Neutrino Oscillation Experiments Research Articles

Recent Progress of Neutrino Oscillation Experiments at J-PARC

Recent Progress of Neutrino Oscillation Experiments at J-PARC

Latest oscillation results from T2K

T2K is a long-baseline neutrino oscillation experiment built to measure νμ disappearance and νe appearance using the J-PARC neutrino beam and the Super-Kamiokande detector. Presented here are the first results in the search for CP violation in neutrino oscillations with a combined analysis of appearance and disappearance channels using data from both neutrino- and antineutrino-mode beams. The data included in this analysis comprises 7.48×1020 protons on target in neutrino mode, giving 37 electron-like and 135 muon-like events at the far detector, and 7.47 × 1020 protons on target in antineutrino mode, giving 4 electron-like and 66 muon-like events. Including a constraint on sin2(2θ13) from reactor measurements, the 90% confidence interval for δCP spans the range [-2.95, -0.44] for the normal mass hierarchy.

Neutrino oscillations in a quantum processor

Quantum computing technologies promise to revolutionize calculations in many areas of physics, chemistry, and data science. Their power is expected to be especially pronounced for problems where direct analogs of a quantum system under study can be encoded coherently within a quantum computer. A first step toward harnessing this power is to express the building blocks of known physical systems within the language of quantum gates and circuits. In this paper, we present a quantum calculation of an archetypal quantum system: neutrino oscillations. We define gate arrangements that implement the neutral lepton mixing operation and neutrino time evolution in two-, three-, and four-flavor systems. We then calculate oscillation probabilities by coherently preparing quantum states within the processor, time evolving them unitarily, and performing measurements in the flavor basis, with close analogy to the physical processes realized in neutrino oscillation experiments, finding excellent agreement with classical calculations. We provide recipes for modeling oscillation in the standard three-flavor paradigm as well as beyond-standard-model scenarios, including systems with sterile neutrinos, non-standard interactions, Lorentz symmetry violation, and anomalous decoherence.

Performances of a resistive Micromegas module for the Time Projection Chambers of the T2K Near Detector upgrade

An upgrade of the Near Detector of the T2K long baseline neutrino oscillation experiment, ND280, has been proposed. This upgrade will include two new Time Projection Chambers, each equipped with 16 resistive Micromegas modules for gas amplification. A first prototype of resistive Micromegas has been designed, built, installed in the HARP field cage, and exposed to a beam of charged particles at CERN. The data have been used to characterize the performances of the resistive Micromegas module. A spatial resolution of 300 μm and a deposited energy resolution of 9% were observed for horizontal electrons crossing the TPCs at 30 cm from the anode. Such performances fully satisfy the requirements for the upgrade of the ND280 TPC.

Impact of cross-sectional uncertainties on DUNE sensitivity due to nuclear effects

In neutrino oscillation experiments precise measurement of neutrino oscillation parameters is of prime importance as well as a challenge. To improve the statistics, presently running and proposed experiments are using heavy nuclear targets. These targets introduce nuclear effects and the quantification of these effects on neutrino oscillation parameters will be decisive in the prediction of neutrino oscillation physics. Limited understanding of neutrino nucleus interactions and inaccurate reconstruction of neutrino energy causes uncertainty in the cross section. The error in the determination of cross section which contributes to systematic error introduces error in the neutrino mixing parameters that are determined by these experiments. In this work we focus on the variation in the predictions of DUNE potential, arising due to systematic uncertainties, using two different event generators-GENIE and GiBUU. These generators have different and independent cross-section models. To check the DUNE potential with the two generators we have checked the sensitivity studies of DUNE for CP violation, mass hierarchy and octant degeneracy.

