arXiv subjects

Y. Fukuda

Publications and source records attributed to Y. Fukuda.

At least 19 recordsLinked to original sources

arXiv2026

First double-differential measurement of pionless charged-current muon neutrino interactions using kinematic imbalance observables on carbon and oxygen with the T2K experiment

We report the first measurement of muon-neutrino charged-current cross section as a function of kinematic imbalance (KI) observables on oxygen with no pions and at least one proton in the final state, using the T2K ND280 detector. The cross section is extracted simultaneously for carbon and oxygen targets and double-differentially as a function of several KI observables, providing new insight into the modeling of nuclear effects. This joint measurement offers direct sensitivity to the correlations between two targets, a key ingredient for reducing systematic uncertainties in neutrino oscillation experiments that employ multiple target nuclei, such as T2K and Hyper-Kamiokande. Comparisons with predictions from widely used neutrino event generators show that none of the models fully describe the data across all regions of measured phase space. These results highlight possible directions where improvements in neutrino-nucleus interaction modeling are needed for current and future neutrino oscillation experiments.

hep-ex↗

arXiv2026

Signal selection and model-independent extraction of pionless charged-current muon neutrino cross section using double-differential kinematic imbalance observables on carbon and oxygen with the T2K experiment

We present the first joint measurement of muon neutrino CC$0\pi Np$ interactions on carbon and oxygen targets, in two double-differential kinematic imbalance (KI) observable spaces, $\delta p_{T}$-$\delta \alpha_{T}$ and $p_{N}$-$\cos\theta_{\mu}$. The measurement employs the ND280 detector of the T2K experiment and includes a detailed description of the event selection used to define signal and control regions, the evaluation of systematic uncertainties, and the signal extraction procedure, together with validation studies supporting a robust cross-section measurement. The results of this analysis indicate that current neutrino-nucleus interaction models do not adequately describe the data, and demonstrate the strong discriminating power of KI observables. This measurement highlights the need for improved theoretical nuclear modeling within neutrino interaction generators to achieve increased precision in neutrino oscillation measurements.

hep-ex↗

arXiv2026

Constraining Neutrino Interaction Uncertainties for Neutrino Oscillation Measurements at the T2K Experiment

In the context of neutrino oscillation measurements from the T2K experiment, the off-axis near detector ND280 plays a crucial role in constraining the incoming neutrino flux and neutrino-nucleus interaction cross sections. The result is a robust control over systematic uncertainties in the fit of neutrino oscillation parameters to the data at the T2K far detector, Super-Kamiokande. This paper details the methodology and results of these constraints in the context of the latest neutrino oscillation analysis from T2K. It describes how a new neutrino cross-section model and refined flux prediction are parameterized and fit to data in new ND280 event selections. Additionally, this work reports the results of extensive robustness studies, including fits with alternative interaction models, consistency checks against publicly available cross-section measurements, and \textit{p}-value evaluations, to demonstrate the reliability and robustness of our methodology. Finally, we present a sensitivity study demonstrating that the upgraded ND280, with improved acceptance and a lower hadron threshold, may enhance future constraints and further reduce systematic uncertainties in oscillation measurements.

hep-ex↗

arXiv2026

Charge-Density Waves of Single and Double NbS$_{3}$ Chains

The physics of a genuine one-dimensional system in which electrons are confined in one direction remains unclear. The actual electronic state of such a genuinely one-dimensional system has not been investigated in previous experiments, for they have all been conducted on quasi-one-dimensional specimens, namely in strongly anisotropic bulk crystals. Conventionally, charge-density waves (CDWs) driven by Fermi surface nesting have been considered to appear in one-dimensional electron-lattice systems. However, the CDW transitions actually observed to date have all occurred in quasi-one-dimensional systems and therefore do not directly indicate a genuine one-dimensional electronic state. We investigated, for the first time, isolated single and double-chain NbS$_{3}$ samples using the carbon-nanotube-sheath method and discovered CDWs in both systems. In the single-chain, surprisingly, a $(1/4)b^*$ CDW was observed, in contrast to the $(1/3)b^*$ CDW that has been observed in bulk samples. In the double-chain, the coexistence of a $(1/2)b^*$ dimer structure and a $(1/3)b^*$ CDW was confirmed. This discovery represents a significant advancement in the field of low-dimensional physics, surpassing the limitations of previous studies on bulk systems.

cond-mat.mes-hall↗

arXiv2025

Measurement of muon neutrino induced charged current interactions without charged pions in the final state using a new T2K off-axis near detector WAGASCI-BabyMIND

