Phenomenon Of Neutrino Oscillations Research Articles

Neutrino Oscillations

In the last decades, a very important breakthrough has been brought about in the elementary particle physics by the discovery of the phenomenon of the neutrino oscillations, which has shown neutrino properties beyond the Standard Model. But a full understanding of the various aspects of the neutrino oscillations is far to be achieved. In this paper the theoretical background of the neutrino oscillation phenomenon is described, referring in particular to the paradigmatic models. Then the various techniques and detectors which studied neutrinos from different sources are discussed, starting from the pioneering ones up to the detectors still in operation and to those in preparation. The physics results are finally presented adopting the same research path which has been crossed by this long saga. The problems not yet fixed in this field are discussed, together with the perspectives of their solutions in the near future.

Interference phenomenon and geometric phase for Dirac neutrino inπ+decay

We analyze the geometric phase in the neutrino oscillation phenomenon, which follows the pion decay \pi+ --> \mu+ + \nu_{\mu}. Its value \pi is consistent with the present-day global analysis of the Standard Model neutrino oscillation parameters, accounting for the nonzero value of \theta_13. The impact of the charge-parity (CP) violating phase \delta, the neutrino's nature, and the new physics is discussed.

Long-Baseline Neutrino Oscillation Experiments

A review of accelerator long-baseline neutrino oscillation experiments is provided, including all experiments performed to date and the projected sensitivity of those currently in progress. Accelerator experiments have played a crucial role in the confirmation of the neutrino oscillation phenomenon and in precision measurements of the parameters. With a fixed baseline and detectors providing good energy resolution, precise measurements of the ratio of distance/energy (L/E) on the scale of individual events have been made and the expected oscillatory pattern resolved. Evidence for electron neutrino appearance has recently been obtained, opening a door for determining the CP violating phase as well as resolving the mass hierarchy and the octant ofθ23; some of the last unknown parameters of the standard model extended to include neutrino mass.

Determining the Neutrino Flux from Accelerator Neutrino Beams

Man made sources of neutrinos, from reactors and proton accelerators, are providing the best experimental sensitivities to determining the unknown neutrino oscillation parameters such as θ13, the mass hierarchy, and the CP phase. In addition, these experiments enable the measurements of the known neutrino oscillation parameters with higher precision and the search for new neutrino oscillation phenomena. A critical component of any neutrino oscillation experiment is the precision determination of the neutrino flux from the source, and its composition. I will summarize the different techniques used by current short and long baseline neutrino accelerator experiments to determine the unoscillated neutrino flux, and discuss the implications for future experiments.

Neutrino oscillations: A breakthrough to new physics

Research in particle physics has recently attracted not only scientific but also public interest. This is largely due to the specifics of experiments under way: huge volumes of financing, labor intensity, and related risks. However, such experiments significantly promote the development of basic knowledge. The article below is based on a talk given at an RAS Presidium meeting dedicated to the neutrino oscillation phenomenon, the experimental discovery and theoretical study of which, in the author’s opinion, may lay the foundation for a revolutionary revision of basic physical concepts.

EFFECTS OF CP VIOLATING PHASES ON THE INVERSE NEUTRINOLESS DOUBLE BETA SCATTERING e-e- → W-W-

The most important open problems of the today's neutrino physics are the absolute values of the neutrino masses, the determination of the Dirac or the Majorana character and better measurements of the mixing matrix elements. Results of the neutrino oscillations experiments strongly confirm that the neutrinos have nonzero masses. Experiments give information about the differences between the squares of the masses but not any knowledge on their absolute values. Similarly neutrino oscillation phenomena does not help us to understand their Dirac or Majorana character. One of the processes that could clarify this important point is the double beta decay and the search is still going on but not yielded any positive results due to the big experimental difficulties. Also the inverse of this decay, e-e- → W-W- is another process that could be tested at the accelerators. This process is possible only if the neutrinos have masses and they are Majorana particles. Since neutrinos could have very tiny masses and the cross section of the above process is proportional to the square of the effective neutrino mass it is an extremely rare process. Also it violates total lepton number by two units, Δ = 2. In the literature the inverse neutrinoless double beta scattering have been extensively studied, in this article we obtain the relevant helicity amplitudes, investigate the effects of the neutrino mixing matrix elements, especially the roles of the CP violating phases and the possible CP asymmetries.

CAN THE EXCESS IN THE Fe XXVI Lyγ LINE FROM THE GALACTIC CENTER PROVIDE EVIDENCE FOR 17 keV STERILE NEUTRINOS?

The standard model of particle physics assumes that neutrinos are massless, although adding non-zeros is required by the experimentally established phenomenon of neutrino oscillations requires neutrinos to have non-zero mass. Sterile neutrinos (or right-handed neutrinos) are a good warm dark matter candidate. We find that the excess of the intensity in the 8.7 keV line (at the energy of the FeXXVI Ly$\gamma$ line) in the spectrum of the Galactic center observed by the Suzaku X-ray mission cannot be explained by standard ionization and recombination processes. We suggest that the origin of this excess is via decays of sterile neutrinos with a mass of 17.4 keV and estimate the value of the mixing angle. The estimated value of the mixing angle $\sin^2(2\theta)=(4.1 \pm 2.2)\times10^{-12}$ lies in the allowed region of the mixing angle of dark matter sterile neutrino with a mass of 17-18 keV.

