arXiv subjects

Y. Taniguchi

Publications and source records attributed to Y. Taniguchi.

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.

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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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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.

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arXiv2022

Differential cross sections and photon beam asymmetries of $\eta$ photoproduction on the proton at $E_\gamma$ = 1.3-2.4 GeV

We have carried out exclusive measurements for the photoproduction of an $\eta$ 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 $\gamma p \to \eta p$ reaction are measured in a center-of-mass energy ($W$) range of $1.82$-$2.32$ GeV and a polar angle range of $-1.0 < \cos{\theta^{\eta}_{\mathrm{c.m.}}} < 0.6$. The reaction is identified by selecting a proton and two $\gamma$'s produced by an $\eta$-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 $\eta$ 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 $\eta$ 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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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, $\gamma{d}${$\to$}$\pi^0\eta{d}$, 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 $\pi^0 \eta$ 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 $\pi^0 \eta$ invariant-mass distribution $d\sigma/dM_{\pi \eta}$, the $\pi^0 d$ invariant-mass distribution $d\sigma/dM_{\pi d}$, the $\eta d$ invariant-mass distribution $d\sigma/dM_{\eta d}$, and the distribution over the deuteron emission angle $d\sigma/d\Omega_d$ in the overall center-of-mass frame. The measured cross section $d\sigma/d\Omega_d$ does not exhibit strongly backward-peaking behavior predicted by the calculations. At all incident energies, an increase in $d\sigma/dM_{\eta d}$ near the $\eta d$ threshold is observed, which indicates a bound or virtual $\eta d$ state resulting from a strong attraction between $\eta$ and a deuteron. The possibilities of using coherent $\pi^0\eta$ photoproduction on a nucleus to study the $\eta$-nuclear interaction are also discussed.

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arXiv2021

COSMOS2020: A panchromatic view of the Universe to $z\sim10$ from two complementary catalogs

The Cosmic Evolution Survey (COSMOS) has become a cornerstone of extragalactic astronomy. Since the last public catalog in 2015, a wealth of new imaging and spectroscopic data has been collected in the COSMOS field. This paper describes the collection, processing, and analysis of this new imaging data to produce a new reference photometric redshift catalog. Source detection and multi-wavelength photometry is performed for 1.7 million sources across the $2\,\mathrm{deg}^{2}$ of the COSMOS field, $\sim$966,000 of which are measured with all available broad-band data using both traditional aperture photometric methods and a new profile-fitting photometric extraction tool, The Farmer, which we have developed. A detailed comparison of the two resulting photometric catalogs is presented. Photometric redshifts are computed for all sources in each catalog utilizing two independent photometric redshift codes. Finally, a comparison is made between the performance of the photometric methodologies and of the redshift codes to demonstrate an exceptional degree of self-consistency in the resulting photometric redshifts. The $i<21$ sources have sub-percent photometric redshift accuracy and even the faintest sources at $25<i<27$ reach a precision of $5\,\%$. Finally, these results are discussed in the context of previous, current, and future surveys in the COSMOS field. Compared to COSMOS2015, reaches the same photometric redshift precision at almost one magnitude deeper. Both photometric catalogs and their photometric redshift solutions and physical parameters will be made available through the usual astronomical archive systems (ESO Phase 3, IPAC IRSA, and CDS).

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arXiv2021

Description of isospin mixing by a generator coordinate method

Background: The isospin mixing is an interesting feature of atomic nuclei. It plays a crucial role in astrophysical nuclear reactions. However, it is not straightforward for variational nuclear structure models to describe it. Purpose: We propose a tractable method to describe the isospin mixing within a framework of the generator coordinate method and demonstrate its usability. Method: We generate the basis wave functions by applying the Fermi transition operator to the wave functions of isobars. The superposition of these basis wave functions and variationally obtained wave functions quantitatively describes the isospin mixing. Results: Using 14N as an example, we demonstrate that our method reasonably describes both T = 0 and 1 states and their mixing. Energy spectrum and E1 transition strengths are compared with the experimental data to confirm isospin mixing. Conclusion: The proposed method is effective enough to describe isospin mixing and is useful, for example, when we discuss {\alpha} capture reactions of N = Z nuclei.

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arXiv2021

Resonance-like structure near the $\eta d$ threshold in the $\gamma{d}${$\to$}$\pi^0\eta{d}$ reaction

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

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arXiv2020

A puzzling non-detection of [O III] and [C II] from a $z \approx 7.7$ galaxy observed with ALMA

