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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 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 10°. Crucially, we detect significant energy-dependent shifts in the centroids of two excess regions: Region B and the newly identified Region $\tilde{\mathrm{D}}$. 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.

We report a measurement of the cosmic ray helium energy spectrum in the energy interval 0.16–13 PeV, derived by subtracting the proton spectrum from the light component (proton and helium) spectrum obtained with observations made by the Large High Altitude Air Shower Observatory (LHAASO) under a consistent energy scale. The helium spectrum shows a significant hardening centered at $E\simeq 1.1\mathrm{PeV}$, followed by a softening at $\sim 7\mathrm{PeV}$, indicating the appearance of a helium “knee.” Comparing the proton and helium spectra in the LHAASO energy range reveals some remarkable facts. In the lower part of this range, in contrast to the behavior at lower energies, the helium spectrum is significantly softer than the proton spectrum. This results in protons overtaking helium nuclei and becoming the largest cosmic ray component at $E\simeq 0.7\mathrm{PeV}$. A second crossing of the two spectra is observed at $E\simeq 5\mathrm{PeV}$, above the proton knee, when helium nuclei overtake protons to become the largest cosmic ray component again. These results have important implications for our understanding of the Galactic cosmic ray sources.

Large- or medium-scale cosmic ray anisotropy at TeV energies has not previously been confirmed to vary with time. Transient anisotropy changes have been observed below 150 GeV, especially near the passage of an interplanetary shock and coronal mass ejection containing a magnetic flux rope ejected by a solar storm, which can trigger a geomagnetic storm with practical consequences. Here, we report the first observation of transient large-scale anisotropy in TeV cosmic ray ions using data from the Large High-Altitude Air Shower Observatory. We analyze hourly skymaps of the transient cosmic ray intensity excess or deficit, the gradient of which indicates the direction and magnitude of transient large-scale anisotropy across the field of view. We observe enhanced anisotropy above typical hourly fluctuations with $>5\sigma$ significance during some hours of November 4, 2021, in separate datasets for four primary cosmic ray energy ranges of median energy from $E=0.6$ to 2.8 TeV. The gradient varies with energy as $E^{\gamma }$, where $\gamma =-0.5$. At a median energy $\le 1.0\mathrm{TeV}$, this gradient corresponds to a dipole anisotropy of at least 0.9%, or possibly a weaker anisotropy of higher order. This new type of observation opens the opportunity to study interplanetary magnetic structures using air shower arrays around the world, complementing existing in situ and remote measurements of plasma properties.

Based upon an over-one-month frequency comparison of two ${}^{40}{\mathrm{Ca}}^{+}$ optical clocks, the frequency difference between the two clocks is measured to be $3.2\times {10}^{-17}$ with a measurement uncertainty of $5.5\times {10}^{-17}$, considering both the statistic ($1.9\times {10}^{-17}$) and the systematic ($5.1\times {10}^{-17}$) uncertainties. This is the first performance of a ${}^{40}{\mathrm{Ca}}^{+}$ clock better than that of Cs fountains. A fractional stability of $7\times {10}^{-17}$ in 20 000 s of averaging time is achieved. The evaluation of the two clocks shows that the shift caused by the micromotion in one of the two clocks limits the uncertainty of the comparison. By carefully compensating the micromotion, the absolute frequency of the clock transition is measured to be 411 042 129 776 401.7(1.1) Hz.

On 9 October 2022, the Large High Altitude Air Shower Observatory (LHAASO) reported the observation of the very early TeV afterglow of the brightest-of-all-time gamma-ray burst 221009A, recording the highest photon statistics in the TeV band ever obtained from a gamma-ray burst. We use this unique observation to place stringent constraints on the energy dependence of the speed of light in vacuum, a manifestation of Lorentz invariance violation (LIV) predicted by some quantum gravity (QG) theories. Our results show that the 95% confidence level lower limits on the QG energy scales are $E_{\mathrm{QG},1}>10$ times the Planck energy $E_{\mathrm{Pl}}$ for the linear LIV effect, and $E_{\mathrm{QG},2}>6\times {10}^{-8}{E}_{\mathrm{Pl}}$ for the quadratic LIV effect. Our limits on the quadratic LIV case improve previous best bounds by factors of 5–7.

