Search

Nickel, one of the most tightly bound nuclei alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE’s excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of cosmic-ray nickel spectrum from 10 GeV/n to 2 TeV/n with nine years of flight data. The nickel spectrum is consistent with a single power law with spectral index $-2.60\pm 0.03$ from 40 GeV/n to 1 TeV/n. This Letter provides an accurate measurement of differential flux of nickel with kinetic energy extending to TeV/n for the first time.

Precise direct cosmic-ray (CR) measurements provide an important probe to study the energetic particle sources in our Galaxy, and the interstellar environment through which these particles propagate. Uncertainties on hadronic models, ion-nucleon cross sections in particular, are currently the limiting factor toward obtaining more accurate CR ion flux measurements with calorimetric space-based experiments. We present an energy-dependent measurement of the inelastic cross section of protons and helium-4 nuclei (alpha particles) on a ${\mathrm{Bi}}_4$${\text{Ge}}_3{\mathrm{O}}_{12}$ target, using 88 months of data collected by the DAMPE space mission. The kinetic energy range per nucleon of the measurement points ranges from 18 GeV to 9 TeV for protons, and from $5\mathrm{GeV}/\mathrm{n}$ to $3\mathrm{TeV}/\mathrm{n}$ for helium-4 nuclei. Our results lead to a significant improvement of the CR flux normalization. In the case of helium-4, these results correspond to the first cross section measurements on a heavy target material at energies above $10\mathrm{GeV}/\mathrm{n}$.

The Dark Matter Particle Explorer (DAMPE) has made significant progress in measuring the fluxes of cosmic rays. These new measurements are pivotal in advancing our understanding of the origins and propagation mechanisms of cosmic rays. The bismuth germanium oxide (BGO) calorimeter plays a crucial role in these measurements, particularly in the precise determination of cosmic ray fluxes. However, for a calorimetric experiment like DAMPE, uncertainties in hadronic models persist as a major barrier in achieving more accurate measurements of fluxes of cosmic ray nuclei. This study centers on the measurement of the inelastic hadronic cross sections of carbon and oxygen nuclei interacting BGO crystals target over an extensive energy range, spanning from 200 GeV to 10 TeV. For carbon nuclei interacting with the BGO target. The measurements of the cross sections have achieved a total relative uncertainty of less than 10% below 8 TeV for carbon, and below 3 TeV for oxygen. For oxygen nuclei, the same level of precision was attained below 3 TeV. Additionally, we compare the experimental results with geant4 and fluka simulations to validate the accuracy and consistency of these simulation tools. Through comprehensive analysis of the inelastic hadronic interaction cross sections, this research provides validation for the hadronic interaction models used in DAMPE’s cosmic-ray flux measurements.

More than a century after the performance of the oil drop experiment, the possible existence of fractionally charged particles (FCPs) still remains unsettled. The search for FCPs is crucial for some extensions of the Standard Model in particle physics. Most of the previously conducted searches for FCPs in cosmic rays were based on experiments underground or at high altitudes. However, there have been few searches for FCPs in cosmic rays carried out in orbit other than AMS-01 flown by a space shuttle and BESS by a balloon at the top of the atmosphere. In this study, we conduct an FCP search in space based on on-orbit data obtained using the Dark Matter Particle Explorer (DAMPE) satellite over a period of five years. Unlike underground experiments, which require an FCP energy of the order of hundreds of GeV, our FCP search starts at only a few GeV. An upper limit of $6.2\times {10}^{-10}{\mathrm{cm}}^{-2}{\mathrm{sr}}^{-1}{\mathrm{s}}^{-1}$ is obtained for the flux. Our results demonstrate that DAMPE exhibits higher sensitivity than experiments of similar types by three orders of magnitude that more stringently restricts the conditions for the existence of FCP in primary cosmic rays.

The measurement of the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV using 4.5 years of data recorded by the Dark Matter Particle Explorer (DAMPE) is reported in this work. A hardening of the spectrum is observed at an energy of about 1.3 TeV, similar to previous observations. In addition, a spectral softening at about 34 TeV is revealed for the first time with large statistics and well controlled systematic uncertainties, with an overall significance of $4.3\sigma$. The DAMPE spectral measurements of both cosmic protons and helium nuclei suggest a particle charge dependent softening energy, although with current uncertainties a dependence on the number of nucleons cannot be ruled out.

By monitoring changes in excitonic photoluminescence (PL) that are induced by terahertz (THz) radiation, we observe resonant THz absorption by magnetoexcitons in ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum wells. Changes in the PL spectrum are explored as a function of temperature and magnetic field, providing insight into the mechanisms which allow THz absorption to modulate PL. The strongest PL-quenching occurs at the heavy hole $1\overrightarrow{s}{2p}^{+}$ resonance where heavy hole excitons are photothermally converted into light hole excitons.

