Results from Super-Kamiokande and K2K

Results from Super-Kamiokande-I’s entire 1496 live days of solar neutrino data are presented, including the absolute flux, energy spectrum, zenith angle (day/night) and seasonal variation. The possibility of MSW and vacuum oscillations is discussed in light of these results. Results from the first 1289 days of Super-K-I’s atmospheric neutrino analysis are also presented, including the evidence for ν_μ →ν _τ oscillations, against ν_μ → ν_sterile oscillations, and the current limits on proton decay. Finally, results based on 56 × 10¹⁹ protons on target are given for the K2K long-baseline neutrino oscillation experiment.     

T2K Experiment: Latest Results and Prospects

Physics of Atomic Nuclei - The international accelerator neutrino experiment T2K (Tokai-to-Kamioka) began accumulating data in 2010 and has since then accomplished 10 runs in the neutrino and...     

Neutrino beam properties of T2K experiment

The neutrino on-axis and off-axis beam was studied in the near neutrino detector of the longbaseline experiment T2K: beam composition, long-term stability, and spatial asymmetry.     

Physics and Performance of the Upgraded T2K’s Near Detector

Physics of Atomic Nuclei - Tokai-to-Kamioka (T2K) is a long-baseline neutrino oscillation experiment currently ongoing in Japan. T2K has been the first experiment to detect the appearance of...     

Status of the T2K experiment

These lectures present the status of the Tokai to Kamioka Experiment (T2K) which just started taking data in early 2010. The goals and methodology for the experiment are presented as well as the challenges and prospects for determining the neutrino mixing parameters leading to neutrino oscillation with a particular attention to the determination of the mixing angle θ₁₃.     

Recent neutrino oscillation results from T2K

The Tokai-to-Kamioka (T2K) experiment studies neutrino oscillations in a ~600 MeV muon neutrino beam sent at 295 km from the Japan Proton Accelerator Complex (J-PARC) to the Super Kamiokande (SK) detector in Kamioka. The primary goals of T2K are to search for the appearance of electron neutrinos at SK resulting from ?? ₁₃?>?0 and to precisely measure ?? ₂₃ and $\Delta m^2_{32}$ via ?? _?? disappearance. We report on T2K results obtained from neutrino data taken in 2010 and 2011.     

KamLAND and T2K

KamLAND announced the first evidence of disappearance, followed by direct evidence for neutrino oscillation by observing distortion of the reactor energy spectrum, demonstrated almost two cycles of the periodic feature expected neutrino oscillation, and determined a precise value for the neutrino oscillation parameter and stringent constraints on θ₁₂. KamLAND also succeeded in detecting geoneutrinos produced by natural radioactivities in the Earth. This detection allows better estimation of the abundances and distributions of radioactive elements in the Earth and of the Earth’s overall heat generation. In the J-PARC neutrino facility, T2K is ready for operation. T2K is supposed to give critical information, which guides the future direction of the neutrino physics. The current status of T2K is shown.     

Results from the T2K experiment

The T2K (Tokai-to-Kamioka) experiment is a long baseline neutrino oscillation experiment designed to probe the θ ₁₃ neutrino mixing parameter by looking for the appearance of ν _e in an almost pure ν _μ beam. The concurrent measurement of the ν _μ disappearance allows refined measurements of the atmospheric Δm ² and θ ₂₃ mixing parameters.     

Results of T2K and NOvA Neutrino Experiments: Neutrino Mass Ordering and CP Symmetry

Journal of Experimental and Theoretical Physics - New data concerning neutrino oscillations as obtained in the T2K and NOvA accelerator neutrino experiments are considered. Both collaborations...     

Summary of ISNP2K

This is a brief summary of the ISNP2K (International Symposium on Nuclear Physics, 2000). Many interesting works were presented on new developments and perspectives of nuclear physics in the plenary and poster sessions. Subjects discussed are 1) high temperature and high density nuclei, new QGP phases and relativistic HI collisions, 2) new degrees of freedoms studied by medium energy reactions, 3) exotic nuclei with large isospin, large A, high J and high E _x , 4) new dynamical properties of many body nucleon systems, 5) neutrino nuclear physics and neutrons for astroparticle physics, and 6) new accelerators and new applications. ISNP2K with extensive discussions on nuclear physics frontiers at the turning point from 2000 to 2001 provides a good bridge to the new century.     

Antikaon Condensation and In-medium Kaon and Antikaon Production in Protoneutron Stars

Antikaon condensation and kaon and antikaon production in protoneutron stars are investigated in a chiral hadronic model （also referred to as the FST model in this paper）. The effects of neutrino trapping on protoneutron stars are analyzed systematically. It is shown that neutrino trapping makes the critical density of K^- condensation delay to higher density and fifo condensation not occur. The equation of state （EOS） of （proto）neutron star matter with neutrino trapping is stiffer than that without neutrino trapping. As a result, the maximum masses of （proto）neutron stars with neutrino trapping are larger than those without neutrino trapping. If hyperons are taken into account, antikaon does not form a condensate in （proto）neutron stars. Meanwhile, the corresponding EOS becomes much softer, and the maximum masses of （proto）neutron stars are smaller than those without hyprons. Finally, our results illustrate that the Q values for K^＋ and K^- production in （proto）neutron stars are not sensitive to neutrino trapping and inclusion of hyperons.     

Neutrino oscillations as a probe of dark energy

We consider a class of theories in which neutrino masses depend significantly on environment, as a result of interactions with the dark sector. Such theories of mass varying neutrinos were recently introduced to explain the origin of the cosmological dark energy density and why its magnitude is apparently coincidental with that of neutrino mass splittings. In this Letter we argue that in such theories neutrinos can exhibit different masses in matter and in vacuum, dramatically affecting neutrino oscillations. As an example of modifications to the standard picture, we consider simple models that may simultaneously account for the LSND anomaly, KamLAND, K2K, and studies of solar and atmospheric neutrinos, while providing motivation to continue to search for neutrino oscillations in short baseline experiments such as BooNE.     