NEUTRINO OSCILLATIONS AND ENERGY–MOMENTUM CONSERVATION

A description of neutrino oscillation phenomena is presented which is based on relativistic quantum mechanics with four-momentum conservation. This is different from both conventional approaches which arbitrarily use either equal energies or equal momenta for the different neutrino mass eigenstates. Both entangled state and source dependence aspects are also included. The time dependence of the wave function is found to be crucial to recovering the conventional result to second order in the neutrino masses. An ambiguity appears at fourth order which generally leads to source dependence, but the standard formula can be promoted to this order by a plausible convention.

Collaboration with Professor Makoto Kobayashi on the Neutrino Oscillation

I would like to introduce the content of my collaboration with Professor Makoto Kobayashi on the subject of “pseudo-Dirac” scenario with respect to the origin of neutrino masses and its implications for the phenomena of neutrino oscillations. In particular, it was suggested in the work that the large mixings in the leptonic sector is the natural consequence of small generation mixings, just as in the Kobayashi-Maskawa matrix, and the pseudo-Dirac nature of neutrinos. Also mentioned is the recent argument on the implication of the scenario for the neutrino telescope.

Multipartite entanglement in neutrino oscillations

Particle mixing is related to multi-mode entanglement of single-particle states The occupation number of both flavor eigenstates and mass eigenstates can be used to define a multiqubit space. In such a framework, flavor neutrino states can be interpreted as multipartite mode-entangled states. By using two different entanglement measures, we analyze the behavior of multipartite entanglement in the phenomenon of neutrino oscillations.

Perturbation theory of neutrino oscillation with nonstandard neutrino interactions

We discuss various physics aspects of neutrino oscillation with non-standard interactions (NSI). We formulate a perturbative framework by taking \Delta m^2_{21} / \Delta m^2_{31}, s_{13}, and the NSI elements \epsilon_{\alpha \beta} (\alpha, \beta = e, \mu, \tau) as small expansion parameters of the same order \epsilon. Within the \epsilon perturbation theory we obtain the S matrix elements and the neutrino oscillation probability formula to second order (third order in \nu_e related channels) in \epsilon. The formula allows us to estimate size of the contribution of any particular NSI element \epsilon_{\alpha beta} to the oscillation probability in arbitrary channels, and gives a global bird-eye view of the neutrino oscillation phenomena with NSI. Based on the second-order formula we discuss how all the conventional lepton mixing as well as NSI parameters can be determined. Our results shows that while \theta_{13}, \delta, and the NSI elements in \nu_e sector can in principle be determined, complete measurement of the NSI parameters in the \nu_\mu - \nu_\tau sector is not possible by the rate only analysis. The discussion for parameter determination and the analysis based on the matter perturbation theory indicate that the parameter degeneracy prevails with the NSI parameters. In addition, a new solar-atmospheric variable exchange degeneracy is found. Some general properties of neutrino oscillation with and without NSI are also illuminated.

Latest Results from the MINOS Experiment

The MINOS experiment utilizes the NuMI neutrino beam to study the phenomenon of neutrino oscillations. Muon neutrinos are sent over a baseline of 735 km, with a detector near the production point at Fermilab and one at the Soudan underground laboratory in northern Minnesota. By observing the {nu}{sub {mu}} disappearance characteristic of oscillations, MINOS can measure the oscillation parameters. MINOS has previously made the best measurement of the atmospheric-regime mass splitting to date. New results are presented in which the data-set is doubled. Further analysis improvements, and the inclusion of additional event samples, further improve the sensitivity to the oscillation parameters. The mixing angle {theta}{sub 13} is currently not measured to differ from zero. By searching for {nu}{sub e} appearance in the {nu}{sub {mu}} beam, MINOS is able to set new limits on the value of {theta}{sub 13}. An observation of the neutral current interaction rate at the far detector allows limits to be placed on the existence of sterile neutrinos. From September 2009 to March 2010, MINOS has taken data with a dedicated {bar {nu}}{sub {mu}} beam, allowing the first direct precision measurement of the antineutrino oscillation parameters in the atmospheric regime.

Effects of solar neutrinos scale on atmospheric neutrino flux

In this work we try to understand the phenomena of neutrino oscillations, and use this to obtain a more precise description of the atmospheric neutrino data. The two neutrino oscillation mechanism solves the problem of the up-down muon neutrino asymmetry successfully. Our main motivation is to describe the excess of events of electron-neutrino type found in the SuperKamiokande results at low energies when compared with the predictions of the two-generation neutrino oscillation. To do this we generalize the oscillation model from two to three neutrino flavors, opening the possibility of oscillation between electron neutrino type and the others. Then we obtain a semi-analytic solution of the three flavors problem using the neutrino phenomenological limits on oscillation parameters, squared masses differences and mixing angles. For this we must take into account matter effects on the electronic neutrino when it cross the Earth and has its oscillation pattern changed.

