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A. Suzuki

Publications and source records attributed to A. Suzuki.

At least 109 records · Page 6Linked to original sources
arXiv2011

Measurement of the 8B Solar Neutrino Flux with the KamLAND Liquid Scintillator Detector

We report a measurement of the neutrino-electron elastic scattering rate from 8B solar neutrinos based on a 123 kton-day exposure of KamLAND. The background-subtracted electron recoil rate, above a 5.5 MeV analysis threshold is 1.49+/-0.14(stat)+/-0.17(syst) events per kton-day. Interpreted as due to a pure electron flavor flux with a 8B neutrino spectrum, this corresponds to a spectrum integrated flux of 2.77+/-0.26(stat)+/-0.32(syst) x 10^6 cm^-2s^-1. The analysis threshold is driven by 208Tl present in the liquid scintillator, and the main source of systematic uncertainty is due to background from cosmogenic 11Be. The measured rate is consistent with existing measurements and with Standard Solar Model predictions which include matter enhanced neutrino oscillation.

hep-ex↗
arXiv2011

Removal of UV cutoff for the Nelson model with variable coefficients

We consider the Nelson model with variable coefficients. Nelson models with variable coefficients arise when one replaces in the usual Nelson model the flat Minkowski metric by a static metric, allowing also the boson mass to depend on position. We study the removal of the ultraviolet cutoff.

math-ph↗
arXiv2011

Infrared divergence of a scalar quantum field model on a pseudo Riemannian manifold

A scalar quantum field model defined on a pseudo Riemann manifold is considered. The model is unitarily transformed the one with a variable mass. By means of a Feynman-Kac-type formula, it is shown that when the variable mass is short range, the Hamiltonian has no ground state. Moreover the infrared divergence of the expectation values of the number of bosons in the ground state is discussed.

math-ph↗
arXiv2010

Absence of ground state for the Nelson model on static space-times

We consider the Nelson model on some static space-times and investigate the problem of absence of a ground state. Nelson models with variable coefficients arise when one replaces in the usual Nelson model the flat Minkowski metric by a static metric, allowing also the boson mass to depend on position. We investigate the absence of a ground state of the Hamiltonian in the presence of the infrared problem, i.e. assuming that the boson mass $m(x)$ tends to $0$ at spatial infinity. Using path space techniques, we show that if $m(x)\leq C |x|^{-μ}$ at infinity for some $C>0$ and $μ>1$ then the Nelson Hamiltonian has no ground state.

math-ph↗
arXiv2010

The new generation CMB B-mode polarization experiment: POLARBEAR

We describe the Cosmic Microwave Background (CMB) polarization experiment called Polarbear. This experiment will use the dedicated Huan Tran Telescope equipped with a powerful 1,200-bolometer array receiver to map the CMB polarization with unprecedented accuracy. We summarize the experiment, its goals, and current status.

astro-ph.IM↗
arXiv2009

Scintillator counters with WLS fiber/MPPC readout for the side muon range detector (SMRD)of the T2K experiment

The T2K neutrino experiment at J-PARC uses a set of near detectors to measure the properties of an unoscillated neutrino beam and neutrino interaction cross-sections. One of the sub-detectors of the near-detector complex, the side muon range detector (SMRD), is described in the paper. The detector is designed to help measure the neutrino energy spectrum, to identify background and to calibrate the other detectors. The active elements of the SMRD consist of 0.7 cm thick extruded scintillator slabs inserted into air gaps of the UA1 magnet yokes. The readout of each scintillator slab is provided through a single WLS fiber embedded into a serpentine shaped groove. Two Hamamatsu multi-pixel avalanche photodiodes (MPPC's) are coupled to both ends of the WLS fiber. This design allows us to achieve a high MIP detection efficiency of greater than 99%. A light yield of 25-50 p.e./MIP, a time resolution of about 1 ns and a spatial resolution along the slab better than 10 cm were obtained for the SMRD counters.

physics.ins-det↗
arXiv2006

A simple model of reactor cores for reactor neutrino flux calculations for the KamLAND experiment

