arXiv subjects

J. Chen

Publications and source records attributed to J. Chen.

At least 37 records · Page 2Linked to original sources

arXiv2026

Exploring Lorentz Invariance Violation from Ultra-high-energy Gamma Rays Observed by LHAASO

Recently the LHAASO Collaboration published the detection of 12 ultra-high-energy gamma-ray sources above 100 TeV, with the highest energy photon reaching 1.4 PeV. The first detection of PeV gamma rays from astrophysical sources may provide a very sensitive probe of the effect of the Lorentz invariance violation (LIV), which results in decay of high-energy gamma rays in the superluminal scenario and hence a sharp cutoff of the energy spectrum. Two highest energy sources are studied in this work. No signature of the existence of LIV is found in their energy spectra, and the lower limits on the LIV energy scale are derived. Our results show that the first-order LIV energy scale should be higher than about 10^5 times the Planck scale M_{pl} and that the second-order LIV scale is >10^{-3}M_{pl}. Both limits improve by at least one order of magnitude the previous results.

astro-ph.HE↗

arXiv2026

Discovery of a new $γ$-ray source LHAASO J0341+5258 with emission up to 200TeV

We report the discovery of a new unidentified extended $γ$-ray source in the Galactic plane named LHAASO J0341+5258 with a pre-trial significance of 8.2 standard deviations above 25 TeV. The best fit position is R.A.$=55.34^{\circ}\pm0.11^{\circ}$ and Dec$=52.97^{\circ}\pm0.07^{\circ}$. The angular size of LHAASO J0341+5258 is $0.29^\circ \pm 0.06^\circ_{stat} \pm0.02^\circ_{sys}$. The flux above 25 TeV is about $20\%$ of the flux of Crab Nebula. Although a power-law fit of the spectrum from 10 TeV to 200 TeV with the photon index $α=2.98 \pm 0.19_{stat} \pm 0.02_{sys}$ is not excluded, the LHAASO data together with the flux upper limit at 10 GeV set by the Fermi LAT observation, indicate a noticeable steepening of an initially hard power-law spectrum %($α\leq 1.75$) spectrum with a cutoff at $\approx 50$ TeV. We briefly discuss the origin of UHE gamma-rays. The lack of an energetic pulsar and a young SNR inside or in the vicinity of LHAASO J0341+5258 challenge, but do not exclude both the leptonic and hadronic scenarios of gamma-ray production.

astro-ph.HE↗

arXiv2026

Discovery of the Ultra-high energy gamma-ray source LHAASO J2108+5157

We report the discovery of a UHE gamma-ray source, LHAASO J2108+5157, by analyzing the LHAASO-KM2A data of 308.33 live days. Significant excess of gamma-ray induced showers is observed in both energy bands of 25-100 TeV and $\gt$100 TeV with 9.5 sigma and 8.5 sigma, respectively. This source is not significantly favored as an extensive source with the angular extension smaller than the point-spread function of KM2A. The measured energy spectrum from 20 to 200 TeV can be approximately described by a power-law function with an index of -2.83$\pm$ 0.18stat. A harder spectrum is demanded at lower energies considering the flux upper limit set by Fermi-LAT observations. The position of the gamma-ray emission is correlated with a giant molecular cloud, which favors a hadronic origin. No obvious counterparts have been found, deeper multiwavelength observations will help to shed new light on this intriguing UHE source.

astro-ph.HE↗

arXiv2025

The BAGLE Python Package for Bayesian Analysis of Gravitational Lensing Events

We present the open-source Python package, BAGLE (Bayesian Analysis of Gravitational Lensing Events), which enables modeling and joint fitting of photometric and astrometric data sets. We describe the model parameterizations and present the equations for microlensing events containing either a point-source, point-lens or a finite-source, point-lens geometry both with and without microlensing parallax due to the motion of the Earth or a satellite around the Sun. Conversions between different coordinate reference frames are also derived. We compare our model light curves to those from other papers and microlens modeling software, finding good agreement, although with some differences in finite-source models at a ~1% level detectable with upcoming observations from space-based facilities. We also use BAGLE to demonstrate the impact of changing lens mass, lens distance, and blended source flux fraction on photometric lightcurves and astrometric trajectories in preparation for upcoming Gaia data releases and the launch of the Nancy Grace Roman Space Telescope and its Galactic Bulge Time Domain Survey (GBTDS). In particular, we show that Roman GBTDS will detect significant microlensing parallax signals for events that are 2x shorter in duration than from ground-based surveys. Additionally, long-duration events with durations of $\t_{E,\odot} >$ 100 days will yield microlensing parallax uncertainties of $σ_{π_E} <$ 0.01 with Roman, enabling confident identification of isolated stellar-mass black holes that can be modeled both astrometrically and photometrically with BAGLE for precise mass determinations. BAGLE is an open-source code and community development is encouraged.