SUPPRESSION OF 0ν2β DECAY FROM CP VIOLATION

The observed phenomenon of neutrino oscillations is interpreted as the proof that neutrinos must have mass. As this is true for the neutrinos in the mass basis, the mass matrix in the flavor (weak) basis may still contain zeros. This can happen if the CP violating phases, usually neglected, come into play and result in suppression of processes which half-life depends on the masses of νe, νμ, or ντ. In the present paper we investigate the possibility of such suppression of the neutrinoless double beta decay (0ν2β).

Neutrino physics at accelerators

Present and future neutrino experiments at accelerators are mainly concerned with understanding the neutrino oscillation phenomenon and its implications. Here a brief account of neutrino oscillations is given together with a description of the supporting data. Some current and planned accelerator neutrino experiments are also explained.

NEUTRINO PHYSICS – THEORY

I discuss the new physics unveiled by neutrino oscillation experiments. It is fair to say that, while significant theoretical progress has been made, we are yet to construct a unique coherent picture that naturally explains non-zero, yet tiny, neutrino masses and the newly revealed pattern of lepton mixing. I discuss what the challenges are, and point to the fact that more experimental input is required. Finally, I draw attention to the fact that neutrinos may have only just begun to reshape fundamental physics, given the fact that we are still to explain the LSND anomaly and because the neutrino oscillation phenomenon is ultimately sensitive to very small new-physics effects.

Measurement of cosmic-ray spectra with the BESS/BESS-TeV

In order to study neutrino oscillation phenomena using atmospheric neutrinos, it is crucially important to calculate their absolute fluxes and spectral shapes accurately. Absolute flux of primary cosmic ray is the most fundamental information for the calculation. Since production and decay processes of muons are accompanied by neutrino production, observation of atmospheric muons gives fundamental information about atmospheric neutrinos. Our measurement of primary and atmopspheric cosmic rays at various sites with the BESS/BESS-TeV spectrometer will help to improve the accuracy of atmospheric neutrino calculations.

Scientific ballooning in Japan – An over view of recent activities

Current status of scientific ballooning in Japan is reviewed. First, I describe successful application of balloon technologies to construct a vessel of transparent plastic film, to contain about 1000 tons of liquid scintillator in Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND). KamLAND is a project to study neutrino oscillation phenomena, by detecting anti-neutrinos produced in distant nuclear reactors. Next, I describe high altitude balloons developed by the ISAS balloon group. They developed balloons made from ultra-thin polyethylene film, producing a balloon of volume 60,000 m 3 which successfully reached an altitude of 53 km in 2002. This is a world record, the greatest altitude that a balloon has ever achieved. ISAS is applying further effort to develop balloons with even thinner films, to achieve a higher altitude than 53 km. Other recent activities by the ISAS balloon group are briefly described. I also review scientific ballooning projects now operating in Japan, particularly focusing on the Balloon-Borne Experiment with a Superconducting Spectrometer (BESS) program. This is a US–Japan collaborative program that has carried out very precise measurements of antiprotons, protons and other components in primary cosmic rays, as well as measuring the fluxes of atmospheric muons and other components. The results of these observations give us important information to improve our understanding of the production mechanism of antiprotons observed in the primary cosmic rays. The data are also important for analysis of atmospheric neutrino events observed by Super-Kamiokande and other ground-based neutrino detectors. Future prospects of BESS and other balloon-borne cosmic-ray research programs are also presented.

Results from the CERN short baseline neutrino experiments

During the years 1994–1998, the NOMAD and CHORUS experiments were taking data in the wide band neutrino beam of the CERN-SPS. The main goal of these experiments was the search for neutrino oscillation phenomena. Results of these searches are summarised here. In addition to the oscillation search measurements of charm production have been performed. NOMAD was able to isolate a high purity charm sample by identifying the D*+ with its decay mode into the D0. A measurement of the rate of D*+ production and a study of the fragmentation process is described here CHORUS made a topological selection of charmed particles and could perform measurements of D0 and charmed baryon production in ν μ charged-current interactions and the total rate of charm production in ν ¯ μ interactions. In addition a measurement of the trimuon production rate is presented here.

NEUTRINOS HAVE MASS — SO WHAT?

In this brief review, we discuss the new physics unveiled by neutrino oscillation experiments over the past several years, and discuss several attempts at understanding the mechanism behind neutrino masses and lepton mixing. It is fair to say that, while significant theoretical progress has been made, we are yet to construct a coherent picture that naturally explains nonzero, yet tiny, neutrino masses and the newly revealed, puzzling patterns of lepton mixing. We discuss what the challenges are, and point to the fact that more experimental input (from both neutrino and "non-neutrino" experiments) is dearly required – and that new data is expected to reveal, in the next several years, new information. Finally, we draw attention to the fact that neutrinos may have only just begun to reshape fundamental physics, given the fact that we are yet to explain the LSND anomaly and because the neutrino oscillation phenomenon is ultimately sensitive to very small new-physics effects.