Search

Large blueshift and linewidth increase in photoluminescence (PL) spectra of InAs quantum dots (QD’s) in n-i-p-i GaAs superlattice were observed. By increasing the excitation intensity from 0.5 to 32 ${\mathrm{W}/\mathrm{c}\mathrm{m}}^2$, the PL peak position blueshifted 18 meV, and the linewidth increased by 20 meV. Such large changes are due to the state-filling effects of the QD’s resulted from the separation of photogenerated electrons and holes caused by the doping potential.

The processes ${\psi }^{\prime }\to p\overline{p}{\pi }^0$ and ${\psi }^{\prime }\to p\overline{p}\eta$ are studied using a sample of $14\times {10}^6$ ${\psi }^{\prime }$ decays collected with the Beijing Spectrometer at the Beijing Electron-Positron Collider. The branching fraction of ${\psi }^{\prime }\to p\overline{p}{\pi }^0$ is measured with improved precision as $(13.2\pm 1.0\pm 1.5)\times {10}^{-5}$, and ${\psi }^{\prime }\to p\overline{p}\eta$ is observed for the first time with a branching fraction of $(5.8\pm 1.1\pm 0.7)\times {10}^{-5}$, where the first errors are statistical and the second ones are systematic.

The decay $J/\psi \to \overline{N}N\pi$ provides an effective isospin $1/2$ filter for the $\pi N$ system due to isospin conservation. Using $58\times {10}^6$ $J/\psi$ decays collected with the Beijing Electromagnetic Spectrometer at the Beijing Electron Positron Collider, more than 100 thousand $J/\psi \to p{\pi }^{-}\overline{n}+\mathrm{c}.\mathrm{c}.$ events are obtained. Besides the two well-known $N^{*}$ peaks at around $1500\mathrm{MeV}/c^2$ and $1670\mathrm{MeV}/c^2$, there are two new, clear $N^{*}$ peaks in the $p\pi$ invariant mass spectrum around $1360\mathrm{MeV}/c^2$ and $2030\mathrm{MeV}/c^2$ with statistical significance of $11\sigma$ and $13\sigma$, respectively. We identify these as the first direct observation of the $N^{*}(1440)$ peak and a long-sought missing $N^{*}$ peak above $2\mathrm{GeV}/c^2$ in the $\pi N$ invariant mass spectrum.

The recent discovery by Advanced LIGO and Advanced Virgo of a gravitational wave signal from a binary neutron star inspiral has enabled tests of general relativity (GR) with this new type of source. This source, for the first time, permits tests of strong-field dynamics of compact binaries in the presence of matter. In this Letter, we place constraints on the dipole radiation and possible deviations from GR in the post-Newtonian coefficients that govern the inspiral regime. Bounds on modified dispersion of gravitational waves are obtained; in combination with information from the observed electromagnetic counterpart we can also constrain effects due to large extra dimensions. Finally, the polarization content of the gravitational wave signal is studied. The results of all tests performed here show good agreement with GR.

The LIGO Scientific and Virgo Collaborations have announced the event GW170817, the first detection of gravitational waves from the coalescence of two neutron stars. The merger rate of binary neutron stars estimated from this event suggests that distant, unresolvable binary neutron stars create a significant astrophysical stochastic gravitational-wave background. The binary neutron star component will add to the contribution from binary black holes, increasing the amplitude of the total astrophysical background relative to previous expectations. In the Advanced LIGO-Virgo frequency band most sensitive to stochastic backgrounds (near 25 Hz), we predict a total astrophysical background with amplitude ${\mathrm{\Omega }}_{\mathrm{GW}}(f=25\mathrm{Hz})=1.8_{-1.3}^{+2.7}\times {10}^{-9}$ with 90% confidence, compared with ${\mathrm{\Omega }}_{\mathrm{GW}}(f=25\mathrm{Hz})=1.1_{-0.7}^{+1.2}\times {10}^{-9}$ from binary black holes alone. Assuming the most probable rate for compact binary mergers, we find that the total background may be detectable with a signal-to-noise-ratio of 3 after 40 months of total observation time, based on the expected timeline for Advanced LIGO and Virgo to reach their design sensitivity.

