving the desired high neutrino flux for very-short baseline neutrino experiments. The target can be placed very close to can existing large neutrino detector, which is typically located deep underground to reduce backgrounds. With such a setup, it is necessary to design a shielding enclosure for the target to prevent neutrons from causing unacceptable activation of the rock walls close to the target. Various materials have been studied including steel to thermalize the high energy neutrons and two new types of concrete developed by Jefferson Laboratory, one very light with shredded plastic aggregate, and the other one enriched with high quantities of boron. The shielding is asymmetrical, having a larger thickness towards the detector in order to suppress the neutron and gamma background in the neutrino detector. Simulation results for rock activation and for detector backgrounds are presented.

Likelihood-free inference of experimental neutrino oscillations using neural spline flows

In machine learning, likelihood-free inference refers to the task of performing an analysis driven by data instead of an analytical expression. We discuss the application of Neural Spline Flows, a neural density estimation algorithm, to the likelihood-free inference problem of the measurement of neutrino oscillation parameters in Long Baseline neutrino experiments. A method adapted to physics parameter inference is developed and applied to the case of the disappearance muon neutrino analysis at the T2K experiment.

Inflation models in the light of self-interacting sterile neutrinos

Short baseline neutrino experiments, like LSND and MiniBooNE experiments, pointed towards the existence of eV mass scale sterile neutrinos. To reconcile sterile neutrinos with cosmology self interaction between sterile neutrinos has been studied. We analysed Planck cosmic microwave background (CMB) data with self-interacting sterile neutrino (SI$\nu$) and study their impact on inflation models. The fit to the CMB data in SI$\nu$ model is as good as the fit to $\Lambda$CDM model. We find that the spectral index ($n_s$) values shift to $0.9361\pm 0.0055$ in SI$\nu$ model. This has significant impact on the validity of different inflation models. For example the Starobinsky and quartic hilltop model, which were allowed within $\Lambda$CDM cosmology, are ruled out. On the other hand some models like natural and Coleman-Weinberg inflation are now favoured. Therefore, the existence of self interacting sterile neutrinos with eV order of mass will play an important role in the selection of correct inflation model.

Bi-probability plots and PMNS compatibility studies with the T2K experiment

Bi-probability plots are a way of displaying the expected P(vμ → ve ) and for long baseline neutrino experiments. They provide an easy visualisation of how δCP and mass hierarchy affect neutrino probabilities, and allow theorists to easily compare their theory predictions to experimental data fit results. We present the electron (anti)neutrino appearance bi-probability plots from the most recent T2K data fit. We also present bi-probability plots from fits with an extra parameter, β, that allows the fit additional freedom compared to the PMNS model and tests the compatibility of the T2K data with the PMNS model.

Large area photo-detection system using 3” PMTs for the Hyper-Kamiokande Outer-Detector

Hyper-Kamiokande, scheduled to begin construction as soon as 2020, is a next generation underground water Cherenkov detector, based on the highly successful Super- Kamiokande experiment. It will serve as a far detector, 295 km away, of a long baseline neutrino experiment for the upgraded J-PARC beam in Japan. It will also be a detector capable of observing — far beyond the sensitivity of the Super-Kamiokande detector — proton decay, atmospheric neutrinos, and neutrinos from astronomical sources.An Outer Detector (OD) consisting of PMTs mounted behind the inner detector PMTs and facing outwards to view the outer shell of the cylindrical tank, would provide topological information to identify interactions originating from particles outside the inner detector. Any optimization would lead to a significant improvement for the physics goals of the experiment, which are the measurement of the CP leptonic phase and the determination of the neutrino mass hierarchy.An original setup using small 3” PMTs is being designed for the Hyper-Kamiokande OD. They would give better redundancy, spatial, and angular resolution, as they would be twice or three times more photosensors that the original 8” design proposal of the experiment, and for a reduce cost. Several 3” PMTs candidates considered for the Hyper-Kamiokande OD have been characterized at Queen Mary University London. They all show a very low dark counts and good collection efficiency, which makes them excellent choice to be used in the experiment.

Recent T2K Neutrino Oscillation Results

T2K is a long baseline neutrino experiment producing a beam of muon neutrinos at the Japan Particle Accelerator Research Centre on the East coast of Japan and measuring their oscillated state 295 km away at the Super Kamiokande detector. Since, 2017 T2K has doubled its data in both neutrino and anti-neutrino beam modes. Coupled with improvements in analysis techniques, this has enabled the experiment to make world-leading measurements of the PMNS oscillation parameters , sin2(θ 23) and the CP violating phase δCP . In particular, the CP conserving values of δCP now appear to be disfavoured at the 95% CL and there are regions of parameter space excluded at the 99.7% CL. This talk will describe these results and the analysis improvements that have enabled them.

The AQUA-RICH project

The AQUA-RICH project, a long baseline and atmospheric neutrino experiment proposed by Tom Ypsilantis during the last decade of the last century, is briefly reviewed. The detector proposal is discussed within the context of the searches for neutrino oscillations at that time and as part of the longstanding seminal ideas and key contributions provided by Tom Ypsilantis in the development of the RICH technique.