arXiv subjects

T. Ishikawa

Publications and source records attributed to T. Ishikawa.

At least 37 records · Page 2Linked to original sources

arXiv2021

Resonance-like structure near the $ηd$ threshold in the $γ{d}${$\to$}$π^0η{d}$ reaction

To investigate the interaction between the nucleon $N$ and nucleon resonance $N(1535)1/2^-$, the $ηd$ threshold structure connected to the isoscalar $S$-wave $N$-$N(1535)1/2^-$ system has been experimentally studied in the $γ{d}${$\to$}$π^0η{d}$ reaction at incident photon energies ranging from the reaction threshold to 1.15 GeV. A strong enhancement is observed near the $ηd$ threshold over the three-body phase-space contribution in the $ηd$ invariant-mass distribution. An analysis incorporating the known isovector resonance $\mathcal{D}_{12}$ with a spin-parity of $2^+$ in the $π^0d$ channel reveals the existence of a narrow isoscalar resonance-like structure with $1^-$ in the $ηd$ system. Using a Flatté parametrization, the mass is found to be $2.427_{-0.006}^{+0.013}$ GeV, close to the $ηd$ threshold, and the width is $\left(0.029_{-0.029}^{+0.006}{\rm\ GeV}\right)+\left(0.00_{-0.00}^{+0.41}\right) p_ηc$, where $p_η$ denotes the $η$ momentum in the rest frame of the $ηd$ system. The observed structure would be attributed to a predicted isoscalar $1^-$ $ηNN$ bound state from $ηNN$ and $πNN$ coupled-channel calculation, or an $ηd$ virtual state owing to strong $ηd$ attraction.

nucl-ex↗

arXiv2021

Theoretical study of reflection spectroscopy for superconducting quantum parametrons

Superconducting parametrons in the single-photon Kerr regime, also called KPOs, have been attracting increasing attention in terms of their applications to quantum annealing and universal quantum computation. It is of practical importance to obtain information of superconducting parametrons operating under an oscillating pump field. Spectroscopy can provide information of a superconducting parametron under examination, such as energy level structure, and also useful information for calibration of the pump field. We theoretically study the reflection spectroscopy of superconducting parametrons, and develop a method to obtain the reflection coefficient. We present formulae of the reflection coefficient, the nominal external and the internal decay rates, and examine the obtained spectra. It is shown that the difference of the populations of energy levels manifests itself as a dip or peak in the amplitude of the reflection coefficient, and one can directly extract the coupling strength between the energy levels by measuring the nominal decay rates when the pump field is sufficiently large.

quant-ph↗

arXiv2021

Low background measurement in CANDLES-III for studying the neutrino-less double beta decay of $^{48}$Ca

We developed a CANDLES-III system to study the neutrino-less double beta (0$νββ$) decay of $^{48}$Ca. The proposed system employs 96 CaF$_{2}$ scintillation crystals (305 kg) with natural Ca ($^{\rm nat.}$Ca) isotope which corresponds 350\,g of $^{48}$Ca. External backgrounds were rejected using a 4$π$ active shield of a liquid scintillator surrounding the CaF$_2$ crystals. The internal backgrounds caused by the radioactive impurities within the CaF$_2$ crystals can be reduced effectively through analysis of the signal pulse shape. We analyzed the data obtained in the Kamioka underground for a live-time of 130.4\,days to evaluate the feasibility of the low background measurement with the CANDLES-III detector. Using Monte Carlo simulations, we estimated the background rate from the radioactive impurities in the CaF$_{2}$ crystals and the rate of high energy $γ$-rays caused by the (n, $γ$) reactions induced by environmental neutrons. The expected background rate was in a good agreement with the measured rate, i.e., approximately 10$^{-3}$ events/keV/yr/(kg of $^{\rm nat.}$Ca), in the 0$νββ$ window. In conclusion, the background candidates were estimated properly by comparing the measured energy spectrum with the background simulations. With this measurement method, we performed the first search for 0$νββ$ decay in a low background condition using a detector with a Ca isotope, in which the Ca present was not enriched, in a scale of hundreds of kg. The $^{48}$Ca isotope has a high potential for use in 0$νββ$ decay search, and is expected to be useful for the development of a next-generation detector for highly sensitive measurements.

hep-ex↗

arXiv2021

Evolution of charge dynamics in FeSe$_{1-x}$Te$_{x}$: Effects of electronic correlations and nematicity

