arXiv subjects

K. Mizutani

Publications and source records attributed to K. Mizutani.

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

Evidence for a $\bar{K}NN$ quasi-bound state in the $γd \to K^0Λp$ reaction

The $γd \to K^{0}Λp$ reaction has been studied to search for a $\bar{K}NN$ quasi-bound state using the LEPS2 solenoid spectrometer at SPring-8. A localized enhancement concentrated at low $q$ is observed in the $(M_{Λp},q)$ distribution below the $K^-pp$ mass threshold, where $M_{Λp}$ is the $Λp$ invariant mass and $q \equiv |\vec{p}_γ-\vec{p}_{K^{0}}| = |\vec{p}_{Λp}|$ is the momentum transfer. A two-dimensional $(M_{Λp},q)$ fit demonstrates that the enhancement near the threshold is statistically significant, yielding a local significance of $7.3,σ$. The enhancement is characterized by effective shape parameters including the Breit--Wigner mass $M$ and width $Γ$, and a Gaussian form-factor momentum scale $Q$: $M = 2.354 \pm 0.011(\mathrm{stat.})^{+0.009}_{-0.005}(\mathrm{syst.})~\mathrm{GeV}/c^{2}$, $Γ= 0.055 \pm 0.023(\mathrm{stat.})^{+0.031}_{-0.009}(\mathrm{syst.})~\mathrm{GeV}/c^{2}$, and $Q = 0.350 \pm 0.041(\mathrm{stat.})^{+0.035}_{-0.010}(\mathrm{syst.})~\mathrm{GeV}/c$. The obtained results support the existence of a $\bar{K}NN$ quasi-bound state in photoproduction.

nucl-ex↗

arXiv2026

Comprehensive measurement of $η^\prime$ photoproduction off the proton at $E_γ< 2.4$ $\mathrm{GeV}$

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

nucl-ex↗

arXiv2025

Measurement of the Total Compton Scattering Cross Section between 6.5 and 11 GeV

The total cross section for Compton scattering off atomic electrons, $γ+e\rightarrowγ'+e'$, was measured using photons with energies between 6.5 and 11.1 GeV incident on a $^9$Be target as part of the PrimEx-eta experiment in Hall D at Jefferson Lab. This is the first measurement of this fundamental QED process within this energy range. The total uncertainties of the cross section, combining the statistical and systematic components in quadrature, averaged to 3.4% across all energy bins. This not only demonstrates the capability of this experimental setup to perform precision cross-section measurements at forward angles but also allows us to compare with state-of-the-art QED calculations.

nucl-ex↗

arXiv2025

Prospects for Pentaquark Baryon Search with the Upgraded LEPS2 Facility

We present prospects for the $Θ^+$ pentaquark baryon search using the newly constructed LEPS2 facility at SPring-8. The LEPS2 detector system features significant improvements in acceptance for multi-particle final states compared to previous experiments. Our search employs two complementary strategies: direct production in the $γn \to K^-Θ^+$ reaction using a liquid deuterium target with a photon beam up to 2.4 GeV, and $\bar{K}^{*0}$-associated $Θ^+$ production using a liquid hydrogen target with a photon beam up to 2.9 GeV. The extended acceptance covers both forward and large angle regions, effectively spanning the kinematic regions explored by previous LEPS and CLAS experiments. The large acceptance and improved resolution of LEPS2, combined with these complementary approaches, provide unprecedented sensitivity for establishing the existence of the $Θ^+$ or placing definitive upper limits on its production.

hep-ex↗

arXiv2025

Upper Limit on the Photoproduction Cross Section of the Spin-Exotic $π_1(1600)$

The spin-exotic hybrid meson $π_{1}(1600)$ is predicted to have a large decay rate to the $ωππ$ final state. Using 76.6~pb$^{-1}$ of data collected with the GlueX detector, we measure the cross sections for the reactions $γp \to ωπ^+ π^- p$, $γp \to ωπ^0 π^0 p$, and $γp\toωπ^-π^0Δ^{++}$ in the range $E_γ=$ 8-10 GeV. Using isospin conservation, we set the first upper limits on the photoproduction cross sections of the $π^{0}_{1}(1600)$ and $π^{-}_{1}(1600)$. We combine these limits with lattice calculations of decay widths and find that photoproduction of $η'π$ is the most sensitive two-body system to search for the $π_1(1600)$.

nucl-ex↗

arXiv2025

First Measurement of $a^0_2(1320)$ Polarized Photoproduction Cross Section

We measure for the first time the differential photoproduction cross section $dσ/dt$ of the $a_2(1320)$ meson at an average photon beam energy of 8.5~GeV, using data with an integrated luminosity of 104~pb$^{-1}$ collected by the GlueX experiment. We fully reconstruct the $γp \to ηπ^0 p$ reaction and perform a partial-wave analysis in the $a_2(1320)$ mass region with amplitudes that incorporate the linear polarization of the beam. This allows us to separate for the first time the contributions of natural- and unnatural-parity exchanges. These measurements provide novel information about the photoproduction mechanism, which is critical for the search for spin-exotic states.