The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to ${\mathrm{\Omega }}_0^T<5.58\times {10}^{-8}$, ${\mathrm{\Omega }}_0^V<6.35\times {10}^{-8}$, and ${\mathrm{\Omega }}_0^S<1.08\times {10}^{-7}$ at a reference frequency $f_0=25\mathrm{Hz}$.

On August 14, 2017 at 10∶30:43 UTC, the Advanced Virgo detector and the two Advanced LIGO detectors coherently observed a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes, with a false-alarm rate of $\lesssim 1$ in 27 000 years. The signal was observed with a three-detector network matched-filter signal-to-noise ratio of 18. The inferred masses of the initial black holes are $30.5_{-3.0}^{+5.7}{M}_{\odot }$ and $25.3_{-4.2}^{+2.8}{M}_{\odot }$ (at the 90% credible level). The luminosity distance of the source is $540_{-210}^{+130}\mathrm{Mpc}$, corresponding to a redshift of $z=0.11_{-0.04}^{+0.03}$. A network of three detectors improves the sky localization of the source, reducing the area of the 90% credible region from $1160{\mathrm{deg}}^2$ using only the two LIGO detectors to $60{\mathrm{deg}}^2$ using all three detectors. For the first time, we can test the nature of gravitational-wave polarizations from the antenna response of the LIGO-Virgo network, thus enabling a new class of phenomenological tests of gravity.

The stochastic gravitational-wave background is a superposition of sources that are either too weak or too numerous to detect individually. In this study, we present the results from a cross-correlation analysis on data from Advanced LIGO’s second observing run (O2), which we combine with the results of the first observing run (O1). We do not find evidence for a stochastic background, so we place upper limits on the normalized energy density in gravitational waves at the 95% credible level of ${\mathrm{\Omega }}_{\mathrm{GW}}<6.0\times {10}^{-8}$ for a frequency-independent (flat) background and ${\mathrm{\Omega }}_{\mathrm{GW}}<4.8\times {10}^{-8}$ at 25 Hz for a background of compact binary coalescences. The upper limit improves over the O1 result by a factor of 2.8. Additionally, we place upper limits on the energy density in an isotropic background of scalar- and vector-polarized gravitational waves, and we discuss the implication of these results for models of compact binaries and cosmic string backgrounds. Finally, we present a conservative estimate of the correlated broadband noise due to the magnetic Schumann resonances in O2, based on magnetometer measurements at both the LIGO Hanford and LIGO Livingston observatories. We find that correlated noise is well below the O2 sensitivity.

Gravitational-wave astronomy has been firmly established with the detection of gravitational waves from the merger of ten stellar-mass binary black holes and a neutron star binary. This paper reports on the all-sky search for gravitational waves from intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network. The search uses three independent algorithms: two based on matched filtering of the data with waveform templates of gravitational-wave signals from compact binaries, and a third, model-independent algorithm that employs no signal model for the incoming signal. No intermediate mass black hole binary event is detected in this search. Consequently, we place upper limits on the merger rate density for a family of intermediate mass black hole binaries. In particular, we choose sources with total masses $M=m_1+m_2\in [120,800]M_{\odot }$ and mass ratios $q=m_2/m_1\in [0.1,1.0]$. For the first time, this calculation is done using numerical relativity waveforms (which include higher modes) as models of the real emitted signal. We place a most stringent upper limit of $0.20{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$ (in comoving units at the 90% confidence level) for equal-mass binaries with individual masses $m_{1,2}=100M_{\odot }$ and dimensionless spins ${\chi }_{1,2}=0.8$ aligned with the orbital angular momentum of the binary. This improves by a factor of $\sim 5$ that reported after Advanced LIGO’s first observing run.

