Type Of Neutrino Mass Hierarchy Research Articles

Charged lepton flavor violating processes and scalar leptoquark decay branching ratios in the colored Zee-Babu model

We consider a neutrino mass generating model which employs a scalar leptoquark, $\Delta$, and a scalar diquark, $S$. The new scalars $\Delta$ and $S$ carry the standard model $SU(3)_c\times SU(2)_L\times U(1)_Y$ quantum numbers $(3,1,-1/3)$ and $(6,1,-2/3)$, respectively. The neutrino masses are generated at the two-loop level, as in the Zee-Babu model\cite{Zee-Babu}, and $\Delta/S$ plays the role of the doubly/singly charged scalar in the Zee-Babu model. With a moderate working assumption that the magnitudes of the six Yukawa couplings between $S$ and the down-type quarks are of the same order, strong connections are found between the neutrino masses and the charged lepton flavor violating processes. In particular, we study $Z\rightarrow \overline{l} l'$, and $l\rightarrow l' \gamma$ and find that some portions of the parameter space of this model are within the reach of the planned charged lepton flavor violating experiments. Interesting lower bounds are predicted that $B(Z\rightarrow \overline{l} l')\gtrsim 10^{-16}-10^{-14}(10^{-14})\times(1\mbox{TeV}\cdot m_S/7 m_\Delta^2)^2$ and $B(l\rightarrow l' \gamma)\gtrsim 10^{-17}-10^{-16}(10^{-18}-10^{-16})\times(1 \mbox{TeV}\cdot m_S/7 m_\Delta^2)^2$ for neutrino masses being the normal(inverted) hierarchical pattern. The type of neutrino mass hierarchy could also be determined by measuring the charged lepton flavor violating double ratios. Moreover, definite leptoquark decay branching ratios are predicted when there is no Yukawa interaction between the right-handed fermions and $\Delta$ ( the branching fraction of $\Delta$ to a charged lepton and a quark is 50\%), which could help refine the collider search limit on the scalar leptoquark mass.

Double Beta Decay Experiments: Beginning of a New Era

Interest in neutrinoless double beta decay (0νββ) has seen a significant renewal in the recent 10 years after evidence for neutrino oscillations was obtained from the results of atmospheric, solar, reactor, and accelerator neutrino experiments. These results are impressive proof that neutrinos have a nonzero mass. The detection and study of 0νββ decay may clarify the following problems of neutrino physics: (i) lepton number non-conservation, (ii) neutrino nature: whether the neutrino is a Dirac or a Majorana particle, (iii) absolute neutrino mass scale, (iv) the type of neutrino mass hierarchy (normal, inverted, or quasidegenerate), and (v) CP violation in the lepton sector (measurement of the Majorana CP-violating phases).

A combined beta-beam and electron capture neutrino experiment

The next generation of long baseline neutrino experiments will aim at determining the value of the unknown mixing angle, θ13, the type of neutrino mass hierarchy and the presence of CP-violation in the lepton sector. Beta-beams and electron capture experiments have been studied as viable candidates for long baseline experiments. They use a very clean electron neutrino beam from the β-decays or electron capture decays of boosted ions. In the present article we consider an hybrid setup which combines a beta-beam with an electron capture beam by using boosted Ytterbium ions. We study the sensitivity to the CP-violating phase δ and the θ13 angle, the CP-discovery potential and the reach to determine the type of neutrino mass hierarchy for this type of long baseline experiment. The analysis is performed for different neutrino beam energies and baselines. Finally, we also discuss how the results would change if a better knowledge of some of the assumed parameters was achieved by the time this experiment could take place.

An intermediate γ beta-beam neutrino experiment with long baseline

In order to address some fundamental questions in neutrino physics a wide, future programme of neutrino oscillation experiments is currently under discussion. Among those, long baseline experiments will play a crucial role in providing information on the value of θ13, the type of neutrino mass ordering and on the value of the CP-violating phase δ, which enters in 3-neutrino oscillations. Here, we consider a beta-beam setup with an intermediate Lorentz factor γ = 450 and a baseline of 1050 km. This could be achieved in Europe with a beta-beam sourced at CERN to a detector located at the Boulby mine in the United Kingdom. We consider a neutrino run alone and show that, by exploiting the oscillatory pattern of the signal, a very good sensitivity to CP-violation and the type of hierarchy can be reached. We analyse the physics potential of this setup in detail and study two different exposures (1 × 1021 and 5 × 1021 ions-kton-years). In both cases, we find that the type of neutrino mass hierarchy could be determined at 99% CL, for all values of δ, for sin 22θ13>0.03. In the high-exposure scenario, we find that the value of the CP-violating phase δ could be measured with a 99% CL error of ~ 20o if sin 22θ13>10−3, with some sensitivity down to values of sin 22θ13 10−4. The ability to determine the octant of θ23 is also studied, and good prospects are found for the high-statistics scenario.