We report a flux-integrated cross section measurement of muon neutrino interactions on water and hydrocarbon via charged current reactions without charged pions in the final state with the WAGASCI-BabyMIND detector which was installed in the T2K near detector hall in 2018. The detector is located 1.5$^\circ$ off-axis and is exposed to a more energetic neutrino flux than ND280, another T2K near detector, which is located at a different off-axis position. The total flux-integrated cross section is measured to be $1.26 \pm 0.18\,(stat.+syst.) \times 10^{-39} $ $\mathrm{cm^{2}/nucleon}$ on CH and $1.44 \pm 0.21\,(stat.+syst.) \times 10^{-39} $ $\mathrm{cm^{2}/nucleon}$ on H$_{2}$O. These results are compared to model predictions provided by the NEUT v5.3.2 and GENIE v2.8.0 MC generators and the measurements are compatible with these models. Differential cross sections in muon momentum and cosine of the muon scattering angle are also reported. This is the first such measurement reported with the WAGASCI-BabyMIND detector and utilizes the 2020 and 2021 datasets.

hep-ex↗

arXiv2025

Low-mass vector-meson production at forward rapidity in $p$$+$$p$ and Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$~GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low-mass vector-meson ($\omega+\rho$ and $\phi$) production through the dimuon decay channel at forward rapidity $(1.2<|\mbox{y}|<2.2)$ in $p$$+$$p$ and Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$~GeV. The low-mass vector-meson yield and nuclear-modification factor were measured as a function of the average number of participating nucleons, $\langle N_{\rm part}\rangle$, and the transverse momentum $p_T$. These results were compared with those obtained via the kaon decay channel in a similar $p_T$ range at midrapidity. The nuclear-modification factors in both rapidity regions are consistent within the uncertainties. A comparison of the $\omega+\rho$ and $J/\psi$ mesons reveals that the light and heavy flavors are consistently suppressed across both $p_T$ and ${\langle}N_{\rm part}\rangle$. In contrast, the $\phi$ meson displays a nuclear-modification factor consistent with unity, suggesting strangeness enhancement in the medium formed.

nucl-ex↗

arXiv2025

Testing T2K's Bayesian constraints with priors in alternate parameterisations

Bayesian analysis results require a choice of prior distribution. In long-baseline neutrino oscillation physics, the usual parameterisation of the mixing matrix induces a prior that privileges certain neutrino mass and flavour state symmetries. Here we study the effect of privileging alternate symmetries on the results of the T2K experiment. We find that constraints on the level of CP violation (as given by the Jarlskog invariant) are robust under the choices of prior considered in the analysis. On the other hand, the degree of octant preference for the atmospheric angle depends on which symmetry has been privileged.

hep-ex↗

arXiv2025

Alloharmonics in Burst Intensification by Singularity Emitting Radiation

Burst Intensification by Singularity Emitting Radiation (BISER) in underdense relativistic laser plasma is a bright source of coherent extreme ultraviolet (XUV) and x-ray radiation. In contrast to all harmonic generation mechanisms, high-resolution experimental BISER spectra in the XUV region contain spectral fringes with separation much finer (down to 0.12 eV) than the initial driving laser frequency (~1.5 eV). We show that these fringe separations result from two main factors: laser frequency downshift (redshift) due to the quasi-adiabatic energy loss to the plasma waves, and spectral interference of different harmonic orders from different emission moments, i.e. alloharmonics [Pirozhkova et al., arXiv:2306.01018]

physics.plasm-ph↗

arXiv2025

Results from the T2K experiment on neutrino mixing including a new far detector $\mu$-like sample

We have made improved measurements of three-flavor neutrino mixing with 19.7(16.3)$\times 10^{20}$ protons on target in (anti-)neutrino-enhanced beam modes. A new sample of muon-neutrino events with tagged pions has been added at the far detector, as well as new proton and photon-tagged samples at the near detector. Significant improvements have been made to the flux and neutrino interaction modeling. T2K data continue to prefer the normal mass ordering and upper octant of $\sin^2\theta_{23}$ with a near-maximal value of the charge-parity violating phase with best-fit values in the normal ordering of $\delta_{\scriptscriptstyle\mathrm{CP}}=-2.18\substack{+1.22 \\ -0.47}$, $\sin^2\theta_{23}=0.559\substack{+0.018 \\ -0.078}$ and $\Delta{}m^2_{32}=(+2.506\substack{+0.039 \\ -0.052})\times 10^{-3}$ eV$^{2}$.

hep-ex↗

arXiv2025

First measurement of neutron capture multiplicity in neutrino-oxygen neutral-current quasi-elastic-like interactions using an accelerator neutrino beam