nucl-ex↗

arXiv2024

First Measurement of Near- and Sub-Threshold $J/ψ$ Photoproduction off Nuclei

We report on the first measurement of $J/ψ$ photoproduction from nuclei in the photon energy range of $7$ to $10.8$ GeV, extending above and below the photoproduction threshold in the free proton of $\sim8.2$ GeV. The experiment used a tagged photon beam incident on deuterium, helium, and carbon, and the GlueX detector at Jefferson Lab to measure the semi-inclusive $A(γ,e^+e^-p)$ reaction with a dilepton invariant mass $M(e^+e^-)\sim m_{J/ψ}=3.1$ GeV. The incoherent $J/ψ$ photoproduction cross sections in the measured nuclei are extracted as a function of the incident photon energy, momentum transfer, and proton reconstructed missing light-cone momentum fraction. Comparisons with theoretical predictions assuming a dipole form factor allow extracting a gluonic radius for bound protons of $\sqrt{\langle r^2\rangle}=0.85\pm0.14$ fm. The data also suggest an excess of the measured cross section for sub-threshold production and for interactions with high missing light-cone momentum fraction protons. The measured enhancement can be explained by modified gluon structure for high-virtuality bound-protons.

nucl-ex↗

arXiv2024

Mini-Proceedings of the "Fourth International Workshop on the Extension Project for the J-PARC Hadron Experimental Facility (HEF-ex 2024)"

The mini proceedings of the "Fourth International Workshop on the Extension Project for the J-PARC Hadron Experimental Facility (HEF-ex 2024) [https://kds.kek.jp/event/46965]" held at J-PARC, February 19-21, 2024, are presented. The workshop was devoted to discussing the physics case that connects both the present and the future Hadron Experimental Facility at J-PARC, covering a wide range of topics in flavor, hadron, and nuclear physics related to both experimental and theoretical activities being conducted at the facility.

nucl-ex↗

arXiv2024

Measurement of Spin-Density Matrix Elements in $Δ^{++}(1232)$ photoproduction

We measure the spin-density matrix elements (SDMEs) of the $Δ^{++}(1232)$ in the photoproduction reaction $γp \to π^-Δ^{++}(1232)$ with the GlueX experiment in Hall D at Jefferson Lab. The measurement uses a linearly--polarized photon beam with energies from $8.2$ to $8.8$~GeV and the statistical precision of the SDMEs exceeds the previous measurement by three orders of magnitude for the momentum transfer squared region below $1.4$ GeV$^2$. The data are sensitive to the previously undetermined relative sign between couplings in existing Regge-exchange models. Linear combinations of the extracted SDMEs allow for a decomposition into natural and unnatural--exchange amplitudes. We find that the unnatural exchange plays an important role in the low momentum transfer region.

nucl-ex↗

arXiv2024

Measurement of the J/$ψ$ photoproduction cross section over the full near-threshold kinematic region

We report the total and differential cross sections for $J/ψ$ photoproduction with the large acceptance GlueX spectrometer for photon beam energies from the threshold at 8.2~GeV up to 11.44~GeV and over the full kinematic range of momentum transfer squared, $t$. Such coverage facilitates the extrapolation of the differential cross sections to the forward ($t = 0$) point beyond the physical region. The forward cross section is used by many theoretical models and plays an important role in understanding $J/ψ$ photoproduction and its relation to the $J/ψ-$proton interaction. These measurements of $J/ψ$ photoproduction near threshold are also crucial inputs to theoretical models that are used to study important aspects of the gluon structure of the proton, such as the gluon Generalized Parton Distribution (GPD) of the proton, the mass radius of the proton, and the trace anomaly contribution to the proton mass. We observe possible structures in the total cross section energy dependence and find evidence for contributions beyond gluon exchange in the differential cross section close to threshold, both of which are consistent with contributions from open-charm intermediate states.

nucl-ex↗

arXiv2024

Measurement of Spin-Density Matrix Elements in $ρ(770)$ Production with a Linearly Polarized Photon Beam at $E_γ= 8.2\,-\,8.8\,\text{GeV}$

The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized $8.5\,\text{GeV}$ photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson $ρ$(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of $s$-channel helicity conservation at small squared four-momentum transfer $t$ and are able to extract the $t$-dependence of natural and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full $t$ range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced $ρ(770)$ differ by two units are negligible for $-t<0.5\,\text{GeV}^{2}/c^{2}$.

nucl-ex↗

arXiv2023

Surface barrier effect as evidence of chiral soliton lattice formation in chiral dichalcogenide CrTa$_{3}$S$_{6}$ crystals