Secondary cosmic ray fluxes are important probes of the propagation and interaction of high-energy particles in the Galaxy. Recent measurements of primary and secondary cosmic ray nuclei have revealed unexpected spectral features that demand a deeper understanding. In this work we report the direct measurement of the cosmic ray boron spectrum from $10\mathrm{GeV}/\mathrm{n}$ to $8\mathrm{TeV}/\mathrm{n}$ with eight years of data collected by the Dark Matter Particle Explorer (DAMPE) mission. The measured spectrum shows a hardening at $182\pm 24\mathrm{GeV}/\mathrm{n}$ with a spectral index of ${\gamma }_1=3.02\pm 0.01$ before the break and an index change of $\mathrm{\Delta }\gamma =0.31\pm 0.05$ after the break. A simple power law model is disfavored at a confidence level of $8\sigma$. Compared with the hardenings measured in the DAMPE proton and helium spectra, the secondary boron spectrum hardens roughly twice as much as these primaries, which is consistent with a propagation related mechanism to interpret the spectral hardenings of cosmic rays observed at hundreds of $\mathrm{GeV}/\mathrm{n}$.

Cosmic microwave background (CMB) polarimeters aspire to measure the faint $B$-mode signature predicted to arise from inflationary gravitational waves. They also have the potential to constrain cosmic birefringence, rotation of the polarization of the CMB arising from parity-violating physics, which would produce nonzero expectation values for the CMB’s temperature to $B$-mode correlation ($TB$) and $E$-mode to $B$-mode correlation ($EB$) spectra. However, instrumental systematic effects can also cause these $TB$ and $EB$ correlations to be nonzero. In particular, an overall miscalibration of the polarization orientation of the detectors produces $TB$ and $EB$ spectra which are degenerate with isotropic cosmological birefringence, while also introducing a small but predictable bias on the $BB$ spectrum. We find that Bicep1 three-year spectra, which use our standard calibration of detector polarization angles from a dielectric sheet, are consistent with a polarization rotation of $\alpha =-2.77°\pm 0.86°\text{(statistical)}\pm 1.3°\text{(systematic)}$. We have revised the estimate of systematic error on the polarization rotation angle from the two-year analysis by comparing multiple calibration methods. We also account for the (negligible) impact of measured beam systematic effects. We investigate the polarization rotation for the Bicep1 100 GHz and 150 GHz bands separately to investigate theoretical models that produce frequency-dependent cosmic birefringence. We find no evidence in the data supporting either of these models or Faraday rotation of the CMB polarization by the Milky Way galaxy’s magnetic field. If we assume that there is no cosmic birefringence, we can use the $TB$ and $EB$ spectra to calibrate detector polarization orientations, thus reducing bias of the cosmological $B$-mode spectrum from leaked $E$-modes due to possible polarization orientation miscalibration. After applying this “self-calibration” process, we find that the upper limit on the tensor-to-scalar ratio decreases slightly, from $r<0.70$ to $r<0.65$ at 95% confidence.

Recent observations of the light component of the cosmic-ray spectrum have revealed unexpected features that motivate further and more precise measurements up to the highest energies. The Dark Matter Particle Explorer is a satellite-based cosmic-ray experiment that has been operational since December 2015, continuously collecting data on high-energy cosmic particles with very good statistics, energy resolution, and particle identification capabilities. In this work, the latest measurements of the energy spectrum of $\mathrm{proton}+\mathrm{helium}$ in the energy range from 46 GeV to 464 TeV are presented. Among the most distinctive features of the spectrum, a spectral hardening at 600 GeV has been observed, along with a softening at 29 TeV measured with a $6.6\sigma$ significance. Moreover, the detector features and the analysis approach allowed for the extension of the spectral measurement up to the sub-PeV region. Even if with small statistical significance due to the low number of events, data suggest a new spectral hardening at about 150 TeV.

The Forbush decrease of cosmic rays is an important probe of the interplanetary environment disturbed by solar activities. In this Letter, we study the properties of eight Forbush decreases’ electrons (including positrons) between 2 and 20 GeV from January 2016 to March 2024 with the Dark Matter Particle Explorer. The maximum decrease amplitudes of these events are about 30%–15%, and the amplitudes reduce with energy. The recovery time of these events shows diverse behaviors of their energy dependence. Some of them show strong energy dependence, while some have a nearly constant recovery time. It has been shown that such diverse behaviors could be related to the geometry of the regions of the interplanetary space disturbed by coronal mass ejections, which can be characterized by the combined effect of the coronal mass ejection velocity, angular spread, and ejection direction.