We present a search for subsolar mass ultracompact objects in data obtained during Advanced LIGO’s second observing run. In contrast to a previous search of Advanced LIGO data from the first observing run, this search includes the effects of component spin on the gravitational waveform. We identify no viable gravitational-wave candidates consistent with subsolar mass ultracompact binaries with at least one component between $0.2M_{\odot }–1.0M_{\odot }$. We use the null result to constrain the binary merger rate of ($0.2M_{\odot }$, $0.2M_{\odot }$) binaries to be less than $3.7\times {10}^5{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$ and the binary merger rate of ($1.0M_{\odot }$, $1.0M_{\odot }$) binaries to be less than $5.2\times {10}^3{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$. Subsolar mass ultracompact objects are not expected to form via known stellar evolution channels, though it has been suggested that primordial density fluctuations or particle dark matter with cooling mechanisms and/or nuclear interactions could form black holes with subsolar masses. Assuming a particular primordial black hole (PBH) formation model, we constrain a population of merging $0.2M_{\odot }$ black holes to account for less than 16% of the dark matter density and a population of merging $1.0M_{\odot }$ black holes to account for less than 2% of the dark matter density. We discuss how constraints on the merger rate and dark matter fraction may be extended to arbitrary black hole population models that predict subsolar mass binaries.

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for $U(1{)}_{B-L}$ gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the $U(1{)}_{B-L}$ gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation timescale of DM.

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 $\mathrm{GeV}/\mathrm{n}$.

The gravitational-wave signal GW250114 was observed by the two LIGO detectors with a network matched-filter signal-to-noise ratio of 80. The signal was emitted by the coalescence of two black holes with near-equal masses $m_1={33.6}_{-0.8}^{+1.2}{M}_{\odot }$ and $m_2={32.2}_{-1.3}^{+0.8}{M}_{\odot }$, and small spins ${\chi }_{1,2}\le 0.26$ (90% credibility) and negligible eccentricity $e\le 0.03$. Postmerger data excluding the peak region are consistent with the dominant quadrupolar $(\ell =|m|=2)$ mode of a Kerr black hole and its first overtone. We constrain the modes’ frequencies to $\pm 30\%$ of the Kerr spectrum, providing a test of the remnant’s Kerr nature. We also examine Hawking’s area law, also known as the second law of black hole mechanics, which states that the total area of the black hole event horizons cannot decrease with time. A range of analyses that exclude up to five of the strongest merger cycles confirm that the remnant area is larger than the sum of the initial areas to high credibility.

We report results of a search for an isotropic gravitational-wave background (GWB) using data from Advanced LIGO’s and Advanced Virgo’s third observing run (O3) combined with upper limits from the earlier O1 and O2 runs. Unlike in previous observing runs in the advanced detector era, we include Virgo in the search for the GWB. The results of the search are consistent with uncorrelated noise, and therefore we place upper limits on the strength of the GWB. We find that the dimensionless energy density ${\mathrm{\Omega }}_{\mathrm{GW}}\le 5.8\times {10}^{-9}$ at the 95% credible level for a flat (frequency-independent) GWB, using a prior which is uniform in the log of the strength of the GWB, with 99% of the sensitivity coming from the band 20–76.6 Hz; ${\mathrm{\Omega }}_{\mathrm{GW}}(f)\le 3.4\times {10}^{-9}$ at 25 Hz for a power-law GWB with a spectral index of $2/3$ (consistent with expectations for compact binary coalescences), in the band 20–90.6 Hz; and ${\mathrm{\Omega }}_{\mathrm{GW}}(f)\le 3.9\times {10}^{-10}$ at 25 Hz for a spectral index of 3, in the band 20–291.6 Hz. These upper limits improve over our previous results by a factor of 6.0 for a flat GWB, 8.8 for a spectral index of $2/3$, and 13.1 for a spectral index of 3. We also search for a GWB arising from scalar and vector modes, which are predicted by alternative theories of gravity; we do not find evidence of these, and place upper limits on the strength of GWBs with these polarizations. We demonstrate that there is no evidence of correlated noise of magnetic origin by performing a Bayesian analysis that allows for the presence of both a GWB and an effective magnetic background arising from geophysical Schumann resonances. We compare our upper limits to a fiducial model for the GWB from the merger of compact binaries, updating the model to use the most recent data-driven population inference from the systems detected during O3a. Finally, we combine our results with observations of individual mergers and show that, at design sensitivity, this joint approach may yield stronger constraints on the merger rate of binary black holes at $z\gtrsim 2$ than can be achieved with individually resolved mergers alone.