Neutrino non-standard interactions: A status report

This report summarizes the present status of neutrino non-standard interactions (NSI). After a brief overview, several aspects of NSIs are discussed, including connection to neutrino mass models, model-building and phenomenology of large NSI with both light and heavy mediators, NSI phenomenology in both short- and long-baseline neutrino oscillation experiments, neutrino cross-sections, complementarity of NSI with other low- and high-energy experiments, fits with neutrino oscillation and scattering data, DUNE sensitivity to NSI, effective field theory of NSI, as well as the relevance of NSI to dark matter and cosmology. We also discuss the open questions and interesting future directions that can be pursued by the community at large. This report is based on talks and discussions during the Neutrino Theory Network NSI workshop held at Washington University in St.~Louis from May 29-31, 2019

A model for neutrino anomalies and IceCube data

We interpret the neutrino anomalies in neutrino oscillation experiments and the high energy neutrino events at IceCube in terms of neutrino oscillations in an extension of the standard model where three sterile neutrinos are introduced so as to make two light neutrinos to be Pseudo-Dirac particles and a light neutrino to be a Majorana particle. Our model is different from the so-called 3 + n model with n sterile neutrinos suggested to interpret short baseline anomalies in terms of neutrino oscillations. While the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix in 3 + n model is simply extended to n × n unitary matrix, the neutrino mixing matrix in our model is parameterized so as to keep the 3 × 3 PMNS mixing matrix for three active neutrinos unitary. There are also no flavor changing neutral current interactions leading to the conversion of active neutrinos to sterile ones or vice versa. We derive new forms of neutrino oscillation probabilities containing the new interference between the active and sterile neutrinos which are characterized by additional new parameters ∆m2 and θ. Based on the new formulae derived, we show how the short baseline neutrino anomalies can be explained in terms of oscillations, and study the implication of the high energy neutrino events detected at IceCube on the probe of pseudo-Dirac neutrinos. New phenomenological effects attributed to the existence of the sterile neutrinos are discussed.

Precision measurements on \u03b4CP in MOMENT

As it is very promising to expect a discovery of CP violation in the leptonic sector, the precision measurement of the Dirac CP phase δCP is going to be one of the key interests in the future neutrino oscillation experiments. In this work, we examine the physics reach of the proposed medium baseline muon decay experiment MOMENT. In order to identify potential bottlenecks and opportunities to improve CP precision in MOMENT, we investigate the effect of statistical error, systematic uncertainties, fraction of the muon beam polarity, and adjusting the baseline length to match the first or second oscillation maximum on the precision measurement of δCP. We also simulate superbeam experiments T2K, NOνA, T2HK, DUNE and T2HKK in comparison and complementary to MOMENT. To reach the precision of δCP at 12° or better at 1 σ confidence level, we find it sufficient to combine the data of MOMENT, DUNE and T2HK.

Cosmological constraints on invisible neutrino decays revisited

Invisible neutrino decay modes are difficult to target at laboratory experiments, and current bounds on such decays from solar neutrino and neutrino oscillation experiments are somewhat weak. It has been known for some time that Cosmology can serve as a powerful probe of invisible neutrino decays. In this work, we show that in order for Big Bang Nucleosynthesis to be successful, the invisible neutrino decay lifetime is bounded to be $\tau_\nu > 10^{-3}\,\text{s}$ at 95\% CL. We revisit Cosmic Microwave Background constraints on invisible neutrino decays, and by using Planck2018 observations we find the following bound on the neutrino lifetime: $\tau_\nu > (1.3-0.3)\times 10^{9}\,\text{s} \, \left({m_\nu}/{ 0.05\,\text{eV} }\right)^3$ at $95\%$ CL. We show that this bound is robust to modifications of the cosmological model, in particular that it is independent of the presence of dark radiation. We find that lifetimes relevant for Supernova observations ($\tau_\nu \sim 10^{5}\,\text{s}\, \left({m_\nu}/{ 0.05\,\text{eV} }\right)^3$) are disfavoured at more than $5\,\sigma$ with respect to $\Lambda$CDM given the latest Planck CMB observations. Finally, we show that when including high-$\ell$ Planck polarization data, neutrino lifetimes $\tau_\nu = (2-16)\times 10^{9}\,\text{s} \, \left({m_\nu}/{ 0.05\,\text{eV} }\right)^3$ are mildly preferred -- with a 1-2 $\sigma$ significance -- over neutrinos being stable.

