Showing papers by "Shoji Yamamoto published in 2006"
TL;DR: In this article, measurements of {nu}{sub {mu}} disappearance in K2K, the KEK to Kamioka long-baseline neutrino oscillation experiment are presented.
Abstract: We present measurements of {nu}{sub {mu}} disappearance in K2K, the KEK to Kamioka long-baseline neutrino oscillation experiment. One-hundred and twelve beam-originated neutrino events are observed in the fiducial volume of Super-Kamiokande with an expectation of 158.1{sub -8.6}{sup +9.2} events without oscillation. A distortion of the energy spectrum is also seen in 58 single-ring muonlike events with reconstructed energies. The probability that the observations are explained by the expectation for no neutrino oscillation is 0.0015% (4.3{sigma}). In a two-flavor oscillation scenario, the allowed {delta}m{sup 2} region at sin{sup 2}2{theta}=1 is between 1.9 and 3.5x10{sup -3} eV{sup 2} at the 90% C.L. with a best-fit value of 2.8x10{sup -3} eV{sup 2}.
672 citations
TL;DR: The results of the second phase of the Super-Kamiokande solar neutrino measurement are presented and compared to the first phase in this paper, showing no evidence of systematic tendencies between the first and second phases.
Abstract: The results of the second phase of the Super-Kamiokande solar neutrino measurement are presented and compared to the first phase. The solar neutrino flux spectrum and time variation as well as oscillation results are statistically consistent with the first phase and do not show spectral distortion. The time-dependent flux measurement of the combined first and second phases coincides with the full period of solar cycle 23 and shows no correlation with solar activity. The measured {sup 8}B total flux is (2.38{+-}0.05(stat.){sub -0.15}{sup +0.16}(sys.))x10{sup 6} cm{sup -2} s{sup -1} and the day-night difference is found to be (-6.3{+-}4.2(stat.){+-}3.7(sys.))%. There is no evidence of systematic tendencies between the first and second phases.
439 citations
University of Tokyo1, Boston University2, Pennsylvania State University3, Brookhaven National Laboratory4, University of California, Irvine5, California State University, Dominguez Hills6, Chonnam National University7, Duke University8, George Mason University9, Gifu University10, Indiana University11, Kobe University12, Kyoto University13, TRIUMF14, Los Alamos National Laboratory15, Louisiana State University16, University of Maryland, College Park17, Massachusetts Institute of Technology18, University of Minnesota19, Miyagi University of Education20, Nagoya University21, Stony Brook University22, Niigata University23, Okayama University24, Osaka University25, Seoul National University26, Shizuoka University27, Sungkyunkwan University28, Tohoku University29, Tokai University30, Tokyo Institute of Technology31, University of Warsaw32, University of Washington33
TL;DR: In this article, the results of a three-flavor oscillation analysis using Super-Kamiokande I atmospheric neutrino data, with the assumption of one mass scale dominance, were reported.
Abstract: We report on the results of a three-flavor oscillation analysis using Super-Kamiokande I atmospheric neutrino data, with the assumption of one mass scale dominance ($\ensuremath{\Delta}{m}_{12}^{2}=0$). No significant flux change due to matter effect, which occurs when neutrinos propagate inside the Earth for ${\ensuremath{\theta}}_{13}\ensuremath{
e}0$, has been seen either in a multi-GeV ${\ensuremath{
u}}_{e}$-rich sample or in a ${\ensuremath{
u}}_{\ensuremath{\mu}}$-rich sample. Both normal and inverted mass hierarchy hypotheses are tested and both are consistent with observation. Using Super-Kamiokande data only, 2-dimensional 90% confidence allowed regions are obtained: mixing angles are constrained to ${sin }^{2}{\ensuremath{\theta}}_{13}l0.14$ and $0.37l{sin }^{2}{\ensuremath{\theta}}_{23}l0.65$ for the normal mass hierarchy. Weaker constraints, ${sin }^{2}{\ensuremath{\theta}}_{13}l0.27$ and $0.37l{sin }^{2}{\ensuremath{\theta}}_{23}l0.69$, are obtained for the inverted mass hierarchy case.
155 citations
TL;DR: In this paper, the weak nucleon axial-vector form factor for quasielastic interactions was determined using neutrino interaction data from the K2K Scintillating Fiber detector.
Abstract: The weak nucleon axial-vector form factor for quasielastic interactions is determined using neutrino interaction data from the K2K Scintillating Fiber detector in the neutrino beam at KEK. More than 12 000 events are analyzed, of which half are charged-current quasielastic interactions ${\ensuremath{
u}}_{\ensuremath{\mu}}n\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}p$ occurring primarily in oxygen nuclei. We use a relativistic Fermi gas model for oxygen and assume the form factor is approximately a dipole with one parameter, the axial-vector mass ${M}_{A}$, and fit to the shape of the distribution of the square of the momentum transfer from the nucleon to the nucleus. Our best fit result for ${M}_{A}=1.20\ifmmode\pm\else\textpm\fi{}0.12\text{ }\text{ }\mathrm{GeV}$. Furthermore, this analysis includes updated vector form factors from recent electron scattering experiments and a discussion of the effects of the nucleon momentum on the shape of the fitted distributions.