We report the first measurement of neutron capture multiplicity in neutrino-oxygen neutral-current quasi-elastic-like interactions at the gadolinium-loaded Super-Kamiokande detector using the T2K neutrino beam, which has a peak energy of about 0.6 GeV. A total of 30 neutral-current quasi-elastic-like event candidates were selected from T2K data corresponding to an exposure of $1.76\times10^{20}$ protons on target. The $\gamma$ ray signals resulting from neutron captures were identified using a neural network. The flux-averaged mean neutron capture multiplicity was measured to be $1.37\pm0.33\text{ (stat.)}$$^{+0.17}_{-0.27}\text{ (syst.)}$, which is compatible within $2.3\,\sigma$ than predictions obtained using our nominal simulation. We discuss potential sources of systematic uncertainty in the prediction and demonstrate that a significant portion of this discrepancy arises from the modeling of hadron-nucleus interactions in the detector medium.

hep-ex↗

arXiv2025

Electron density structure measurements with scattered intense laser beam

Short-pulse intense lasers have the potential to model extreme astrophysical environments in laboratories. Although there are diagnostics for energetic electrons and ions resulting from laser-plasma interactions, the diagnostics to measure velocity distribution functions at the interaction region of laser and plasma are limited. We have been developing the diagnostics of the interaction between intense laser and plasma using scattered intense laser. We performed experiments to measure electron density by observing the spatial distributions and ratio of horizontal to vertical polarization components of scattered laser beam using optical imaging. The observed ratio of polarization components is consistent with the drive laser beam indicating the observed light originates from the drive laser. Imaging of the scattered light shows the structure of electron density, the zeros moment of electron velocity distribution function, interacting with the intense laser. We observed the change of structure due to the laser pre-pulse that destroys the target before the arrival of the main pulse.

physics.plasm-ph↗

arXiv2025

First Measurement of the Electron Neutrino Charged-Current Pion Production Cross Section on Carbon with the T2K Near Detector

The T2K Collaboration presents the first measurement of electron neutrino-induced charged-current pion production on carbon in a restricted kinematical phase space. This is performed using data from the 2.5$^{\deg}$ off-axis near detector, ND280. The differential cross sections with respect to the outgoing electron and pion kinematics, in addition to the total flux-integrated cross section, are obtained. Comparisons between the measured and predicted cross section results using the Neut, Genie and NuWro Monte Carlo event generators are presented. The measured total flux-integrated cross section is [2.52 $\pm$ 0.52 (stat) $\pm$ 0.30 (sys)] x $10^{-39}$ cm$^2$ nucleon$^{-1}$, which is lower than the event generator predictions.

hep-ex↗

arXiv2025

Signal selection and model-independent extraction of the neutrino neutral-current single $\pi^+$ cross section with the T2K experiment

This article presents a study of single $\pi^+$ production in neutrino neutral-current interactions (NC1$\pi^+$) using the FGD1 hydrocarbon target of the ND280 detector of the T2K experiment. We report the largest sample of such events selected by any experiment, providing the first new data for this channel in over four decades and the first using a sub-GeV neutrino flux. The signal selection strategy and its performance are detailed together with validations of a robust cross section extraction methodology. The measured flux-averaged integrated cross-section is $ \sigma = (6.07 \pm 1.22 )\times 10^{-41} \,\, \text{cm}^2/\text{nucleon}$, 1.3~$\sigma~$ above the NEUT v5.4.0 expectation.

hep-ex↗

arXiv2025

First differential measurement of the single $\mathbf{\pi}^+$ production cross section in neutrino neutral-current scattering

Since its first observation in the 1970s, neutrino-induced neutral-current single positive pion production (NC1$\pi^+$) has remained an elusive and poorly understood interaction channel. This process is a significant background in neutrino oscillation experiments and studying it further is critical for the physics program of next-generation accelerator-based neutrino oscillation experiments. In this Letter we present the first double-differential cross-section measurement of NC1$\pi^+$ interactions using data from the ND280 detector of the T2K experiment collected in $\nu$-beam mode. The measured flux-averaged integrated cross-section is $ \sigma = (6.07 \pm 1.22 )\times 10^{-41} \,\, \text{cm}^2/\text{nucleon}$. We compare the results on a hydrocarbon target to the predictions of several neutrino interaction generators and final-state interaction models. While model predictions agree with the differential results, the data shows a weak preference for a cross-section normalization approximately 30\% higher than predicted by most models studied in this Letter.