KamLAND is a reactor neutrino oscillation experiment with a very long baseline. This experiment successfully measured oscillation phenomena of reactor antineutrinos coming mainly from 53 reactors in Japan. In order to extract the results, it is necessary to accurately calculate time-dependent antineutrino spectra from all the reactors. A simple model of reactor cores and code implementing it were developed for this purpose. This paper describes the model of the reactor cores used in the KamLAND reactor analysis.

physics.data-an↗
arXiv2005

Measurement of the response of a Ga solar neutrino experiment to neutrinos from an 37Ar source

An intense source of 37Ar was produced by the (n,alpha) reaction on 40Ca by irradiating 330 kg of calcium oxide in the fast neutron breeder reactor at Zarechny, Russia. The 37Ar was released from the solid target by dissolution in acid, collected from this solution, purified, sealed into a small source, and brought to the Baksan Neutrino Observatory where it was used to irradiate 13 tonnes of gallium metal in the Russian-American gallium solar neutrino experiment SAGE. Ten exposures of the gallium to the source, whose initial strength was 409 +/- 2 kCi, were carried out during the period April to September 2004. The 71Ge produced by the reaction 71Ga(nu_e,e^-)71Ge was extracted, purified, and counted. The measured production rate was 11.0 ^+1.0 _-0.9 (stat) +/- 0.6 (syst) atoms of 71Ge/d, which is 0.79 ^+0.09_-0.10 of the theoretically calculated production rate. When all neutrino source experiments with gallium are considered together, there is an indication the theoretical cross section has been overestimated.

nucl-ex↗
arXiv2005

Neutrino geophysics with KamLAND and future prospects

The Kamioka liquid scintillator anti-neutrino detector (KamLAND) is a low-energy and low-background neutrino detector which could be a useful probe for determining the U and Th abundances of the Earth. We constructed a model of the Earth in order to evaluate the rate of geologically produced anti-neutrinos (geo-neutrinos) detectable by KamLAND. We found that KamLAND can be used to determine the absolute abundances of U and Th in the Earth with an accuracy sufficient for placing important constraints on Earth's accretional process and succeeding thermal history. The present observation of geo-neutrinos with KamLAND is consistent with our model prediction based on the bulk silicate Earth (BSE) composition within the uncertainty of the measurement. If a neutrino detector were to be built in Hawaii, where effects of the continental crust would be negligible, it could be used to estimate the U and Th content in the lower mantle and the core. Our calculation of the geo-neutrino event rate on the Earth's surface indicates that geo-neutrino observation can provide key information for testing the current models for the content and distribution of U and Th in the Earth.

hep-ph↗
arXiv2005

Real space imaging of the metal - insulator phase separation in the band width controlled organic Mott system $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br

Systematic investigation of the electronic phase separation on macroscopic scale is reported in the organic Mott system $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br. Real space imaging of the phase separation is obtained by means of scanning micro-region infrared spectroscopy using the synchrotron radiation. The phase separation appears near the Mott boundary and changes its metal-insulator fraction with the substitution ratio $x$ in $κ$-[($h$-BEDT-TTF)$_{1-x}$($d$-BEDT-TTF)$_{x}$]$_{2}$Cu[N(CN)$_{2}$]Br, of which band width is controlled by the substitution ratio $x$ between the hydrogenated BEDT-TTF molecule ($h$-BEDT-TTF) and the deuterated one ($d$-BEDT-TTF). The phase separation phenomenon observed in this class of organics is considered on the basis of the strongly correlated electronic phase diagram with the first order Mott transition.

