arXiv subjects

H. Chen

Publications and source records attributed to H. Chen.

At least 19 recordsLinked to original sources

arXiv2026

Measurements of transverse kinematic imbalance in muon neutrino charged-current interactions on argon with a single proton and no pions in the final state with SBND

This letter presents the first neutrino-argon cross-section measurement from the Short-Baseline Near Detector (SBND) at the Fermi National Accelerator Laboratory. We report the nominal flux-averaged single-differential cross sections of muon neutrino charged-current interactions on argon with a single proton and no pions in the final state as functions of the transverse kinematic imbalance variables. Using a subset of Run~1 data corresponding to $8.8\times10^{19}$ protons-on-target, we select 12,804 signal candidates with a purity of 91%. The extracted cross sections discriminate strongly among event-generator predictions, owing to the high statistics and the design of the analysis. Among the compared models, none successfully describes all three variables, with the largest discrepancies in the transverse missing momentum variable. These results set new benchmarks for neutrino-argon interaction modeling, which is crucial for high-precision measurements at current and future accelerator neutrino experiments.

hep-ex↗

arXiv2026

Search for Neutrino-Produced Long-Lived Particles Using the SBND Cosmic Ray Tagger Beam Telescope

The Short-Baseline Near Detector (SBND) is a liquid argon time projection chamber in Fermilab's Short-Baseline Neutrino Program, positioned 110 meters from the neutrino target along the Booster Neutrino Beam (BNB). In addition to its neutrino physics goals, SBND enables searches for new physics, including long-lived particles (LLPs) produced via neutrino-nucleus upscattering that decay into visible final states. Although neutrino data taking with the full SBND experiment began in December 2024, a subset of the Cosmic Ray Tagger (CRT) system operated from 2017--2018 as a standalone detector, referred to as the CRT Beam Telescope, collecting data corresponding to $2.95\times 10^{20}$ protons on target from the BNB. Originally intended for commissioning and performance studies, the substantial dataset collected also enables searches for displaced LLP decays. This paper presents the first search for physics beyond the Standard Model using data from the SBND CRT Beam Telescope, targeting LLP decays into electron-positron pairs. We observe no significant excess above the expected background and set 90% confidence-level upper limits on an effective production cross section at the level of $10^{-38}$ cm$^2$ for laboratory decay lengths of 0.3-100 m. These results complement existing searches by probing displaced decay signatures at meter-scale decay lengths.

hep-ex↗

arXiv2026

Measurements and models of enhanced recombination following inner-shell vacancies in liquid xenon

Electron-capture decays of $^{125}$Xe and $^{127}$Xe, and double-electron-capture decays of $^{124}$Xe, are backgrounds in searches for weakly interacting massive particles (WIMPs) conducted by dual-phase xenon time projection chambers such as LUX-ZEPLIN (LZ). These decays produce signals with more light and less charge than equivalent-energy $β$ decays, and correspondingly overlap more with WIMP signals. We measure three electron-capture charge yields in LZ: the 1.1~keV M-shell, 5.2~keV L-shell, and 33.2~keV K-shell at drift fields of 193 and 96.5~V/cm. The LL double-electron-capture decay of $^{124}$Xe exhibits even more pronounced shifts in charge and light. We provide a first model of double-electron-capture charge yields using the link between ionization density and electron-ion recombination, and identify a need for more accurate calculations. Finally, we discuss the implications of the reduced charge yield of these decays and other interactions creating inner-shell vacancies for future dark matter searches.

hep-ex↗

arXiv2026

Magneto-optical signatures of plateau states in the kagome spin-ice HoAgGe

Coupling of itinerant electrons to non-collinear spin structures in frustrated rare-earth magnets leads to unusual transport properties. While these complex magnetic orders are expected to modify the electronic structure, underlying microscopic mechanisms have been rarely identified. Using magnetoreflectance spectroscopy and \textit{ab initio} calculations, we reveal reconstructions of the electronic structure across the magnetization plateaus of the kagome spin-ice HoAgGe. We find an unusual optical anisotropy: a larger conductivity perpendicular to the kagome planes originating from the hybridization of Ho $4f$ flat bands with conduction electrons. Moreover, these flat bands are also responsible for the pronounced magnetoreflectance observed at the metamagnetic transitions. Most importantly, the magnetoreflectance behaves completely differently for excitations near the Fermi level and higher-energy interband transitions. The former, expected to sensitively probe variations in band topology near the Fermi level, shows abrupt non-monotonous changes between the magnetic states, while the interband excitations mimic the field dependence of the magnetization. These observations imply that in HoAgGe, the unusual magnetotransport likely reflects variation of band topology between plateau states. More generally, our study shows that heavy-electron bands near the Fermi level offer an efficient way to control the band structure and thereby the transport and optical properties of non-collinear magnets.