We present the electronic structure of ferrimagnetic ${\mathrm{Zn}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Fe}}_2$${\mathrm{O}}_4$ compounds obtained by a combination of O K-edge x-ray-absorption measurements and first-principles spin-unrestricted calculations using the pseudofunction method. The two distinct preedge features are found to vary systematically as a function of the Zn content. From both experimental and theoretical analyses, we find that substitution of Ni with Zn enhances localization of the 3d states of Fe on the octahedral sites, so that the O 2p–Fe 3d hybridized states can be resolved into two distinct twofold and threefold features. © 1996 The American Physical Society.

The photoabsorption processes of ${\text{Au}}^{2+}$, ${\text{Au}}^{3+}$, and ${\text{Au}}^{4+}$ have been investigated experimentally and theoretically in the 70–127 eV region. Using the dual laser-produced plasma technique, the $4f$ and $5p$ photoabsorption spectrum has been recorded at 50 ns time delay and was found to be dominated by a great number of lines from $4f\text{−}5d$, $6d$ and $5p\text{−}5d$, $6s$ transitions, which have been identified by comparison with the aid of Hartree-Fock with configuration interaction calculations. The characteristic feature of the spectrum is that satellite lines from excited configurations containing one or two $6s$ electrons are more important than resonance lines, and with increasing ionization, satellite contributions from states with one $6s$ spectator electron gradually become more important than those with two $6s$ spectator electrons. Based on the assumption of a normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model, we succeeded in reproducing a spectrum which is in good agreement with experiment.

The $4d$ photoabsorption spectra of ${\mathrm{I}}^{2+}$, ${\mathrm{I}}^{3+}$, and ${\mathrm{I}}^{4+}$ have been obtained in the $70–127\mathrm{eV}$ region with the dual laser-produced plasma technique at time delays ranging from $400\text{to}520\mathrm{ns}$. With decreasing time delay, the dominant contribution to the spectra evolves from the ${\mathrm{I}}^{2+}$ to the ${\mathrm{I}}^{4+}$ ions, and each spectrum contains discrete $4d\text{−}nf$ transitions and a broad $4d\text{−}\epsilon f$ shape resonance, which are identified with the aid of multiconfiguration Hartree-Fock calculations. The excited states decay by direct autoionization involving $5s$ or $5p$ electrons, and rates for the different processes and resulting linewidths were calculated. With increasing ionization, the $4d\text{−}\epsilon f$ shape resonance become intense and broader in going from ${\mathrm{I}}^{2+}$ to ${\mathrm{I}}^{3+}$, and then vanishes at ${\mathrm{I}}^{5+}$. In addition, the discrete structure of the calculated spectrum of each ion gradually approaches the corresponding shape resonance position. Based on the assumption of a normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model, we reproduced spectra which are in good agreement with experiment.

Driving a double-quantum-well excitonic intersubband resonance with a terahertz (THz) electric field of frequency ${\omega }_{\mathrm{THz}}$ generated terahertz optical sidebands $\omega ={\omega }_{\mathrm{THz}}+{\omega }_{\mathrm{NIR}}$ on a weak near-infrared probe. At high THz intensities, the intersubband dipole energy which coupled two excitons was comparable to the THz photon energy. In this strong-field regime, the sideband intensity displayed a nonmonotonic dependence on the THz field strength. The oscillating refractive index which gives rise to the sidebands may be understood by the formation of dressed states that oscillate with the same periodicity as the driving THz field.

Theoretical calculations have been made for the dielectronic recombination (DR) rate coefficients of Sn${}^{12+}$ ion using a relativistic flexible atomic code with configuration interaction. Comparison of the rate coefficients for $4s$, $4p$, and $4d$ subshell excitation shows that while the $4p$ subshell excitation dominates over the whole temperature region, $4d$ subshell excitation at low temperature and $4s$ subshell excitation at high temperature cannot be neglected. In order to facilitate simple applications, the calculated DR rate coefficients are fitted to an empirical formula. The total DR rate coefficient is greater than either the radiative recombination or three-body recombination coefficients for electron temperatures greater than 1 eV. Therefore, DR can strongly influence the ionization balance of laser-produced tin plasmas.

We report the Ni ${\mathrm{L}}_{2,3}$-edge magnetic circular dichroism (MCD) measurements of ferrimagnetic ${\mathrm{Zn}}_{\mathrm{x}}$${\mathrm{Ni}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Fe}}_2$${\mathrm{O}}_4$ (x=0.0, 0.26, 0.50, and 0.75). The Ni MCD asymmetry ratio was found to decrease with increasing x, showing a reduction of the Ni average magnetic moment with Zn content. This observation is interpreted in terms of the variations in the Yafet-Kittel-type canted angles of the Ni moment, giving new insight into the superexchange interactions involving the Ni ions. A comparison with the non-Ni-specific neutron scattering and Mössbauer studies is given.

