arXiv subjects

Kazuya Aoki

Publications and source records attributed to Kazuya Aoki.

11 recordsLinked to original sources

arXiv2026

Feasibility demonstration of a high-momentum, high-purity muon beamline at the J-PARC Hadron Experimental Facility

We have established and characterized a novel high-purity muon beam delivery scheme, designated as $μ$20, at the high-momentum hadron beamline (B-line) of the J-PARC Hadron Experimental Facility. This scheme delivers tertiary muons produced via the in-flight backward decays of secondary pions in the straight section of the beamline, inherently suppressing parent hadron contamination. In a systematic performance evaluation, the muon beam achieved a standalone intensity of $1.7\times10{^3}$ particles/spill with a spatial spread (standard deviation, $σ$) of approximately 15 mm at the downstream detector position. A systematic attenuation analysis utilizing an iron absorber verified a high muon purity of 98.0$\pm$0.6% for the 3 GeV/$c$ muon beam mode. Crucially, this work marks the first successful feasibility study of a high-momentum and high-purity muon beamline operation at an experimental facility in Japan.

physics.acc-ph↗

arXiv2026

The Silicon Tracking System of the E16 experiment at J-PARC: construction, installation and commissioning in beam test experiments

The J-PARC E16 experiment aims to search for signatures of chiral symmetry restoration. It studies in-medium modifications of vector mesons that decay via the dielectron channel. The measurements use a high-intensity 30 GeV proton beam with C and Cu targets at rates up to 10 MHz. To achieve this, the experiment upgrades its tracking, by introducing innermost detector modules constructed with the same technology and procedures as the modules of the Silicon Tracking System (STS) of the Compressed Baryonic Matter (CBM) experiment at Facility for Antiproton and Ion Research (FAIR). A total of 15 modules were assembled, tested, characterized and then installed in the E16 detector setup. The detector was commissioned in a beam test experiment at Tsukuba, where the detector modules could be exposed to a 3 GeV electron beam. In preparation for the beam test the modules were characterized and calibrated, and performance studies were accomplished to assess the quality of the setup. During beamtime, three modules were operated and illuminated in two planes by the electron beam. This paper presents the results of the construction, characterization, commissioning, and operation of the E16-STS modules in beam test experiments.

physics.ins-det↗

arXiv2026

First measurement of $ϕ$ meson production in 30 GeV proton-nucleus reactions via di-electron decay at J-PARC

We present the first measurement of the production of the $ϕ$ meson in 30 GeV proton-nucleus interactions on carbon and copper targets via the di-electron decay channel. The measurement was conducted at the high-momentum beamline of the J-PARC Hadron Experimental Facility, which was commissioned in 2020. The $e^+e^-$ pairs were detected using the E16 spectrometer, during a commissioning run of the J-PARC E16 experiment. The $ϕ$ mesons are successfully reconstructed on all experimental targets. The obtained yields are converted to the total production cross section, assuming a kinematical distribution of the event generator JAM. The total cross sections derived are 2.0 $\pm$ 0.9 (stat.) $\pm$ 1.0 (syst.) mb on the carbon target and 10.3 $\pm$ 4.4 (stat.) $\pm$ 4.4 (syst.) mb on the copper target. The mass-number dependence of the cross section is discussed using the parameter $α$, defined as $σ\propto A^α$, resulting in $α= $ 0.99 $\pm$ 0.38 (stat.) $\pm$ 0.34 (syst.). The extrapolation to $A=1$, which means that the cross section of proton-proton reactions, is in good agreement with the existing measurements at comparable energies.

nucl-ex↗

arXiv2025

Studying the in-medium $ϕ$ meson spectrum through kaons in proton-nucleus reactions

Exploring the mass modifications of $ϕ$ mesons in nuclei provides insights into the nature of strongly interacting matter. Specifically, $ϕ$ meson mass shifts can be related to the in-medium modification of the strange quark condensate. Therefore, the partial restoration of chiral symmetry can be studied by observing the mass shifts through the decay channels $ϕ\rightarrow e^+e^-$, and $ϕ\rightarrow K^+K^-$. In this paper, we examine the possibility of observing the $ϕ$ meson mass modifications of the $ϕ$ mesons in 30 GeV proton-nucleus (C, Cu, Pb) collisions, to be studied at the J-PARC E88 experiment, through the kaonic decay channel, with the off-shell Budapest Boltzmann-Uehling-Uhlenbeck (BuBUU) transport model. By applying different mean fields to the kaons, we examine their effects on the invariant mass spectra. Our simulations suggest that, although different mean fields for the kaons do affect the spectrum, there is a common observable effect primarily driven by the $ϕ$ mass shift. However, due to the threshold associated with the two kaons, the signal we observe is quite different from the one expected in dilepton spectra. Therefore, to meaningfully constrain the mass shift, it will be useful to include both kaon and dilepton channels in the analysis of the experimental data.

hep-ph↗

arXiv2025

Velocity dependence of the mass modifications of $ρ$ and $ω$ mesons in 12 GeV $p+A$ reactions

