Neutrino CP Violation Research Articles

Study of quantum decoherence at the Protvino to ORCA experiment

Protvino to ORCA (oscillation research with cosmics in the abyss) (P2O) is an upcoming neutrino oscillation experiment with a very long baseline of 2595 km. Because of the substantial baseline, this experiment provides a unique opportunity to study the Earth matter effects over very large distances. This makes it a suitable experiment to investigate the environmental decoherence in neutrino oscillations, where the neutrino system could interact with a stochastic environment and lead to a loss in the coherence of neutrino states. In this work, we consider an open quantum system framework to simulate the neutrino oscillations in the P2O experiment and obtain bounds on the decoherence parameters in different phenomenological models. Here, we also consider that the decoherence parameter Γ depends on neutrino energy Eν as Γjk(Eν)=Γ0(EνE0)n. Furthermore, assuming the presence of decoherence in nature, we study the effect of it on the determination of neutrino mass hierarchy and CP violation at the P2O experiment. Published by the American Physical Society 2024

Collimated muon beam proposal for probing neutrino charge-parity violation

AbstractThe phenomenon of neutrino oscillation is of great theoretical and experimental interest for our understand of the nature of the neutrino and its implication for physics beyond the standard Model. Currently available neutrino oscillation experiments can already constrain neutrino mixing parameters with a confidence level up to 3 standard deviations (σ). However, it remains challenging to provide a deterministic constraint on the Charge-Parity (CP) violation phase of the neutrino mixing matrix. Here, we propose an experimental setup that exploits collimated muon beams to probe neutrino CP-violation. In our proposed acceleration experiment, a 45 GeV positron source with additional muon collimation, interfaces with near-future neutrino detectors like DUNE and T2K, to probe neutrino CP-violation phase with a significantly higher sensitivity than obtained with the neutrino detectors alone, and to determine tau neutrino properties. Simulations estimate the collection of 104 tau (anti-) neutrino in 5 years, and a sensitivity of over 7 standard deviations for δCP = ∣π/2∣ in 5 years. Collecting ντ appearance events from μ− and μ+ beams over 10 years can attain a 3-4 standard deviation sensitivity. This proposal may serve as a tau factory.

Trimaximal neutrino mixing from scotogenic A4 family symmetry

We propose a flavor theory of leptons implementing an A4 family symmetry. Our scheme provides a simple way to derive trimaximal neutrino mixing from first principles, leading to simple and testable predictions for neutrino mixing and CP violation. Dark matter mediates neutrino mass generation, as in the simplest scotogenic model.

Radiative decays of charged leptons as constraints of unitarity polygons for active-sterile neutrino mixing and CP violation

We calculate the rates of radiative beta ^- rightarrow alpha ^- + gamma decays for (alpha , beta ) = (e, mu ), (e, tau ) and (mu , tau ) by taking the unitary gauge in the (3+n) active-sterile neutrino mixing scheme, and make it clear that constraints on the unitarity of the 3times 3 Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrix U extracted from beta ^- rightarrow alpha ^- + gamma decays in the minimal unitarity violation scheme differ from those obtained in the canonical seesaw mechanism with n heavy Majorana neutrinos by a factor 5/3. In such a natural seesaw case we show that the rates of beta ^- rightarrow alpha ^- + gamma can be used to cleanly and strongly constrain the effective apex of a unitarity polygon, and compare its geometry with the geometry of its three sub-triangles formed by two vectors U^{}_{alpha i} U^*_{beta i} and U^{}_{alpha j} U^*_{beta j} (for i ne j) in the complex plane. We find that the areas of such sub-triangles can be described in terms of the Jarlskog-like invariants of CP violation {{mathcal {J}}}^{ij}_{alpha beta }, and their small differences signify slight unitarity violation of the PMNS matrix U.

Lepton flavor mixing and CP violation in the minimal type-(I+II) seesaw model with a modular A4 symmetry

In this paper, we study the implications of the modular A4 flavor symmetry in constructing a supersymmetric minimal type-(I+II) seesaw model, in which only one right-handed neutrino and two Higgs triplets are introduced to account for the tiny neutrino masses, flavor mixing and CP violation. We consider the most economical case where the right-handed neutrino and the Higgs triplets in this model are assigned into the trivial one-dimensional irreducible representation of the modular group A4, and all the modular forms are with the lowest weights they can take. We find that the octant of the mixing angle θ23 strongly depends on the hierarchy of free model parameters in the charged-lepton sector. We also show that the neutrino mass matrix can possess an approximate μ−τ reflection symmetry for some specific values of free parameters. Moreover, our model predicts relatively large masses of three light neutrinos, thus can be easily tested in future neutrino experiments.

