arXiv subjects

Yasuhito Sakaki

Publications and source records attributed to Yasuhito Sakaki.

At least 19 recordsLinked to original sources

arXiv2026

Toward AI-Agent-Driven Particle Transport Simulations: Implementation of AI-Assisted Workflows for PHITS

Monte Carlo particle transport codes are powerful tools, but their use requires substantial knowledge of input preparation, execution, and result analysis. In this study, we present a code-side strategy for applying existing AI assistants and AI agents to PHITS. Two complementary sets of AI-ready resources were prepared from manuals, lecture materials, sample inputs, utility information, and developer-curated cautions: a bundled knowledge base for retrieval-augmented generation (RAG)-based assistants and a compact agent reference for direct use by AI agents. The knowledge base was loaded into NotebookLM to provide conversational PHITS support, while the agent reference was combined with PHITS-specific policies and execution rules to enable Codex and Claude Code to edit input files, execute calculations, inspect errors, analyze results, and assist with source-code modification and compilation. Five demonstration tasks covered input modification, repeated simulations, parameter optimization, program compilation, post-processing, and result interpretation. The results showed that AI agents could handle complex PHITS workflows when appropriate resources and rules were provided. Practical lessons included precise prompts, human verification, well-documented sample files, explicit execution policies, and command-line-accessible tools. These findings support bundling AI-ready resources with particle transport codes to enable the use of general-purpose AI tools without requiring dedicated code-specific applications.

physics.comp-ph↗

arXiv2026

Quantitative Evaluation of a Hybrid Target for Ultraslow-Muon Production in $μ$TRISTAN

We present the first quantitative evaluation of the hybrid target concept proposed in $μ$TRISTAN. The $μ$TRISTAN project is a positive-muon collider concept based on the ultraslow-muon production technique, in which thermal muonium emitted from a material surface is subsequently laser-ionized. The hybrid target consists of a pion production target and a surrounding pion- and muon-stopping target that also serves as a muonium-production target. In this paper, Monte Carlo simulations of the hybrid target are performed to evaluate the yield of positive muons stopped near the tungsten surface, where they can contribute to muonium emission. The ultraslow-muon yield at the hybrid target before extraction is estimated to reach the 10$^{-3}$ level per p--Li nuclear collision, assuming unit muon-to-muonium conversion efficiency. This study provides a quantitative benchmark for hybrid-target design toward an intense ultraslow-muon source.

physics.acc-ph↗

arXiv2026

Search for Sub-GeV Axion-Like Particles at EBES Pilot Run Using 4 GeV Positron Beam at KEK LINAC

We report the results of a search for sub-GeV axion-like particles (ALPs) using pilot run data from the Electron Beam-dump Experiment at KEK LINAC Switching Yard 3 (EBES). The data were collected in December 2023 with a 4 GeV positron beam and correspond to $1.3\times10^{14}$ positrons on target. In the pilot run setup, a tungsten beam dump and a single PbO calorimeter were used. We consider ALP production via the Primakoff process induced by bremsstrahlung photons in the beam dump, followed by the decay $a\toγγ$. The background was estimated with a data-driven method, and a signal region was defined such that the expected background yield is below 0.1 events. No events were observed after unblinding. Upper limits at the 90% confidence level were derived in the ALP mass-coupling plane, extending the experimental coverage into a region of parameter space not explored by previous searches.

hep-ex↗

arXiv2026

Muon collider experiments as electron/positron beam sources: case studies of new light-particle searches

