arXiv subjects

M. Yamaguchi

Publications and source records attributed to M. Yamaguchi.

At least 19 recordsLinked to original sources

arXiv2025

Determining the \Xi-Nucleus Potential from the Measured Binding Energies of ^15_\Xi^C

The recent observation of the deeply bound \Xi - hypernucleus ^15_\Xi^-C through the IRRAWADDY and KINKA events provided a crucial benchmark for determining the \Xi-nucleus interaction. This work aims to constrain the depth of this potential by calculating the binding energy B_\Xi of the ^15_\Xi C system, which forms a \Xi^- -^14 N bound state. We achieve this by numerically solving the Schroedinger equation for a \Xi hyperon within a phenomenological Woods-Saxon potential, using the stable Numerov method, incorporating the Coulomb interaction. For a potential well depth V_0 = 12 MeV, our calculations yield a 0^+_1 state binding energy of 6.35 MeV and a 1^-_1 state energy of 0.87 MeV. These results are in excellent agreement with the IRRAWADDY event (B_\Xi = 6.27 \pm 0.27 MeV) and the shallower 1^-_1 states (KISO/IBUKI events, B_\Xi \approx 1 MeV), respectively. Assuming \Xi^0 instead of \Xi^-, we predict the ground state 0^+ of _{\Xi^0}^{15}N with (B_{\Xi^0} = 2.636 MeV) by omitting the Coulomb interaction as a first approximation.

nucl-th↗

arXiv2017

Performance measurement of HARPO: a Time Projection Chamber as a gamma-ray telescope and polarimeter

We analyse the performance of a gas time projection chamber (TPC) as a high-performance gamma-ray telescope and polarimeter in the e$^+$e$^-$ pair creation regime. We use data collected at a gamma-ray beam of known polarisation. The TPC provides two orthogonal projections $(x,z)$ and $(y,z)$ of the tracks induced by each conversion in the gas volume. We use a simple vertex finder in which vertices and pseudo-tracks exiting from them are identified. We study the various contributions to the single-photon angular resolution using Monte Carlo simulations and compare them with the experimental data and find that they are in excellent agreement. The distribution of the azimutal angle of pair conversions shows a bias due to the non-cylindrical-symmetric structure of the detector. This bias would average out for a long duration exposure on a space mission, but for this pencil-beam characterisation we have ensured its accurate simulation by a double systematics control scheme, data taking with the detector rotated at several angles with respect to the beam polarisation direction and systematics control with a non-polarised beam. We measure, for the first time, the polarisation asymmetry of a linearly polarised gamma-ray beam in the low energy pair creation regime. This sub-GeV energy range is critical for cosmic sources as their spectra are power laws which fall quickly as a function of increasing energy. This work could pave the way to extending polarised gamma-ray astronomy beyond the MeV energy regime.

astro-ph.IM↗

arXiv2016

First measurement of polarisation asymmetry of a gamma-ray beam between 1.74 to 74 MeV with the HARPO TPC

Current $γ$-ray telescopes suffer from a gap in sensitivity in the energy range between 100keV and 100MeV, and no polarisation measurement has ever been done on cosmic sources above 1MeV. Past and present e$^+$e$^-$ pair telescopes are limited at lower energies by the multiple scattering of electrons in passive tungsten converter plates. This results in low angular resolution, and, consequently, a drop in sensitivity to point sources below 1GeV. The polarisation information, which is carried by the azimuthal angle of the conversion plane, is lost for the same reasons. HARPO (Hermetic ARgon POlarimeter) is an R\&D program to characterise the operation of a gaseous detector (a Time Projection Chamber or TPC) as a high angular-resolution and sensitivity telescope and polarimeter for $γ$ rays from cosmic sources. It represents a first step towards a future space instrument in the MeV-GeV range. We built and characterised a 30cm cubic demonstrator [SPIE 91441M], and put it in a polarised $γ$-ray beam at the NewSUBARU accelerator in Japan. Data were taken at photon energies from 1.74MeV to 74MeV, and with different polarisation configurations. We describe the experimental setup in beam. We then describe the software we developed to reconstruct the photon conversion events, with special focus on low energies. We also describe the thorough simulation of the detector used to compare results. Finally we will present the performance of the detector as extracted from this analysis and preliminary measurements of the polarisation asymmetry. This beam-test qualification of a gas TPC prototype in a $γ$-ray beam could open the way to high-performance $γ$-ray astronomy and polarimetry in the MeV-GeV energy range in the near future.