cond-mat.str-el↗

arXiv2026

Measurement of the Muon Flux at the Sanford Underground Research Facility with the LUX-ZEPLIN Dark Matter Detector

High-energy cosmic-ray muons reaching deep underground laboratories can cause events in detectors that mimic signals expected from dark matter particles, neutrinos, or rare decays. Knowledge of the muon flux and energy spectrum is important for evaluating the background rate caused by muons and their secondaries. In this paper, we report the measurement of the cosmic-ray muon flux in the Davis Campus of the Sanford Underground Research Facility with the LUX-ZEPLIN detector. Using 366.4~days of exposure, the muon rate through the detector was measured as $10.94\pm0.17_\textrm{stat.}~\textrm{day}^{-1}$ with energy thresholds of 20~MeV in the inner xenon detector and 8 MeV in the outer liquid scintillator detector. This rate corresponds to a muon flux of $(5.09\pm0.08_\textrm{stat.}\pm0.10_\textrm{sys.})\times10^{-9}~\textrm{cm}^{-2}\textrm{s}^{-1}$ in the Davis Cavern.

hep-ex↗

arXiv2026

Short-Baseline Near Detector (SBND): Design and Initial Performance

The Short-Baseline Near Detector (SBND) is a 112 tonne active mass liquid argon time projection chamber (LArTPC) situated in the Booster Neutrino Beam at Fermilab, forming part of the Short-Baseline Neutrino (SBN) Program. SBND began operation in 2024 and has since accumulated the world's largest sample of neutrino-argon interactions. This paper describes the as-built detector and presents performance results from the first year of beam operation. All detector systems performed at or above design requirements. The liquid argon purity achieved an electron lifetime exceeding 30ms, ten times the design requirement, for more than 95% of Run 1. The TPC wire plane readout achieved noise levels at the theoretical minimum for the given wire geometry (an average of 388e$^-$ for the 4m long collection plane wires) with 99.3% of readout channels live. Together, the liquid argon purity and TPC performance are enabling extremely clean event reconstruction in the SBND TPC. The photon detection system, consisting of passive reflectors and multiple active components (PMTs and X-ARAPUCAs), has achieved a light yield exceeding 10 photoelectrons per MeV throughout the detector volume and a timing resolution of a few nanoseconds, sufficient to resolve the 19ns bunch structure of the Booster Neutrino Beam. A nearly 4$π$ cosmic ray tagger system surrounds the TPC to mitigate cosmic backgrounds in neutrino and BSM physics analyses. The data acquisition system has demonstrated stable performance up to an event rate of 8Hz, and a data collection efficiency of 98.6% was achieved throughout SBND's first neutrino run in 2025. These results demonstrate that SBND represents the state of the art in multi-tonne-scale LArTPC detector performance.

hep-ex↗

arXiv2026

The NOvA Test Beam Experiment

NOvA is a long-baseline neutrino oscillation experiment designed to study the neutrino mixing parameters, mass ordering, and CP violation in the lepton sector. A key component of the success of the experiment is a robust understanding of the systematic uncertainties associated with detector response and calibration. To address this, NOvA deployed a Test Beam experiment at the Fermilab Test Beam Facility, which collected data from April 2019 through July 2022. The NOvA Test Beam experiment used a 30-ton segmented liquid scintillator detector functionally identical to the NOvA Near and Far Detectors to analyze tagged particles produced from p-Cu collisions, with instrumentation capable of selecting and identifying electrons, muons, pions, kaons, and protons with momentum ranging from 0.4-1.5GeV/c. Analysis of the collected data provides a better understanding of the largest systematic uncertainties impacting NOvA's analyses, which include the detector response, energy calibration, and hadronic and electromagnetic energy resolutions.