astro-ph.SR↗

arXiv2025

Giant enhancement of attosecond tunnel ionization competes with disorder-driven decoherence in silicon

High-harmonic generation (HHG) is a strong-field phenomenon that is sensitive to the attosecond dynamics of tunnel ionization and coherent transport of electron-hole pairs in solids. While the foundations of solid HHG have been established, a deep understanding into the nature of decoherence on sub-cycle timescales remains elusive. Furthermore, there is a growing need for tools to control ionization at the nanoscale. Here, we study HHG in silicon along a crystalline-to-amorphous (c-Si to a-Si) structural phase transition and observe a dramatic reshaping of the spectrum, with enhanced lower-order harmonic yield accompanied by quenching of the higher-order harmonics. Modelling the real-space quantum dynamics links our observations to a giant enhancement (>250 times) of tunnel ionization yield in the amorphous phase and a disorder-induced decoherence that damps the electron-hole polarization over approximately six lattice sites. HHG spectroscopy also reveals remnant order that was not apparent with conventional probes. Finally, we observe a rapid and targeted non-resonant laser annealing of amorphous silicon islands. Our results offer a unique insight into attosecond decoherence in strong-field phenomena, establish HHG spectroscopy as a probe of structural disorder, and pave the way for new opportunities in lightwave nanoelectronics.

cond-mat.mtrl-sci↗

arXiv2025

Probing hard/soft factorization via beam-spin asymmetry in exclusive pion electroproduction from the proton

Deep exclusive meson production (DEMP) reactions, such as $p(\vec{e},e'π^+)n$, provide opportunities to study the three-dimensional structure of the nucleon through differential cross section and beam- and target-spin asymmetry measurements. This work aims to probe the onset of the hard/soft factorization regime through the exclusive $p(\vec{e},e'π^+)n$ reaction, as measured in the KaonLT experiment at Jefferson Lab Hall C. A 10.6 GeV longitudinally polarized electron beam was incident on an unpolarized liquid hydrogen target, and the scattered electron and produced meson were detected in two magnetic focusing spectrometers, enabling precision cross section measurements. The cross section ratio $σ_{LT'}/σ_0$ was extracted from the beam-spin asymmetry $A_{LU}$. The $t$-dependence of $σ_{LT'}/σ_0$ was determined at fixed $Q^2$ and $x_B$ over a range of kinematics from $2 2$ GeV). Furthermore, these data are combined with recent results from CLAS/CLAS12 to determine the $Q^2$-dependence of $σ_{LT'}/σ_0$ at two ($x_B$, $t$) settings. This was fairly flat, with $Q^2$ not having a measurable effect on the value of $σ_{LT'}/σ_0$ in the range explored. Results are compared to predictions from the generalized parton distribution (GPD) formalism, which relies explicitly on hard/soft factorization, and Regge formalism. The Regge models better predict $σ_{LT'}/σ_0$, which suggests that the factorization regime is not yet reached.

nucl-ex↗

arXiv2025

Backward-angle electroproduction of $η'$ mesons off protons at $W=2.13~\text{GeV}$ and $Q^{2}=0.46~\left(\text{GeV}/c\right)^{2}$

The electroproduction of $η'$ mesons from a $\mathrm{^{1}H}$ target at $W=2.13~\text{GeV}$, $Q^{2} = 0.46~\left( \text{GeV}/c\right)^{2}$ and $\cos θ^{\text{CM}}_{γ^{*}η'} \approx -1$ has been experimentally measured. The differential cross section of virtual-photoproduction has been obtained as $4.4 \pm 0.8 ~\left( \text{stat.} \right) \pm 0.4 ~\left( \text{sys.} \right)~ \text{nb/sr}$ in the One-Photon-Exchange Approximation. This value is one-sixth of that of real-photoproduction at backward angles. A comparison with newly-developed isobar model calculations not only shows validity of the theoretical framewark employed, but also imposes new constrains on coupling strength between the $η'p$ final state and nucleon resonances.