At muon colliders, muon decays naturally produce intense electrons and positrons with unique features, namely high energies, high repetition rates, and small intrinsic uncertainties, that are unavailable at existing accelerator facilities. We quantitatively study the feasibility of extracting such particles in two representative future muon collider designs, IMCC and $μ$TRISTAN. Using Monte Carlo simulations with the corresponding design parameters, we study the spatial, angular, and energy distributions of decay electrons and positrons in the curved sections of the collider ring. We find that typical deflections of $0.1-10~\mathrm{mrad}$ can be achieved even for high-energy electrons carrying large energy fractions ($\simeq 0.6 - 1.0$) of the muon beam energy, with the ring bending magnets (or magnets providing an equivalent field) effectively serving as a pre-septum magnet, that partially deflects the beam before the main septum magnet, suggesting that the extraction scheme could be practically feasible. Exploiting the distinct beam properties of IMCC and $μ$TRISTAN, we propose complementary search strategies, missing energy and momentum searches for dark matter at $μ$TRISTAN and visible-decay searches for axion-like particles and light scalars at IMCC, which probe parameter space beyond the reach of current and other proposed experiments.

hep-ph↗

arXiv2024

Sub-GeV dark matter search at ILC beam dumps

Light dark matter particles may be produced in electron and positron beam dumps of the International Linear Collider (ILC). We propose an experimental setup to search for such events, the Beam-Dump eXperiment at the ILC (ILC-BDX). The setup consists of a muon shield placed behind the beam dump, followed by a multi-layer tracker and an electromagnetic calorimeter. The calorimeter can detect electron recoils due to elastic scattering of dark matter particles produced in the dump, while the tracker is sensitive to decays of excited dark-sector states into the dark matter particle. We study the production, decay and scattering of sub-GeV dark matter particles in this setup in several models with a dark photon mediator. Taking into account beam-related backgrounds due to neutrinos produced in the beam dump as well as the cosmic-ray background, we evaluate the sensitivity reach of the ILC-BDX experiment. We find that the ILC-BDX will be able to probe interesting regions of the model parameter space and, in many cases, reach well below the relic target.

hep-ph↗

arXiv2023

The potential of the ILC beam dump for high-intensity and large-area irradiation field with atmospheric-like neutrons and muons

We evaluate the neutron and muon fluxes produced in the ILC beam dumps by Monte Carlo simulations and discuss their potential use in irradiation fields. We show that the beam dumps can provide high-intensity neutron and muon fluxes with spectra quite similar to secondary cosmic rays, which are suitable for soft error studies. The beam dumps deliver neutrons about $10^{11}$ times the secondary cosmic rays on spaces perpendicular to the beam axis and muons $10^8$ times downstream of the beam dumps in the initial phase of the ILC. Large-area irradiation of 1\,m$^2$ or more is possible. Differences in the energy distribution of muons in electron and positron beam dumps are also discussed for particle physics experiments.

physics.acc-ph↗

arXiv2021

New physics searches at the ILC positron and electron beam dumps

We study capability of the ILC beam dump experiment to search for new physics, comparing the performance of the electron and positron beam dumps. The dark photon, axion-like particles, and light scalar bosons are considered as new physics scenarios, where all the important production mechanisms are included: electron-positron pair-annihilation, Primakoff process, and bremsstrahlung productions. We find that the ILC beam dump experiment has higher sensitivity than past beam dump experiments, with the positron beam dump having slightly better performance for new physics particles which are produced by the electron-positron pair-annihilation.

hep-ph↗

arXiv2021

Search for axion-like particles with electron and positron beams at KEK Linac

We propose a fixed-target experiment to search for Axion-like particles (ALPs) coupling to photons, which utilizes electron and positron beams available at KEK Linac. The sensitivity to ALP is evaluated for two shielding setups in conjunction with other beam dump experiments, fixed-target experiments, and $e^+e^-$ collider experiments. This study shows that the two setups can explore the gap between the search region excluded by the beam dump experiments and the $e^+e^-$ collider experiments.

hep-ph↗

arXiv2021

Search for new light particles at ILC main beam dump

We perform a feasibility study of a beam dump experiment at the International Linear Collider (ILC). To investigate the sensitivity to new light particles at the experiment, we consider models for axion-like particles (ALPs) and a light scalar particle coupled to charged leptons. For both models, we show that the detection sensitivity is almost an order of magnitude higher than other beam dump experiments in the small coupling region. For ALPs, it is shown that the ILC beam dump experiment is highly complementary to bounds from astrophysics. In addition, for the model of the scalar particle, the region favored by the muon $g-2$ experiment can be explored.