Characterizing the galaxy population in the early Universe holds the key to understanding the evolution of these objects and the role they played in cosmic reionization. However, the number of observations at the very highest redshifts are to date, few. In order to shed light on the properties of galaxies in the high-redshift Universe and their interstellar media, we observe the Lyman-$α$ emitting galaxy z7\_GSD\_3811 at $z=7.664$ with band 6 and 8 at the Atacama Large Millimeter/submillimeter Array (ALMA). We target the far-infrared [O III] 88 $μm$, [C II] 158 $μm$ emission lines and dust continuum in the star-forming galaxy z7\_GSD\_3811 with ALMA. We combine these measurements with earlier observations in the rest-frame ultraviolet (UV) in order to characterize the object, and compare results to those of earlier studies observing [O III] and [C II] emission in high-redshift galaxies. The [O III] 88 $μm$ and [C II] 158 $μm$ emission lines are undetected at the position of z7\_GSD\_3811, with $3σ$ upper limits of $1.6 \ \times \ 10^{8} \ L_{\odot}$ and $4.0 \ \times \ 10^{7} \ L_{\odot}$, respectively. We do not detect any dust continuum in band 6 nor band 8. The measured rms in the band 8 and band 6 continuum is 26 and 9.9 $μJy \ beam^{-1}$, respectively. Similar to several other high-redshift galaxies, z7\_GSD\_3811 exhibits low [C II] emission for its star formation rate compared to local galaxies. Furthermore, our upper limit on the [O III] line luminosity is lower than all the previously observed [O III] lines in high-redshift galaxies with similar ultraviolet luminosities. Our ALMA band 6 and 8 dust continuum observations imply that z7\_GSD\_3811 likely has a low dust content, and our non-detections of the [O III] and [C II] lines could indicate that z7\_GSD\_3811 has a low metallicity ($Z \lesssim 0.1 \ Z_{\odot}$).

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arXiv2020

alpha+28Si and 16O+16O molecular states, and their isoscalar monopole strengths

The properties of the alpha+28Si and 16O+16O molecular states which are embedded in the excited states of 32S and can have an impact on the stellar reactions are investigated using the antisymmetrized molecular dynamics. From the analysis of the cluster spectroscopic factors, the candidates of alpha+28Si and 16O+16O molecular states are identified close to and above the cluster threshold energies. The calculated properties of the alpha+28Si molecular states are consistent with those reported by the alpha+28Siresonant scattering experiments. On the other hand, the 16O+16O molecular state, which is predicted to be identical to the superdeformation of 32S, is inconsistent with the assignment proposed by an alpha inelastic scattering experiment. Our calculation suggests that the monopole transition from the ground state to the 16O+16O molecular state is rather weak and is not strongly excited by the alpha inelastic scattering.

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arXiv2019

Finite size effect on vector meson and baryon sectors in 2+1 flavor QCD at the physical point

We investigate the finite size effect on the vector meson and the baryon sectors using a subset of the "PACS10" configurations which are generated, keeping the space-time volumes over (10 fm$)^4$ in 2+1 flavor QCD at the physical point. Comparing the results on (5.5 fm$)^4$ and (10.9 fm$)^4$ lattices the ground states of octet baryons , which are stable on the lattice, show no finite size effect within less than 0.5% level of statistical errors. For those of vector mesons, which are unstable on the lattice, we observe that the effective masses are well below the experimental resonance levels both on (5.5 fm$)^4$ and (10.9 fm$)^4$ lattices. For the decuplet baryon sector we have found that the time dependence of the effective mass looks quite similar to that for the vector meson sector including the $Ω$ baryon channel. We discuss its origin due to a possible mixing with the nearby multihadron states. Since the $Ξ$ baryon mass can be determined with the smallest ambiguity among the vector meson and the baryon masses, we use it together with the pion and kaon masses as the physical inputs to determine the physical point.

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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.

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arXiv2019

Finite size effect on pseudoscalar meson sector in 2+1 flavor QCD at the physical point

We investigate the finite size effect on pseudoscalar meson masses and decay constants using a subset of the "PACS10" configurations which are generated keeping the space-time volumes over (10 fm$)^4$ in 2+1 flavor QCD at the physical point. We have tried two kinds of analyses, fixing $κ$ values or measured axial Ward identity quark masses. Comparing the results on (5.4 fm$)^4$ and (10.8 fm$)^4$ lattices, we have found a sizable finite size effect on the pseudoscalar meson sector in the former analysis: a 2.1(8)%, 4.8(1.6)%, and 0.36(31)% finite size effect on $m_π$, $m_{\rm ud}$, and $f_π$, respectively, on the (5.4 fm$)^4$ lattice. For the latter analysis, the finite size effect on the pseudoscalar meson decay constants is 0.66(33)% for $f_π$, 0.26(13)% for $f_K$, and 0.40(32)% for $f_K/f_π$. These values with two-sigma error bars are consistent with the predictions from the full one-loop SU(3) chiral perturbation theory, which are 0.20% for $f_π$, 0.08% for $f_K$, and 0.13% for $f_K/f_π$. The finite size effect on the pseudoscalar meson masses is hardly detected under the current statistical precision.

hep-lat↗

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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arXiv2017

ALMA Twenty-six arcmin$^2$ Survey of GOODS-S at One-millimeter (ASAGAO): X-ray AGN Properties of Millimeter-Selected Galaxies