cond-mat.supr-con↗
arXiv2001

The JHF-Kamioka neutrino project

The JHF-Kamioka neutrino project is a second generation long base line neutrino oscillation experiment that probes physics beyond the Standard Model by high precision measurements of the neutrino masses and mixing. A high intensity narrow band neutrino beam is produced by secondary pions created by a high intensity proton synchrotron at JHF (JAERI). The neutrino energy is tuned to the oscillation maximum at ~1 GeV for a baseline length of 295 km towards the world largest water Cerenkov detector, Super-Kamiokande. Its excellent energy resolution and particle identification enable the reconstruction of the initial neutrino energy, which is compared with the narrow band neutrino energy, through the quasi-elastic interaction. The physics goal of the first phase is an order of magnitude better precision in the nu_mu to nu_tau oscillation measurement (delta(Delta m_23^2)=10^-4 eV^2 and delta(sin^22theta_23)=0.01), a factor of 20 more sensitive search in the nu_mu to nu_e appearance (sin^22theta_{mu e} ~ 0.5sin^22theta_{13}>0.003), and a confirmation of the nu_mu to nu_tau oscillation or discovery of sterile neutrinos by detecting the neutral current events. In the second phase, an upgrade of the accelerator from 0.75 MW to 4 MW in beam power and the construction of 1 Mt Hyper-Kamiokande detector at Kamioka site are envisaged. Another order of magnitude improvement in the nu_mu to nu_e oscillation sensitivity, a sensitive search of the CP violation in the lepton sector (CP phase "delta" down to 10-20 degrees), and an order of magnitude improvement in the proton decay sensitivity is also expected.

hep-ex↗
arXiv2000

Design, construction, and operation of SciFi tracking detector for K2K experiment

We describe the construction and performance of a scintillating fiber detector used in the near detector for the K2K (KEK to Kamioka, KEK E362) long baseline neutrino oscillation experiment. The detector uses 3.7 m long and 0.692 mm diameter scintillating fiber coupled to image-intensifier tubes (IIT), and a CCD camera readout system. Fiber sheet production and detector construction began in 1997, and the detector was commissioned in March, 1999. Results from the first K2K runs confirm good initial performance : position resolution is estimated to be about 0.8 mm, and track finding efficiency is $98 \pm 2$ % for long tracks (i.e., those which intersect more than 5 fiber planes). The hit efficiency was estimated to be $92 \pm 2$ % using cosmic-ray muons, after noise reduction at the offline stage. The possibility of using the detector for particle identification is also discussed.

hep-ex↗
arXiv1998

TeV gamma-ray observations of southern BL Lacs with the CANGAROO 3.8m Imaging Telescope

Observational and theoretical results indicate that low-redshift BL Lacertae objects are the most likely extragalactic sources to be detectable at TeV energies. In this paper we present the results of observations of 4 BL Lacertae objects (PKS0521-365, EXO0423.4-0840, PKS2005-489 and PKS2316-423) made between 1993 and 1996 with the CANGAROO 3.8m imaging Cherenkov telescope. During the period of these observations the gamma-ray energy threshold of the 3.8m telescope was ~2TeV. Searches for steady long-term emission have been made, and, inspired by the TeV flares detected from Mkn421 and Mkn501, a search on a night-by-night timescale has also been performed for each source. Comprehensive Monte Carlo simulations are used to estimate upper limits for both steady and short timescale emission.

astro-ph↗
arXiv1998

Discovery of TeV Gamma Rays from SN1006: Further Evidence for the SNR Origin of Cosmic Rays

