arXiv subjects

Y. Honda

Publications and source records attributed to Y. Honda.

At least 19 recordsLinked to original sources

arXiv2026

Direct measurement of the in-medium $\eta^{\prime}$ mass spectrum through the $\gamma\gamma$ decay channel

We measured the invariant mass of the $\eta^{\prime}(958)$ meson through the $\eta^{\prime}\to\gamma\gamma$ decay channel to search for possible character change of $\eta^{\prime}$ in a nuclear medium. The measured invariant-mass spectra were analyzed by fitting realistic spectral functions. An enhancement was observed in the lower tail of the $\eta^{\prime}$ mass peak for low-momentum ($P_{\gamma\gamma} < 1$~$\mathrm{GeV/c}$) events. Three statistical methods were applied to assess the significance of the enhancement. All methods yield a statistical significance above 3.7$\sigma$. The spectral fitting indicates a mass reduction of $57.5^{+~5.7}_{-27.8}$~$\mathrm{MeV/c}^{2}$. Our result provides the first evidence for an in-medium spectral modification of the $\eta^{\prime}$ meson obtained through a direct measurement of its invariant mass.

nucl-ex↗

arXiv2026

Isoscalar Giant Resonances in the even-A Pd Isotopes

Studies of the isoscalar giant monopole resonance (ISGMR) across the chart of nuclides provide insight into the incompressibility of nuclear matter near saturation density, K(infinity). Such studies had revealed a discrepancy between theoretical approaches: quasiparticle random phase approximation (QRPA) derived from Skyrme interactions reproduce the strength distributions of the ISGMR in the doubly-closed-shell nuclei 90Zr and 208Pb, but their descriptions of strength distributions in open-shell medium-heavy nuclei suggest higher centroid energies should be experimentally observed. The latter nuclei required a smaller K(infinity) and were thus deemed softer. The present work serves to add to this softness discourse by extracting ISGMR strength distributions for 104,106,108,110Pd via 386-MeV inelastic alpha-scattering. The extracted giant resonance strength distributions are consistent with expectations in this isotopic range. Additional Quasiparticle Vibration Coupling (QPVC) effects are included with the QRPA approach and compared to aforementioned ISGMR strength distributions.

nucl-ex↗

arXiv2026

Comprehensive measurement of $\eta^\prime$ photoproduction off the proton at $E_\gamma < 2.4$ $\mathrm{GeV}$

For the spectroscopy of nucleon resonances at the total energies from the $\eta^\prime$-meson production threshold to $2.32$ $\mathrm{GeV}$, photon beam asymmetries of the reaction $\gamma p \to \eta^\prime p$ were measured together with total and differential cross sections by analyzing the two decay modes $\eta^\prime \to \gamma \gamma$ and $\pi^0 \pi^0 \eta$. New constraints for amplitude decomposition were given by the first-time result of photon beam asymmetries at $E_\gamma > 1.84$ $\mathrm{GeV}$ and the most precise data of differential cross sections to date at extremely backward $\eta^\prime$ angles. The possibility of a larger coupling constant of the $\eta^\prime$-nucleon system to the $N(2250)$ resonance was implied in the partial wave analyses using the present data.

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arXiv2025

Nuclear level density of ${}^{128}$Te from $(\mathrm{p},\mathrm{p}'\gamma)$ scattering and complementary photonuclear data

We have extracted the nuclear level density of ${}^{128}$Te from a $(\mathrm{p},\mathrm{p} '\gamma)$ scattering experiment using the large-volume \labr\ and \cebr\ detectors from ELI-NP at the 9~MV Tandem facilities at IFIN-HH. The decay data were normalised using photonuclear data, resulting in nuclear level densities without intrinsic model dependencies from the constant temperature or Fermi gas models. The deduced nuclear level density follows in between the expectations from these two models, but we observe a clear divergence from a microscopic model based on the Skyrme force.

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arXiv2023

Search for the 6$α$ condensed state in $^{24}$Mg using the $^{12}\rm{C}+{}^{12}\rm{C}$ scattering

