Aspects of the two-component and four-component neutrino theories in connection with weak lepton and semilepton processes

A comparison is made of the results found in the application of two-component and four-component theories of the two neutrinos to weak lepton processes (muon decay) and semilepton processes. The predictions of the two theories clearly differ in the V-A version of the coupling of electron and muon currents and of muon and baryon currents. In contrast with the theory of two-component neutrinos (the V-A interaction), four-component theory predicts that a V + A interaction of electron and muon currents is responsible for muon decay.     

Cosmic-ray muon and atmospheric neutrino fluxes at very high energies

Estimates of cosmic-ray muon and atmospheric neutrino fluxes at TeV energies are obtained taking into account a “prompt” production of muons and neutrinos through charmed-particle decays and a “direct” lepton-pair production through the Drell-Yan mechanism and resonances. It is found that the contribution of charmed particles to the muon flux is equal to that from the conventional sources (pion and kaon decays) at 60 TeV, and the same equality can take place at 10 and 1 TeV for muon and electron neutrinos, respectively (for particles coming to sea level in the vertical direction). This “direct” production contribution to muon and neutrino fluxes is estimated very arbitrarily, but it cannot be excluded that this contribution is equal to that from the conventional source at energies of 0.5 and 0.05 PeV for muons and muon neutrinos, respectively. Currently, the estimates of the “prompt” and the “direct” contributions to cosmic-ray muons and atmospheric neutrinos are only qualitative. This is true especially for the “direct” contribution. Nevertheless, it seems reasonable to attract attention to these potentially important sources of atmospheric muons and neutrinos.     

Tau neutrinos favored over sterile neutrinos in atmospheric muon neutrino oscillations

The previously published atmospheric neutrino data did not distinguish whether muon neutrinos were oscillating into tau neutrinos or sterile neutrinos, as both hypotheses fit the data. Using data recorded in 1100 live days of the Super-Kamiokande detector, we use three complementary data samples to study the difference in zenith angle distribution due to neutral currents and matter effects. We find no evidence favoring sterile neutrinos, and reject the hypothesis at the 99% confidence level. On the other hand, we find that oscillation between muon and tau neutrinos suffices to explain all the results in hand.     

Monochromatic neutrinos from the annihilation of fourth-generation massive stable neutrinos in the Sun and in the Earth

The accumulation of relic fourth-generation heavy neutrinos (of mass 50 GeV) in the Earth and the Sun, which is followed by their annihilation, is considered. The most conservative estimates of the fluxes of monochromatic electron, muon, and tau neutrinos and antineutrinos of energy 50 GeV from the annihilation of heavy neutrinos are 4.1×10^?6 cm^?2 s^?1 from Earth’s core and 1.1×10^?7 cm^?2 s^?1 from Sun’s core, whence it follows that an analysis of data from underground neutrino observatories may furnish additional information about the existence of fourth-generation neutrinos. It is shown that, because of kinetic equilibrium between the arrival of cosmic neutrinos and their annihilation, the existence of new U(1) gauge interaction of fourth-generation neutrinos has virtually no effect on the estimates of the annihilation fluxes of electron, muon, and tau neutrinos.     

High-energy interactions

Summary This paper, based on the rapporteur talk given at the XXIV International Cosmic-Ray Conference (Roma, 28 August–8 September 1995), concerns the sessions HE1, HE2, HE6. Multihadron production in cosmic rays, models, emulsion chamber measurements, simulation of electromagnetic and hadronic cascades, new particles and processes are summarized in the frame of the special phenomenology adapted to the collisions of ultrahigh-energy particles in the atmosphere. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

中微子振荡实验——超出标准模型的实验检验（Ⅰ）

文章总结了中微子振荡实验在历史和现状,介绍了几个太阳中微子丢失实验的结果和几个大气μ中微子丢失实验结果,这些结果表明存在中微子振荡,即中微子具有质量,它是超出标准模型的信号,文章还介绍了21世纪初研究中微子振荡和若干重要实验,噬基线中微子振荡实验以及建造μ子贮存环来产生高能电子中微子束进行中微子振荡的实验以及测量中微子振荡时的CP破坏的设想。     

Oscillation properties of active and sterile neutrinos and neutrino anomalies at short distances