Numerical analysis of neutrino physics within a high-scale supersymmetry model via machine learning

A machine learning method is applied to analyze lepton mass matrices numerically. The matrices were obtained within a framework of high-scale supersymmetry (SUSY) and a flavor symmetry, which are too complicated to be solved analytically. In this numerical calculation, the heuristic method in machine learning is adopted. Neutrino masses, mixings, and CP violation are obtained. It is found that neutrinos are normally ordered and the favorable effective Majorana mass is about [Formula: see text].

Theia: an advanced optical neutrino detector

New developments in liquid scintillators, high-efficiency, fast photon detectors, and chromatic photon sorting have opened up the possibility for building a large-scale detector that can discriminate between Cherenkov and scintillation signals. Such a detector could reconstruct particle direction and species using Cherenkov light while also having the excellent energy resolution and low threshold of a scintillator detector. Situated deep underground, and utilizing new techniques in computing and reconstruction, this detector could achieve unprecedented levels of background rejection, enabling a rich physics program spanning topics in nuclear, high-energy, and astrophysics, and across a dynamic range from hundreds of keV to many GeV. The scientific program would include observations of low- and high-energy solar neutrinos, determination of neutrino mass ordering and measurement of the neutrino CP-violating phase delta , observations of diffuse supernova neutrinos and neutrinos from a supernova burst, sensitive searches for nucleon decay and, ultimately, a search for neutrinoless double beta decay, with sensitivity reaching the normal ordering regime of neutrino mass phase space. This paper describes Theia, a detector design that incorporates these new technologies in a practical and affordable way to accomplish the science goals described above.

Closing in on neutrino CP violation

Closing in on neutrino <em>CP</em> violation

Neutrino CP Violation with the European Spallation Source neutrino Super Beam project

After measuring in 2012 a relatively large value of the neutrino mixing angle θ 13, the door is now open to observe for the first time a possible CP violation in the leptonic sector. The measured value of θ 13 also privileges the 2nd oscillation maximum for the discovery of CP violation instead of the usually used 1st oscillation maximum. The sensitivity at this 2nd oscillation maximum is about three times higher than for the 1st oscillation maximum inducing a lower influence of systematic errors. Going to the 2nd oscillation maximum necessitates a very intense neutrino beam with the appropriate energy. The world’s most intense pulsed spallation neutron source, the European Spallation Source (ESS), will have a proton linac with 5 MW power and 2 GeV energy. This linac, under construction, also has the potential to become the proton driver of the world’s most intense neutrino beam with very high potential to discover a neutrino CP violation. The physics performance of that neutrino Super Beam in conjunction with a megaton underground Water Cherenkov neutrino detector installed at a distance of about 500 km from ESS has been evaluated. In addition, the choice of such detector will extent the physics program to proton–decay, atmospheric neutrinos and astrophysics searches. The ESS proton linac upgrades, the accumulator ring needed for proton pulse compression, the target station optimization and the physics potential are described. In addition to neutrinos, this facility will also produce at the same time a copious number of muons which could be used by a muon collider. The ESS neutron facility will be fully ready by 2023 at which moment the upgrades for the neutrino facility could start.

Covert symmetries in the neutrino mass matrix

The flavour neutrino puzzle is often addressed by considering neutrino mass matrices m with a certain number of vanishing entries (mij = 0 for some values of the indices), since a reduction in the number of free parameters increases the predictive power. Symmetries that can enforce textures zero can also enforce a more general type of conditions f(mij) = 0 with f some function of the matrix elements mij. In this case m can have all entries non-vanishing with no reduction in its predictive power. We classify all generation-dependent U(1) symmetries which, in the presence of two leptonic Higgs doublets, can reduce the number of independent high-energy parameters of type-I seesaw to the minimum number compatible with non-vanishing neutrino mixings and CP violation. These symmetries are broken above the scale where the effective operator is generated and can thus remain covert, in the sense that no explicit evidence of the symmetry can be read off the neutrino mass matrix, and different symmetries can give rise to the same low-energy structure. We find that only two cases are viable: one yields a structure with two zero-textures already considered in the literature, the other has no zero-textures and has never been considered before. It predicts normal ordering, a lightest neutrino mass ∼ 10 meV, a Dirac phase δ ∼ frac{3pi }{2} and definite values for the Majorana phases.

Electron versus Muon Neutrino Induced Cross Sections in Charged Current Quasielastic Processes.