hep-ex↗

arXiv2024

Demonstration of The Brightest Nano-size Gamma Source

Gamma rays selectively interact with nuclei, induce and mediate nuclear reactions and elementary particle interactions, and exceed x-rays in penetrating power and thus are indispensable for analysis and modification of dense objects. Yet, the available gamma sources lack sufficient power and brightness. The predicted and highly desirable laser-driven gamma flash, from here on termed "Gamma Flash", based on inverse Compton scattering from solid targets at extreme irradiances (>$10^{23}W/cm^2$), would be the highest-power and the brightest terrestrial gamma source with a 30-40% laser-to-gamma energy conversion. However, Gamma Flash remains inaccessible experimentally due to the Bremsstrahlung background. Here we experimentally demonstrate a new interaction regime at the highest effective irradiance where Gamma Flash scaled quickly with the laser power and produced several times the number of Bremsstrahlung photons. Simulations revealed an attosecond, Terawatt Gamma Flash with a nanometre source size achieving a record brightness exceeding $~10^{23}photons/mm^2mrad^2s$ per 0.1% bandwidth at tens of MeV photon energies, surpassing astrophysical Gamma Ray Bursts. These findings could revolutionize inertial fusion energy by enabling unprecedented sub-micrometre/femtosecond resolution radiography of fuel mixing instabilities in extremely-compressed targets. The new gamma source could facilitate significant advances in time-resolved nuclear physics, homeland security, nuclear waste management and non-proliferation, while opening possibilities for spatially-coherent gamma rays.

physics.plasm-ph↗

arXiv2024

Measurement of elliptic flow of J$/\psi$ in $\sqrt{s_{_{NN}}}=200$ GeV Au$+$Au collisions at forward rapidity

We report the first measurement of the azimuthal anisotropy of J$/\psi$ at forward rapidity ($1.2<|\eta|<2.2$) in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV at the Relativistic Heavy Ion Collider. The data were collected by the PHENIX experiment in 2014 and 2016 with integrated luminosity of 14.5~nb$^{-1}$. The second Fourier coefficient ($v_2$) of the azimuthal distribution of $J/\psi$ is determined as a function of the transverse momentum ($p_T$) using the event-plane method. The measurements were performed for several selections of collision centrality: 0\%--50\%, 10\%--60\%, and 10\%-40\%. We find that in all cases the values of $v_2(p_T)$, which quantify the elliptic flow of J$/\psi$, are consistent with zero. The results are consistent with measurements at midrapidity, indicating no significant elliptic flow of the J$/\psi$ within the quark-gluon-plasma medium at collision energies of $\sqrt{s_{_{NN}}}=200$ GeV.

nucl-ex↗

arXiv2024

Measurements at forward rapidity of elliptic flow of charged hadrons and open-heavy-flavor muons in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

We present the first forward-rapidity measurements of elliptic anisotropy of open-heavy-flavor muons at the BNL Relativistic Heavy Ion Collider. The measurements are based on data samples of Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV collected by the PHENIX experiment in 2014 and 2016 with integrated luminosity of 14.5~nb$^{-1}$. The measurements are performed in the pseudorapidity range $1.2<|\eta|<2$ and cover transverse momenta $1<p_T<4$~GeV/$c$. The elliptic flow of charged hadrons as a function of transverse momentum is also measured in the same kinematic range. We observe significant elliptic flow for both charged hadrons and heavy-flavor muons. The results show clear mass ordering of elliptic flow of light- and heavy-flavor particles. The magnitude of the measured $v_2$ is comparable to that in the midrapidity region. This indicates that there is no strong longitudinal dependence in the quark-gluon-plasma evolution between midrapidity and the rapidity range of this measurement at $\sqrt{s_{_{NN}}}=200$~GeV.

nucl-ex↗

arXiv2024

Multiplicity dependent $J/\psi$ and $\psi(2S)$ production at forward and backward rapidity in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV

The $J/\psi$ and $\psi(2S)$ charmonium states, composed of $c\bar{c}$ quark pairs and known since the 1970s, are widely believed to serve as ideal probes to test quantum chromodynamics in high-energy hadronic interactions. However, there is not yet a complete understanding of the charmonium-production mechanism. Recent measurements of $J/\psi$ production as a function of event charged-particle multiplicity at the collision energies of both the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC) show enhanced $J/\psi$ production yields with increasing multiplicity. One potential explanation for this type of dependence is multiparton interactions (MPI). We carry out the first measurements of self-normalized $J/\psi$ yields and the $\psi(2S)$ to $J/\psi$ ratio at both forward and backward rapidities as a function of self-normalized charged-particle multiplicity in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV. In addition, detailed {\sc pythia} studies tuned to RHIC energies were performed to investigate the MPI impacts. We find that the PHENIX data at RHIC are consistent with recent LHC measurements and can only be described by {\sc pythia} calculations that include MPI effects. The forward and backward $\psi(2S)$ to $J/\psi$ ratio, which serves as a unique and powerful approach to study final-state effects on charmonium production, is found to be less dependent on the charged-particle multiplicity.

hep-ex↗