We systematically studied in-plane optical conductivity of FeSe$_{1-x}$Te$_{x}$ thin films fabricated on CaF$_{2}$ substrates for $x$ = 0, 0.1, 0.2, and 0.4. This system shows a large enhancement of superconducting transition temperature $T_{\mathrm{c}}$ at $x \sim$ 0.2 and a gentle decrease in $T_{\mathrm{c}}$ with further increasing $x$. The low-energy optical conductivity spectrum is described by the sum of narrow and broad Drude components, associated with coherent and incoherent charge dynamics, respectively. With increasing Te content, the spectral weight of the narrow Drude component decreases, while the total weight of the two Drude components increases. As a consequence, the fraction of the narrow Drude weight significantly decreases, indicating that Te substitution leads to stronger electronic correlations. Below the nematic transition temperature, the narrow Drude weight decreases with decreasing temperature. This indicates the reduction of the coherent carrier density, resulting from the Fermi-surface modification induced by the development of the orbital order. The reduction of the narrow Drude weight with temperature stopped at $x \sim$ 0.2, corresponding to the disappearance of the nematic transition. Our result suggests that the increase in the coherent carrier density induced by the suppression of the nematic transition gives rise to the enhancement of $T_{\mathrm{c}}$. The decrease in $T_{\mathrm{c}}$ with further Te substitution likely arises from too strong electronic correlations, which are not favorable for superconductivity.

cond-mat.supr-con↗

arXiv2020

Observation of a $\bar{K}NN$ bound state in the $^3{\rm He} (K^-, Λp)n$ reaction

We have performed an exclusive measurement of the $K^{-}+\! ~^{3}{\rm He} \to Λpn$ reaction at an incident kaon momentum of $1\ {\rm GeV}/c$.In the $Λp$ invariant mass spectrum, a clear peak was observed below the mass threshold of $\bar{K}\!+\!N\!+\!N$, as a signal of the kaonic nuclear bound state, $\bar{K}NN$.The binding energy, decay width, and $S$-wave Gaussian reaction form-factor of this state were observed to be $B_{K} = 42\pm3({\rm stat.})^{+3}_{-4}({\rm syst.})\ {\rm MeV}$, $Γ_{K} = 100\pm7({\rm stat.})^{+19}_{-9}({\rm syst.})\ {\rm MeV}$, and $Q_{K} = 383\pm11({\rm stat.})^{+4}_{-1}({\rm syst.})\ {\rm MeV}/c$, respectively. The total production cross-section of $\bar{K}NN$, determined by its $Λp$ decay mode, was $σ^{tot}_{K} \cdot BR_{Λp} = 9.3\pm0.8({\rm stat.})^{+1.4}_{-1.0}({\rm syst.})\ μ{\rm b}$.We estimated the branching ratio of the $\bar{K}NN$ state to the $Λp$ and $Σ^{0}p$ decay modes as $BR_{Λp}/BR_{Σ^{0}p} \sim 1.7$, by assuming that the physical processes leading to the $ΣN\!N$ final states are analogous to those of $Λpn$.

nucl-ex↗

arXiv2020

Search for $η'$ bound nuclei in the $^{12}{\rm C}(γ,p)$ reaction with simultaneous detection of decay products

We measured missing mass spectrum of the $^{12}{\rm C}(γ,p)$ reaction for the first time in coincidence with potential decay products from $η'$ bound nuclei. We tagged an ($η+p$) pair associated with the $η'N\toηN$ process in a nucleus. After applying kinematical selections to reduce backgrounds, no signal events were observed in the bound-state region. An upper limit of the signal cross section in the opening angle $\cosθ^{ηp}_{lab}<-0.9$ was obtained to be 2.2 nb/sr at the 90$\%$ confidence level. It is compared with theoretical cross sections, whose normalization ambiguity is suppressed by measuring a quasifree $η'$ production rate. Our results indicate a small branching fraction of the $η'N\toηN$ process and/or a shallow $η'$-nucleus potential.

nucl-ex↗

arXiv2020

Rheology of a concentrated suspension of spherical squirmers: monolayer in simple shear flow