A generalized phenomenological (3 + 2 + 1) model featuring three active and three sterile neutrinos that is intended for calculating oscillation properties of neutrinos for the case of a normal activeneutrino mass hierarchy and a large splitting between the mass of one sterile neutrino and the masses of the other two sterile neutrinos is considered. A new parametrization and a specific form of the general mixing matrix are proposed for active and sterile neutrinos with allowance for possible CP violation in the lepton sector, and test values are chosen for the neutrino masses and mixing parameters. The probabilities for the transitions between different neutrino flavors are calculated, and graphs representing the probabilities for the disappearance of muon neutrinos/antineutrinos and the appearance of electron neutrinos/antineutrinos in a beam of muon neutrinos/antineutrinos versus the distance from the neutrino source for various values of admissible model parameters at neutrino energies not higher than 50 MeV, as well as versus the ratio of this distance to the neutrino energy, are plotted. It is shown that the short-distance accelerator anomaly in neutrino data (LNSD anomaly) can be explained in the case of a specific mixing matrix for active and sterile neutrinos (which belongs to the a₂ type) at the chosen parameter values. The same applies to the short-distance reactor and gallium anomalies. The theoretical results obtained in the present study can be used to interpret and predict the results of ground-based neutrino experiments aimed at searches for sterile neutrinos, as well as to analyze some astrophysical observational data.     

Possible CP-violation effects in core-collapse supernovae

We study CP-violation effects when neutrinos are present in dense matter, such as outside the proto-neutron star formed in a core-collapse supernova. Using general arguments based on the Standard Model, we confirm that there are no CP-violating effects at the tree level on the electron neutrino and anti-neutrino fluxes in a core-collapse supernova. On the other hand significant effects can be obtained for muon and tau neutrinos even at the tree level. We show that CP-violating effects can be present in the supernova electron (anti-)neutrino fluxes as well, if muon and tau neutrinos have different fluxes at the neutrinosphere. Such differences could arise due to physics beyond the Standard Model, such as the presence of flavor-changing interactions.     

The potential for neutrino physics at muon colliders and dedicated high current muon storage rings

Conceptual design studies are underway for muon colliders and other high-current muon storage rings that have the potential to become the first true “neutrino factories”. Muon decays in long straight sections of the storage rings would produce precisely characterized beams of electron and muon type neutrinos of unprecedented intensity. This article reviews the prospects for these facilities to greatly extend our capabilities for neutrino experiments, largely emphasizing the physics of neutrino interactions.     

Cosmic rays in the heliosphere

Summary This is a rapporteur paper for the XXIV International Cosmic-Ray Conference covering topics of anomalous cosmic rays, shock acceleration, modulation and transport theory, cosmic-ray gradients, corotating interaction regions, coronal-mass ejections, and solar neutrinos. Among the highlights of the meeting are —conclusive proof that most anomalous cosmic rays are singly charged,—undisputed detection of anomalous cosmic-ray hydrogen,—discovery of unexpectedly large anisotropies of pickup ions,—observation of pronounced solar rotational modulation of cosmic-ray fluxes to the highest heliolatitudes (∼80°) probed by the Ulysses spacecraft, and—new measurements of modulation effects sensitive to particle charge sign. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

The possibility of searching for new physics in cosmic rays

One possible explanation of cosmic-ray energy spectrum behavior around the knee (3–5 PeV) by means of production of new heavy particles or a new state of matter is considered. It is shown that, in this case, a large excess of muons and neutrinos with energies of >100 TeV must be generated. The existing VHE muon experimental data are analyzed. Possible experiments on VHE muon investigations are discussed.     

Cosmic-ray propagation in the Galaxy

Summary More than 95 contributed papers on cosmic-ray transport and acceleration in the Galaxy were presented at the XXIV International Cosmic-Ray Conference. The present summary covers part of the rapporteur talk and reflects a personal view of the subject. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Discovery of atmospheric neutrino oscillations**

Atmospheric neutrinos are produced by cosmic ray interactions in the atmosphere. The zenith‐angle and energy dependence of the muon‐ and electron‐ neutrino events are observed in atmospheric neutrino experiments. Through these studies neutrino oscillations were discovered. In this article, studies of atmospheric neutrinos in the Kamiokande and Super‐Kamiokande experiments are described.     