We searched for the 6$α$-condensed state in $^{24}$Mg by measuring the $^{12}\rm{C}+{}^{12}\rm{C}$ scattering with the SAKRA Si detector array at $E_\rm{cm}$ = 17.5-25.0 MeV. By using the invariant-mass method for the detected 3$α$ particles, the inclusive cross sections for the $^{12}\rm{C}+{}^{12}\rm{C}\to{}^{12}\rm{C}(0^+_2)+X$ and $^{12}\rm{C}(3^-_1)+X$ reactions were determined. In addition, the missing-mass spectroscopy was successfully utilized to determine the excitation energy of the residual $^{12}\rm{C}$ nucleus and the exclusive cross sections for the $^{12}\rm{C}+{}^{12}\rm{C}\to{}^{12}\rm{C}(0^+_2)+{}^{12}\rm{C}(0^+_1)$, $^{12}\rm{C}(0^+_2)+{}^{12}\rm{C}(2^+_1)$, and $^{12}\rm{C}(0^+_2)+{}^{12}\rm{C}(0^+_2)$ reactions. In both the inclusive $^{12}\rm{C}(0^+_2)+X$ channel and the exclusive $^{12}\rm{C}(0^+_2)+{}^{12}\rm{C}(0^+_1)$ channel, the cross section peaked at $E_rm{cm}$ = 19.4 MeV, which correspond to the excitation energy of $E_x$ = 33.3 MeV in $^{24}\rm{Mg}$. This 19.4-MeV state is a candidate for the 6$α$-condensed state because of the agreement of the excitation energy with the theoretical value and its decay property. In the exclusive $^{12}\rm{C}(0^+_2)+{}^{12}\rm{C}(0^+_2)$ channel, a broad state was observed at $E_\rm{cm}$ = 22.5 MeV, which correspond to the excitation energy of $E_x$ = 36.4 MeV in $^{24}\rm{Mg}$. From the angular distribution of the differential cross section, the spin and parity of this 22.5-MeV state was assigned to be $4^+$. In addition, a $2^+$ state was suggested at the low-energy side of the 22.5-MeV state. Because their excitation energies are higher than the theoretical value of the 6$α$-condensed state, these states might be excited states of the 6$α$-condensed state such as the $2^+_2$ and $4^+_1$ states in $^{12}\rm{C}$.

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arXiv2022

PANDORA project: photo-nuclear reactions below $A=60$

Photo-nuclear reactions of light nuclei below a mass of $A=60$ are studied experimentally and theoretically by the PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) project. Two experimental methods, virtual-photon excitation by proton scattering and real-photo absorption by a high-brilliance gamma-ray beam produced by laser Compton scattering, will be applied to measure the photo-absorption cross sections and the decay branching ratio of each decay channel as a function of the photon energy. Several nuclear models, e.g. anti-symmetrized molecular dynamics, mean-field type models, a large-scale shell model, and ab initio models, will be employed to predict the photo-nuclear reactions. The uncertainty in the model predictions will be evaluated from the discrepancies between the model predictions and the experimental data. The data and the predictions will be implemented in a general reaction calculation code TALYS . The results will be applied to the simulation of the photo-disintegration process of ultra-high-energy cosmic rays in inter-galactic propagation.

nucl-ex↗

arXiv2022

Coherent photoproduction of the neutral pion and eta meson on the deuteron at incident energies below 1.15 GeV

Coherent photoproduction of the neutral pion and eta meson on the deuteron, $γ{d}${$\to$}$π^0η{d}$, has been experimentally studied at incident photon energies ranging from the reaction threshold to 1.15 GeV. The total cross section demonstrates a rapid rise below 1 GeV. The data are underestimated by the existing theoretical calculations based on quasi-free $π^0 η$ photoproduction on the nucleon followed by deuteron coalescence. At the same time, the data are rather well reproduced by the calculations taking into account the final-state interaction. We have also measured for the first time the differential cross sections: the $π^0 η$ invariant-mass distribution $dσ/dM_{πη}$, the $π^0 d$ invariant-mass distribution $dσ/dM_{πd}$, the $ηd$ invariant-mass distribution $dσ/dM_{ηd}$, and the distribution over the deuteron emission angle $dσ/dΩ_d$ in the overall center-of-mass frame. The measured cross section $dσ/dΩ_d$ does not exhibit strongly backward-peaking behavior predicted by the calculations. At all incident energies, an increase in $dσ/dM_{ηd}$ near the $ηd$ threshold is observed, which indicates a bound or virtual $ηd$ state resulting from a strong attraction between $η$ and a deuteron. The possibilities of using coherent $π^0η$ photoproduction on a nucleus to study the $η$-nuclear interaction are also discussed.

nucl-ex↗

arXiv2022

Differential cross sections and photon beam asymmetries of $η$ photoproduction on the proton at $E_γ$ = 1.3-2.4 GeV

We have carried out exclusive measurements for the photoproduction of an $η$ meson from a proton target with an egg-shaped calorimeter made of BGO crystals (BGOegg) and forward charged-particle detectors at the SPring-8 LEPS2 beamline. The differential cross sections and photon beam asymmetries of the $γp \to ηp$ reaction are measured in a center-of-mass energy ($W$) range of $1.82$-$2.32$ GeV and a polar angle range of $-1.0 < \cos{θ^η_{\mathrm{c.m.}}} < 0.6$. The reaction is identified by selecting a proton and two $γ$'s produced by an $η$-meson decay. The kinematic fit method was employed to select the reaction candidate with the confidence level larger than $1$\%. A bump structure at $W$ = $2.0$-$2.3$ GeV in the differential cross section is confirmed at extremely backward $η$ polar angles, where the existing data are inconsistent with each other. This bump structure is likely associated with high-spin resonances that couple with $s\bar{s}$ quarks. The results of the photon beam asymmetries in a wide $η$ polar angle range are new for the photon beam energies exceeding $2.1$ GeV. These results are not reproduced by the existing partial wave analyses. They provide an additional constraint to nucleon resonance studies at high energies.

