arXiv subjects

S. Kido

Publications and source records attributed to S. Kido.

5 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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arXiv2025

Automated segmentation of pediatric neuroblastoma on multi-modal MRI: Results of the SPPIN challenge at MICCAI 2023

Surgery plays an important role within the treatment for neuroblastoma, a common pediatric cancer. This requires careful planning, often via magnetic resonance imaging (MRI)-based anatomical 3D models. However, creating these models is often time-consuming and user dependent. We organized the Surgical Planning in Pediatric Neuroblastoma (SPPIN) challenge, to stimulate developments on this topic, and set a benchmark for fully automatic segmentation of neuroblastoma on multi-model MRI. The challenge started with a training phase, where teams received 78 sets of MRI scans from 34 patients, consisting of both diagnostic and post-chemotherapy MRI scans. The final test phase, consisting of 18 MRI sets from 9 patients, determined the ranking of the teams. Ranking was based on the Dice similarity coefficient (Dice score), the 95th percentile of the Hausdorff distance (HD95) and the volumetric similarity (VS). The SPPIN challenge was hosted at MICCAI 2023. The final leaderboard consisted of 9 teams. The highest-ranking team achieved a median Dice score 0.82, a median HD95 of 7.69 mm and a VS of 0.91, utilizing a large, pretrained network called STU-Net. A significant difference for the segmentation results between diagnostic and post-chemotherapy MRI scans was observed (Dice = 0.89 vs Dice = 0.59, P = 0.01) for the highest-ranking team. SPPIN is the first medical segmentation challenge in extracranial pediatric oncology. The highest-ranking team used a large pre-trained network, suggesting that pretraining can be of use in small, heterogenous datasets. Although the results of the highest-ranking team were high for most patients, segmentation especially in small, pre-treated tumors were insufficient. Therefore, more reliable segmentation methods are needed to create clinically applicable models to aid surgical planning in pediatric neuroblastoma.

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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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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.

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