Lepton mixing matrix in standard model extended by one sterile neutrino

We consider the simplest extension of the standard electroweak model by one sterile neutrino that allows for neutrino masses and mixing. We find that its leptonic sector contains much less free physical parameters than previously realized. In addition to the two neutrino masses, the lepton mixing matrix in charged current interactions involves (n-1) free physical mixing angles for n generations. The mixing matrix in neutral current interactions of neutrinos is completely fixed by the two masses. Both interactions conserve CP. We illustrate the phenomenological implications of the model by vacuum neutrino oscillations, tritium β decay and neutrinoless double β decay. It turns out that, due to the revealed specific structure in its mixing matrix, the model with any n generations cannot accommodate simultaneously the data by KamLAND, K2K and CHOOZ. PACS 14.60.Pq; 14.60.St; 23.40.-s     

Investigation of neutrino oscillations in the T2k long-baseline accelerator experiment

High-sensitivity searches for transitions of muon neutrinos to electron neutrinos are the main task of the T2K (Tokai-to-Kamioka) second-generation long-baseline accelerator neutrino experiment. The present article is devoted to describing basic principles of T2K, surveying experimental apparatuses that it includes, and considering in detail the muon-range detector (SMRD) designed and manufactured by a group of physicists from the Institute of Nuclear Research (Russian Academy of Sciences, Moscow). The results of the first measurements with a neutrino beam are presented, and plans for the near future are discussed.     

Neutrino masses and mixings: a theoretical perspective

We briefly review the recent activity on neutrino masses and mixings which was prompted by the confirmation of neutrino oscillations by the Superkamiokande experiment.     

Neutrino wave function and oscillation suppression

We consider a thought experiment, in which a neutrino is produced by an electron on a nucleus in a crystal. The wave function of the oscillating neutrino is calculated assuming that the electron is described by a wave packet. If the electron is relativistic and the spatial size of its wave packet is much larger than the size of the crystal cell, then the wave packet of the produced neutrino has essentially the same size as the wave packet of the electron. We investigate the suppression of neutrino oscillations at large distances caused by two mechanisms: (1) spatial separation of wave packets corresponding to different neutrino masses; (2) neutrino energy dispersion for given neutrino mass eigenstates. We resolve the contributions of these two mechanisms. Received: 26 July 2005, Published online: 6 October 2005     

The see-saw mechanism: Neutrino mixing,leptogenesis and lepton flavour violation

The see-saw mechanism to generate small neutrino masses is reviewed. After summarizing our current knowledge about the low energy neutrino mass matrix, we consider reconstructing the see-saw mechanism. Indirect tests of see-saw are leptogenesis and lepton flavour violation in supersymmetric scenarios, which together with neutrino mass and mixing define the framework of see-saw phenomenology. Several examples are given, both phenomenological and GUT-related.      

A large scale double beta and dark matter experiment: GENIUS

The recent results from the HEIDELBERG-MOSCOW experiment have demonstrated the large potential of double beta decay to search for new physics beyond the Standard Model. To increase by a major step the present sensitivity for double beta decay and dark matter search much bigger source strengths and much lower backgrounds are needed than used in experiments under operation at present or under construction. We present here a study of a project proposed recently [1], which would operate one ton of ‘naked’ enriched GErmanium-detectorsinliquid NItrogenas shielding in an Underground Setup (GENIUS). It improves the sensitivity to neutrino masses to 0.01 eV. A ten ton version would probe neutrino masses even down to 10^?3 eV. The first version would allow to test the atmospheric neutrino problem, the second at least part of the solar neutrino problem. Both versions would allow in addition significant contributions to testing several classes of GUT models. These are especially tests of R-parity breaking supersymmetry models, leptoquark masses and mechanism and right-handed W-boson masses comparable to LHC. The second issue of the experiment is the search for dark matter in the universe. The entire MSSM parameter space for prediction of neutralinos as dark matter particles could be covered already in a first step of the full experiment with the same purity requirements, but using only 100 kg of ⁷⁶Ge or even of natural Ge making the experiment competitive to LHC in the search for supersymmetry. The layout ofthe proposed experiment is discussed and the shielding and purity requirements are studied using GEANT Monte Carlo simulations. As a demonstration of the feasibility of the experiment first results of operating a ‘naked’ Ge detector in liquid nitrogen are presented.     

Progress in neutrino oscillation searches and their implications

Neutrino oscillation, in which a given flavor of neutrino transforms into another is a powerful tool for probing small neutrino masses. The intrinsic neutrino properties involved are neutrino mass squared difference Δm ² and the mixing angle in vacuum θ. In this paper I will summarize the progress that we have achieved in our search for neutrino oscillation with special emphasis on the recent results from the Sudbury Neutrino Observatory (SNO) on the measurement of solar neutrino fluxes. I will outline the current bounds on the neutrino masses and mixing parameters and discuss the major physics goals of future neutrino experiments in the context of the present picture.     

Indications of neutrino oscillation in a 250 km long-baseline experiment

The K2K experiment observes indications of neutrino oscillation: a reduction of nu(mu) flux together with a distortion of the energy spectrum. Fifty-six beam neutrino events are observed in Super-Kamiokande (SK), 250 km from the neutrino production point, with an expectation of 80.1(+6.2)(-5.4). Twenty-nine one ring mu-like events are used to reconstruct the neutrino energy spectrum, which is better matched to the expected spectrum with neutrino oscillation than without. The probability that the observed flux at SK is explained by statistical fluctuation without neutrino oscillation is less than 1%.