We investigate the X-ray active galactic nucleus (AGN) properties of millimeter galaxies in the Great Observatories Origins Deep Survey South (GOODS-S) field detected with the Atacama Large Millimeter/submillimeter Array (ALMA), by utilizing the Chandra 7-Ms data, the deepest X-ray survey to date. Our millimeter galaxy sample comes from the ASAGAO survey covering 26 arcmin$^2$ (12 sources at a 1.2-mm flux-density limit of $\approx$0.6 mJy), supplemented by the deeper but narrower 1.3-mm survey of a part of the ASAGAO field by Dunlop et al.\ (2017). Fourteen out of the total 25 millimeter galaxies have Chandra counterparts. The observed AGN fractions at $z=1.5-3$ is found to be 90$^{+8}_{-19}$\% and $57^{+23}_{-25}$\% for the ultra/luminous infrared galaxies with $\log L_{\rm IR}/L_{\odot} = 12-12.8$ and $\log L_{\rm IR}/L_{\odot} = 11.5-12$, respectively. The majority ($\sim$2/3) of the ALMA and/or Herschel detected X-ray AGNs at $z=1.5-3$ appear to be star-formation dominant populations, having $L_{\rm X}$/ $L_{\rm IR}$ ratios smaller than the "simultaneous evolution" value expected from the local black-hole mass to stellar mass ($M_{\rm BH}$-$M_*$) relation. On the basis of the $L_{\rm X}$ and stellar mass relation, we infer that a large fraction of star-forming galaxies at $z=1.5-3$ have black hole masses smaller than those expected from the local $M_{\rm BH}$-$M_*$ relation. This is opposite to previous reports on luminous AGN at same redshifts detected in wider and shallower surveys, which are subject to selection biases against lower luminosity AGN. Our results are consistent with an evolutionary scenario that star formation occurs first, and an AGN-dominant phase follows later, in objects finally evolving into galaxies with classical bulges.

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arXiv2017

Deep submillimeter and radio observations in the SSA22 field. I. Powering sources and Lyα escape fraction of Lyα blobs

We study the heating mechanisms and Lyα escape fractions of 35 Lyα blobs (LABs) at z = 3.1 in the SSA22 field. Dust continuum sources have been identified in 11 of the 35 LABs, all with star formation rates (SFRs) above 100 Msun/yr. Likely radio counterparts are detected in 9 out of 29 investigated LABs. The detection of submm dust emission is more linked to the physical size of the Lyα emission than to the Lyα luminosities of the LABs. A radio excess in the submm/radio detected LABs is common, hinting at the presence of active galactic nuclei. Most radio sources without X-ray counterparts are located at the centers of the LABs. However, all X-ray counterparts avoid the central regions. This may be explained by absorption due to exceptionally large column densities along the line-of-sight or by LAB morphologies, which are highly orientation dependent. The median Lyα escape fraction is about 3\% among the submm-detected LABs, which is lower than a lower limit of 11\% for the submm-undetected LABs. We suspect that the large difference is due to the high dust attenuation supported by the large SFRs, the dense large-scale environment as well as large uncertainties in the extinction corrections required to apply when interpreting optical data.

astro-ph.GA↗

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.

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arXiv2016

The FMOS-COSMOS survey of star-forming galaxies at z~1.6. IV: Excitation state and chemical enrichment of the interstellar medium

We investigate the physical conditions of ionized gas in high-z star-forming galaxies using diagnostic diagrams based on the rest-frame optical emission lines. The sample consists of 701 galaxies with an Ha detection at $1.4\lesssim z\lesssim1.7$, from the FMOS-COSMOS survey, that represent the normal star-forming population over the stellar mass range $10^{9.6} \lesssim M_\ast/M_\odot \lesssim 10^{11.6}$ with those at $M_\ast>10^{11}~M_\odot$ being well sampled. We confirm an offset of the average location of star-forming galaxies in the BPT diagram ([OIII]/Hb vs. [NII]/Ha), primarily towards higher [OIII]/Hb, compared with local galaxies. Based on the [SII] ratio, we measure an electron density ($n_e=220^{+170}_{-130}~\mathrm{cm^{-3}}$), that is higher than that of local galaxies. Based on comparisons to theoretical models, we argue that changes in emission-line ratios, including the offset in the BPT diagram, are caused by a higher ionization parameter both at fixed stellar mass and at fixed metallicity with additional contributions from a higher gas density and possibly a hardening of the ionizing radiation field. Ionization due to AGNs is ruled out as assessed with Chandra. As a consequence, we revisit the mass-metallicity relation using [NII]/Ha and a new calibration including [NII]/[SII] as recently introduced by Dopita et al. Consistent with our previous results, the most massive galaxies ($M_\ast\gtrsim10^{11}~M_\odot$) are fully enriched, while those at lower masses have metallicities lower than local galaxies. Finally, we demonstrate that the stellar masses, metallicities and star formation rates of the FMOS sample are well fit with a physically-motivated model for the chemical evolution of star-forming galaxies.

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