hep-ph↗

arXiv2020

Implementation of muon pair production in PHITS and verification by comparing with the muon shielding experiment at SLAC

We implemented a model of muon pair production through a real photon in PHITS and compared our calculations with data of the muon shielding experiment conducted at SLAC to verify the validity of the implemented model. Our predictions of the muon fluence induced by electrons are in good agreement with the experimental data. To understand the known differences between the calculations of the muon fluence, which have been determined using other Monte-Carlo codes, we quantitatively evaluate the fluctuations in the Monte-Carlo results due to systematic errors in multiple Coulomb scattering, differences in the approximation methods and energy loss models, and whether incoherent production is considered.

physics.acc-ph↗

arXiv2019

Quark jet rates and quark/gluon discrimination in multi-jet final states

We estimate the number of quark jets in QCD multi-jet final states at hadron colliders. In the estimation, we develop the calculation of jet rates into that of quark jet rates. From the calculation, we estimate the improvement on the signal-to-background ratio for a signal semi-analytically by applying quark/gluon discrimination, where the signal predicts many quark jets. We introduce a variable related to jet flavors in multi-jet final states and propose a data-driven method using the variable to reduce systematic uncertainties of analysis results. As the same with the semi-analytical result, the improvements on the signal-to-background ratio using the variable in Monte-Carlo analysis are estimated.

hep-ph↗

arXiv2018

Testing leptoquark models in $\bar B \to D^{(*)} τ\barν$

We study potential New Physics effects in the $\bar B \to D^{(*)} τ\barν$ decays. As a particular example of New Physics models we consider the class of leptoquark models and put the constraints on the leptoquark couplings using the recently measured ratios $R(D^{(*)})=BR(\bar B \to D^{(*)} τ\barν)/BR(\bar B \to D^{(*)} μ\barν)$. For consistency, some of the constraints are compared with the ones coming from the current experimental bound on $BR(B \to X_s ν\barν)$. In order to discriminate various New Physics scenarios, we examine the correlations between different observables that can be measured in future.

hep-ph↗

arXiv2018

Combined analysis of double Higgs production via gluon fusion at the HL-LHC in the effective field theory approach

We perform the combined analysis of the double Higgs production via gluon fusion in the $b\bar{b} γγ$ and $b\bar{b}τ^+τ^-$ decay channels at the High-Luminosity LHC (HL-LHC). To validate our analysis, we reproduce the ATLAS result of the $b\bar{b} γγ$ process including all contributions from fakes. For the $b\bar{b}τ^+τ^-$ decay channel, we perform the similar analysis to the CMS one. As an improvement, we also perform the multivariate analysis employing the boosted decision tree algorithm. Then, we derive 68% probability contours on anomalous Higgs couplings in the effective field theory (EFT) approach for various analyses. We find that the $b\bar{b}τ^+τ^-$ process outperforms the $b\bar{b}γγ$ for the measurement of energy-growing operators, while adding the $b\bar{b}τ^+τ^-$ process is least beneficial for improving the precision of the Higgs self-coupling (mainly set by the $b\bar{b}γγ$ process). We illustrate that the double Higgs production alone can be comparable to the single Higgs process in constraining the modification of the top Yukawa coupling in the positive direction. Focusing on the Higgs self-coupling as a special interest, we derive the precision as a function of various improvable parameters such as tag and mistag rates of tau leptons, heavy flavor jets, photon identification, diphoton mass resolution, and jet energy resolution to take into account future phenomenological studies. As an optimistic benchmark scenario, we illustrate that the 68% and 95% probability intervals of the Higgs self-coupling, $λ_3/λ_{3}^{SM}$, at the HL-LHC can reach $[0.2,\, 2.3]$ and $[-0.1,\, 3.5] \cup [4.0,\, 6.5]$, respectively, where the correlation among the EFT coefficients is taken into account.