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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.

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arXiv2021

The nylon balloon for xenon loaded liquid scintillator in KamLAND-Zen 800 neutrinoless double-beta decay search experiment

The KamLAND-Zen 800 experiment is searching for the neutrinoless double-beta decay of $^{136}$Xe by using $^{136}$Xe-loaded liquid scintillator. The liquid scintillator is enclosed inside a balloon made of thin, transparent, low-radioactivity film that we call Inner Balloon (IB). The IB, apart from guaranteeing the liquid containment, also allows to minimize the background from cosmogenic muon-spallation products and $^{8}$B solar neutrinos. Indeed these events could contribute to the total counts in the region of interest around the Q-value of the double-beta decay of $^{136}$Xe. In this paper, we present an overview of the IB and describe the various steps of its commissioning minimizing the radioactive contaminations, from the material selection, to the fabrication of the balloon and its installation inside the KamLAND detector. Finally, we show the impact of the IB on the KamLAND background as measured by the KamLAND detector itself.

physics.ins-det↗

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

Performance evaluation of a silicon strip detector for positrons/electrons from a pulsed a muon beam

A high-intensity pulsed muon beam is becoming available at the at the Japan Proton Accelerator Research Complex (J-PARC). Many experiments to study fundamental physics using this high-intensity muon beam are proposed. An experiment to measure the muon magnetic moment anomaly ($g-2$) and the muon electric dipole moment (EDM) is one of these experiments and it requires a tracking detector for positrons from muon decay. Fine segmentation is required in a detector to tolerate the high rate of positrons. The time resolution is required to be much better than the muon anomalous spin precession period while a buffer depth of a front-end electronics needs to be much longer than the accelerated muon lifetime. Requirements of this detector also meet requirements of a measurement of the muonium hyperfine structure interval at the J-PARC and another experiment to measure the proton charge radius at Tohoku University. We have developed a single-sided silicon strip sensor with a 190 $μ$m pitch, a front-end electronics with a sampling rate of 200 MHz and a buffer memory depth of 8192, and a data acquisition system based on DAQ-Middleware for the J-PARC muon $g-2$/EDM experiment. We have fabricated detector modules consisting of this sensor and the front-end electronics. Performance of fabricated detector modules was evaluated at a laboratory and a beam test using the positron beam at Tohoku University. The detector is confirmed to satisfy all requirements of the experiments except for the time walk, which will be solved by the next version of a front-end electronics.

physics.ins-det↗

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↗

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.

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arXiv2018

Overview of LLRF System for iBNCT Accelerator

At the Ibaraki Neutron Medical Research Center, an accelerator-based neutron source for iBNCT (Ibaraki - Boron Neutron Capture Therapy) is being developed using an 8-MeV proton linac and a beryllium-based neutron production target. The proton linac consists of an RFQ and a DTL, which is almost the same as the front part of J-PARC linac. However, here only one high-power klystron is used as the RF source to drive the two cavities, which have quite different Q-values and responses. From June 2016, a cPCI based digital feedback system was applied to the iBNCT accelerator. It serves not only as a controller for the feedback of acceleration fields, but also as a smart operator for the auto-tuning of the two cavities in the meantime, especially during the RF startup process to the full power. The details will be described in this report.

physics.acc-ph↗

arXiv2017

Development of optical resonant cavities for laser-Compton scattering

We have been developing optical resonant cavities for laser-Compton scattering experiment at the Accelerator Test Facility in KEK. The main subject of the R&D is to increase laser pulse energy by coherently accumulating the pulses in an optical resonant cavity. We report previous results, current status and future prospects, including a new idea of an optical resonant cavity.

physics.acc-ph↗

arXiv2017

First measurement of coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV

The total cross sections were measured for coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV for the first time. No clear resonance-like behavior is observed in the excitation function for $W_{γd}=2.38$--2.61 GeV, where the $d^*(2380)$ dibaryon resonance observed at COSY is expected to appear. The measured excitation function is consistent with the existing theoretical calculation for this reaction. The upper limit of the total cross section is found to be $0.034$~$μ$b for the dibaryon resonance at $W_{γd}=2.37$~GeV (90\% confidence level) in the $γd \to π^0π^0 d$ reaction.

nucl-ex↗

arXiv2017

Femtosecond response time measurements of a Cs2Te photocathode

We present the response time measurements of a Cs2Te photocathode illuminated with two 100 fs duration, variable time separation laser pulses at 266 nm wavelength. The response time was confirmed in dispersive region downstream of a 12-cell standing wave S-band acceleration structure using a well-known RF zero-crossing technique. At the same time it was also measured by changing mechanical path-length difference between two micro-bunches. Both methods agree that Cs2Te photocathode time response is of the order of 250 fs and thereby it is possible to generate and control a THz sequence of relativistic electron bunches by a conventional S-band RF gun. This result further opens a possibility to construct wide-range tunable THz FEL.

physics.acc-ph↗