arXiv subjects

K. Yamazaki

Publications and source records attributed to K. Yamazaki.

9 recordsLinked to original sources

arXiv2026

Observation of the Forbush decrease on 2024 May 10, using the ALPAQUITA air-shower array at the 70-1000 GV rigidity range

The Andes Large area PArticle detector for Cosmic ray and Astronomy (ALPACA) is a new air-shower array experiment under construction in the Bolivian Andes, and its prototype ALPAQUITA surface array has been operating since 2023 April. In addition to the traditional $\ge$3-hit or $\ge$4-hit coincidences to trigger recording air-shower events, ALPAQUITA records the counting rates of the $\ge$1-hit and $\ge$2-hit events (Any1 and Any2, respectively). We report a successful detection of a Forbush decrease occurred on 2024 May 10 caused by a passage of an interplanetary shock formed ahead of the Interplanetary Coronal Mass Ejection. The amplitude detected in the Any1 rate is 4.26$\pm$0.33% at the median primary rigidity of 76GV which is consistent with the observations with the worldwide neutron monitor and muon detector networks. Under the assumption of a power-law rigidity spectrum, we renormalized the errors of the observed amplitude ($A_{obs}$) and fitted them as a function of the median primary rigidity ($R_{m}$) of each detector and observational method. The result $A_{obs} = (10.9\% \pm 0.9\%) \times (R_{m}/10\,GV)^{-0.55 \pm 0.07}$ exhibits a hard nature of this event. Our non-detection in the Any2 rate decrease constrains the amplitude with a 2$\sigma$ upper limit to be 0.95% at 960GV. This marginally suggests an existence of a spectral softening between 100GV and 1000GV as also suggested by the Misato underground muon detector at 145GV. Although a strong geomagnetic storm was observed during this period, we conclude it does not impact our results. Our novel technique realizes a unique coverage to study the behavior of the Forbush decreases at the highest rigidity.

astro-ph.HE↗

arXiv2024

A new air shower array in the Southern Hemisphere looking for the origins of Cosmic rays: the ALPACA experiment

The Tibet AS$\gamma$ experiment successfully detected sub-PeV $\gamma$-rays from the Crab nebula using a Surface Array and underground muon detector. Considering this, we are building in Bolivia a new experiment to explore the Southern Hemisphere, looking for the origins of cosmic rays in our Galaxy. The name of this project is Andes Large area PArticle detector for Cosmic ray physics and Astronomy (ALPACA). A prototype array called ALPAQUITA, with $1/4$ the total area of the full ALPACA, started observations in September $2022$. In this paper we introduce the status of ALPAQUITA and the plans to extend the array. We also report the results of the observation of the moon shadow in cosmic rays.

astro-ph.HE↗

arXiv2023

Small-scale cosmic ray anisotropy observed by the GRAPES-3 experiment at TeV energies

GRAPES-3 is a mid-altitude (2200 m) and near equatorial ($11.4^{\circ}$ North) air shower array, overlapping in its field of view for cosmic ray observations with experiments that are located in Northern and Southern hemispheres. We analyze a sample of $3.7\times10^9$ cosmic ray events collected by the GRAPES-3 experiment between 1 January 2013 and 31 December 2016 with a median energy of $\sim16$ TeV for study of small-scale ($<60^{\circ}$) angular scale anisotropies. We observed two structures labeled as A and B, deviate from the expected isotropic distribution of cosmic rays in a statistically significant manner. Structure `A' spans $50^{\circ}$ to $80^{\circ}$ in the right ascension and $-15^{\circ}$ to $30^{\circ}$ in the declination coordinate. The relative excess observed in the structure A is at the level of $(6.5\pm1.3)\times10^{-4}$ with a statistical significance of 6.8 standard deviations. Structure `B' is observed in the right ascension range of $110^{\circ}$ to $140^{\circ}$. The relative excess observed in this region is at the level of $(4.9\pm1.4)\times10^{-4}$ with a statistical significance of 4.7 standard deviations. These structures are consistent with those reported by Milagro, ARGO-YBJ, and HAWC. These observations could provide a better understanding of the cosmic ray sources, propagation and the magnetic structures in our Galaxy.

astro-ph.HE↗

arXiv2022

A multiple scattering theoretical approach to time delay in high energy core-level photoemission of heteronuclear diatomic molecules

We present analytical expressions of momentum-resolved core-level photoemission time delay in a molecular frame of a heteronuclear diatomic molecule upon photoionization by a linearly polarized soft x-rays attosecond pulse. For this purpose, we start to derive a general expression of photoemission time delay based on the first order time dependent perturbation theory within the one electron and single channel model in the fixed-in-space system (atoms, molecules and crystals) and apply it to the core-level photoemission within the electric dipole approximation. By using multiple scattering theory and applying series expansion, plane wave and muffin-tin approximations, the core-level photoemission time delay $t$ is divided into three components, $t_{\rm abs}$, $t_{\rm path}$ and $t_{\rm sc}$, which are atomic photoemission time delay, delays caused by the propagation of photoelectron among the surrounding atoms and the scattering of photoelectron by them, respectively. We applied single scattering approximation to $t_{\rm path}$ and obtained $t_{\rm path}^{(1)}(k,θ)$ with polarization vector parallel to the molecular axis for a heteronuclear diatomic molecule, where $θ$ is the angle of measured photoelectron from the molecular axis. $t$ is approximated well with this simplified expression $t_{\rm path}^{(1)}(k,θ)$ in the high energy regime ($k\gtrsim 3.5\,\, {\rm a.u.}^{-1}$), and the validity of this estimated result is confirmed by comparing it with multiple scattering calculations for C 1$s$ core-level photoemission time delay of CO molecules. $t_{\rm path}^{(1)}(k,θ)$ shows characteristic dependence on $θ$, it becomes zero at $θ=0$, exhibits EXAFS type oscillation with $2kR$ at $θ=π$, where $R$ is the bondlength, and gives just the travelling time of photoelectron from the absorbing atom to the neighbouring atom at $θ=π/2$.

