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S. Chen

Publications and source records attributed to S. Chen.

At least 19 recordsLinked to original sources

Indication of Electron Antineutrinos from the Diffuse Supernova Neutrino Background

We report an indication of $\barν_e$ from the diffuse supernova neutrino background (DSNB) based on a spectral fit analysis of a 5003.0-day dataset in Super-Kamiokande. Key improvements over previous searches include enhanced rejection of atmospheric $ν$ backgrounds, updated evaluations of systematic uncertainties, and a refined spectral fitting method. Using a representative DSNB model, the best-fit flux was determined to be $3.6^{+1.6}_{-1.5}~\mathrm{cm^{-2}\,s^{-1}}$ for $E_ν>13.3$~MeV, corresponding to a $2.6σ$ tension with a null hypothesis ($99.5\%$ C.L., one-sided). Similar significances were obtained with signal models of varying spectral shapes.

astro-ph.HE↗

Search for Ultra-Relativistic Magnetic Monopoles with LHAASO-KM2A

Ultra-relativistic magnetic monopoles traversing the atmosphere are expected to initiate extensive air showers characterized by a muon deficit and a compact lateral profile. Using 1438.81 live days of data from the LHAASO-KM2A array, we present a search for these cosmic particles within the Lorentz factor range of $10^5$ to $10^7$. A machine-learning classifier utilizing lateral shower shape observables from the electromagnetic detectors is deployed to separate the signal from the hadronic background. No statistical excess above the background expectation is observed, and upper limits at the 90\% confidence level are established on the isotropic monopole flux. The resulting upper limit is $2.6 \times 10^{-16}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}\,\mathrm{sr}^{-1}$ at $γ= 10^5$ and reaches $8.8 \times 10^{-19}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}\,\mathrm{sr}^{-1}$ at $γ= 10^7$, which improves upon the astrophysical Parker bound by over three orders of magnitude. This work establishes constraints on the monopole flux within a previously unconstrained velocity window.

astro-ph.HE↗

Open-H-RF: A Large-Scale Ultrasound Raw Channel Dataset Initiative

Medical ultrasound is a widely accessible, real-time imaging modality, yet progress in data-driven ultrasound research is constrained by the scarcity of large, open collections of raw channel data. Existing public datasets are predominantly based on reconstructed images, while the smaller number of open raw channel datasets is generally specialized to individual reconstruction or imaging tasks, limiting the development of general-purpose methods and foundation models that operate directly on ultrasound signals. While interpretive tasks can be performed on reconstructed images, many of the key technical challenges in ultrasound imaging, such as aberration correction and reverberation reduction, require the raw channel data itself. We introduce Open-H-RF, a community-driven open dataset initiative comprising approximately 40 TB of medical ultrasound raw channel data in 19,332 acquisitions, contributed by 38 institutions across academia and industry, spanning in-vivo, phantom, and simulated data. Each dataset is annotated with a number of supported tasks, ranging from generalized reconstruction, speed-of-sound estimation, and aberration correction to blood flow imaging, motion estimation, quantitative ultrasound, and image interpretation. Open-H-RF provides a unified, self-contained data format that captures raw channel data together with the acquisition, probe, metadata, and reconstruction information required for reproducible processing across scanners and acquisition schemes. The corpus is publicly hosted under a permissive CC BY 4.0 license and can be streamed programmatically and selectively at scale. By bringing heterogeneous ultrasound data into a common representation, backed by modern data infrastructure, Open-H-RF lowers the barrier to working with raw channel data and aims to open medical ultrasound research to new communities. See https://open-h.github.io/Open-H-RF.

eess.SP↗

Error Correction in a Distributed Quantum Computer

Building fault-tolerant quantum computers with large numbers of logical qubits requires both scalable hardware architectures and error-correcting codes that make efficient use of physical qubits. Photonic interconnects address both of these challenges by allowing the physical qubits to be distributed across multiple processors while providing the non-local connectivity necessary to implement resource-efficient codes such as high-rate quantum low-density parity-check (qLDPC) codes. A key requirement for realising this architecture is the ability to perform stabiliser measurements between remote processors, which has not previously been demonstrated experimentally. Here we report the first experimental demonstration of distributed quantum error detection and correction. We generate entanglement between network qubits in two separate trapped-ion processors and use it to perform remote syndrome measurements on data qubits. We first realise a distributed [[2, 1, 1]] repetition code, detecting phase-flip errors on a logical qubit encoded across the two modules in real time and suppressing logical errors. We then combine these mid-circuit syndrome measurements with real-time feedforward to actively correct arbitrary single-qubit Pauli errors on a distributed Bell state. These results provide an experimental foundation for quantum error correction (QEC) across modular quantum architectures.

