arXiv subjects

N. Tomida

Publications and source records attributed to N. Tomida.

15 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 $\gamma d \to K^0\Lambda p$ reaction

The $\gamma d \to K^{0}\Lambda p$ 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 $(M_{\Lambda p},q)$ distribution below the $K^-pp$ mass threshold, where $M_{\Lambda p}$ is the $\Lambda p$ invariant mass and $q \equiv |\vec{p}_{\gamma}-\vec{p}_{K^{0}}| = |\vec{p}_{\Lambda p}|$ is the momentum transfer. A two-dimensional $(M_{\Lambda p},q)$ fit demonstrates that the enhancement near the threshold is statistically significant, yielding a local significance of $7.3,\sigma$. The enhancement is characterized by effective shape parameters including the Breit--Wigner mass $M$ and width $\Gamma$, and a Gaussian form-factor momentum scale $Q$: $M = 2.354 \pm 0.011(\mathrm{stat.})^{+0.009}_{-0.005}(\mathrm{syst.})~\mathrm{GeV}/c^{2}$, $\Gamma = 0.055 \pm 0.023(\mathrm{stat.})^{+0.031}_{-0.009}(\mathrm{syst.})~\mathrm{GeV}/c^{2}$, 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.

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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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arXiv2025

Three-dimensional imaging of hadrons with hard exclusive reactions: advances in experiment, theory, phenomenology, and lattice QCD

Generalized Parton Distributions (GPDs) have emerged as a powerful framework for exploring the internal structure of hadrons in terms of their partonic constituents. Over the past three decades, the field has witnessed significant theoretical and experimental advancements. The interpretation of GPDs in impact parameter space offers a vivid three-dimensional visualization of hadron structure, correlating longitudinal momentum and transverse spatial distributions, thereby enabling tomographic imaging of hadrons. Furthermore, the link between GPDs and the matrix elements of the QCD energy-momentum tensor provides access to fundamental properties of hadrons, including spin decomposition and internal pressure distributions. Notably, recent analyses of Deeply Virtual Compton Scattering (DVCS) data have enabled the empirical extraction of the quark pressure profile inside the proton. Motivated by the rapidly evolving experimental landscape, this white paper provides a timely and focused overview of recent developments in GPD theory, phenomenology, and lattice QCD studies. Its scope is shaped by the needs and opportunities of forthcoming experimental programs, and it highlights advances that are particularly relevant for the next generation of dedicated measurements, including the extended Jefferson Lab 12 GeV program and its potential 22 GeV upgrade, J-PARC, COMPASS/AMBER, LHC ultra-peripheral collisions, and the future electron-ion colliders EIC and EicC.

hep-ph↗

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.

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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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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↗

arXiv2020

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

We measured missing mass spectrum of the $^{12}{\rm C}(\gamma,p)$ reaction for the first time in coincidence with potential decay products from $\eta'$ bound nuclei. We tagged an ($\eta+p$) pair associated with the $\eta'N\to\eta N$ 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 $\cos\theta^{\eta p}_{lab}<-0.9$ 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 $\eta'$ production rate. Our results indicate a small branching fraction of the $\eta'N\to\eta N$ process and/or a shallow $\eta'$-nucleus potential.

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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

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

A compensated multi-gap RPC with 2 m-long strips for the LEPS2 experiment

We have developed multi-gap resistive plate chambers (MRPCs) with 2.5 x 200 cm2 readout strips for the time-of-flight (TOF) detector system of the LEPS2 experiment at SPring-8. These chambers consist of 2 stacks and 5 gas gaps per stack, in a mirrored configuration. A time resolution of sigma ~ 80 ps was achieved for any position within a strip (at above 99% detection efficiency); after performing the time-charge slewing correction, this value could be reduced to 60 ps. A link between the small contribution of the slewing correction to timing and the suppression of modal dispersion in the detector could be established.

physics.ins-det↗

arXiv2017

$\phi$ photoproduction on the proton at $E_{\gamma}$ = 1.5 - 2.9 GeV

Differential cross sections at $t=t_{\text{min}}$ and decay asymmetries for the $\gamma p\rightarrow\phi p$ reaction have been measured using linearly polarized photons in the range 1.5 to 2.9 GeV. These cross sections were used to determine the Pomeron strength factor. The cross sections and decay asymmetries are consistently described by the $t$-channel Pomeron and pseudoscalar exchange model in the $E_{\gamma}$ region above 2.37 GeV. In the lower energy region, an excess over the model prediction is observed in the energy dependence of the differential cross sections at $t=t_{\text{min}}$. This observation suggests that additional processes or interference effects between Pomeron exchange and other processes appear near the threshold region.

nucl-ex↗

arXiv2016

Performance of TOF-RPC for the BGOegg experiment

We constructed a new time-of-flight (TOF) detector consisting of resistive plate chambers (RPCs) to measure particle energy in the BGOegg experiment. The BGOegg-RPC has a unique feature which enables us to cover a large area with a small number of readout channels. For this purpose, we developed the RPC with a strip size of 2.5 cm $\times$ 100 cm. The BGOegg-RPC covers an area of 320 cm $\times$ 200 cm with only 256 channels of readout electronics. In case of large readout RPCs, an originated signal is distorted and dispersed during propagation. In addition, there happens a signal reflection at the end of the strip. Although we designed the BGOegg-RPC and front-end electronics with minimized signal reflection, a small reflection still remained, deteriorating the resulting time resolution. After establishing calibration and correction methods to improve the performance of the BGOegg-RPC, we obtained the time resolution of σ~60 ps around the central region of strips.

physics.ins-det↗

arXiv2014

High-resolution search for the $Θ^{+}$ pentaquark via a pion-induced reaction at J-PARC

The pentaquark $Θ^+$ has been searched for via the $π^-p \to K^-X$ reaction with beam momenta of 1.92 and 2.01 GeV/$c$ at J-PARC. A missing mass resolution of 2 MeV (FWHM) was achieved but no sharp peak structure was observed. The upper limits on the production cross section averaged over the scattering angle from 2$^{\circ}$ to 15$^{\circ}$ in the laboratory frame were found to be less than 0.28 $μ$b/sr at the 90\% confidence level for both the 1.92- and 2.01-GeV/$c$ data. The systematic uncertainty of the upper limits was controlled within 10\%. Constraints on the $Θ^+$ decay width were also evaluated with a theoretical calculation using effective Lagrangian. The present result implies that the width should be less than 0.36 and 1.9 MeV for the spin-parity of $1/2^+$ and $1/2^-$, respectively.

nucl-ex↗

arXiv2012

Search for the $Θ^{+}$ pentaquark via the $π^-p\to K^-X$ reaction at 1.92 GeV/$c$

The $Θ^+$ pentaquark baryon was searched for via the $π^-p\to K^-X$ reaction in a missing-mass resolution of 1.4 MeV/$c^2$(FWHM) at J-PARC. $π^-$ meson beams were incident on the liquid hydrogen target with the beam momentum of 1.92 GeV/$c$. No peak structure corresponding to the $Θ^+$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2$^{\circ}$ to 15$^{\circ}$ in the laboratory frame was obtained to be 0.26 $μ$b/sr in the mass region of 1.51$-$1.55 GeV/$c^2$.The upper limit of the $Θ^+$ decay width using the effective Lagrangian approach was obtained to be 0.72 MeV/$c^2$ and 3.1 MeV/$c^2$ for $J^P_Θ=1/2^+$ and $J^P_Θ=1/2^-$, respectively.

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