Results from atmospheric neutrinos

With the announcement of new evidence for muon neutrino disappearance observed by the super-Kamiokande experiment, the more than a decade old atmospheric neutrino anomaly moved from a possible indication for neutrino oscillations to an apparently inescapable fact. The evidence is reviewed, and new indications are presented that the oscillations are probably between muon and tau neutrinos. Implications and future directions are discussed.     

Measurement of neutrino oscillations with the MINOS detectors in the NuMI beam

This Letter reports new results from the MINOS experiment based on a two-year exposure to muon neutrinos from the Fermilab NuMI beam. Our data are consistent with quantum-mechanical oscillations of neutrino flavor with mass splitting |Deltam2| = (2.43+/-0.13) x 10(-3) eV2 (68% C.L.) and mixing angle sin2(2theta) > 0.90 (90% C.L.). Our data disfavor two alternative explanations for the disappearance of neutrinos in flight: namely, neutrino decays into lighter particles and quantum decoherence of neutrinos, at the 3.7 and 5.7 standard-deviation levels, respectively.     

Status of the Sudbury Neutrino Observatory

Solar neutrinos from the decay of ⁸B have been detected at the Sudbury Neutrino Observatory via the charged-current (CC) and neutral-current (NC) reactions on deuterium and by the elastic scattering (ES) of electrons. The CCr eaction is sensitive exclusively to electron neutrinos, the NCr eaction is sensitive to all neutrino species, and the ES reaction also has a small sensitivity to muon and tau neutrinos. These measurements provided strong evidence that neutrinos change flavor as they propagate from the center of the Sun to the Earth at the 5.3σ level. It will also be shown that a global solar neutrino analysis of matter-enhanced neutrino oscillations of two active flavors strongly favors the large mixing angle solution.     

Superluminal neutrinos at OPERA confront pion decay kinematics

Violation of Lorentz invariance (VLI) has been suggested as an explanation of the superluminal velocities of muon neutrinos reported by OPERA. In this Letter, we show that the amount of VLI required to explain this result poses severe difficulties with the kinematics of the pion decay, extending its lifetime and reducing the momentum carried away by the neutrinos. We show that the OPERA experiment limits α=(ν(ν)-c)/c<4×10(-6). We then take recourse to cosmic-ray data on the spectrum of muons and neutrinos generated in Earth's atmosphere to provide a stronger bound on VLI: (ν-c)/c<10(-12).     

Pair creation constrains superluminal neutrino propagation

The OPERA collaboration claims that muon neutrinos with a mean energy of 17.5 GeV travel 730 km from CERN to the Gran Sasso at a speed exceeding that of light by about 7.5 km/s or 25 ppm. However, we show that superluminal neutrinos may lose energy rapidly via the bremsstrahlung of electron-positron pairs (ν → ν + e- + e+). For the claimed superluminal velocity and at the stated mean energy, we find that most of the neutrinos would have suffered several pair emissions en route, causing the beam to be depleted of higher energy neutrinos. This presents a significant challenge to the superluminal interpretation of the OPERA data. Furthermore, we appeal to Super-Kamiokande and IceCube data to establish strong new limits on the superluminal propagation of high-energy neutrinos.     

Oscillation of Dirac and Majorana neutrinos from muon decay in the case of a general interaction

We analyse the possibility of distinguishing Dirac and Majorana neutrinos in future neutrino factory experiments in which neutrinos are produced in muon decay when, in addition to a vector type as in the SM, there are also scalar interactions. We check this possibility in an experiment with a near detector, where the observed neutrinos do not oscillate, and in a far detector, after the neutrino oscillations. Neglecting higher-order corrections, even neutrino observation in the near detector does not give a chance to differentiate their character. However, this possibility appears in the leading-order after the neutrino oscillations observed in far detector.     

Neutrino mass and mixing implied by underground deficit of low energy muon-neutrino events

Recent observations of a deficit of cosmic ray muon-neutrino interactions in underground detectors suggest that the muon neutrinos may have oscillated to another state. We examine possible neutrino mass and mixing patterns, and their implications for vacuum and matter effects on solar neutrinos, on neutrinos passing through the earth, and on terrastrial neutrino beams. By invoking the see-saw mechanism of neutrino mass generation, we draw inferences on closure of the universe with neutrino masses, on the number of generations, on t-quark and fourth generation masses, and on the Peccei-Quinn symmetry breaking scale. Testable predictions are suggested.