Supernova remnants (SNRs) have been considered as the primary contributors to cosmic rays (CRs) in our Galaxy. However, the maximum energy of particles that can be accelerated by shocks of SNRs is uncertain, and SNRs’ contribution to CRs around PeV energies is unclear. In this Letter, we present observations of high-energy $\gamma$-ray emission from the SNR IC 443 using the Large High Altitude Air Shower Observatory (LHAASO). The morphological analysis reveals a pointlike source whose location and spectrum are consistent with those of the Fermi-LAT-detected compact source with ${\pi }^0$-decay signature, and a more extended source that is associated with a newly discovered Fermi source. The spectrum of the point source can be described by a power-law function with an index of $\sim 3.0$, extending beyond $\sim 30\mathrm{TeV}$ without apparent cutoff. Assuming a hadronic origin of the $\gamma$-ray emission, the 95% lower limit of accelerated protons reaches about 300 TeV. The extended source might be associated with IC 443, SNR $\mathrm{G}189.6+3.3$, or the putative pulsar wind nebula CXOU $\mathrm{J}061705.3+222127$, and can be explained by either a hadronic or a leptonic model with particles reaching hundreds of TeV. These LHAASO results provide compelling evidence that sub-PeV CRs can be accelerated efficiently by shocks of SNRs.

The attenuation length of the muon content in extensive air showers provides important information regarding the generation and development of air showers. This information can be used not only to improve the description of such showers but also to test fundamental models of hadronic interactions. Using data from the LHAASO-KM2A experiment, the development of the muon content in high-energy air showers was studied. The attenuation length of muon content in the air showers was measured from experimental data in the energy range from 0.3 to 30 PeV using the constant intensity cut method. By comparing the attenuation length of the muon content with predictions from high-energy hadronic interaction models (qgsjet-II-04, sibyll 2.3d, and epos-lhc), it is evident that LHAASO results are significantly shorter than those predicted by the first two models (qgsjet-II-04 and sibyll 2.3d) but relatively close to those predicted by the third model (epos-lhc). Thus, the LHAASO data favor the epos-lhc model over the other two models. The three interaction models confirmed an increasing trend in the attenuation length as the cosmic-ray energy increases.

We report the first detection of gamma-ray emission up to ultrahigh-energy (UHE; $>100\mathrm{TeV}$) emission from the prototypical gamma-ray binary system LS I $+61°$ 303 using data from the Large High Altitude Air Shower Observatory. It is detected with significances of $9.2\sigma$ in the Water Cherenkov Detector Array (WCDA, $1.4-30.5\mathrm{TeV}$) and $6.2\sigma$ in the Kilometer Square Array (KM2A, $25-267\mathrm{TeV}$); in KM2A alone we identify 16 photonlike events above 100 TeV against an estimated 5.1 background events, corresponding to a $3.8\sigma$ detection. These results provide compelling evidence of extreme particle acceleration in LS I $+61°$ 303. Furthermore, we observe orbital modulation at $3.9\sigma$ confidence level, between 25 and 100 TeV, with a hint that the orbital modulation is energy dependent. These features can be understood in a composite scenario in which leptonic and hadronic processes jointly contribute.

We present the measurements of all-particle energy spectrum and mean logarithmic mass of cosmic rays in the energy range of 0.3–30 PeV using data collected from LHAASO-KM2A between September 2021 and December 2022, which is based on a nearly composition-independent energy reconstruction method, achieving unprecedented accuracy. Our analysis reveals the position of the knee at $3.67\pm 0.05\pm 0.15\mathrm{PeV}$. Below the knee, the spectral index is found to be $-2.7413\pm 0.0004\pm 0.0050$, while above the knee, it is $-3.128\pm 0.005\pm 0.027$, with the sharpness of the transition measured with a statistical error of 2%. The mean logarithmic mass of cosmic rays is almost heavier than helium in the whole measured energy range. It decreases from 1.7 at 0.3 PeV to 1.3 at 3 PeV, representing a 24% decline following a power law with an index of $-0.1200\pm 0.0003\pm 0.0341$. This is equivalent to an increase in abundance of light components. Above the knee, the mean logarithmic mass exhibits a power law trend towards heavier components, which is reversal to the behavior observed in the all-particle energy spectrum. Additionally, the knee position and the change in power-law index are approximately the same. These findings suggest that the knee observed in the all-particle spectrum corresponds to the knee of the light component, rather than the medium-heavy components.