physics.chem-ph↗

arXiv2021

Construction of an Engel manifold with trivial automorphism group

An Engel manifold is a 4-manifold with a completely non-integrable 2-distribution called Engel structure. I research the functorial relation between Engel manifolds and Contact 3-orbifolds. And I construct an Engel manifold that the automorphism group is trivial.

math.SG↗

arXiv2021

Detectability of southern gamma-ray sources beyond 100 TeV with ALPAQUITA, the prototype experiment of ALPACA

Andes Large-area PArticle detector for Cosmic-ray physics and Astronomy (ALPACA) is an international experiment that applies southern very-high-energy (VHE) gamma-ray astronomy to determine the origin of cosmic rays around the knee energy region ($10^{15}\, {\rm eV} - 10^{16}\, {\rm eV}$). The experiment consists of an air shower (AS) array with a surface of $83, 000\, {\rm m}^2$ and an underground water Cherenkov muon detector (MD) array covering $5, 400\, {\rm m}^2$. The experimental site is at the Mt. Chacaltaya plateau in La Paz, Bolivia, with an altitude of $4, 740\, {\rm m}$ corresponding to $572\, {\rm g}/{\rm cm}^2$ atmospheric thickness. As the prototype experiment of ALPACA, the ALPAQUITA experiment aims to begin data acquisition in late 2021. The ALPAQUITA array consists of a smaller AS array ($18, 450\, {\rm m}^2$) and underground MD ($900\, {\rm m}^2$), which are now under construction. ALPAQUITA's sensitivity to gamma-ray sources is evaluated with Monte Carlo simulations. The simulation finds that five gamma-ray sources observed by H.E.S.S. and HAWC experiments will be detected by ALPAQUITA beyond 10 TeV and one out of these five - HESS J1702-420A - above 300 TeV in one calendar year observation. The latter finding means that scientific discussions can be made on the emission mechanism of gamma rays beyond 100 TeV from southern sources on the basis of the observational results of this prototype experiment.

astro-ph.HE↗

arXiv2015

Detection of ultra-high energy cosmic ray showers with a single-pixel fluorescence telescope

We present a concept for large-area, low-cost detection of ultra-high energy cosmic rays (UHECRs) with a Fluorescence detector Array of Single-pixel Telescopes (FAST), addressing the requirements for the next generation of UHECR experiments. In the FAST design, a large field of view is covered by a few pixels at the focal plane of a mirror or Fresnel lens. We report first results of a FAST prototype installed at the Telescope Array site, consisting of a single 200 mm photomultiplier tube at the focal plane of a 1 m$^2$ Fresnel lens system taken from the prototype of the JEM-EUSO experiment. The FAST prototype took data for 19 nights, demonstrating remarkable operational stability. We detected laser shots at distances of several kilometres as well as 16 highly significant UHECR shower candidates.

astro-ph.IM↗

arXiv2011

A contribution of stellar flares to the GRXE -- based on MAXI observations --

Using unbiased observations of MAXI/GSC the potential contribution of stellar flares and CVs to GRXE luminosity is estimated in the energy range of 2 - 10 keV. Currently, a reasonable luminosity has been obtained extrapolating the number of stellar flares and that of CVs toward the Galactic ridge from those of the observed flares and CVs near the solar system. The ionized emission lines of Si to Fe are also simulated making the composite thermal spectrum which is based on MAXI observations of stellar flares and CVs. The present estimated result strongly supports a picture that the cumulative stellar flares contribute primarily to the GRXE in terms of the composite thermal spectrum with emission lines and secondary contribution is due to the thermal spectrum with high temperature from CVs.

astro-ph.HE↗

arXiv2007

Unmasking the nodal quasiparticle dynamics in cuprate superconductors using low-energy photoemission

Nodal quasiparticles of Bi2Sr2CaCu2O8 have been studied by angle-resolved photoemission spectroscopy with high momentum and energy resolution. Low-energy tunable photons have enabled us to resolve a small nodal bilayer splitting, unmasking the intrinsic single-particle scattering rate. The nodal scattering rate is abruptly suppressed upon the superconducting transition, and shows a linear energy dependence at low energies, indicating the nontrivial effect of elastic scatterings on the quasiparticles. With increasing energy, the antibonding-band scattering rate becomes higher than the bonding one. The observations imply the character of the scatterers dominant at low energies.

cond-mat.supr-con↗