quant-ph↗

Very Long Baseline Interferometry with the SKA Observatory

Very Long Baseline Interferometry (VLBI) is a fundamental technique that combines signals from telescopes separated by thousands of kilometres to obtain some of the highest-resolution images in astronomy. The Square Kilometre Array Observatory (SKAO) will provide sensitive elements to current VLBI arrays, enabling deep VLBI observations (including the first low-frequency VLBI capability in the Southern Hemisphere). This summary chapter outlines the science that the SKAO, when participating in a VLBI array, will achieve (such as AGN physics, explosive transient localisation, Galactic structure, and gravitational waves), and the current understanding of how VLBI with the SKAO will operate. Given that VLBI requires partnerships with other instruments, the chapter concludes with outstanding issues and considerations for the community needed to maximise the scientific return on investment in SKA-VLBI.

astro-ph.IM↗

First observation of electron antineutrinos from nuclear reactors at Super-Kamiokande

In 2020, Super-Kamiokande entered the SK-Gd phase, improving its sensitivity to low-energy electron antineutrinos through the detection of neutrons captured on gadolinium dissolved in the detector water. An analysis of reactor electron antineutrino data has been carried out using data from SK-Gd, with a total exposure of 411.52 live days. The observed prompt energy spectra and monthly event rates are consistent with the oscillated reactor antineutrino prediction after accounting for accidental, geoneutrino, and spallation backgrounds. The no-reactor hypothesis is disfavored with a reactor-antineutrino signal significance of approximately $6σ$. The oscillation parameters are measured to be $\sin^2θ_{12} = 0.500\pm0.155$ and $Δm^2_{21} = (9.08_{-0.54}^{+0.55}) \times 10^{-5} \mathrm{eV}^2$. A comparison with Super-Kamiokande solar neutrino measurements shows a statistical compatibility between the two datasets at the $1.9σ$ level. A combined solar and reactor fit in Super-Kamiokande yields best-fit values of $\sin^2θ_{12} = 0.332_{-0.026}^{+0.028}$ and $Δm^2_{21} = (8.94_{-0.47}^{+0.46}) \times 10^{-5} \mathrm{eV}^2$.

hep-ex↗

Search for the $^{16}\text{O}(ppp) \rightarrow ^{13}\text{C} π^+ π^+ e^+$ Decay Mode in Super-Kamiokande Using Machine Learning Techniques

We report a new partial lifetime limit of $4.2 \times 10^{32}$ years for the trinucleon decay mode $^{16}\text{O}(ppp) \rightarrow ^{13}\text{C} π^+ π^+ e^+$, obtained from a search conducted using the Super-Kamiokande detector with 0.401 megaton-years of exposure across five operational periods (SK-I: 1996--2001, SK-II: 2002--2005, SK-III: 2006--2008, SK-IV: 2008--2018, SK-V: 2019--2020). This represents an improvement of six orders of magnitude over previous experimental constraints. The analysis utilizes a convolutional neural network (CNN) incorporating an attention mechanism---a computational technique that enables the model to focus on the most relevant regions of Cherenkov ring patterns---to enhance event classification, thereby improving the sensitivity of the search. This is the first application of a CNN to a nucleon decay search in Super-Kamiokande. Furthermore, the large dataset available in Super-Kamiokande (hereafter "SK") strengthens the statistical power of the study, enabling a more stringent constraint than those set by prior experiments.

hep-ex↗

Electromagnetic transition strength in $^{53}$Ca: the lifetime of the $5/2^{-}$ state

High-resolution in-beam $γ$-ray spectroscopy of $^{53}$Ca was performed at the Radioactive Isotope Beam Factory (RIBF) at RIKEN. Excited states in $^{53}$Ca were populated via one-neutron and one-proton removal reactions from a $^{55}$Sc radioactive beam, and the emitted $γ$ rays were detected using the HiCARI hybrid germanium detector array. The lifetime of the first excited $5/2^{-}$ state in $^{53}$Ca was measured for the first time through an analysis of Doppler-roadened $γ$-ray line shapes arising from relativistic recoil velocities. A lifetime of $τ = 11.3_{-11.3}^{+5.3(stat)+3(sys)}$ ps was deduced, corresponding to a reduced transition probability of $B(E2;5/2^{-}{\rightarrow}1/2^{-}) > 2.6 e^{2}fm^{4}$ at the 1$σ$ level, with a best-fit value of $4.5 e^{2}fm^{4}$. The measured transition strength is compared with state-of-the-art shell-model and ab initio calculations, providing a stringent benchmark for shell-model Hamiltonians and effective charges and modern ab initio descriptions of the neutron-rich calcium isotopes approaching the potential $N$ = 40 shell closure.