The diffuse Galactic gamma-ray emission is a very important tool used to study the propagation and interaction of cosmic rays in the Milky Way. In this Letter, we report the measurements of the diffuse emission from the Galactic plane—covering Galactic longitudes from 15° to 235° and latitudes from $-5°$ to $+5°$, in an energy range of 1 to 25 TeV—made with the Water Cherenkov Detector Array (WCDA) of the Large High Altitude Air Shower Observatory. After the sky regions of known sources are masked, the diffuse emission is detected with $24.6\sigma$ and $9.1\sigma$ significance in the inner Galactic plane ($15°<l<125°$, $|b|<5°$) and outer Galactic plane ($125°<l<235°$, $|b|<5°$), respectively. The WCDA spectra in both regions can be well described by a power-law function, with spectral indices of $-2.67\pm 0.05_{\mathrm{stat}}$ in the inner region and $-2.83\pm 0.19_{\mathrm{stat}}$ in the outer region, respectively. Combined with the Square Kilometer Array (KM2A) measurements at higher energies, a clear softening of the spectrum is found in the inner region, with change of spectral indices by $\sim 0.5$ at a break energy around 30 TeV. The fluxes of the diffuse emission are higher by a factor of 1.5–2.7 than the model prediction assuming local cosmic ray spectra and the gas column density, which are consistent with those measured by the KM2A. Along the Galactic longitude, the spatial distribution of the diffuse emission shows deviation from that of the gas column density. The spectral shape of the diffuse emission may vary in different longitude regions. The WCDA measurements bridge the gap between the low-energy measurements by space detectors and the ultra-high-energy observations by KM2A and other experiments. These results suggest that improved modeling of the wideband diffuse emission is required.

Cosmic-ray electrons and positrons (CREs) offer valuable insights into the origins of local cosmic rays, as they rapidly cool in interstellar magnetic and radiation fields, limiting their propagation range. The CRE spectrum reveals a spectral break around 1 TeV, followed by a continuous power-law behavior that possibly extends beyond 40 TeV. Deviations from a pure power-law in this spectrum could provide important clues about the local origins of CREs. However, due to the rapidly falling flux of CRE, the ratio of hadron/CRE increases with energy, making the rejection more and more challenging. Equipped with a large detection aperture and strong background rejection capability, LHAASO has the potential to extend CRE spectrum measurements beyond 25 TeV, which is almost the highest energy measured by existing experiments. In this work, we study the detector performance and explore the optimized background rejection of cosmic nuclei background specifically for CRE observations in LHAASO. Our analysis reveals that muon-poor nuclei showers have a strong dependence on the hadronic model when estimating the cosmic nuclei background and rejection capability. Consequently, we derived a 90% CL upper limit for the CRE spectrum from 25 to 160 TeV, providing a new and restrictive constraint in the hundreds of TeV range for the first time.

Primordial black holes (PBHs) are hypothetical black holes with a wide range of masses that formed in the early Universe. As a result, they may play an important cosmological role and provide a unique probe of the early Universe. A PBH with an initial mass of approximately ${10}^{15}\mathrm{g}$ is expected to explode today in a final burst of Hawking radiation. In this Letter, we conduct an all-sky search for individual PBH burst events using the data collected from March 2021 to July 2024 by the Water Cherenkov Detector Array of the Large High Altitude Air Shower Observatory (LHAASO). Three PBH burst durations, 10, 20, and 100 s, are searched in the gamma-ray energy range from about 1 to 15 TeV, with no significant PBH bursts observed. The upper limit on the local PBH burst rate density is set to be as low as $181{\mathrm{pc}}^{-3}{\mathrm{yr}}^{-1}$ at 99% confidence level, representing the most stringent limit achieved to date.