Electroweak pion production on nuclei within the extended factorization scheme

We have applied the extended factorization scheme to investigate the electroweak pion production on nuclei. The ANL-Osaka model, which was obtained by analyzing the data of $\pi N$, $\gamma N$, $N(e,e'\pi)$ and $N(\nu,\mu\,\pi) $ reactions up to invariant mass $W=$ 2 GeV, is used to generate the matrix elements of current operators relevant to pion-production off the nucleon. Medium effects on the $\Delta$ (1232) component of meson-exchange current are included by using a $\Delta$-nucleus potential determined from the previous $\Delta$-hole model studies of pion-nucleus reactions. Nuclear correlations in the initial target state and in the spectator system(s) are modeled using realistic hole spectral functions. As a first step, we show that the data of $^{12}$C$(e,e')$ up to the $\Delta$ (1232) region can be described reasonably well. The interplay between the pion production and two-body meson-exchange mechanisms is shown to be essential in improving the agreement with the data in the ``dip'' region, between the quasielastic and the $\Delta$ (1232) peaks. Predictions for $^{12}$C$(\nu,\mu\,\pi)$ have also been made. They can be used to estimate pion-emission rates in neutrino-nucleus cross section, which constitutes an important systematic uncertainty to the reconstructed neutrino energy. With further improvements of the Metropolis Monte-Carlo techniques to account for final states comprised of more than two particles, our approach can be employed up to $W=$ 2 GeV, where two-pion production and higher mass nucleon resonances must be included for analyzing the data from accelerator-based neutrino-oscillation experiments.

Heavy Neutrinos at Large Colliders

In this work we discuss the state of the art of the heavy neutrinos at colliders. The neutrinos in the Standard Model (SM) are considered to be massless which is in contradiction with the evidence from the neutrino oscillations experiments. These cosmological observations established that at least two SM neutrinos have non-zero masses and that individual lepton number is violated. Therefore a strong conclusive first evidence of new physics caused by the neutrino mass mechanism is emerged. In this work we discuss the collider phenomenology of neutrino mass models at the existing (LHC) and next generation large colliders (FCC: ee, hh, eh, ILC and CePC) at different high synergies. It is naturally known that colliders are not sensitive to the SM light neutrinos; however the production of heavy neutrinos is very possible to be detected; giving rise to several signal processes which are categorised by different final state topologies according to theirs physics interests. We will present the state of the art of the heavy neutrinos generated with radiative neutrino mass models and their experimental searches; mainly for Majorana neutrino signals allowing for probing the nature of the Dark Matter candidates at high energy colliders. The focus will be on the well-motivated neutrino mass models which provide an elegant framework to explore new directions in Dark Matter phenomenology at the TeV scale and the future experimental prospects.

Latest Results from Neutrino Oscillation Experiment Daya Bay

The Daya Bay Reactor Neutrino Experiment was designed to measure Θ13, the smallest mixing angle in the three-neutrino mixing framework, with unprecedented precision. The experiment consists of eight identically designed detectors placed underground at different baselines from three pairs of nuclear reactors in South China. Since Dec. 2011, the experiment has been running stably for more than 7 years, and has collected the largest reactor antineutrino sample to date. Daya Bay greatly improved the precision on Θ13 and made an independent measurement of the effective mass splitting in the electron antineutrino disappearance channel. Daya Bay also performed a number of other precise measurements such as a high-statistics determination of the absolute reactor antineutrino flux and the spectrum evolution, as well as a search for the sterile neutrino mixing, among others. The most recent results from Daya Bay are discussed in this paper, as well as the current status and future prospects of the experiment.

Results on Neutrino and Antineutrino Oscillations from the NOvA Experiment

NOvA is a two-detector long-baseline neutrino oscillation experiment using Fermilab’s 700 kW NuMI muon neutrino beam. With a total exposure of 8.85×1020 +12.33×1020 protons on target delivered to NuMI in the neutrino + antineutrino beam mode (78% more antineutrino data than in 2018), the experiment has made a 4.4q-significant observation of the ve appearance in a vм beam, measured oscillation parameters |Δm232|, sin2O23, and excluded most values near бCP = п/2 for the inverted neutrino mass hierarchy by more than 3q.

Confronting tridirect CP -symmetry models with neutrino oscillation experiments

Tridirect $CP$ symmetry is an economical neutrino model building paradigm, and it allows for the description of neutrino masses, mixing angles, and $CP$ violation phases in terms of four free parameters. The viability of a class of tridirect $CP$ models is examined with a comprehensive simulation of current and future neutrino oscillation experiments. The full parameter space of four independent parameters is carefully scanned, and the problem of parameter degeneracy appears for the constraints from one group of neutrino oscillation experiments. Two benchmark models which are promising from a model building point of view are also examined. Complementary roles from accelerator neutrino experiments (e.g., T2HK and DUNE) and reactor neutrino experiments (e.g., JUNO) are crucial to break the degeneracy and nail down the fundamental neutrino mixing parameters of the underlying theory.