nucl-ex↗

Combined tracer analysis for DESI 2024 BAO

This paper demonstrates how the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1) and future baryon acoustic oscillations (BAO) analyses can optimally combine overlapping tracers (galaxies of distinct types) in the same redshift range. We make a unified catalog of Luminous Red Galaxies (LRGs) and Emission Line Galaxies (ELGs) in the redshift range 0.8 < z < 1.1 and investigate the impact on the BAO constraints. DESI DR1 contains ~30% of the final DESI LRG sample and less than 25% of the final ELG sample, and the combination of LRGs and ELGs increases the number density and reduces the shot noise. We developed a pipeline to merge the overlapping tracers using galaxy bias as an approximately optimal weight and tested the pipeline on a suite of Abacus simulations, calibrated on the final version of the DESI Early Data Release. When applying our pipeline to the DESI DR1 catalog, we find an improvement in the BAO constraints of 11% for $α_\mathrm{iso}$ and ~7.0% for $α_\mathrm{AP}$ consistent with our findings in mock catalogs. Our analysis was integrated into the DESI DR1 BAO analysis to produce the LRG+ELG result in the 0.8 < z < 1.1 redshift bin, which provided the most precise BAO measurement from DESI DR1 with a 0.86% constraint on the BAO distance scale and a $9.1σ$ detection of the isotropic BAO feature.

astro-ph.CO↗

LHAASO-WCDA observed a $\sim$ 5 days TeV-delayed flaring event in blazar 1ES 1959+650

We report a day-scale hard lag between GeV and TeV $γ$-ray emission from the HBL 1ES~1959+650 in early 2024. Since the LHAASO-WCDA real-time monitoring system began operation in late 2023, multiple TeV flares from this source have been triggered, including the 1st trigger flare on 2024 February 9. A Bayesian-block analysis of the WCDA light curve identifies three TeV flares in 2024. For the second triggered flare, a discrete cross-correlation analysis reveals a $>3\,σ$ correlation (relative to uncorrelated red-noise simulations) at a time delay of $Δt = 5.0_{-2.1}^{+2.1}$ days, with the TeV emission lagging the GeV. Time-resolved spectroscopy shows that this flare has the softest TeV spectrum among these flares (intrinsic spectral index $Γ=3.16\pm0.18$), while the 1st trigger flare is harder ($Γ=2.48\pm0.21$). The observed five-day hard lag is difficult to reconcile with a purely cooling-driven temporal ordering and is consistent with scenarios in which particle energization and/or transport may contribute to the evolution. However, the current data do not uniquely identify the underlying mechanism.

astro-ph.HE↗

Search for proton decay into a single charged antilepton and a massless invisible particle using the full pure water data set of Super-Kamiokande

A search for proton decay via $p\rightarrow l^{+}+X$, where $l^{+}$ is a positively charged lepton and $X$ is an invisible, massless, neutral particle, was performed using a 401~kton$\cdot$years exposure representing the entire pure water phase of Super-Kamiokande. No significant indication of a proton decay was observed beyond the expected atmospheric neutrino background. Lower limits on the partial lifetime of the proton were set to at $1.72\times10^{33}$ years for $p\rightarrow e^{+}+X$ and $0.61\times10^{33}$ years for $p\rightarrow μ^{+}+X$ at the $90\%$ confidence level. These results improve on previous limits by factors of 2 and 1.5, respectively.

hep-ex↗

Probing the Size of Neutron and Proton Single-Particle Orbitals from Nucleon Knockout Reactions

The size of neutron and proton single-particle orbitals of $^{52}$Ca, $^{53}$Ca, $^{54}$Ca, and $^{55}$Sc were investigated via nucleon knockout reactions at $\sim$ 230 MeV/nucleon. The determination method is based on the measured fragment momentum distributions in $(p,pn)$ and $(p,2p)$ reactions, which are shown to be sensitive to the spatial extension of the wave function of the knocked-out nucleon, interpreted within the distorted wave impulse approximation (DWIA) framework. A systematic sensitivity study is carried out for the $(p,pn)$ recoil-momentum distribution method and is presented in this work. The experimental momentum distributions are compared to state-of-the-art mean field and $ab$ $initio$ in-medium similarity renormalization group and self-consistent Green's function calculations in combination with DWIA reaction theory calculations. Based on this work, the 1$p$ neutron orbitals are consistently found $0.48-0.78$ fm larger than the $0f_{7/2}$ neutron orbitals in $^{52-54}$Ca, while the size evolution of the valence proton orbitals remains inconclusive due to the large associated statistical uncertainties.

nucl-ex↗

Anisotropic Particle Transport from a Pulsar Wind Nebula Revealed by Einstein Probe and LHAASO