astro-ph.IM↗

arXiv2016

Measurement of 1.7 to 74 MeV polarised gamma rays with the HARPO TPC

Current γ-ray telescopes based on photon conversions to electron-positron pairs, such as Fermi, use tungsten converters. They suffer of limited angular resolution at low energies, and their sensitivity drops below 1 GeV. The low multiple scattering in a gaseous detector gives access to higher angular resolution in the MeV-GeV range, and to the linear polarisation of the photons through the azimuthal angle of the electron-positron pair. HARPO is an R&D program to characterise the operation of a TPC (Time Projection Chamber) as a high angular-resolution and sensitivity telescope and polarimeter for γ rays from cosmic sources. It represents a first step towards a future space instrument. A 30 cm cubic TPC demonstrator was built, and filled with 2 bar argon-based gas. It was put in a polarised γ-ray beam at the NewSUBARU accelerator in Japan in November 2014. Data were taken at different photon energies from 1.7 MeV to 74 MeV, and with different polarisation configurations. The electronics setup is described, with an emphasis on the trigger system. The event reconstruction algorithm is quickly described, and preliminary measurements of the polarisation of 11 MeVphotons are shown.

physics.ins-det↗

arXiv2015

Atomistic study on the cross-slip process of a screw dislocation in magnesium

The cross-slip process of a screw $<$a$>$ dislocation from the basal to the prismatic plane in magnesium was studied using the density functional theory and the molecular dynamics calculations. An atomistic method for calculating the total Peierls energy map has been devised to track the transition path of a dissociated and/or constricted screw $<$a$>$ dislocation in the cross-slip process. The barrier of a screw $<$a$>$ dislocation from the basal to the prismatic plane is estimated by the density functional theory for the first time to be $61.4\pm 2.0$ meV per Burgers vector length. The activation enthalpy for the cross slip is calculated using a line tension model based on the density functional theory to be $1.4$ to $1.7$ eV, which is in reasonable agreement with experiments. On the basis of the results, the effect of temperature on the cross-slip process of the dissociated screw $<$a$>$ dislocation on the basal plane is studied in detail using the molecular dynamics method with the embedded-atom-method (EAM) interatomic potential, in which the critical resolved shear stress for the cross slip is evaluated. It is confirmed that the bowed-out dislocation line on the prismatic plane consists of slightly dissociated rectilinear segments with connecting jogs at low temperatures and, as the temperature rises, the curved dislocation line becomes smooth with many segments. The motion of an $<$a$>$ dislocation on the prismatic plane is jerky in the low temperature region, while it is retarded by the formation of the largely dissociated plateau segment above the room temperature. A large reduction of the critical shear stress for the cross slip is obtained when the $<$a$>$ screw dislocation interacts with a hard-sphere particle placed on the basal plane in the low temperature region

cond-mat.mtrl-sci↗

arXiv2015

$γ$ ray spectroscopy of $^{19}$C via single neutron knock-out reaction

The one neutron knock-out reaction $^1$H($^{20}$C,$^{19}$C$γ$) was studied at RIKEN using the DALI2 array. A $γ$ ray transition was observed at 198(10) keV. Based on the comparison between the experimental production cross section and theoretical predictions, the transition was assigned to the decay of the 3/2$_1^+$ state to the ground state.

nucl-ex↗

arXiv2013

The effect of Hydrogen atom on the Screw Dislocation Mobility in BCC Iron: A First-Principles Study