hep-ex↗

arXiv2026

NOvA Dual-Baseline Search for Active-to-Sterile Neutrino Oscillations using Neutrino- and Antineutrino-Enriched Samples

We report a search for neutrino oscillations to sterile neutrinos in the NOvA detectors under a model with three active and one sterile neutrinos. This search simultaneously fits data in the two NOvA detectors and is the first from NOvA to use both neutrino- and antineutrino-mode beams, with exposures of $26.61\times10^{20}$ and $12.50\times10^{20}$ protons on target, respectively. There is no evidence for sterile neutrinos in the data and we are able to exclude regions of parameter space that were allowed by previous experiments, including most of the allowed region reported by IceCube.

hep-ex↗

arXiv2026

Neutron detector response modeling in NOvA

Neutrons can present a significant challenge for neutrino experiments in which energy reconstruction is critical. With the ability to escape detection completely and with a weak correlation between their kinetic energy and any eventual energy deposition, it is difficult to fully account for neutrons produced in neutrino interactions. This in turn leads to significant model dependence when evaluating neutron-related systematic uncertainties. The NOvA experiment is a long-baseline neutrino oscillation experiment with a high-statistics sample of antineutrino data collected by its near detector. We report an excess relative to data of simulated neutron candidates with low energy depositions when using standard Geant4 physics lists. The simulation excess is traced to an overabundance of secondary photons produced from interactions of neutrons with kinetic energy greater than \SI{20}{\mega\eV}. Improved agreement with data is obtained by applying the data-driven neutron-on-carbon \menate model for neutrons between \SI{20}{\mega\eV} and ${\sim}$\SI{100}{\mega\eV}. With \menate, the residual oversimulation is more uniform across the calorimetric neutron energy spectrum, suggesting possible overproduction of primary neutrons by the GENIE neutrino interaction generator. These results motivate the adoption of \menate-supplemented Geant4 simulation as the nominal simulation in the production of future \nova simulation.

hep-ex↗

arXiv2026

Pushing the Limits of Pulse Shape Discrimination in a Large Liquid Xenon Detector

The LUX-ZEPLIN (LZ) experiment is a direct-detection dark matter experiment, optimized to search for weakly interacting massive particles (WIMPs) through WIMP-nucleon interactions. The main challenge in dark matter detection is differentiating between WIMP signals and background events. In LZ, the ratio of ionization to scintillation signals (charge-to-light) is the primary method for rejecting electronic recoil (ER) background. Pulse shape discrimination (PSD) offers a method for additional ER backgrounds rejection in liquid xenon detectors. In this paper, the discrimination power of PSD with the LZ experiment is discussed. To precisely characterize the scintillation pulse shape, an analysis framework is developed to reconstruct the detection time of individual photons. Using LZ calibration data, the photon-timing prompt fraction discriminator is optimized and achieves ER leakage as low as $15\%$. For specific background processes such as $^{124}$Xe double electron capture, the leakage is reduced further to about $5\%$. PSD is combined with charge-to-light to form two-factor discrimination (TFD). The optimized TFD performance is compared with the performance of the charge-to-light method, with the corresponding false positive rate reduced by up to a factor of two for large scintillation pulses. Finally, PSD and TFD are applied to data from LZ's WS2024 run and their performance is summarized.

physics.ins-det↗

arXiv2026

Flow-dependent tagging of $^{214}$Pb decays in the LZ dark matter detector

The LUX-ZEPLIN (LZ) experiment is searching for dark matter interactions in a liquid xenon time projection chamber (LXe-TPC). This article demonstrates how control of the flow state in the LXe-TPC enables the identification of pairs of sequential alpha-decays, which are used to map fluid flow and ion drift in the liquid target. The resulting transport model is used to tag \UChPb~ beta-decays, a leading background to dark matter signals in LZ. Temporally evolving volume selections, at a cost of 9.0\% of exposure, target the decay of each \UChPb~ atom up to 81 minutes after production, resulting in (63~$\pm$~6$_{(\mathrm{stat})}$~$\pm$~7$_{(\mathrm{sys})}$)\% identification of \UChPb~decays to ground state. We also demonstrate how flow-based tagging techniques enable a novel calibration side band that is concurrent with science data. Finally we report updated estimates of radon-chain charge branching fractions in liquid xenon, finding branching to $^{218}$Po$^+$ at $0.49 \pm 0.01$, $^{214}$Pb$^+$ at $0.48 \pm 0.12$, and $^{214}$Bi$^+$ at $0.74 \pm 0.05$, with a mean charged ion lifetime in the LZ TPC of $49 \pm 4$ min.