The formation of chiral magnetic soliton lattice (CSL) is investigated in monoaxial chiral dichalcogenide CrTa$_{3}$S$_{6}$ crystals in terms of a surface barrier, which prevents a penetration of chiral solitons into the system and is an intrinsic origin of hysteresis for the continuous phase transition of nucleation-type, as discussed in the system of quantized vortices in type-II superconductors. The magnetoresistance (MR) was examined with microfabricated platelet samples in different dimensions with regard to the $c$-axis direction of the crystal. The CSL formation was confirmed by the discrete MR changes, reflecting the number of chiral solitons, as well as by the presence of surface barrier, recognized as a fixed ratio of critical magnetic fields during the hysteresis field cycle. We also argue the influence of the surface barrier in the bulk CrTa$_{3}$S$_{6}$ crystals.

cond-mat.mtrl-sci↗

arXiv2022

An emergence of chiral helimagnetism or ferromagnetism governed by Cr intercalation in a dichalcogenide CrNb$_{3}$S$_{6}$

A synthesis of single crystals of chiral dichalcogenides $TM_{3}X_{6}$ ($T$: 3$d$ transition metal, $M$: Nb or Ta, $X$: S or Se) remains an intriguing issue for the investigation of emergent quantum properties such as chiral helimagnetism. In this study, we investigated a correlation between the quantity of Cr intercalation $x$ and magnetic property in single crystals of a chromium (Cr) intercalated chiral disulfide Cr$_x$Nb$_3$S$_6$ in order to optimize the synthesis condition for the intercalation-controlled single crystals. The magnetic properties including a magnetic transition temperature $T_{c}$ take different values depending on the samples. We systematically grew single crystals of Cr$_{x}$Nb$_{3}$S$_{6}$ with $x$ ranged from 0.89 to 1.03 and found that the amount of the Cr intercalation $x$ is an essential factor in controlling the magnetic properties of the grown crystals. The magnetization anomaly, which appears in the temperature dependence as evidence of the formation of chiral magnetic soliton lattice (CSL), was observed only in a narrow region of $x$ from 0.98 to 1.03. The single crystals with $x$ being 0.98 and 0.99 showed the CSL behavior with the highest $T_{c}$ of 133 K. These results indicate that small amount of defects on the sites for $T$ ions dramatically affects the quality of the single crystals in the synthesis of $TM_{3}$S$_{6}$. We also discuss an importance of synthesizing enantiopure single crystals of chiral dichalgogenides in order to observe chiral physical properties unique to chiral compounds such as magneto-chiral effect and chiral-induced spin selectivity.

cond-mat.mtrl-sci↗

arXiv2022

Search for photoproduction of axion-like particles at GlueX

We present a search for axion-like particles, $a$, produced in photon-proton collisions at a center-of-mass energy of approximately 4 GeV, focusing on the scenario where the $a$-gluon coupling is dominant. The search uses $a\toγγ$ and $a\toπ^+π^-π^0$ decays, and a data sample corresponding to an integrated luminosity of 168 pb$^{-1}$ collected with the GlueX detector. The search for $a\toγγ$ decays is performed in the mass range of $180 < m_a < 480$ MeV, while the search for $a\toπ^+π^-π^0$ decays explores the $600 < m_a < 720$ MeV region. No evidence for a signal is found, and 90% confidence-level exclusion limits are placed on the $a$-gluon coupling strength. These constraints are the most stringent to date over much of the mass ranges considered.

hep-ex↗

arXiv2022

Measurement of Spin Density Matrix Elements in $Λ(1520)$ Photoproduction at 8.2-8.8 GeV

We report on the measurement of spin density matrix elements of the $Λ(1520)$ in the photoproduction reaction $γp\rightarrow Λ(1520)K^+$, via its subsequent decay to $K^{-}p$. The measurement was performed as part of the GlueX experimental program in Hall D at Jefferson Lab using a linearly polarized photon beam with $E_γ=$ 8.2-8.8 GeV. These are the first such measurements in this photon energy range. Results are presented in bins of momentum transfer squared, $-(t-t_\text{0})$. We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are dominant in $Λ(1520)$ photoproduction.

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.

nucl-ex↗

arXiv2021

SPring-8 LEPS2 beamline: A facility to produce a multi-GeV photon beam via laser Compton scattering

We have constructed a new laser-Compton-scattering facility, called the LEPS2 beamline, at the 8-GeV electron storage ring, SPring-8. This facility provides a linearly polarized photon beam in a tagged energy range of 1.3--2.4 GeV. Thanks to a small divergence of the low-emittance storage-ring electrons, the tagged photon beam has a size (sigma) suppressed to about 4 mm even after it travels about 130 m to the experimental building that is independent of the storage ring building and contains large detector systems. This beamline is designed to achieve a photon beam intensity higher than that of the first laser-Compton-scattering beamline at SPring-8 by adopting the simultaneous injection of up to four high-power laser beams and increasing a transmittance for the long photon-beam path up to about 77%. The new beamline is under operation for hadron photoproduction experiments.

physics.acc-ph↗