Probing late neutrino mass properties with supernova neutrinos

Models of late-time neutrino mass generation contain new interactions of the cosmic background neutrinos with supernova relic neutrinos (SRNs). Exchange of an on-shell light scalar may lead to significant modification of the differential SRN flux observed at earth. We consider an Abelian U(1) model for generating neutrino masses at low scales, and show that there are cases for which the changes induced in the flux allow one to distinguish the Majorana or Dirac nature of neutrinos, as well as the type of neutrino mass hierarchy (normal or inverted or quasidegenerate). In some region of parameter space the determination of the absolute values of the neutrino masses is also conceivable. Measurements of the presence of these effects may be possible at the next-generation water Cerenkov detectors enriched with Gadolinium, or a 100 kton liquid argon detector.

Super-NOνA: a long-baseline ν experiment with two off-axis detectors

We consider here the NOνA experiment configuration and propose to place a second off-axis detector, with a shorter baseline, such that the type of neutrino mass hierarchy could be determined, by exploiting matter effects, with only the neutrino run. We show that the determination of this parameter is free of degeneracies, provided the ratio L / E , where L the baseline and E is the neutrino energy, is the same for both detectors.

Determining the neutrino mass hierarchy with atmospheric neutrinos

The possibility to determine the type of neutrino mass hierarchy by studying atmospheric neutrino oscillations with a detector capable to distinguish between neutrino and antineutrino events, such as magnetized iron calorimeters, is considered. We discuss how the ability to distinguish between the neutrino mass spectrum with normal and inverted hierarchy depends on detector characteristics like neutrino energy and direction resolutions or charge miss-identification, and on the systematical uncertainties related to the atmospheric neutrino fluxes. We show also how the neutrino mass hierarchy determination depends on the true values of θ 13 and θ 23 , as well as on the type of the true hierarchy. We find that for μ-like events, an accurate reconstruction of the energy and direction of the neutrino greatly improves the sensitivity to the type of neutrino mass spectrum. For sin 2 2 θ 13 ≅ 0.1 and a precision of 5% in the reconstruction of the neutrino energy and 5° in the neutrino direction, the type of neutrino mass hierarchy can be identified at the 2 σ C.L. with approximately 200 events. For resolutions of 15% for the neutrino energy and 15° for the neutrino direction roughly one order of magnitude larger event numbers are required. For a detector capable to distinguish between ν e and ν ¯ e induced events the requirements on energy and direction resolutions are, in general, less demanding than for a detector with muon charge identification.

Super-NOνA: A long-baseline neutrino experiment with two off-axis detectors

Establishing the neutrino mass hierarchy is one of the fundamental questions that will have to be addressed in the near future. Its determination could be obtained with long-baseline experiments but typically suffers from degeneracies with other neutrino parameters. We consider here the $\mathrm{NO}\ensuremath{\nu}\mathrm{A}$ experiment configuration and propose to place a second off-axis detector, with a shorter baseline, such that, by exploiting matter effects, the type of neutrino mass hierarchy could be determined with only the neutrino run. We show that the determination of this parameter is free of degeneracies, provided the ratio $L/E$, where $L$ is the baseline and $E$ is the neutrino energy, is the same for both detectors.

Precision neutrino oscillation physics with an intermediate baseline reactor neutrino experiment

We discuss the physics potential of intermediate $L \sim 20 \div 30$ km baseline experiments at reactor facilities, assuming that the solar neutrino oscillation parameters $\Delta m^2_{\odot}$ and $\theta_{\odot}$ lie in the high-LMA solution region. We show that such an intermediate baseline reactor experiment can determine both $\Delta m^2_{\odot}$ and $\theta_{\odot}$ with a remarkably high precision. We perform also a detailed study of the sensitivity of the indicated experiment to $\Delta m^2_{\rm atm}$, which drives the dominant atmospheric $\nu_{\mu}$ ($\bar{\nu}_{\mu}$) oscillations, and to $\theta$ - the neutrino mixing angle limited by the data from the CHOOZ and Palo Verde experiments. We find that this experiment can improve the bounds on $\sin^2\theta$. If the value of $\sin^2\theta$ is large enough, $\sin^2\theta \gtap 0.02$, the energy resolution of the detector is sufficiently good and if the statistics is relatively high, it can determine with extremely high precision the value of $\Delta m^2_{\rm atm}$. We also explore the potential of the intermediate baseline reactor neutrino experiment for determining the type of the neutrino mass spectrum, which can be with normal or inverted hierarchy. We show that the conditions under which the type of neutrino mass hierarchy can be determined are quite challenging, but are within the reach of the experiment under discussion.

Complementarity of eastern and western hemisphere long-baseline neutrino oscillation experiments

We present a general formalism for extracting information on the fundamental parameters associated with neutrino masses and mixings from two or more long baseline neutrino oscillation experiments. This formalism is then applied to the current most likely experiments using neutrino beams from the Japan Hadron Facility (JHF) and Fermilab's NuMI beamline. Different combinations of muon neutrino or muon anti-neutrino running are considered. To extract the type of neutrino mass hierarchy we make use of the matter effect. Contrary to naive expectation, we find that both beams using neutrinos is more suitable for determining the hierarchy provided that the neutrino energy divided by baseline ($E/L$) for NuMI is smaller than or equal to that of JHF. Whereas to determine the small mixing angle, $\theta_{13}$, and the CP or T violating phase $\delta$, one neutrino and the other anti-neutrino is most suitable. We make extensive use of bi-probability diagrams for both understanding and extracting the physics involved in such comparisons.