hep-ph↗

arXiv2016

Quark-gluon discrimination in the search for gluino pair production at the LHC

We study the impact of including quark- and gluon-initiated jet discrimination in the search for strongly interacting supersymmetric particles at the LHC. Taking the example of gluino pair production, considerable improvement is observed in the LHC search reach on including the jet substructure observables to the standard kinematic variables within a multivariate analysis. In particular, quark and gluon jet separation has higher impact in the region of intermediate mass-gap between the gluino and the lightest neutralino, as the difference between the signal and the standard model background kinematic distributions is reduced in this region. We also compare the predictions from different Monte Carlo event generators to estimate the uncertainty originating from the modelling of the parton shower and hadronization processes.

hep-ph↗

arXiv2015

Evolution variable dependence of jet substructure

Studies on jet substructure have evolved significantly in recent years. Jet substructure is essentially determined by QCD radiations and non-perturbative effects. Predictions of jet substructure are usually different among Monte Carlo event generators, and are governed by the parton shower algorithm implemented. For leading logarithmic parton shower, even though one of the core variables is the evolution variable, its choice is not unique. We examine evolution variable dependence of the jet substructure by developing a parton shower generator that interpolates between different evolution variables using a parameter $α$. Jet shape variables and associated jet rates for quark and gluon jets are used to demonstrate the $α$-dependence of the jet substructure. We find angular ordered shower predicts wider jets, while relative transverse momentum ($p_{\bot}$) ordered shower predicts narrower jets. This is qualitatively in agreement with the missing phase space of $p_{\bot}$ ordered showers. Such difference can be reduced by tuning other parameters of the showering algorithm, especially in the low energy region, while the difference tends to increase for high energy jets.

hep-ph↗

arXiv2015

Associated jet and subjet rates in light-quark and gluon jet discrimination

We show that in studies of light quark- and gluon-initiated jet discrimination, it is important to include the information on softer reconstructed jets (associated jets) around a primary hard jet. This is particularly relevant while adopting a small radius parameter for reconstructing hadronic jets. The probability of having an associated jet as a function of the primary jet transverse momentum ($p_T$) and radius, the minimum associated jet $p_T$ and the association radius is computed upto next-to-double logarithmic accuracy (NDLA), and the predictions are compared with results from Herwig++, Pythia6 and Pythia8 Monte Carlos (MC). We demonstrate the improvement in quark-gluon discrimination on using the associated jet rate variable with the help of a multivariate analysis. The associated jet rates are found to be only mildly sensitive to the choice of parton shower and hadronization algorithms, as well as to the effects of initial state radiation and underlying event. In addition, the number of $k_T$ subjets of an anti-$k_T$ jet is found to be an observable that leads to a rather uniform prediction across different MC's, broadly being in agreement with predictions in NDLA, as compared to the often used number of charged tracks observable.

hep-ph↗

arXiv2014

Probing New Physics with $q^2$ distributions in $\bar{B} \to D^{(*)} τ\barν$

Recent experimental results for the ratios of the branching fractions of the decays $\bar{B} \to D^{(*)} τ\barν$ and $\bar{B} \to D^{(*)} μ\barν$ came as a surprise and lead to a discussion of possibility of testing New Physics beyond the Standard Model through these modes. We show that these decay channels can provide us with good constraints on New Physics and several New Physics cases are favored by the present experimental data. In order to discriminate various New Physics scenarios, we examine the $q^2$ distributions and estimate the sensitivity of this potential measurement at the SuperKEKB/Belle II experiment.

hep-ph↗

arXiv2014

CP violation in $B\to Dτν_τ$ using multi-pion tau decays

Present experimental datas have shown a 3.8$σ$ level discrepancy with the standard model in $\overline{B}\to D^{(*)}τ\barν_τ$. Some new physics models have been considered to explain this discrepancy possibly with new source of the CP violation. In this paper, we construct CP violating observables by using multi-pion decays in $B\to Dτν_τ$, and estimate sensitivity of these observables to generic CP violating operators. We also discuss possibilities of CP violation in leptoquark models and in 2HDM of type-III.

hep-ph↗