Differences between ν_{e} and ν_{μ} quasielastic cross sections are essential in neutrino oscillation analyses and CP violation searches for experiments such as DUNE and T2HK. The ratio of these is however poorly known experimentally and for certain kinematic regions theoretical models give contradictory answers. We use two independent mean-field based models to investigate this ratio using ^{40}Ar and ^{12}C targets. We demonstrate that a proper treatment of the final nucleon's wave function confirms the dominance of ν_{μ} over ν_{e} induced cross sections at forward lepton scattering.

Highly predictive and testable A4 flavor model within type-I and II seesaw framework and associated phenomenology

We investigate neutrino mass model based on A4 discrete flavor symmetry in type-I+II seesaw framework. The model has imperative predictions for neutrino masses, mixing and CP violation testable in the current and upcoming neutrino oscillation experiments. The important predictions of the model are: normal hierarchy for neutrino masses, a higher octant for atmospheric angle (θ23>45°) and near-maximal Dirac-type CP phase (δ≈π/2 or 3π/2) at 3σ C.L. These predictions are in consonance with the latest global-fit and results from Super-Kamiokande (SK), NOνA and T2K. Also, one of the important feature of the model is the existence of a lower bound on effective Majorana mass, |Mee|≥0.047 eV (at 3σ) which corresponds to the lower part of the degenerate spectrum and is within the sensitivity reach of the neutrinoless double beta decay (0νββ) experiments.

Search for CP Violation in Neutrino and Antineutrino Oscillations by the T2K Experiment with 2.2×10^{21} Protons on Target.

The T2K experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and antineutrino beams. With an exposure of 14.7(7.6)×10^{20} protons on target in the neutrino (antineutrino) mode, 89 ν_{e} candidates and seven anti-ν_{e} candidates are observed, while 67.5 and 9.0 are expected for δ_{CP}=0 and normal mass ordering. The obtained 2σ confidence interval for the CP-violating phase, δ_{CP}, does not include the CP-conserving cases (δ_{CP}=0, π). The best-fit values of other parameters are sin^{2}θ_{23}=0.526_{-0.036}^{+0.032} and Δm_{32}^{2}=2.463_{-0.070}^{+0.071}×10^{-3} eV^{2}/c^{4}.

Zooming in on neutrino oscillations with DUNE

We examine the capabilities of the DUNE experiment as a probe of the neutrino mixing paradigm. Taking the current status of neutrino oscillations and the design specifications of DUNE, we determine the experiment's potential to probe the structure of neutrino mixing and CP violation. We focus on the poorly determined parameters $\theta_{23}$ and $\delta_{CP}$ and consider both two and seven years of run. We take various benchmarks as our true values, such as the current preferred values of $\theta_{23}$ and $\delta_{CP}$, as well as several theory-motivated choices. We determine quantitatively DUNE's potential to perform a precision measurement of $\theta_{23}$, as well as to test the CP violation hypothesis in a model-independent way. We find that, after running for seven years, DUNE will make a substantial step in the precise determination of these parameters, bringing to quantitative test the predictions of various theories of neutrino mixing.

Neutrino CP violation and sign of baryon asymmetry in the minimal seesaw model

We discuss the correlation between the CP violating Dirac phase of the lepton mixing matrix and the cosmological baryon asymmetry based on the leptogenesis in the minimal seesaw model with two right-handed Majorana neutrinos and the trimaximal mixing for neutrino flavors. The sign of the CP violating Dirac phase at low energy is fixed by the observed cosmological baryon asymmetry since there is only one phase parameter in the model. According to the recent T2K and NOνA data of the CP violation, the Dirac neutrino mass matrix of our model is fixed only for the normal hierarchy of neutrino masses.

Neutrino mixing and leptonic CP violation from S4 flavour and generalised CP symmetries

We consider a class of models of neutrino mixing with S4 lepton flavour symmetry combined with a generalised CP symmetry, which are broken to residual Z2 and Z2 × HCPν symmetries in the charged lepton and neutrino sectors, respectively, HCPν being a remnant CP symmetry of the neutrino Majorana mass term. In this set-up the neutrino mixing angles and CP violation (CPV) phases of the neutrino mixing matrix depend on three real parameters — two angles and a phase. We classify all phenomenologically viable mixing patterns and derive predictions for the Dirac and Majorana CPV phases. Further, we use the results obtained on the neutrino mixing angles and leptonic CPV phases to derive predictions for the effective Majorana mass in neutrinoless double beta decay.