nucl-ex↗

arXiv2025

Valence $1s-0d$ proton vacancy of the $^{32}$Si ground state

The $^{32}$Si($^3$He,$d$)$^{33}$P reaction was studied in inverse kinematics at 6.3~MeV/$u$. States in $^{33}$P corresponding to the proton $1s-0d$ single-particle orbitals were identified up to $\sim$4.5 MeV in excitation energy. The ($^{3}$He,$d$) spectroscopic factors were determined from Distorted Wave Born Approximation calculations. When combined with complementary neutron-adding data, the $1s-0d$ proton vacancies in the $^{32}$Si ground state were extracted. In conjunction with a re-analysis of data from previous single-particle measurements, the trends in proton and neutron vacancy were explored across the $^{28,30,32,34}$Si isotopes. Both proton and neutron vacancy data show gradual changes in their occupancies. The proton $1s_{1/2}$ orbitals in $^{32}$Si and $^{34}$Si are both consistent with being empty. The ground-state nucleon distributions are described by shell-model calculations constrained to the $1s-0d$ model space.

nucl-ex↗

arXiv2025

Measurement of charged hadron multiplicity in Au+Au collisions at $\sqrt{\text{s}_{\text{NN}}} = 200$ GeV with the sPHENIX detector

The pseudorapidity distribution of charged hadrons produced in Au+Au collisions at a center-of-mass energy of $\sqrt{s_\mathrm{NN}} = 200$ GeV is measured using data collected by the sPHENIX detector. Charged hadron yields are extracted by counting cluster pairs in the inner and outer layers of the Intermediate Silicon Tracker, with corrections applied for detector acceptance, reconstruction efficiency, combinatorial pairs, and contributions from secondary decays. The measured distributions cover $|η| < 1.1$ across various centralities, and the average pseudorapidity density of charged hadrons at mid-rapidity is compared to predictions from Monte Carlo heavy-ion event generators. This result, featuring full azimuthal coverage at mid-rapidity, is consistent with previous experimental measurements at the Relativistic Heavy Ion Collider, thereby supporting the broader sPHENIX physics program.

nucl-ex↗

arXiv2025

Disentangling Core and Edge Mechanisms of the Density Limit in DIII-D Negative Triangularity Plasmas

The density limit is investigated in the DIII-D negative triangularity (NT) plasmas which lack a standard H-mode edge. We find the limit may not be a singular disruptive boundary but a multifaceted density saturation phenomenon governed by distinct core and edge transport mechanisms. Sustained, non-disruptive operation is achieved at densities up to 1.8 times the Greenwald limit ($n_\mathrm{G}$) until the termination of auxiliary heating. Systematic power scans reveal distinct power scalings for the core ($n_e \propto P_\mathrm{SOL}^{0.27\pm0.03}$) and edge ($n_e \propto P_\mathrm{SOL}^{0.42\pm0.04}$) density limits. The edge density saturation is triggered abruptly by the onset of a non-disruptive, high-field side radiative instability that clamps the edge density below $n_\mathrm{G}$. In contrast, the core density continues to rise until it saturates, a state characterized by substantially enhanced core turbulence. Core transport evolves from a diffusive to an intermittent, avalanche-like state, as indicated by heavy-tailed probability density functions (kurtosis $\approx 6$), elevated Hurst exponents, and a $1/f$-type power spectrum. These findings suggest that the density limit in the low-confinement regime is determined by a combination of edge radiative instabilities and core turbulent transport. This distinction provides separate targets for control strategies aimed at extending the operational space of future fusion devices.

physics.plasm-ph↗

arXiv2025

Measurement of the transverse energy density in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV with the sPHENIX detector

This paper reports measurements of the transverse energy per unit pseudorapidity ($dE_{T}/dη$) produced in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, performed with the sPHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The results cover the pseudorapidity range $\left|η\right| < 1.1$ and constitute the first such measurement performed using a hadronic calorimeter at RHIC. Measurements of $dE_{T}/dη$ are presented for a range of centrality intervals and the average $dE_{T}/dη$ as a function of the number of participating nucleons, $N_{\mathrm{part}}$, is compared to a variety of Monte Carlo heavy-ion event generators. The results are in agreement with previous measurements at RHIC, and feature an improved granularity in $η$ and improved precision in low-$N_{\mathrm{part}}$ events.

nucl-ex↗

arXiv2025

SPLENDOR: a novel detector platform to search for light dark matter with narrow-gap semiconductors