The second Gravitational-Wave Transient Catalog, GWTC-2, reported on 39 compact binary coalescences observed by the Advanced LIGO and Advanced Virgo detectors between 1 April 2019 $15:00$ UTC and 1 October 2019 $15:00$ UTC. Here, we present GWTC-2.1, which reports on a deeper list of candidate events observed over the same period. We analyze the final version of the strain data over this period with improved calibration and better subtraction of excess noise, which has been publicly released. We employ three matched-filter search pipelines for candidate identification, and estimate the probability of astrophysical origin for each candidate event. While GWTC-2 used a false alarm rate threshold of 2 per year, we include in GWTC-2.1, 1201 candidates that pass a false alarm rate threshold of 2 per day. We calculate the source properties of a subset of 44 high-significance candidates that have a probability of astrophysical origin greater than 0.5. Of these candidates, 36 have been reported in GWTC-2. We also calculate updated source properties for all binary black hole events previously reported in GWTC-1. If the eight additional high-significance candidates presented here are astrophysical, the mass range of events that are unambiguously identified as binary black holes (both objects $\ge 3M_{\odot }$) is increased compared to GWTC-2, with total masses from $\sim 14M_{\odot }$ for GW190924_021846 to $\sim 182M_{\odot }$ for GW190426_190642. Source properties calculated using our default prior suggest that the primary components of two new candidate events (GW190403_051519 and GW190426_190642) fall in the mass gap predicted by pair-instability supernova theory. We also expand the population of binaries with significantly asymmetric mass ratios reported in GWTC-2 by an additional two events (the mass ratio is less than 0.65 and 0.44 at 90% probability for GW190403_051519 and GW190917_114630 respectively), and find that two of the eight new events have effective inspiral spins ${\chi }_{\mathrm{eff}}>0$ (at 90% credibility), while no binary is consistent with ${\chi }_{\mathrm{eff}}<0$ at the same significance. We provide updated estimates for rates of binary black hole and binary neutron star coalescence in the local Universe.

We present a search for short-duration gravitational-wave transients in data from the first eight months of Advanced LIGO-Virgo-KAGRA’s fourth observing run, denoted O4a. We use four analyses which are sensitive to a wide range of potential signals lasting up to a few seconds in the 16–4096 Hz band. Excluding binary black hole merger candidates that were already identified by low-latency analyses, we find no statistically significant evidence for other gravitational-wave transients. We measure the sensitivity of the search for representative signals, including sine-Gaussians, Gaussian pulses, and white-noise bursts with different frequencies and durations, adopting a false alarm rate of 1 per 100 years as detection threshold. Depending on signal type, we find improvements over previous searches by factors of 2 to 10 in terms of sensitivity to strain amplitude and of 90% confidence upper limit on the rate density of sources. We also evaluate a variety of core-collapse supernova models and find that, for some models, the search could have detected gravitational waves from stellar core-collapse throughout the Milky Way. Finally, we consider neutron star $f$-modes associated with pulsar glitches and find that, assuming a source similar to the Vela Pulsar, the search could have detected a gravitational-wave signal from a glitch with fractional frequency change as small as $\sim 2$ to $6\times {10}^{-5}$ depending on the neutron star mass.