A concentrated, vertical monolayer of identical spherical squirmers, which may be bottom-heavy, and which are subjected to a linear shear flow, is modelled computationally by two different methods: Stokesian dynamics, and a lubrication-theory-based method. Inertia is negligible. The aim is to compute the effective shear viscosity and, where possible, the normal stress differences as functions of the areal fraction of spheres $ϕ$, the squirming parameter $β$ (proportional to the ratio of a squirmer's active stresslet to its swimming speed), the ratio $Sq$ of swimming speed to a typical speed of the shear flow, the bottom-heaviness parameter $G_{bh}$, the angle $α$ that the shear flow makes with the horizontal, and two parameters that define the repulsive force that is required computationally to prevent the squirmers from overlapping when their distance apart is less than a critical value $εa$, where $ε$ is very small and $a$ is the sphere radius. The Stokesian dynamics method allows the rheological quantities to be computed for values of $ϕ$ up to $0.75$; the lubrication-theory method can be used for $ϕ> 0.5$. A major finding of this work is that, despite very different assumptions, the two methods of computation give overlapping results for viscosity as a function of $ϕ$ in the range $0.5 < ϕ< 0.75$. This suggests that lubrication theory, based on near-field interactions alone, contains most of the relevant physics, and that taking account of interactions with more distant particles than the nearest is not essential to describe the dominant physics.

physics.flu-dyn↗

arXiv2019

EMPHATIC: A proposed experiment to measure hadron scattering and productioncross sections for improved neutrino flux predictions

Hadron scattering and production uncertainties are a limiting systematic on accelerator and at-mospheric neutrino flux predictions. New hadron measurements are necessary for neutrino fluxpredictions with well-understood and reduced uncertainties. We propose a new compact experimentto measure hadron scattering and production cross sections at beam energies that are inaccessibleto currently operating experiments. These measurements can reduce the current 10% neutrino fluxuncertainties by an approximate factor of two.

hep-ex↗

arXiv2019

$ωN$ scattering length from $ω$ photoproduction on the proton near the threshold

Photoproduction of the $ω$ meson on the proton has been experimentally studied near the threshold. The total cross sections are determined at incident energies ranging from 1.09 to 1.15 GeV. The 1/2 and 3/2 spin-averaged scattering length $a_{ωp}$ and effective range $r_{ωp}$ between the $ω$ meson and proton are estimated from the shape of the total cross section as a function of the incident photon energy: $a_{ωp} = \left(-0.97^{+0.16_{\rm stat}}_{-0.16_{\rm stat}}{}^{+0.03_{\rm syst}}_{-0.00_{\rm syst}}\right)+i \left(0.07^{+0.15_{\rm stat}}_{-0.14_{\rm stat}}{}^{+0.17_{\rm syst}}_{-0.09_{\rm syst}}\right)$ fm and $r_{ωp}=\left(+2.78^{+0.68_{\rm stat}}_{-0.54_{\rm stat}}{}^{+0.11_{\rm syst}}_{-0.13_{\rm syst}}\right)+i\left(-0.01^{+0.46_{\rm stat}}_{-0.50_{\rm stat}}{}^{+0.07_{\rm syst}}_{-0.00_{\rm syst}}\right)$ fm, resulting in a repulsive force. The real and imaginary parts for $a_{ωp}$ and $r_{ωp}$ are determined separately for the first time. A small $P$-wave contribution does not affect the obtained values.

nucl-ex↗

arXiv2019

Write-ups for workshop on the project for the hadron experimental facility of J-PARC, Partial collection of LOIs at the extended hadron hall and the related topics

This write-up document is a summary of International workshop on the project for the extended hadron experimental facility which was held from March 26 to 28, 2018 at KEK Tokai Campus. This document is a collection of Letter Of Intents (LOIs) related to the proposed beam lines in the extended hadron experimental facility at J-PARC.

nucl-ex↗

arXiv2018

Non-strange Dibaryon Resonances Observed in the $γd\to π^0π^0 d$ Reaction

Coherent double neutral-pion photoproduction on the deuteron, $γ{d}${$\to$}$π^0π^0{d}$, has been experimentally studied at incident photon energies ranging from 0.75 to 1.15 GeV. The total cross section as a function of the $γ{d}$ center-of-mass energy shows resonance-like behavior, which peaks at approximately 2.47 and 2.63 GeV. The measured angular distribution of deuteron emission is rather flat, which cannot be reproduced by the kinematics of quasi-free $π^0π^0$ production with deuteron coalescence. In $π^0d $ invariant-mass distributions, a clear peak is observed at $2.14{\pm}0.01$ GeV$/c^2$ with a width of $0.09{\pm}0.01$ GeV$/c^2$. The spin-parity of this state is restricted to $1^+$, $2^+$ or $3^-$ from the angular distributions of the two $π^0$s. The present work shows strong evidence for the existence of an isovector dibaryon resonance with a mass of 2.14 GeV$/c^2$. The $2^+$ assignment is consistent with the theoretically predicted ${\cal{D}}_{12}$ state, and also with the energy dependence of the $π{d}$ partial-wave amplitude $^3\!P_2$ for the $π^{\pm}d${$\to$}$π^{\pm}d$ and $π^+d${$\to$}${pp}$ reactions.