135 citations
University of Tokyo1, Boston University2, Brookhaven National Laboratory3, University of California, Irvine4, California State University, Dominguez Hills5, Chonnam National University6, Duke University7, George Mason University8, Gifu University9, Indiana University10, Kobe University11, Kyoto University12, Los Alamos National Laboratory13, Louisiana State University14, University of Maryland, College Park15, University of Minnesota16, Miyagi University of Education17, Nagoya University18, Stony Brook University19, Niigata University20, Okayama University21, Osaka University22, Seoul National University23, Shizuoka University24, Sungkyunkwan University25, Tohoku University26, Tokai University27, Tokyo Institute of Technology28, University of Warsaw29, University of Washington30
TL;DR: A search for the appearance of tau neutrino appearance from nu(mu) <--> nu(tau) oscillations in the atmospheric neutrinos has been performed using 1489.2 days of atmospheric neutRino data from the Super-Kamiokande-I experiment.
Abstract: A search for the appearance of tau neutrinos from ${\ensuremath{
u}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{
u}}_{\ensuremath{\tau}}$ oscillations in the atmospheric neutrinos has been performed using 1489.2 days of atmospheric neutrino data from the Super-Kamiokande-I experiment. A best fit tau neutrino appearance signal of $138\ifmmode\pm\else\textpm\fi{}48(\mathrm{stat}{)}_{\ensuremath{-}32}^{+15}(\mathrm{syst})$ events is obtained with an expectation of $78\ifmmode\pm\else\textpm\fi{}26(\mathrm{syst})$. The hypothesis of no tau neutrino appearance is disfavored by 2.4 sigma.
92 citations
TL;DR: In this paper, an improved search for the K2K long-baseline neutrino oscillation was performed using the full data sample of 9.2x10{sup 19} protons on target.
Abstract: We performed an improved search for {nu}{sub {mu}}{yields}{nu}{sub e} oscillation with the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment, using the full data sample of 9.2x10{sup 19} protons on target. No evidence for a {nu}{sub e} appearance signal was found, and we set bounds on the {nu}{sub {mu}}{yields}{nu}{sub e} oscillation parameters. At {delta}m{sup 2}=2.8x10{sup -3} eV{sup 2}, the best-fit value of the K2K {nu}{sub {mu}} disappearance analysis, we set an upper limit of sin{sup 2}2{theta}{sub {mu}}{sub e}<0.13 at a 90% confidence level.
43 citations
University of Tokyo1, Boston University2, Pennsylvania State University3, Brookhaven National Laboratory4, University of California, Irvine5, California State University, Dominguez Hills6, Chonnam National University7, Duke University8, George Mason University9, Gifu University10, University of Hawaii11, Indiana University12, KEK13, Kobe University14, Kyoto University15, TRIUMF16, Los Alamos National Laboratory17, Louisiana State University18, University of Maryland, College Park19, Massachusetts Institute of Technology20, University of Minnesota21, Miyagi University of Education22, Nagoya University23, State University of New York System24, Niigata University25, Okayama University26, Osaka University27, Seoul National University28, Shizuoka University29, Sungkyunkwan University30, Tohoku University31, Tokai University32, Tokyo Institute of Technology33, University of Warsaw34, University of Washington35
TL;DR: In this article, the results from several studies used to search for astrophysical sources of high-energy neutrinos using the Super-Kamiokande I (1996 April-2001 July) neutrino-induced upward-going muon data were presented.
Abstract: We present the results from several studies used to search for astrophysical sources of high-energy neutrinos using the Super-Kamiokande I (1996 April-2001 July) neutrino-induced upward-going muon data. The data set consists of 2359 events with minimum energy 1.6 GeV, of which 1892 are through-going and 467 stop within the detector. The results of several independent analyses are presented, including searches for point sources using directional and temporal information and a search for signatures of cosmic-ray interactions with the interstellar medium in the upward-going muons. No statistically significant evidence for point sources or any diffuse flux from the plane of the Galaxy was found, so specific limits on fluxes from likely point sources are calculated. The 90% confidence level (CL) upper limits on upward-going muon flux from astronomical sources that are located in the southern hemisphere and always under the horizon for Super-Kamiokande are ~ × 10-15 cm-2 s-1.
31 citations
TL;DR: In this article, the upward-going muon flux induced by neutrinos from active galactic nuclei is expected to exceed the flux due to atmospheric neutrinuclear sources, and a search for this astrophysical neutrino flux is performed by looking for upwardgoing muons in the highest energy data sample from the Super-Kamiokande detector using 1679.6 live days of data.