This study measured the invariant mass spectra of $ρ$ and $ω$ mesons in the $e^+e^-$ decay channel for 12 GeV (12.9 GeV/$c$) $p+\mathrm{C}$ and $p+\mathrm{Cu}$ reactions ($\sqrt{s}_{NN}=5.1$ GeV) at the KEK 12-GeV Proton Synchrotron. The measured spectra were divided into three $βγ$ regions to examine their velocity dependence. Across all regions, significant excesses were observed on the low-mass side of the $ω$ meson peak, beyond the contributions of known hadronic sources, in the data of the C and Cu targets. Model calculations were subsequently performed to evaluate the magnitudes of the mass modifications of $ρ$ and $ω$ mesons.

nucl-ex↗

arXiv2024

Separating the transverse and longitudinal modes of $ϕ$, $ρ$, $K^*$ and $K_1$ mesons through their angular-dependent two-body decay modes

The mass shift a spin-1 particle moving in the nuclear medium will depend on its polarization direction. To study polarization-independent mass shifts in the medium, we explore methods to isolate each polarization direction of spin-1 mesons through the angular-dependent two-body decay modes. Specifically, we study $ϕ\to K^{+}K^{-}$, $ρ\toππ$, $K^{*}\to Kπ$, $ϕ\to e^{+}e^{-}$ and $K_{1}\toρK(K^{*}π)$ decays. While each polarization mode can be isolated through angular dependencies, accomplishing the decomposition for the $K_1$ meson further requires measuring the polarization of the $ρ(K^*)$ meson. Concerning $K^{*}$ and $K_1$ mesons, since both particles have vacuum widths smaller than 100 MeV, they are ideal candidates for experimentally measuring chiral partners. The simultaneous observation of mass shifts of these chiral partners would provide valuable insights into the contribution of chiral symmetry breaking to the generation of hadron masses.

hep-ph↗

arXiv2024

Identifying the transverse and longitudinal modes of the $K^*$ and $K_{1}$ mesons through their angular dependent decay modes

Observing the mass shifts of chiral partners will provide invaluable insight into the role of chiral symmetry breaking in the generation of hadron masses. Because both the $K^*$ and $K_1$ mesons have vacuum widths smaller than 100 MeV, they are ideal candidates for realizing mass shift measurements. On the other hand, the different momentum dependence of the longitudinal and transverse modes smear the peak positions. In this work, we analyze the angular dependence of the two-body decays of both the $K^*$ and $K_1$. It is found that the longitudinal and transverse modes of the $K^*$ can be isolated by observing the pseudoscalar decay in either the forward or perpendicular directions, respectively. For the $K_1$ decaying into a vector meson and a pseudoscalar meson, one can accomplish the same goal by further observing the polarization of the vector meson through its angular dependence on the two pseudoscalar meson decay.

hep-ph↗

arXiv2023

Disentangling longitudinal and transverse modes of the $ϕ$ meson through dilepton and kaon decays

Angular distributions of $ϕ$ meson decay amplitudes of $e^+e^-$ and $K^+K^-$ channels are computed using both specific interaction Lagrangians and simple arguments relying on angular momentum conservation. Based on the obtained results, we assess methods to experimentally disentangle the longitudinal and transverse polarization modes of the $ϕ$ meson and discuss advantages and disadvantages of employing either the leptonic or hadronic decay modes for this task.

hep-ph↗

arXiv2021

Extension of the J-PARC Hadron Experimental Facility: Third White Paper

The J-PARC Hadron Experimental Facility was constructed with an aim to explore the origin and evolution of matter in the universe through the experiments with intense particle beams. In the past decade, many results on particle and nuclear physics have been obtained at the present facility. To expand the physics programs to unexplored regions never achieved, the extension project of the Hadron Experimental Facility has been extensively discussed. This white paper presents the physics of the extension of the Hadron Experimental Facility for resolving the issues in the fields of the strangeness nuclear physics, hadron physics, and flavor physics.

nucl-ex↗

arXiv2020

Data acquisition system in Run-0a for the J-PARC E16 experiment

J-PARC E16 is an experiment to examine the origin of hadron mass through a systematic measurement of spectral changes of vector mesons in nuclei. The measurement of $e^{+}e^{-}$ pairs from the decay of vector mesons will provide the information of the partial restoration of the chiral symmetry in a normal nuclear density. To resolve a pulse pile-up and achieve good discrimination of $e^{\pm}$ from the background of a reaction rate of an order of 10 MHz, the data acquisition (DAQ) system uses waveform sampling chips of APV25 and DRS4. The trigger rate and data rate are expected to be 1 kHz and 130--330 MiB/s, respectively. The DAQ system for readout of APV25 and DRS4 were developed, where events were synchronized by common trigger and tag data. The first commissioning in beam, called Run-0a, was performed in June 2020 with about 1/4 of the designed setup. The DAQ worked with a trigger rate of 300 Hz in the Run-0a and the main bottleneck was a large data size of APV25. Further optimization of the DAQ system will improve the performance.

physics.ins-det↗

arXiv2015

Study of in-medium mass modification at J-PARC

Study of in-medium mass modification has attracted interest in terms of the restoration of the spontaneously broken chiral symmetry, which is responsible for the generation of hadron mass. Many experiments were performed to measure in-medium property of hadrons but there is no consensus yet. J-PARC E16 has been proposed to study in-medium property of vector mesons via dilepton decay channel. The status of spectrometer R \& D is explained. Other related experiments planned at J-PARC are also introduced.

nucl-ex↗