Pati-Salam unification with a spontaneous CP violation

Recent neutrino oscillation experiments suggest that the PMNS matrix in the lepton sector has a $CP$ violating phase as the CKM matrix in the quark sector. However, origin of these phases in both matrices are not clarified by now. Although complex Yukawa couplings could induce these phases, they remain as free parameters of the model even in that case. If the $CP$ symmetry is considered to be spontaneously broken, they are expected to be determined by some physics at a much lower energy scale than the Planck scale. We study such a possibility in a framework of Pati-Salam type unification. We also discuss other phenomenological issues in it.

Z′s in neutrino scattering at DUNE

Novel leptophilic neutral currents can be tested at upcoming neutrino oscillation experiments using two complementary processes, neutrino trident production and neutrino-electron ($\nu-e$) elastic scattering. Considering generic anomaly-free $U(1)$ extensions of the Standard Model, we discuss the characteristics of $\nu-e$ scattering as well as $e^+e^-$ and $\mu^+\mu^-$ trident production at the DUNE near detector in the presence of such BSM scenarios. We then determine the sensitivity of DUNE in constraining the well-known $L_e - L_\mu$ and $L_\mu - L_\tau$ models. We conclude that DUNE will be able to probe these leptophilic models with unprecedented sensitivity, covering unproved explanations of the $(g-2)_\mu$ discrepancy.

CP symmetries as guiding posts: Revamping tribimaximal mixing. II.

In this follow up of arXiv:1812.04663 we analyze the generalized CP symmetries of the charged lepton mass matrix compatible with the complex version of the Tri-Bi-Maximal (TBM) lepton mixing pattern. These symmetries are used to `revamp' the simplest TBM \textit{Ansatz} in a systematic way. Our generalized patterns share some of the attractive features of the original TBM matrix and are consistent with current oscillation experiments. We also discuss their phenomenological implications both for upcoming neutrino oscillation and neutrinoless double beta decay experiments.

Neutron measurements from antineutrino hydrocarbon reactions

Charged-current anti-neutrino interactions on hydrocarbon scintillator in the MINERvA detector are used to study activity from their final-state neutrons. To ensure that most of the neutrons are from the primary interaction, rather than hadronic reinteractions in the detector, the sample is limited to momentum transfers below 0.8 GeV/c. From 16,129 interactions, 15,246 neutral particle candidates are observed. The reference simulation predicts 64\% of these candidates are due to neutrons from the anti-neutrino interaction directly, but also overpredicts the number of candidates by 15\% overall, which is beyond the standard uncertainty estimates for models of neutrino interactions and neutron propagation in the detector. Using the measured distributions for energy deposition, time of flight, position, and speed, we explore the sensitivity to the details those two aspects of the models. We also use multiplicity distributions to evaluate the presence of a two-nucleon knockout process. These results provide critical new information toward a complete description of the hadronic final state of neutrino interactions, which is vital to neutrino oscillation experiments.

Polarization of τ in quasielastic (anti)neutrino scattering: The role of spectral functions

We present a study of the $\ensuremath{\tau}$ polarization in charged-current quasielastic (anti)neutrino-nucleus scattering. The spectral function formalism is used to compute the differential cross section and the polarization components for several kinematical setups, relevant for neutrino-oscillation experiments. The effects of the nuclear corrections in these observables are investigated by comparing the results obtained using two different realistic spectral functions, with those deduced from the relativistic global Fermi gas model, where only statistical correlations are accounted for. We show that the spectral functions, although they play an important role when predicting the differential cross sections, produce much less visible effects on the polarization components of the outgoing $\ensuremath{\tau}$.

Constraining sterile neutrino cosmology with terrestrial oscillation experiments

We explore the complementarity between terrestrial neutrino oscillation experiments and astrophysical/cosmological measurements in probing the existence of sterile neutrinos. We find that upcoming accelerator neutrino experiments will not improve on constraints by the time they are operational, but that reactor experiments can already probe parameter space beyond the reach of Planck. We emphasize the tension between cosmological experiments and reactor antineutrino experiments and enumerate several possibilities for resolving this tension.