We have probed the internal structure and nonlinear response of magnetoexcitons in GaAs/AlGaAs quantum wells by resonantly driving one- and two-photon internal transitions with intense terahertz electric fields. Strong near-band-gap emission lines, or optical sidebands, appear at frequencies ${\omega }_{\mathrm{NIR}}\pm 2n{\omega }_{\mathrm{THz}}$, where ${\omega }_{\mathrm{NIR}}$ is the interband exciton-creation frequency, ${\omega }_{\mathrm{THz}}$ is the frequency of the driving field, and $n$ is an integer. The intensity of the sidebands exhibits pronounced enhancement when ${\omega }_{\mathrm{THz}}$ coincides with transitions between magnetically tuned energy levels in the excitons, providing new and accurate information on the internal dynamics of excitons.

Certain quantum states are well known to be particularly fragile in the presence of decoherence, as illustrated by Schrödinger's famous gedanken cat experiment. More recently it has been considered that quantum states can be characterized through a hierarchy of quantum quantities such as entanglement, quantum correlations, and quantum coherence. It has been conjectured that each of these quantities has various degrees of fragility in the presence of decoherence. Here we experimentally confirm this conjecture by preparing tripartite photonic states and subjecting them to controlled amounts of dephasing. When the dephasing is applied to all the qubits, we find that the entanglement is the most fragile quantity, followed by the quantum coherence and then mutual information. This is in agreement with the widely held expectation that multipartite quantum correlations are a highly fragile manifestation of quantumness. We also perform dephasing on one of the three qubits on star and $W\overline{W}$ states. Here the distribution of the correlations and coherence in the star state becomes more important in relation to the dephasing location.

The nature of the $\gamma$-ray emission from the Fermi bubbles is unknown. Both hadronic and leptonic models have been formulated to explain the peculiar $\gamma$-ray signal observed by the Fermi-LAT between 0.1–500 GeV. If this emission continues above $\sim 30\mathrm{TeV}$, hadronic models of the Fermi bubbles would provide a significant contribution to the high-energy neutrino flux detected by the IceCube observatory. Even in models where leptonic $\gamma$-rays produce the Fermi bubbles flux at GeV energies, a hadronic component may be observable at very high energies. The combination of IceCube and HAWC measurements have the ability to distinguish these scenarios through a comparison of the neutrino and $\gamma$-ray fluxes at a similar energy scale. We examine the most recent four-year data set produced by the IceCube Collaboration and find no evidence for neutrino emission originating from the Fermi bubbles. In particular, we find that previously suggested excesses are consistent with the diffuse astrophysical background with a p-value of 0.22 (0.05 in an extreme scenario that all the IceCube events that overlap with the bubbles come from them). Moreover, we show that existing and upcoming HAWC observations provide independent constraints on any neutrino emission from the Fermi bubbles due to the close correlation between the $\gamma$-ray and neutrino fluxes in hadronic interactions. The combination of these results disfavors a significant contribution from the Fermi bubbles to the IceCube neutrino flux.

Following Kamionkowski (2008), a quadratic estimator of the rotation of the plane of polarization of the cosmic microwave background (CMB) is constructed. This statistic can estimate a spatially varying rotation angle $\alpha (n)$. We use this estimator to quantify the prospects of detecting such a rotation field with forthcoming experiments. For PLANCK and CMBPol experiments, we find that the estimator containing the product of the $E$ and $B$ components of the polarization field is the most sensitive. The variance of this $EB$ estimator $N(L)$ is roughly independent of the multipole $L$ and is only weakly dependent on the instrumental beam. For FWHM of the beam size ${\Theta }_{\mathrm{fwhm}}\sim 5^{\prime }–{50}^{\prime }$ and instrument noise ${\Delta }_p\sim 5–50\mu \mathrm{K}\mathrm{\text{−}}\mathrm{arcmin}$, the scaling of variance $N(L)$ can be fitted by a power law $N(L)=3.3\times {10}^{-7}{\Delta }_p^2{\Theta }_{\mathrm{fwhm}}^{1.3}{deg}^2$. For small instrumental noise ${\Delta }_p\le 5\mu \mathrm{K}\mathrm{\text{−}}\mathrm{arcmin}$, the lensing $B$ modes become important, saturating the variance to $\sim {10}^{-6}{deg}^2$ even for an ideal experiment. Upcoming experiments like PLANCK will be able to detect a power spectrum of the rotation angle, $C^{\alpha \alpha }(L)$, as small as $0.01{deg}^2$, while futuristic experiments like CMBPol will be able to detect rotation angle power spectrum as small as $2.5\times {10}^{-5}{deg}^2$. We discuss the implications of such constraints, both for the various physical effects that can rotate the polarization as photons travel from the last scattering surface as well as for constraints on instrumental systematics that can also lead to a spurious rotation signal. Rotation of the CMB polarization generates $B$ modes which will act as contamination for the primordial $B$-mode detection. We discuss an application of our estimator to derotate the CMB to increase the sensitivity for the primordial $B$ modes.