Showing papers by "Petr Vogel published in 2015"

Reexamining the light neutrino exchange mechanism of the 0 ν β β decay with left- and right-handed leptonic and hadronic currents

Abstract: The extension of the Majorana neutrino mass mechanism of the neutrinoless double-beta decay (0νββ) with the inclusion of right-handed leptonic and hadronic currents is revisited. While only the exchange of light neutrinos is assumed, the s_(1/2) and p_(1/2) states of emitted electrons as well as recoil corrections to the nucleon currents are taken into account. Within the standard approximations the decay rate is factorized into a sum of products of kinematical phase-space factors, nuclear matrix elements, and the fundamental parameters that characterize the lepton number violation. Unlike in the previous treatments, the induced pseudoscalar term of hadron current is included, resulting in additional nuclear matrix elements. An improved numerical computation of the phase-space factors is presented, based on the exact Dirac wave functions of the s_(1/2) and p_(1/2) electrons with finite nuclear size and electron screening taken into account. The dependence of values of these phase-space factors on the different approximation schemes used in evaluation of electron wave functions is discussed. The upper limits for effective neutrino mass and the parameters ⟨λ⟩ and ⟨η⟩ characterizing the right-handed current mechanism are deduced from data on the 0νββ decay of ^(76)Ge and ^(136)Xe using nuclear matrix elements calculated within the nuclear shell model and quasiparticle random phase approximation. The differential decay rates, i.e., the angular correlations and the single electron energy distributions for various combinations of the total lepton number violating parameters that can help to disentangle the possible mechanism, are described and discussed.

Neutrino oscillation studies with reactors

Abstract: Nuclear reactors are one of the most intense, pure, controllable, cost-effective and well-understood sources of neutrinos. Reactors have played a major role in the study of neutrino oscillations, a phenomenon that indicates that neutrinos have mass and that neutrino flavours are quantum mechanical mixtures. Over the past several decades, reactors were used in the discovery of neutrinos, were crucial in solving the solar neutrino puzzle, and allowed the determination of the smallest mixing angle θ13. In the near future, reactors will help to determine the neutrino mass hierarchy and to solve the puzzling issue of sterile neutrinos.

Neutrino Mass Hierarchy

Abstract: The neutrino mass hierarchy, i.e., whether the $ u_3$ neutrino mass eigenstate is heavier or lighter than the $ u_1$ and $ u_2$ mass eigenstates, is one of the remaining undetermined fundamental features of the neutrino Standard Model. Its determination would represent an important step in the formulation of the generalized model, and would have a profound impact on the quest of the nature of neutrinos (Dirac or Majorana) and the search for a theory of flavor. In this review, we summarize the status of experimental and theoretical work in this field and explore the future opportunities that emerge in light of the recently discovered non-zero and relatively large third neutrino mixing angle $\theta_{13}$.