This paper reports the first discovery of TeV gamma-ray emission from a supernova remnant made with the CANGAROO 3.8 m Telescope. TeV gamma rays were detected at the sky position and extension coincident with the north-east (NE) rim of shell-type Supernova remnant (SNR) SN1006 (Type Ia). SN1006 has been a most likely candidate for an extended TeV Gamma-ray source, since the clear synchrotron X-ray emission from the rims was recently observed by ASCA (Koyama et al. 1995), which is a strong evidence of the existence of very high energy electrons up to hundreds of TeV in the SNR. The observed TeV gamma-ray flux was $(2.4\pm 0.5(statistical) \pm 0.7(systematic)) \times 10^{-12}$ cm$^{-2}$ s$^{-1}$ ($\ge 3.0\pm 0.9$ TeV) and $ (4.6\pm 0.6 \pm 1.4) \times 10^{-12}$ cm$^{-2}$ s$^{-1}$ ($\ge 1.7\pm 0.5$ TeV) from the 1996 and 1997 observations, respectively. Also we set an upper limit on the TeV gamma-ray emission from the SW rim, estimated to be $ 1.1 \times 10^{-12}$ cm$^{-2}$ s$^{-1}$ ($\ge 1.7\pm 0.5$ TeV, 95% CL) in the 1997 data. The TeV gamma rays can be attributed to the 2.7 K cosmic background photons up-scattered by electrons of energies up to about 10$^{14}$ eV by the inverse Compton (IC) process. The observed flux of the TeV gamma rays, together with that of the non-thermal X-rays, gives firm constraints on the acceleration process in the SNR shell; a magnetic field of $6.5\pm2$ $μ$G is inferred from both the synchrotron X-rays and inverse Compton TeV gamma-rays, which gives entirely consistent mechanisms that electrons of energies up to 10$^{14}$ eV are produced via the shock acceleration in SN1006.

astro-ph↗
arXiv1997

Detection of Gamma Rays of Up to 50 TeV From the Crab Nebula

Gamma rays with energies greater than 7 TeV from the Crab pulsar/nebula have been observed at large zenith angles, using the Imaging Atmospheric Technique from Woomera, South Australia. CANGAROO data taken in 1992, 1993 and 1995 indicate that the energy spectrum extends up to at least 50 TeV, without a change of the index of the power law spectrum. The observed differential spectrum is \noindent $(2.01\pm 0.36)\times 10^{-13}(E/{7 TeV})^{-2.53 \pm 0.18} TeV^{-1}cm^{-2}s^{-1}$ between 7 TeV and 50 TeV. There is no apparent cut-off. The spectrum for photon energies above $\sim$10 TeV allows the maximum particle acceleration energy to be inferred, and implies that this unpulsed emission does not originate near the light cylinder of the pulsar, but in the nebula where the magnetic field is not strong enough to allow pair creation from the TeV photons. The hard gamma-ray energy spectrum above 10 TeV also provides information about the varying role of seed photons for the inverse Compton process at these high energies, as well as a possible contribution of $π^{\circ}$-gamma rays from proton collisions.

astro-ph↗
arXiv1997

Very High Energy Gamma Rays from the Vela Pulsar Direction

We have observed the Vela pulsar region at TeV energies using the 3.8 m imaging Cherenkov telescope near Woomera, South Australia between January 1993 and March 1995. Evidence of an unpulsed gamma-ray signal has been detected at the 5.8 sigma level. The detected gamma-ray flux is (2.9 +/- 0.5 +/- 0.4) x 10^-12 photons cm^-2 sec^-1 above 2.5 +/- 1.0 TeV and the signal is consistent with steady emission over the two years. The gamma-ray emission region is offset from the Vela pulsar position to the southeast by about 0.13 deg. No pulsed emission modulated with the pulsar period has been detected and the 95 % confidence flux upper limit to the pulsed emission from the pulsar is (3.7 +/- 0.7) x 10^-13 photons cm^-2 sec^-1 above 2.5 +/- 1.0 TeV.

astro-ph↗
arXiv1997

Observations of Pulsars, PSR 1509-58 and PSR 1259-63, by CANGAROO 3.8 m Telescope

The data for VHE (~TeV) gamma rays from young gamma-ray pulsar PSR1509-58 observed in 1996 with the CANGAROO 3.8m Cerenkov imaging telescope are presented, as well as the additional data from March to June of 1997. The high spin-down luminosity of the pulsar and the plerionic feature around the pulsar observed with radio and X-rays suggest that VHE gamma-ray emission is quite likely above the sensitivity of the CANGAROO telescope. The CANGAROO results on other pulsars, such as PSR1259-63, are also presented. PSR1259-63 is a highly eccentric X-ray binary system, which includes a high mass Be companion star, and a preliminary analysis on the data taken 4 months after the periastron in 1994 suggests emission of VHE gamma rays.

astro-ph↗