We present the design and current status of SPLENDOR, a novel detector platform that combines narrow-gap semiconductor targets with low-noise charge readout to achieve sensitivity to dark matter energy deposits well below the eV scale. SPLENDOR is designed to be a modular and scalable system able to accommodate different target materials and signal readout technologies. SPLENDOR's present strategy entails: (i) the use of strongly correlated f-electron semiconductors with anisotropic electronic structures to enable not only sub-eV energy thresholds, but also directional sensitivity to the incoming dark matter flux, allowing for signal-background discrimination via daily modulation, and (ii) custom charge readout based on cryogenic high-electron-mobility transistor (cryoHEMT) amplifiers approaching single-electron resolution. We report on the selection and characterization of Eu$_5$In$_2$Sb$_6$ as the target material for SPLENDOR's first prototype detector, as well as the development and calibration of the prototype amplifier chain, achieving a measured charge resolution of 20$\pm$7 electrons in silicon test samples, consistent with predicted performance. This provides a demonstration of the detector architecture, which is now ready for deployment in a dark matter search campaign to deliver SPLENDOR's first science results. Finally, we present estimates of sensitivity reach in the parameter space of athermally produced relic dark matter under high- and low-background environments, and for various amplifier technology upgrades with increasing performance, including planned quantum sensing upgrades in order to achieve our ultimate goal of sub-electron resolution in optimized systems. SPLENDOR provides a novel approach to dark matter direct detection, combining quantum sensing with material's design to open new avenues of exploration in the sub-MeV mass range of dark matter parameter space.

physics.ins-det↗

arXiv2025

Slowly generated anomalously large nuclear field in bulk n-AlGaAs

This study investigated the formation and relaxation dynamics of nuclear spin polarization in three Al$_x$Ga$_{1-x}$As bulk samples with different aluminum concentrations $x$ of 0.00, 0.05, and 0.15. The time-resolved Kerr rotation technique was primarily used. The samples with $x$ = 0.15 and 0.05 exhibited anomalously large nuclear magnetic fields BN exceeding 1 T, approximately twice the applied magnetic field. Further investigations revealed that BN formation occurred in two-stages, a rapid initial rise followed by a gradual increase toward a saturation value. Relaxation measurements revealed that the relaxation time of BN was longer for AlGaAs than for GaAs. The comparison of the results obtained under strong and weak magnetic fields indicated the suppression of quadrupole-induced relaxation. We modified the dynamics model of nuclear spin polarization and explained the two-stage formation and the accompanying large BN in AlGaAs bulks.

cond-mat.mtrl-sci↗

arXiv2025

Onset of Constituent Quark Number Scaling in Heavy-Ion Collisions at RHIC

Partonic collectivity is one of the necessary signatures for the formation of quark-gluon plasma in high-energy nuclear collisions. Number of constituent quarks (NCQ) scaling has been observed for hadron elliptic flow $v_2$ in top energy nuclear collisions at the Relativistic Heavy Ion Collider and the LHC, and this has been theoretically suggested as strong evidence for partonic collectivity. In this Letter, a systematic analysis of $v_2$ of $π^{\pm}$, $K^{\pm}$, $K^{0}_{S}$, $p$, and $Λ$ in Au+Au collisions at ${\sqrt{s_{_{\rm{NN}}}}}$ = 3.2, 3.5, 3.9, and 4.5 GeV, with the STAR experiment at the Relativistic Heavy Ion Collider, is presented. NCQ scaling is markedly violated at 3.2 GeV, consistent with a hadronic-interaction dominated equation of state. However, as the collision energy increases, a gradual evolution to NCQ scaling is observed. This beam-energy dependence of $v_2$ for all hadrons studied provides evidence for the onset of dominant partonic interactions by ${\sqrt{s_{_{\rm{NN}}}}}$ = 4.5 GeV.

nucl-ex↗

arXiv2025

AION-10: Technical Design Report for a 10m Atom Interferometer in Oxford

This Technical Design Report presents AION-10, a 10-meter atom interferometer to be located at Oxford University using ultracold strontium atoms to make precision measurements of fundamental physics. AION-10 serves as both a prototype for future larger-scale experiments and a versatile scientific instrument capable of conducting its own diverse physics programme. The design features a 10-meter vertical tower housing two atom interferometer sources in an ultra-high vacuum environment. Key engineering challenges include achieving nanometer-level vibrational stability and precise magnetic field control. Solutions include active vibration isolation, specialized magnetic shielding, and a modular assembly approach using professional lifting equipment. Detailed analysis confirms the design meets all performance requirements, with critical optical components remaining within our specifications 97% of the time under realistic operating conditions. Vacuum and vibration measurements in the host building validate that the instrument will achieve the precision needed for quantum sensing applications. This work establishes the technical foundation for scaling atom interferometry to longer baselines while creating a cutting-edge facility for precision measurements that could advance our understanding of fundamental physics.