We present a precise measurement of the westward rigidity-dependent shift of the Moon’s shadow using three and a half years of cosmic ray data collected by the kilometer square array (KM2A) of the Large High Altitude Air Shower Observatory (LHAASO) experiment. These measurements enable us to calibrate the detector energy response in the range of 20 to 260 TeV, with results showing excellent agreement with the energy response derived from Monte Carlo (MC) simulations of the KM2A detector. We also measure a best-fit parameter $\epsilon =0.015\pm 0.08$, corresponding to a 95% CI of $[-14\%,+17\%]$ for the energy scale estimation. This result establishes the exceptional accuracy of the KM2A-MC in simulating the detector’s response within this energy range.

Circular dichroism (CD) caused by the response of a chiral object to circularly polarized light has been well established, and the strong CD of plasmonic metamolecules has also become of interest in recent years; however, their response if the light also has orbital angular momentum is unclear. In this paper, the dichroism of a plasmonic cuboid-protuberance chiral structure under the illumination of a light beam with both orbital and spin angular momenta is numerically investigated. Distinguished spectra are observed under the different momenta. The circular dichroism under the combination of vortex beam and light spin is enhanced. This phenomenon is attributed to the partial spatial excitation of the nanoparticle, and the strong dichroism is simultaneously caused because of the interaction of the induced electric and magnetic modes and other higher-order modes caused by the partial excitation of the vortex beam. This research provides further insight into chiral light-matter interactions and the dichroism of light with orbital angular momentum.

We demonstrate experimentally the existence of magic wavelengths and determine the ratio of oscillator strengths for a single trapped ion. For the first time, two magic wavelengths near 396 nm for the ${{}^{40}\mathrm{Ca}}^{+}$ clock transition are measured simultaneously with high precision. By tuning the applied laser to an intermediate wavelength between transitions $4s_{1/2}\to 4p_{1/2}$ and $4s_{1/2}\to 4p_{3/2}$, the sensitivity of the clock transition Stark shift to the oscillator strengths is greatly enhanced. Furthermore, with the measured magic wavelengths, we determine the ratio of the oscillator strengths with a deviation of less than 0.5%. Our experimental method may be applied to measure magic wavelengths for other ion clock transitions. Promisingly, the measurement of these magic wavelengths paves the way to building all-optical trapped ion clocks.

Two-dimensional hole gases (2DHGs) confined in Ge/SiGe quantum wells offer a promising platform for exploring low-dimensional spintronic phenomena and valence band dynamics, due to their strong spin-orbit interaction and long spin coherence times. Biaxial compressive strain arising from the lattice mismatch between the Ge well and SiGe barriers defines the fundamental physical properties of the 2DHG. Meanwhile, practical device architectures introduce additional sources of strain. For instance, differential thermal contraction between gate electrodes and the quantum well leads to anisotropic strain, which in turn modulates the electronic structure and transport symmetry. This paper provides a systematic and quantitative investigation into the impact of deliberately in situ applied uniaxial strain on the properties of the 2DHG in Ge/SiGe quantum wells. Using a piezoelectric-based strain cell, uniaxial in-plane strain along the $\left[110\right]$ crystallographic direction is applied and magnetotransport measurements are performed. The results reveal significant anisotropic modulation of the hole effective mass, mobility, and out-of-plane $g$-factor due to strain-induced deformation of the valence band. While the carrier density remains isotropic, the modification of mobility, effective mass, and the out-of-plane $g$-factor show pronounced anisotropy along different crystallographic directions. These findings highlight the critical role of uniaxial strain in shaping the fundamental transport coefficients of Ge/SiGe quantum wells and provide precise experimental benchmarks for strain engineering in future design of high-performance heterostructures and devices.

In light of the diverse range of reported values for the lifetimes of metastable states of ${}^{40}{\mathrm{Ca}}^{+}$, we have carried out afresh both measurements and theoretical investigation to confirm the lifetime of its $3d{}^2{D}_{5/2}$ state $\left({\tau }_{3d5/2}\right)$. A high-efficiency quantum state detection method by monitoring the quantum jumps of a laser-cooled single ${\mathrm{Ca}}^{+}$ ion in a miniature ring Paul trap was employed in the measurement. Also, sophisticated calculations were performed considering higher order nonlinear terms in the relativistic coupled-cluster (RCC) method with all possible single and double excitations, but accounting only for the important triple excitations from both the core and the valence orbitals. Systematic factors affecting measurement, such as collision with background gases, heating effects, the power of the 866-nm laser, and state detection errors were carefully analyzed. Our observational and theoretical values for ${\tau }_{3d5/2}$ are 1174(10) ms and 1172(3) ms, respectively, which agree well with the experimental results reported by P. A. Barton et al. [Phys. Rev. A 62, 032503 (2000)] and A. Kreuter et al. [Phys. Rev. A 71, 032504 (2005)]. The present theoretical analysis demonstrates that the contributions from the core triples and Breit interaction are notable, as they improve the theoretical results obtained in the previous RCC calculations [B. K. Sahoo, Phys. Rev. A 74, 062504 (2006)].