Abstract: Many astrophysical models predict a diffuse flux of high-energy neutrinos from active galactic nuclei and other extragalactic sources. At muon energies above 1 TeV, the upward-going muon flux induced by neutrinos from active galactic nuclei is expected to exceed the flux due to atmospheric neutrinos. We have performed a search for this astrophysical neutrino flux by looking for upward-going muons in the highest energy data sample from the Super-Kamiokande detector using 1679.6 live days of data. We found one extremely high energy upward-going muon event, compared with an expected atmospheric neutrino background of 0.46 ± 0.23 events. Using this result, we set an upper limit on the diffuse flux of upward-going muons due to neutrinos from astrophysical sources in the muon energy range 3.16-100 TeV.
22 citations
TL;DR: In this article, the low-lying adiabatic potential energy surfaces of a one-dimensional extended Peierls-Hubbard model were calculated to reveal the relaxation mechanism of photogenerated charge-transfer excitations in quasi-one-dimensional halogen-bridged diplatinum complexes.
Abstract: In order to reveal the relaxation mechanism of photogenerated charge-transfer excitations in quasi-one-dimensional halogen-bridged diplatinum complexes, we calculate the low-lying adiabatic potential energy surfaces of a one-dimensional extended Peierls-Hubbard model. High-energy excitations above the electron-hole continuum may relax into polarons, while excitons pumped within the optical gap are self-localized and then either decay by luminescence or divide into solitons. Neutral solitons, charged solitons, and polarons may be simultaneously photogenerated in a diplatinum-halide chain, which has never been observed in any conventional platinum-halide chain. Optical conductivity is also simulated along the decay paths for experimental verification.
15 citations
TL;DR: In this paper, the ground-state properties of newly synthesized metal-halide ladder compounds were investigated based on a symmetry argument, and a fully dressed two-band Peierls-Hubbard model was employed to reveal possible charge- or spin-ordered states.
Abstract: Based on a symmetry argument, we investigate the ground-state properties of newly synthesized metal–halide ladder compounds (C 8 H 6 N 4 )[Pt(C 2 H 8 N 2 ) X ] 2 (ClO 4 ) 4 ·2H 2 O ( X =Cl, Br, and I). Employing a fully dressed two-band Peierls–Hubbard model, we systematically reveal possible charge- or spin-ordered states. Numerical phase diagrams demonstrate a variety of competing Peierls and Mott insulators with particular emphasis on the transition between two types of mixed-valent state of Pt II and Pt IV driven by varying interchain hopping integrals and Coulomb interactions.
13 citations
TL;DR: In this article, the nuclear spin-lattice relaxation time T 1 of 31 P nuclei in the title compound is measured for the first time and interpreted in terms of a modified spinwave theory.
Abstract: The nuclear spin–lattice relaxation time T 1 of 31 P nuclei in the title compound is measured for the first time and interpreted in terms of a modified spin–wave theory. We establish a novel scenario for one-dimensional ferrimagnetic spin dynamics – it is three-magnon processes enhanced by exchange scattering , rather than Raman processes, that make the major contribution to 1/ T 1 .
TL;DR: In this article, the nuclear spin-lattice relaxation rate for magnetic ring clusters was calculated by fully diagonalizing their microscopic spin Hamiltonians, and whether the nearest-neighbor exchange interactio...
Abstract: The nuclear spin–lattice relaxation rate 1/ T 1 is calculated for magnetic ring clusters by fully diagonalizing their microscopic spin Hamiltonians. Whether the nearest-neighbor exchange interactio...
TL;DR: The nuclear spin-lattice relaxation rate for magnetic ring clusters by fully diagonalizing their microscopic spin Hamiltonians was calculated in this article, where the lifetime broadening of discrete energy levels is in proportion to T^3^.
Abstract: The nuclear spin-lattice relaxation rate 1/T_1_ is calculated for magnetic ring clusters by fully diagonalizing their microscopic spin Hamiltonians. Whether the nearest-neighbor exchange interaction J is ferromagnetic or antiferromagnetic, 1/T_1_ versus temperature T in ring nanomagnets may be peaked at around k_B_T=|J| provided the lifetime broadening of discrete energy levels is in proportion to T^3^. Experimental findings for ferromagnetic and antiferromagnetic Cu^II^ rings are reproduced with crucial contributions of magnetic anisotropies as well as acoustic phonons.
TL;DR: In this paper, the nuclear spin-lattice relaxation time of the P-nodes in the title compound was measured for the first time and interpreted in terms of a modified spin-wave theory.
Abstract: The nuclear spin-lattice relaxation time $T_1$ of $^{31}P$ nuclei in the title compound is measured for the first time and interpreted in terms of a modified spin-wave theory. We establish a novel scenario for one-dimensional ferrimagnetic spin dynamics -- it is three-magnon processes enhanced by exchange scattering, rather than Raman processes, that make the major contribution to $1/T_1$.
Journal Article•
Journal Article•
TL;DR: In this article, the nuclear spin-lattice relaxation rate for magnetic ring clusters was calculated by fully diagonalizing their microscopic spin Hamiltonians, and whether the nearest-neighbor exchange interactio...
Abstract: The nuclear spin–lattice relaxation rate 1/ T 1 is calculated for magnetic ring clusters by fully diagonalizing their microscopic spin Hamiltonians. Whether the nearest-neighbor exchange interactio...