Pulsar wind nebulae (PWNe) are major cosmic ray accelerators, yet the mechanisms transporting high-energy particles into the interstellar medium remain elusive. Building on the LHAASO discovery of an ultra-high-energy (UHE) $γ$-ray source near the bow-shock PWN powered by the pulsar PSR J1740+1000, we present a joint Einstein Probe (EP) and LHAASO study of this system. EP observations reveal an extended X-ray tail far exceeding the structure previously seen by XMM-Newton. Updated LHAASO observations show that the $γ$-ray emission is elongated, with its major axis aligned with the extended X-ray tail revealed by EP. This is the first detection of an X-ray pulsar tail associated with a spatially coincident extended UHE $γ$-ray emission. The X-ray and $γ$-ray spectrum can be well explained with a single population of relativistic electrons via synchrotron and inverse Compton radiation, respectively, removing the need for particle re-acceleration during propagation. The results unambiguously show that electrons/positrons above 100 TeV are escaping from the PWN. Instead of the immediate, isotropic diffusion into ambient interstellar medium that is typically assumed, these particles are transported anisotropically over at least $\sim$10 pc, either guided by the background magnetic field or carried by an advective outflow.

astro-ph.HE↗

The Extended Ultrahigh-energy Gamma-Ray Emission in the Vicinity of PSR J2238+5903

We present a comprehensive analysis of the recently discovered TeV gamma-ray source, LHAASO J2238+5900. Based on data collected from the LHAASO, our fitting results suggest that the source is significantly extended with an angular extension of 0.54° \pm 0.01° and is spatially coincident with the pulsar PSR J2238+5903. Its spectrum is characterized by a power-law with a cutoff at 41.0\pm 3.5 TeV. Additionally, the source exhibits a significant signal of 7.9σabove 100 TeV, implying that it is a PeVatron candidate. While the gamma-ray emission is consistent with a pulsar wind nebula (PWN) scenario, the relatively large extension size also allows for a halo interpretation, potentially caused by electron-positron pairs escaping from the PWN.

astro-ph.HE↗

DashChat: Interactive Authoring of Performance Dashboard Design Prototypes through Conversation with LLM-Powered Agent

Performance dashboards are dashboards designed for and deployed within industrial settings (e.g., enterprises, government agencies) to showcase and monitor their operational performance. They have evolved into an important and well-commercialized format for data visualization. In practice, the ideation and negotiation phases demand rapid prototyping and iteration to align with evolving client needs. However, existing tools compel designers to compromise either on iteration speed or on the meticulous handling of visual complexities. To address these gaps, we introduce DashChat for generating performance dashboard prototypes. Collaborating with industry experts, we derived the design requirements and analyzed 114 dashboards to extract common design patterns. Informed by the findings, our solution integrates a chat interface with an LLM-driven multi-agent pipeline, translating textual requirements into prototypes. We evaluated the system by comparing it with a baseline, demonstrating its effectiveness in facilitating the prototyping process while ensuring design quality.

cs.HC↗

Energy-Dependent Shifts of Medium-Scale Anisotropies in Very-High-Energy Cosmic Rays Observed by LHAASO-KM2A

Small deviations from isotropy in the arrival directions of Galactic cosmic rays serve as a unique probe of the local magnetic environment. In this Letter, we report observations of medium-scale anisotropies (MSA) at energies above 10 TeV using the LHAASO-KM2A array. Our analysis identifies four regions of excess and four regions of deficit, each spanning angular scales of approximately ten degrees. Crucially, we detect significant energy-dependent shifts in the centroids of two excess regions: Region B and the newly identified Region $\mathrm{\widetilde{D}}$. We also characterize the energy evolution of the fractional relative intensity across both excess and deficit regions. These findings imply that the observed anisotropies are shaped by the specific realization of the local turbulent magnetic field within the cosmic ray scattering length. Such energy-dependent behaviors impose strict constraints on local turbulence models and cosmic ray propagation theories.

astro-ph.HE↗

Extreme PeV accelerator associated with GRS 1915+105

Microquasars, binary systems featuring relativistic jets, have emerged as sources for particle acceleration beyond PeV energies. We present a study of the broadband $γ$-ray emission from one of the most prominent Galactic microquasars GRS 1915+105 based on data accumulated by LHAASO and Fermi-LAT over 4 and 17 years, respectively. A joint analysis of LHAASO-WCDA and LHAASO-KM2A data reveals extended $γ$-ray emission whose centroid appears significantly shifted, by ~ 0.13°, from the binary system and its jets. The spectral energy distribution is well described by a curved spectrum with progressive steepening that can be described by a log-parabola function with no evidence for a sharp cutoff, consistent with parent particles reaching multi-PeV energies and an extreme acceleration efficiency approaching the limit set by the available potential drop across the source. Several features, most notably the shift of the emission and single-power-law spectrum down to GeV band, favor radiation by cosmic rays accelerated in the source interacting with the dense ambient medium. Our spectral modeling implies that at least a few percent of the jet mechanical power is transferred to protons, whose maximum energy reaches beyond 5 PeV. These results strengthen the case for microquasars as exceptionally efficient accelerators in our Galaxy.

astro-ph.HE↗