physics.atom-ph↗

arXiv2025

Quenching of single-particle strength inferred from nucleon-removal transfer reactions on $^{15}$C

The difference in the proton and neutron separation energies ($ΔS$) of the weakly bound $^{15}$C ground state is -19.86 MeV, an extreme value. Data from intermediate-energy heavy-ion induced (HI-induced) knockout reactions on nuclei spanning $-20\lesssimΔS\lesssim+20$ MeV, suggest that the degree to which single-particle strength is quenched, $R\mathrm{_{s}}$, has a negative correlation with $ΔS$, decreasing from unity around $-20$~MeV to around 0.2 at $+20$~MeV. For the $^{15}$C ground state ($R_s=0.96(4)$ in HI-induced knockout), contrasting results have recently been obtained via the neutron-adding transfer reaction, which reveal a value of $R_s=0.64(15)$, similar to the value observed at modest $ΔS$ and more extreme values of $ΔS$ with reaction probes other than HI knockout. In order to explore the any potential differences between $adding$ and $removing$ processes in transfer reactions at extreme $ΔS$, single-neutron removal transfer reactions on $^{15}$C were performed at 7.1MeV/u in inverse kinematics. The removal of a valence neutron in 2$s_{1/2}$ orbit using both ($p$,$d$) and ($d$,$t$) reactions shows consistent quenching factors and agrees with those from the neutron-adding reaction. The present results, which can be compared with neutron knockout reaction, suggest that correlations, represented by the quenching factor, show limited dependence on neutron-proton asymmetry under the most extreme asymmetry conditions so far achieved in transfer reactions.

nucl-ex↗

arXiv2025

Inclusive studies of two- and three-nucleon short-range correlations in $^3$H and $^3$He

Inclusive electron scattering at carefully chosen kinematics can isolate scattering from the high-momentum nucleons in short-range correlations (SRCs). SRCs are produced by the hard, short-distance interactions of nucleons in the nucleus, and because the two-nucleon (2N) SRCs arise from the same N-N interaction in all nuclei, the cross section in the SRC-dominated regime is identical up to an overall scaling factor. This scaling behavior has been used to identify SRC dominance and to measure the contribution of SRCs in a wide range of nuclei. We examine this scaling behavior over a range of momentum transfers using new data on $^2$H, $^3$H, and $^3$He, and find an expanded scaling region compared to heavy nuclei. Motivated by this improved scaling, we examine the $^3$H and $^3$He data in kinematics where three-nucleon SRCs may play an important role. The data for the largest struck nucleon momenta are consistent with isolation of scattering from three-nucleon SRCs, and suggest that the very highest momentum nucleons in $^3$He have a nearly isospin-independent momentum configuration.

nucl-ex↗

arXiv2025

A large-scale ring galaxy at z = 2.2 revealed by JWST/NIRCam: kinematic observations and analytical modelling

A unique galaxy at z = 2.2, zC406690, has a striking clumpy large-scale ring structure that persists from rest UV to near-infrared, yet has an ordered rotation and lies on the star-formation main sequence. We combine new JWST/NIRCam and ALMA band 4 observations, together with previous VLT/SINFONI integral field spectroscopy and HST imaging to re-examine its nature. The high-resolution H$α$ kinematics are best fitted if the mass is distributed within a ring with total mass $M_{\rm{ring}} = 2 \times 10^{10} M_\odot$ and radius $R_{ring}$ = 4.6 kpc, together with a central undetected mass component (e.g., a "bulge") with a dynamical mass of $M_{bulge} = 8 \times 10^{10} M_\odot$. We also consider a purely flux emitting ring superposed over a faint exponential disk, or a highly "cuspy" dark matter halo, both disfavored against a massive ring model. The low-resolution CO(4-3) line and 142GHz continuum emission imply a total molecular and dust gas masses of $M_{mol,gas} = 7.1 \times 10^{10}M_\odot$ and $M_{dust} = 3 \times 10^8 M_\odot$ over the entire galaxy, giving a dust-to-mass ratio of 0.7%. We estimate that roughly half the gas and dust mass lie inside the ring, and that $\sim 10\%$ of the total dust is in a foreground screen that attenuates the stellar light of the bulge in the rest-UV to near-infrared. Sensitive high-resolution ALMA observations will be essential to confirm this scenario and study the gas and dust distribution.

astro-ph.GA↗