nucl-ex↗

arXiv2018

$η$ photoproduction off the deuteron and low-energy $η$-nucleon interaction

We study $η$ photoproduction off the deuteron ($γd\toηpn$) at a special kinematics: $\sim 0.94$ GeV of the photon beam energy and $\sim 0^\circ$ of the scattering angle of the proton. This kinematics is ideal to extract the low-energy $η$-nucleon scattering parameters such as $a_{ηN}$ (scattering length) and $r_{ηN}$ (effective range) because the $η$-nucleon elastic scattering is significantly enhanced. We show that if a ratio $R$, the $γd\toηpn$ cross section divided by the $γp\toηp$ cross section convoluted with the proton momentum distribution in the deuteron, is measured with 5% error, ${\rm Re}[a_{ηN}]$ (${\rm Re}[r_{ηN}]$) can be determined at the precision of $\sim\pm$0.1 fm ($\sim\pm$0.5 fm), significantly narrowing down the currently estimated range of the parameters. The measurement is ongoing at the Research Center for Electron Photon Science (ELPH), Tohoku University.

nucl-th↗

arXiv2018

"$\mathbf{{\textit K^-}{\textit p}{\textit p}}$", a ${\overline{K}}$-Meson Nuclear Bound State, Observed in $^{3}{\rm He}({K^-}, Λ p)n$ Reactions

We observed a distinct peak in the $Λp$ invariant mass spectrum of $^{3}{\rm He}(K^-, \, Λp)n$, well below the mass threshold of $m_K + 2 m_p$. By selecting a relatively large momentum-transfer region $q = 350 \sim 650$ MeV/$c$, one can clearly separate the peak from the quasi-free process, $\overline{K}N \rightarrow \overline{K}N$ followed by the non-resonant absorption by the two spectator-nucleons $\overline{K}NN \rightarrow ΛN $. We found that the simplest fit to the observed peak gives us a Breit-Wigner pole position at $B_{\rm {\it Kpp}} = 47 \pm 3 \, (stat.) \,^{+3}_{-6} \,(sys.)$ MeV having a width $Γ_{\rm {\it Kpp}} = 115 \pm 7 \, (stat.) \,^{+10}_{-9} \,(sys.)$ MeV, and the $S$-wave Gaussian reaction form-factor parameter $Q_{\rm {\it Kpp}} = 381 \pm 14 \, (stat.)\,^{+57}_{-0} \,(sys.)$ MeV/$c$, as a new form of the nuclear bound system with strangeness -- "$K^-pp$".

nucl-ex↗

arXiv2018

Differential cross section and photon-beam asymmetry for the gamma p -> pi- Delta++(1232) reaction at forward pi- angles for Egamma=1.5-2.95 GeV

Differential cross sections and photon-beam asymmetries for the gamma p -> pi- Delta++(1232) reaction have been measured for 0.7<cos(theta)<1 and Egamma=1.5-2.95 GeV at SPring-8/LEPS. The first-ever high statistics cross section data are obtained in this kinematical region, and the asymmetry data for 1.5<Egamma(GeV)<2.8 are obtained for the first time. This reaction has a unique feature for studying the production mechanisms of a pure $u\bar{u}$ quark pair in the final state from the proton. Although there is no distinct peak structure in the cross sections, a non-negligible excess over the theoretical predictions is observed at Egamma=1.5-1.8 GeV. The asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of pi-exchange in the t-channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions which produce a $d\bar{d}$ or an $s\bar{s}$ quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural parity exchanges are needed to reproduce the present data.

nucl-ex↗

arXiv2018

Regularization with Numerical Extrapolation for Finite and UV-Divergent Multi-loop Integrals