The binary black hole signal GW250114, the loudest gravitational wave detected to date, offers a unique opportunity to test Einstein’s general relativity (GR) in the high-velocity, strong-gravity regime and probe whether the remnant conforms to the Kerr metric. Upon perturbation, black holes emit a spectrum of damped sinusoids with specific, complex frequencies. Our analysis of the postmerger signal shows that at least two quasinormal modes are required to explain the data, with the most damped remaining statistically significant for about one cycle. We probe the remnant’s Kerr nature by constraining the spectroscopic pattern of the dominant quadrupolar ($\ell =m=2$) mode and its first overtone to match the Kerr prediction to tens of percent at multiple postpeak times. The measured mode amplitudes and phases agree with a numerical-relativity simulation having parameters close to GW250114. By fitting a parametrized waveform that incorporates the full inspiral-merger-ringdown sequence, we constrain the fundamental $(\ell =m=4)$ mode to tens of percent and bound the quadrupolar frequency to within a few percent of the GR prediction. We perform a suite of tests—spanning inspiral, merger, and ringdown—finding constraints that are comparable to, and in some cases 2–3 times more stringent than those obtained by combining dozens of events in the fourth Gravitational-Wave Transient Catalog. These results constitute the most stringent single-event verification of GR and the Kerr nature of black holes to date, and outline the power of black-hole spectroscopy for future gravitational-wave observations.

Using photon conversions to $e^{+}{e}^{-}$ pairs, the energy spectrum of inclusive photons from $\psi (2S)$ radiative decays is measured with photon energy resolution (${\sigma }_{E_{\gamma }}$) in the range from 2.3 to 3.8 MeV by BESII at the Beijing Electron-Positron Collider. The ${\chi }_{cJ}(1P)$ states ($J=0,1,2$) are clearly observed, and their masses and the spin-averaged ${\chi }_{cJ}$ mass are determined to be $M_{{\chi }_{c0}}=3414.21\pm 0.39\pm 0.27$, $M_{{\chi }_{c1}}=3510.30\pm 0.14\pm 0.16$, $M_{{\chi }_{c2}}=3555.70\pm 0.59\pm 0.39$, and $M({}^{3}P_{\mathrm{cog}})=3524.85\pm 0.32\pm 0.30\mathrm{MeV}/c^2$, respectively.

Magnetic, electronic, and thermal transport properties of ${\mathrm{Eu}}_{0.55}{\mathrm{Sr}}_{0.45}\mathrm{Mn}{\mathrm{O}}_3$ have been experimentally studied. The compound is found to exhibit a complex magnetic behavior with the change of temperature and magnetic field. Without magnetic field, it stays in a Griffiths-like state in a wide temperature range above $\sim 100\mathrm{K}$, characterized by the presence of ferromagnetic (FM) clusters of the size of $\sim 8$ Mn ions, and an antiferromagnetic (AFM) state below $\sim 100\mathrm{K}$, evidenced by thermopower and heat conductivity. FM phase emerges and grows in the AFM matrix with applied field, resulting in a series of phase transitions from the paramagnetic (PM) state first to the AFM state, then to the FM and the AFM states upon cooling $(\sim 0.8\mathrm{T}<H<\sim 1\mathrm{T})$, or a simple PM-FM transition $(H>\sim 2.3\mathrm{T})$. The AFM state is unstable under high fields, and the high- and low-temperature AFM transitions are depressed by the fields above $\sim 1$ and $\sim 2.3\mathrm{T}$, respectively. The FM transition is incomplete when the field is below $\sim 1.5\mathrm{T}$, leading to a coexistence of the FM and PM (or AFM) phases in the intermediate temperature range. A spin-glass-like behavior is observed in the AFM background below $\sim 50\mathrm{K}$. Significant response of resistance, thermopower, and heat conduction to magnetic transition, either FM or AFM transition, has been observed. Unlike the typical AFM manganites, for which usually a depression of thermal conduction occurs at the AFM state, the AFM transition in ${\mathrm{Eu}}_{0.55}{\mathrm{Sr}}_{0.45}\mathrm{Mn}{\mathrm{O}}_3$ enhances the thermal conduction. From the PM phase to the AFM phase and to the FM phase, thermal conductivity increases monotonically. A remarkable result of the present work is the different behaviors of thermopower and resistivity. The former displays a metallic behavior below a distinct temperature that is significantly lower than the metal-to-insulator transition temperature determined by resistivity. Furthermore, thermopower remains metallic while the resistivity shows up an upturn due to the AFM transition in the low-temperature range under the field of $1.5\mathrm{T}$. Based on these data, a magnetic phase diagram is proposed.