physics.ins-det↗

arXiv2026

Quality control and quality assurance evaluation of ALFE2, a large-dynamic-range front-end ASIC de-veloped for the ATLAS Liquid Argon Calorimeter high-luminosity LHC upgrade

ALFE2 is a front-end ASIC developed for the ATLAS Liquid Argon (LAr) Calorimeter upgrade during the High-Luminosity Large Hadron Collider (HL-LHC) phase. ALFE2 comprises four preamplifier/shaper channels, each providing two distinct gain outputs to cover a 16-bit dynamic range. A robotic system has been developed for the automatic quality control test of ALFE2, and over 10% of the 80,000 chips have been evaluated by September 2025. The evaluation has allowed us to establish grading criteria. Using these criteria, a yield of over 85% was achieved in the evaluation tests, and these criteria are now being applied to the ongoing full-production QC. Irradiation tests were also performed for the quality assurance of ALFE2. No significant performance degradation was observed during the total-ionizing-dose (TID) test. Based on the single-event effect (SEE) test results, an error rate of fewer than 4.6 single-event upsets (SEUs) per day is extrapolated for the entire ATLAS LAr Calorimeter during HL-LHC operation.

physics.ins-det↗

arXiv2026

Search for New Physics via Low-Energy Electron Recoils with a 4.2 Tonne\times Year Exposure from the LZ Experiment

We report results from searches for new physics models through electron recoils using data collected by the LUX-ZEPLIN (LZ) experiment during its first two science runs, with a total exposure of 4.2 tonne-years. The observed data are consistent with a background-only hypothesis. Constraints are derived for electromagnetic interactions of solar neutrinos, solar axion-like particles (ALPs), mirror dark matter, and the absorption of bosonic dark matter candidates. The inverse Primakoff process for 57Fe de-excitation solar ALPs is considered for the first time. These results represent the most stringent constraints to date on keV-scale Primakoff and 57Fe solar ALPs, bosonic dark matter, mirror dark matter, and neutrino millicharge, while remaining competitive for the other signal models investigated.

hep-ex↗

arXiv2026

Strange metallicity encompasses high magnetic field-induced superconductivity in UTe2

A strange metallic state - characterized by an electrical resistivity that rises linearly in temperature $T$ at a rate governed by Planckian energetic dissipation - is present in a number of unconventional superconductors. Despite widespread investigative efforts, the microscopic properties of strange metallicity continue to defy elementary description. Here we investigate heavy fermion UTe$_2$, which hosts a suite of exotic spin-triplet superconducting phases, the most extreme of which resides in a narrow angular window of intense magnetic fields $>$ 40 T. Through angle-dependent magnetotransport measurements in pulsed magnetic fields, we find that this superconductive phase emerges from a strange metallic state with Planckian $T$-linear resistivity confined to a small region of phase space where the field-induced superconductivity is strongest, suggesting a shared underlying mechanism. These findings reveal a novel setting for strange metallicity - in contrast to the general case of singlet superconductivity emerging on the border of antiferromagnetism, here strange metallicity accompanies field-induced triplet superconductivity within a spin-polarized magnetic state. This result demonstrates the remarkable ubiquity of strange metallicity across diverse materials settings, and highlights UTe$_2$ as a unique platform for exploring the interplay between unconventional superconductivity and quantum criticality.

cond-mat.str-el↗

arXiv2026

Searches for Light Dark Matter and Evidence of Coherent Elastic Neutrino-Nucleus Scattering of Solar Neutrinos with the LUX-ZEPLIN (LZ) Experiment