We give numerical integration results for Feynman loop diagrams such as those covered by Laporta [1] and by Baikov and Chetyrkin [2], and which may give rise to loop integrals with UV singularities. We explore automatic adaptive integration using multivariate techniques from the PARINT package for multivariate integration, as well as iterated in- tegration with programs from the QUADPACK package, and a trapezoidal method based on a double exponential trans- formation. PARINT is layered over MPI (Message Passing Interface), and incorporates advanced parallel/distributed techniques including load balancing among processes that may be distributed over a cluster or a network/grid of nodes. Results are included for 2-loop vertex and box diagrams and for sets of 2-, 3- and 4-loop self-energy diagrams with or without UV terms. Numerical regularization of integrals with singular terms is achieved by linear and non-linear extrapolation methods.

hep-ph↗

arXiv2018

Photoproduction of $Λ$ and $Σ^{0}$ hyperons off protons with linearly polarized photons at $E_γ = 1.5-3.0$ GeV

We report the measurement of the $γp \rightarrow K^{+}Λ$ and $γp \rightarrow K^{+}Σ^{0}$ reactions at SPring-8. The differential cross sections and photon-beam asymmetries are measured at forward $K^{+}$ production angles using linearly polarized tagged-photon beams in the range of $E_γ=1.5$--3.0 GeV. With increasing photon energy, the cross sections for both $γp \rightarrow K^{+}Λ$ and $γp \rightarrow K^{+}Σ^{0}$ reactions decrease slowly. Distinct narrow structures in the production cross section have not been found at $E_γ=1.5$--3.0 GeV. The forward peaking in the angular distributions of cross sections, a characteristic feature of $t$-channel exchange, is observed for the production of $Λ$ in the whole observed energy range. A lack of similar feature for $Σ^{0}$ production reflects a less dominant role of $t$-channel contribution in this channel. The photon-beam asymmetries remain positive for both reactions, suggesting the dominance of $K^{*}$ exchange in the $t$ channel. These asymmetries increase gradually with the photon energy, and have a maximum value of +0.6 for both reactions. Comparison with theoretical predictions based on the Regge trajectory in the $t$ channel and the contributions of nucleon resonances indicates the major role of $t$-channel contributions as well as non-negligible effects of nucleon resonances in accounting for the reaction mechanism of hyperon photoproduction in this photon energy regime.

nucl-ex↗

arXiv2018

First measurement of coherent $ϕ$-meson photoproduction from helium-4 near threshold

The differential cross sections and decay angular distributions for coherent $ϕ$-meson photoproduction from helium-4 have been measured for the first time at forward angles with linearly polarized photons in the energy range $E_γ = \text{1.685-2.385 GeV}$. Thanks to the target with spin-parity $J^{P} = 0^{+}$, unnatural-parity exchanges are prohibited, and thus natural-parity exchanges can be investigated clearly. The decay asymmetry with respect to photon polarization is shown to be very close to the maximal value. This ensures the dominance ($> 94\%$) of natural-parity exchanges in this reaction. To evaluate the contribution from natural-parity exchanges to the forward cross section ($θ= 0^\circ$) for the $γp \rightarrow ϕp$ reaction near the threshold, the energy dependence of the forward cross section ($θ= 0^\circ$) for the $γ{^{4}\text{He}} \rightarrow ϕ{^{4}\text{He}}$ reaction was analyzed. The comparison to $γp \rightarrow ϕp$ data suggests that enhancement of the forward cross section arising from natural-parity exchanges, and/or destructive interference between natural-parity and unnatural-parity exchanges is needed in the $γp \rightarrow ϕp$ reaction near the threshold.

nucl-ex↗

arXiv2018

Differential cross section and photon beam asymmetry for the gamma p -> pi+ n reaction at forward pi+ angles at Egamma=1.5-2.95 GeV

Differential cross sections and photon beam asymmetries for the gamma p -> pi+ n reaction have been measured for 0.6<cos(theta)<1 and Egamma=1.5-2.95 GeV at SPring-8/LEPS. The cross sections monotonically decrease as the photon beam energy increases for 0.6<cos(theta)<0.9. However, the energy dependence of the cross sections for 0.9<cos(theta)<1 and Egamma=1.5-2.2 GeV (W=1.9-2.2 GeV) is different, which may be due to a nucleon or Delta resonance. The present cross sections agree well with the previous cross sections measured by other groups and show forward peaking, suggesting significant t-channel contributions in this kinematical region. The asymmetries are found to be positive, which can be explained by rho-exchange in the t-channel. Large positive asymmetries in the small |t| region, where the rho-exchange contribution becomes small, could be explained by introducing pi-exchange interference with the s-channel.

nucl-ex↗