The ESS neutrino facility for CP violation discovery

The comparatively large value of the neutrino mixing angle θ13 measured in 2012 by neutrino reactor experiments has opened the possibility to observe for the first time CP violation in the leptonic sector. The measured value of θ13 also privileges the 2nd oscillation maximum for the discovery of CP violation instead of the usually used 1st oscillation maximum. The sensitivity at the 2nd oscillation maximum is about three times higher than at the 1st oscillation maximum implying a significantly lower sensitivity to systematic errors. Measuring at the 2nd oscillation maximum necessitates a very intense neutrino beam with the appropriate energy. The world’s most intense pulsed spallation neutron source, the European Spallation Source, has a proton linac with 5 MW power and 2 GeV energy. This linac also has the potential to become the proton driver of the world’s most intense neutrino beam with very high potential for the discovery of neutrino CP violation. The physics performance of that neutrino Super Beam in conjunction with a megaton Water Cherenkov neutrino detector installed ca 1000 m down in a mine at a distance of about 500 km from ESS has been evaluated. In addition, the use of such a detector will make it possible to extent the physics program to proton decay, atmospheric neutrinos and astrophysics searches. The ESS proton linac upgrade, the accumulator ring needed for proton pulse compression, the target station optimization and the physics potential are described. In addition to the production of neutrinos, this facility will also be a copious source of muons which could be used to feed a low energy nuSTORM facility, a future neutrino factory or a muon collider. The ESS linac, under construction, will reach full operation at 5 MW by 2023 after which the upgrades for the neutrino facility could start.

A hybrid setup for fundamental unknowns in neutrino oscillations using T2HK (\u03bd) and \u03bc-DAR left(overline{nu}right)

Neutrino mass hierarchy, CP-violation, and octant of θ23 are the fundamental unknowns in neutrino oscillations. In order to address all these three unknowns, we study the physics reach of a setup, where we replace the antineutrino run of T2HK with antineutrinos from muon decay at rest (μ-DAR). This approach has the advantages of having higher statistics in both neutrino and antineutrino modes, and lower beam-on backgrounds for antineutrino run with reduced systematics. We find that a hybrid setup consisting of T2HK (ν) and μ-DAR left(overline{nu}right) in conjunction with full exposure from T2K and NOνA can resolve the issue of mass hierarchy at greater than 3σ C.L. irrespective of the choices of hierarchy, δCP, and θ23. This hybrid setup can also establish the CP-violation at 5σ C.L. for ∼ 55% choices of δCP, whereas the same for conventional T2HK left(nu + overline{nu}right) setup along with T2K and NOνA is around 30%. As far as the octant of θ23 is concerned, this hybrid setup can exclude the wrong octant at 5σ C.L. if θ23 is at least 3° away from maximal mixing for any δCP.

Exponential parameterization of neutrino mixing matrix with account of CP-violation data

The exponential parameterization of Pontecorvo-Maki-Nakagawa-Sakata mixing matrix for neutrino is discussed. The exponential form allows easy factorization and separate analysis of the CP-violating and Majorana terms. Based upon the recent experimental data on the neutrino mixing, the values for the exponential parameterization matrix for neutrinos are determined. The matrix entries for the pure rotational part in charge of the mixing without CP-violation are derived. The complementarity hypothesis for quarks and neutrinos is demonstrated. The comparison of the results, based on most recent and on old data is held. The CP-violating parameter value is estimated, based on the so far imprecise experimental indications, regarding CP-violation for neutrinos. The unitarity of the exponential parameterisation and the CP-violating term transform is confirmed. The transform of the neutrino mass state vector by the exponential matrix with account for CP-violation is shown.

Hyper-Kamiokande: a Next Generation Neutrino Observatory to search for CP Violation in the Lepton Sector

Hyper-Kamiokande (HK), a proposed one-megaton water Cherenkov detector to be built in Japan, is the logical continuation of the highly successful program of neutrino (astro)physics and proton decay using the water Cherenkov technique. HK will search for CP violation in neutrino oscillations associated with the irreducible phase δ in the lepton mixing matrix using the neutrino beam produced at J-PARC. With an exposure of 7.5 MW × 107sec, δ can be measured to better than 19 degrees at all values, and CP violation can be detected with more than 3 σ significance for 76% of values of delta. In addition to the search for neutrino CP violation, HK will offer a broad program of neutrino astrophysics, including continued studies of atmospheric neutrinos and the detection of neutrinos produced in supernovae as far as the Andromeda Galaxy. It will also extend the sensitivity to proton decay, an incontrovertible sign of new physics and grand unification, by an order of magnitude.