We investigate the effect of hydrogen on the mobility of a screw dislocation in body-centered cubic (bcc) iron using first-principles calculations, and show that an increase of screw dislocation velocity is expected for a limited temperature range. The interaction energy between a screw dislocation and hydrogen atoms is calculated for various hydrogen positions and dislocation configurations with careful estimations of the finite size effects, and the strongest binding energy of a hydrogen atom to the stable screw dislocation configuration is estimated to be $256\pm32$ meV. These results are incorporated into a line tension model of a curved dislocation line to elucidate the effect of hydrogen on the dislocation migration process. Both the softening and hardening effect of hydrogen, caused by the reduction of kink nucleation enthalpy and kink trapping, respectively, are evaluated. A clear transition between softening and hardening behavior at the lower critical temperature is predicted, which is in qualitative agreement with the experimental observation.

cond-mat.mtrl-sci↗

arXiv2013

Core-excitation three-cluster model description of ^8He and ^10He

We introduce a new model applying to the core-nucleus and two-neutron system. The Faddeev equations of 6He-n-n and 8He-n-n systems for 8He and 10He are solved, respectively. The potential of the subsystem in the model has been determined to make a coupling both of the ground state and the excited one inside the core nucleus. By a similar mechanism the three-nucleon system is solved with the three-body force originating from an isobar excitation of the nucleon. Inputting only the information of subsystem energy levels and widths we get the coupling constants of rank 1 Yamaguchi potential between the core nucleus and neutron. We calculate the Faddeev three-cluster equations to obtain the low-lying energy levels of 8He and 10He. The 1- state of 10He, which has not been detected yet in experiments, is located in the energy level between the 0+ and 2+ states.

nucl-th↗

arXiv2011

Analyzing power in elastic scattering of 6He from polarized proton target at 71 MeV/nucleon

The vector analyzing power has been measured for the elastic scattering of neutron-rich 6He from polarized protons at 71 MeV/nucleon making use of a newly constructed solid polarized proton target operated in a low magnetic field and at high temperature. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a 6He nucleus. An optical model analysis revealed that the spin-orbit potential for 6He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semimicroscopic analysis with a alpha+n+n cluster folding model suggests that the interaction between a proton and the alpha core is essentially important in describing the p+6He elastic scattering. The data are also compared with fully microscopic analyses using non-local optical potentials based on nucleon-nucleon g-matrices.

nucl-ex↗

arXiv2010

Analyzing power for the proton elastic scattering from neutron-rich 6He nucleus

Vector analyzing power for the proton-6He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target working at low magnetic field of 0.09 T. The results are found to be incompatible with a t-matrix folding model prediction. Comparisons of the data with g-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The alpha-core distribution in 6He is suggested to be a possible key to understand the nuclear structure sensitivity.

nucl-ex↗

arXiv2010

Nuclear structure study of 19,20,21N nuclei by gamma spectroscopy

The structure of neutron rich nitrogen nuclei has been studied by use of neutron removal reaction and inelastic scattering. Mass and charge deformations have been deduced for the first excited state of 21N, which indicates the partial persitence of the N=14 subshell closure in nitrogen isotopes. The spectroscopic information obtained on the structure of 19,20,21N confirms the results from a previous experiment.

nucl-ex↗

arXiv2009

Cosmic Ray Tests of the Prototype TPC for the ILC Experiment

A time projection chamber (TPC) is a strong candidate for the central tracker of the international linear collider (ILC) experiment and we have been conducting a series of cosmic ray experiments under a magnetic field up to 4 T, using a small prototype TPC with a replaceable readout device: multi-wire proportional chamber (MWPC) or gas electron multiplier (GEM). We first confirmed that the MWPC readout could not be a fall-back option of the ILC-TPC under a strong axial magnetic field of 4 T since its spatial resolution suffered severely from the so called E x B effect in the vicinity of the wire planes. The GEM readout, on the other hand, was found to be virtually free from the E x B effect as had been expected and gave the resolution determined by the transverse diffusion of the drift electrons (diffusion limited). Furthermore, GEMs allow a wider choice of gas mixtures than MWPCs. Among the gases we tried so far a mixture of Ar-CF4-isobutane, in which MWPCs could be prone to discharges, seems promising as the operating gas of the ILC-TPC because of its small diffusion constant especially under a strong magnetic field. We report the measured drift properties of this mixture including the diffusion constant as a function of the electric field and compare them with the predictions of Magboltz. Also presented is the spatial resolution of a GEM-based ILC-TPC estimated from the measurement with the prototype.