We present searches for light dark matter (DM) with masses 3-9 GeV/$c^2$ in the presence of coherent elastic neutrino-nucleus scattering (CE$ν$NS) from $^{8}$B solar neutrinos with the LUX-ZEPLIN experiment. This analysis uses a 5.7 tonne-year exposure with data collected between March 2023 and April 2025. In an energy range spanning 1-6 keV, we report no significant excess of events attributable to dark matter nuclear recoils, but we observe a significant signal from $^{8}$B CE$ν$NS interactions that is consistent with expectation. We set world-leading limits on spin-independent and spin-dependent-neutron DM-nucleon interactions for masses down to 5 GeV/$c^2$. In the no-dark-matter scenario, we observe a signal consistent with $^{8}$B CE$ν$NS events, corresponding to a $4.5σ$ statistical significance. This is the most significant evidence of $^{8}$B CE$ν$NS interactions and is enabled by robust background modeling and mitigation techniques. This demonstrates LZ's ability to detect rare signals at keV-scale energies.

hep-ex↗

arXiv2026

Absolute Calibration of a Time-Resolved High Resolution X-ray Spectrometer for the National Ignition Facility (invited)

A high resolution, Diagnostic Instrument Manipulator (DIM)-based x-ray Bragg crystal spectrometer has been calibrated for and deployed at the National Ignition Facility (NIF) to diagnose plasma conditions in ignition capsules near stagnation times. The spectrometer has two conical crystals in the Hall geometry focusing rays from the Kr He$α$, Ly$α$, and He$β$ complexes onto a streak camera, with the physics objectives of measuring time-resolved electron density and temperature through observing Stark broadening and the relative intensities of dielectronic satellites. A third von Hámos crystal that time-integrates the Kr He$α$, He$β$ and intervening energy range provides in-situ calibration for the streak camera signals. The spectrometer has been absolutely calibrated using a microfocus x-ray source, an array of CCD and single-photon-counting detectors, and multiple K- and L-absorption edge filters at the Princeton Plasma Physics Laboratory (PPPL) x-ray laboratory. Measurements of the integrated reflectivity, energy range, and energy resolution for each crystal are discussed. These calibration data provide absolute x-ray signal levels for NIF measurements, enabling precise filter selection and comparisons to simulations.

physics.plasm-ph↗

arXiv2026

Hot Spot Evolution Measured by High-Resolution X-Ray Spectroscopy at the National Ignition Facility

Evolution of the hot spot plasma conditions was measured using high-resolution x-ray spectroscopy at the National Ignition Facility (NIF). The capsules were filled with DD gas with trace levels of Kr, and had either a high-density-carbon (HDC) ablator or a tungsten (W)-doped HDC ablator. Time-resolved measurement of the Kr He$β$ spectra, absolutely calibrated by a simultaneous time-integrated measurement, allows inference of the electron density and temperature through observing Stark broadening and the relative intensities of dielectronic satellites. By matching the calculated hot spot emission using a collisional-radiative code to experimental observations, the hot spot size and areal density are determined. These advanced spectroscopy techniques further reveal the effect of W dopant in the ablator on the hot spot parameters for their improved implosion performance.

physics.plasm-ph↗

arXiv2026

Production and installation of wavelength-shifting reflective light enhancers for the Short-Baseline Near Detector

We report on the design, production, and installation of a wavelength-shifting reflective system on the cathode of the Short-Baseline Near Detector (SBND), a liquid argon time projection chamber located along the Fermilab Booster Neutrino Beam. To increase and homogenize scintillation-light collection, 64 double-sided plates were fabricated from FR4, laminated with specular reflector film and coated with 300 $μ$g/cm$^2$ of tetraphenyl butadiene (TPB) wavelength shifter using controlled physical vapor deposition. The coating uniformity was validated through dedicated measurements of deposited mass and profilometry studies. Because exposure to ambient blue/UV light could degrade the TPB, protective filtering and controlled storage conditions were implemented during handling and installation. The coated plates were assembled between conductive meshes for high-voltage compatibility and installed in situ during detector integration. This system constitutes the largest TPB-coated area deployed in a neutrino detector. It operates in conjunction with SBND's photon detection system, which consists of photomultiplier tubes and X-ARAPUCAs. Early light-collection measurements show high uniformity and light response across the detector, supporting improved triggering, calorimetry, and position reconstruction in SBND.

physics.ins-det↗