Atomic heterodyne dressed by a local oscillator resonant with Rydberg transitions allows high sensitivity and robust phase measurement of a microwave electric field, but it is typically limited to detection of discrete frequencies within the narrow bandwidth of Rydberg transitions. Here we demonstrate an atomic heterodyne scheme for continuous-frequency electric field measurement based on multilevel Rydberg atoms in a room-temperature vapor cell. Driven by two off-resonant microwaves acting as a tunable local oscillator field, the heterodyne receiver can retrieve the amplitude, phase, and frequency information of signal microwave in a continuous frequency band. In our experiment, the receiver achieves an electric field sensitivity of up to $1.5\mu \mathrm{V}{\mathrm{cm}}^{-1}{\mathrm{Hz}}^{-1/2}$, 80-dB linear dynamic range, and over 1 GHz of continuous frequency range. We also demonstrate the reliable reception of continuously tunable phase-modulated carriers in the digital communication. This work will facilitate the application of atomic heterodyne in the areas such as radar technique, radio monitoring, and radio astronomy.

The interplay among Coulomb interaction, electron-phonon coupling, and phonon-phonon coupling has a significant impact on the low-energy behavior of three-dimensional type-I tilted Dirac semimetals. To investigate this phenomenon, we construct an effective theory, calculate one-loop corrections arising from all these interactions, and establish the coupled energy-dependent flows of all associated interaction parameters by adopting the renormalization-group approach. Deciphering such coupled evolutions allows us to determine a series of low-energy critical properties for these materials. At first, we present the low-energy tendencies of all interaction parameters. The tilting parameter exhibits distinct tendencies that depend heavily upon the initial anisotropy of fermion velocities. In comparison, the latter is mainly dominated by its initial value but is less sensitive to the former. Variations in these two quantities drive certain interaction parameters toward the strong anisotropy in the low-energy regime, indicating the screened interaction in specific directions, and others toward an approximate isotropy. Additionally, we observe that the tendencies of interaction parameters can be qualitatively clustered into three distinct types of fixed points, accompanied by the potential instabilities that induce an interaction-driven phase transition to a certain superconducting state. Furthermore, approaching these fixed points leads to the critical behavior of physical quantities, such as the density of states, compressibility, and specific heat, which exhibit quite different from their noninteracting counterparts and even deviate slightly from Fermi-liquid behavior. Our investigation sheds light on the intricate relationship between different types of interactions in these semimetals and provides useful insights into their fundamental properties.

In this paper, based on the noncommutative geometry-inspired Schwarzschild black hole, we employ a third-order WKB approximation approach to systematically calculate the quasinormal mode frequencies (QNFs), greybody factors (GFs), and absorption cross section (ACS) under massive scalar field perturbations. The results show that the QNFs satisfy $\mathrm{Im}(\omega )<0$, confirming the stability of the black hole under perturbations. Furthermore, increasing the noncommutative parameter $\theta$ reduces the absolute values of both the real and imaginary parts of the frequency, while increasing the mass $\mu$ increases the real part and reduces the imaginary part. The GFs and ACS increase with increasing $\theta$ and decrease with increasing $\mu$, indicating opposite modulation effects of these two types of parameters. It is worth emphasizing that the QNFs of the extreme black hole approach the corresponding values of the classical Schwarzschild black hole at angular quantum number $\ell =1$ and large $\mu$, suggesting that the effects of mass and noncommutative geometry quantum corrections cancel each other out to some extent. It is hoped that these results provide a viable theoretical basis for both the theoretical and experimental aspects of the perturbative dynamics of black holes.