physics.ins-det↗

arXiv2006

Separability of a Low-Momentum Effective Nucleon-Nucleon Potential

A realistic nucleon-nucleon potential is transformed into a low-momentum effective one (LMNN) using the Okubo theory. The separable potentials are converted from the LMNN with a universal separable expansion method and a simple Legendre expansion. Through the calculation of the triton binding energies, the separability for the convergence of these ranks is evaluated. It is found that there is a tendency for the lower momentum cutoff parameter $Λ$ of LMNN to gain good separability.

nucl-th↗

arXiv2006

Non-local Control of the Kondo Effect in a Double Quantum Dot-Quantum Wire Coupled System

We have performed low-temperature transport measurements on a double quantum dot-quantum wire coupled device and demonstrated non-local control of the Kondo effect in one dot by manipulating the electronic spin states of the other. We discuss the modulation of the local density of states in the wire region due to the Fano-Kondo antiresonance, and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) exchange interaction as the mechanisms responsible for the observed features.

cond-mat.mes-hall↗

arXiv2004

Photoluminescence measurements in Be-delta-doped back-gate induced quantum well

The photoluminescence (PL) spectra of a two-dimensional electron system induced in a Be-delta-doped GaAs/AlGaAs quantum well (QW) with a back gate are measured. The electron density is controlled from 1 X 10^{9} cm^{-2} to 2.5 X 10^{11} cm^{-2} by changing the back gate voltage. There is a linear increase in the acceptor PL spectrum around 1.49 eV with an increase in the back gate voltage and the PL disappears from the exciton bound to neutral donors (D^{0}X) around 1.51 eV at 1.2 X 10^{10} cm^{-2}.

cond-mat.mes-hall↗

arXiv2003

A new screening function for Coulomb renormalization

We introduce a new screening function which is useful for the few-body Coulomb scattering problem in ``screening and renormalization'' scheme. The new renormalization phase factor of the screening function is analytically shown. The Yukawa type of the screening potential has been used in several decades, we modify it to make more useful. As a concrete example, we compare the proton-proton scattering phase shifts calculated from these potentials. The numerical results document that high precision calculations of the renormalization are performed by the new screening function.

nucl-th↗

arXiv1998

Supersymmetry Breakdown at a Hidden Wall

We consider hidden sector supersymmetry breakdown in the strongly coupled heterotic $E_8\times E_8$ theory of Hořava and Witten. Using effective field theory methods in four dimensions, we can show that gravitational interactions induce soft breaking terms in the observable sector that are of order of the gravitiono mass. We apply these methods to the mechanism of gaugino condensation at the hidden wall. Although the situation is very similar to the weakly coupled case, there is a decisive difference concerning the observable sector gaugino mass; with desirable phenomenological as well as cosmological consequences.

hep-th↗

arXiv1998

Relic Abundance of Neutralinos in Heterotic String Theory: Weak Coupling vs. Strong Coupling

The relic abundance of stable neutralinos is investigated in $E_8 \times E_8'$ heterotic string theory when supersymmetry is spontaneously broken by hidden-sector gaugino condensates. In the weak coupling regime, very large scalar masses (compared to gaugino masses) are shown to lead to a too large relic abundance of the neutralinos, incompatible with cosmological observations in most of parameter space. The problem does not arise in the strong coupling regime (heterotic M-theory) because there scalar and gaugino masses are generically of the same order of magnitude.

hep-ph↗