We measured the ratios of electroproduction cross sections from a proton target for three exclusive meson-baryon final states: $\mathrm{\Lambda }{K}^{+}$, $p{\pi }^0$, and $n{\pi }^{+}$, with the CLAS detector at Jefferson Lab. Using a simple model of quark hadronization, we extract $q\overline{q}$ creation probabilities for the first time in exclusive two-body production, in which only a single $q\overline{q}$ pair is created. We observe a sizable suppression of strange quark-antiquark pairs compared to nonstrange pairs, similar to that seen in high-energy production.

If the supermassive black hole Sgr ${\mathrm{A}}^{*}$ at the center of the Milky Way grew adiabatically from an initial seed embedded in a Navarro-Frenk-White dark matter (DM) halo, then the DM profile near the hole has steepened into a spike. We calculate the dramatic enhancement to the gamma-ray flux from the Galactic center (GC) from such a spike if the 1–3 GeV excess observed in Fermi data is due to DM annihilations. We find that for the parameter values favored in recent fits, the point-source-like flux from the spike is 35 times greater than the flux from the inner 1° of the halo, far exceeding all Fermi point source detections near the GC. We consider the dependence of the spike signal on astrophysical and particle parameters and conclude that if the GC excess is due to DM, then a canonical adiabatic spike is disfavored by the data. We discuss alternative Galactic histories that predict different spike signals, including (i) the nonadiabatic growth of the black hole, possibly associated with halo and/or black hole mergers, (ii) gravitational interaction of DM with baryons in the dense core, such as heating by stars, or (iii) DM self-interactions. We emphasize that the spike signal is sensitive to a different combination of particle parameters than the halo signal and that the inclusion of a spike component to any DM signal in future analyses would provide novel information about both the history of the GC and the particle physics of DM annihilations.

One of the enduring challenges in graphene research and applications is the extreme sensitivity of its charge carriers to external perturbations, especially those introduced by the substrate. The best available substrates to date, graphite and hexagonal boron nitride ($h\text{−}\mathrm{BN}$), still pose limitations: graphite being metallic does not allow gating, while both $h\text{−}\mathrm{BN}$ and graphite, having lattice structures closely matched to that of graphene, may cause significant band structure reconstruction. Here we show that the atomically smooth surface of exfoliated ${\mathrm{MoS}}_2$ provides access to the intrinsic electronic structure of graphene without these drawbacks. Using scanning tunneling microscopy and Landau-level (LL) spectroscopy in a device configuration that allows tuning of the carrier concentration, we find that graphene on ${\mathrm{MoS}}_2$ is ultraflat, producing long mean free paths, while avoiding band structure reconstruction. Importantly, the screening of the ${\mathrm{MoS}}_2$ substrate can be tuned by changing the position of the Fermi energy with relatively low gate voltages. We show that shifting the Fermi energy from the gap to the edge of the conduction band gives rise to enhanced screening and to a substantial increase in the mean free path and quasiparticle lifetime. ${\mathrm{MoS}}_2$ substrates thus provide unique opportunities to access the intrinsic electronic properties of graphene and to study in situ the effects of screening on electron-electron interactions and transport.

Because of conservation of energy we cannot directly turn a quantum system with a definite energy into a superposition of different energies. However, if we have access to an additional resource in terms of a system with a high degree of coherence, as for standard models of laser light, we can overcome this limitation. The question is to what extent coherence gets degraded when utilized. Here it is shown that coherence can be turned into a catalyst, meaning that we can use it repeatedly without ever diminishing its power to enable coherent operations. This finding stands in contrast to the degradation of other quantum resources and has direct consequences for quantum thermodynamics, as it shows that latent energy that may be locked into superpositions of energy eigenstates can be released catalytically.

A beam with an angular-dependant phase $\mathrm{\Phi }=\ell \varphi$ about the beam axis carries an orbital angular momentum of $\ell \hslash$ per photon. Such beams are exploited to provide superresolution in microscopy. Creating extreme ultraviolet or soft-x-ray beams with controllable orbital angular momentum is a critical step towards extending superresolution to much higher spatial resolution. We show that orbital angular momentum is conserved during high-harmonic generation. Experimentally, we use a fundamental beam with $|\ell |=1$ and interferometrically determine that the harmonics each have orbital angular momentum equal to their harmonic number. Theoretically, we show how any small value of orbital angular momentum can be coupled to any harmonic in a controlled manner. Our results open a route to microscopy on the molecular, or even submolecular, scale.

A measurement of the ratio of the branching fractions of the $B^{+}\to K^{+}{\mu }^{+}{\mu }^{-}$ and $B^{+}\to K^{+}{e}^{+}{e}^{-}$ decays is presented using proton-proton collision data, corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$, recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. The value of the ratio of branching fractions for the dilepton invariant mass squared range $1<q^2<6{\mathrm{GeV}}^2/c^4$ is measured to be $0.745_{-0.074}^{+0.090}(\text{stat})\pm 0.036(\text{syst})$. This value is the most precise measurement of the ratio of branching fractions to date and is compatible with the standard model prediction within 2.6 standard deviations.

We study lattice QCD with four flavors of staggered quarks. In the limit of infinite gauge coupling, “dual” variables can be introduced, which render the finite-density sign problem mild and allow a full determination of the $\mu -T$ phase diagram by Monte Carlo simulations, also in the chiral limit. However, the continuum limit coincides with the weak coupling limit. We propose a strong-coupling expansion approach towards the continuum limit. We show first results, including the phase diagram and its chiral critical point, from this expansion truncated at next-to-leading order.

This Letter presents results from the first fully integrated experiments testing the magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)], in which a cylinder of deuterium gas with a preimposed 10 T axial magnetic field is heated by $Z$ beamlet, a 2.5 kJ, 1 TW laser, and magnetically imploded by a 19 MA, 100 ns rise time current on the $Z$ facility. Despite a predicted peak implosion velocity of only $70\mathrm{km}/\mathrm{s}$, the fuel reaches a stagnation temperature of approximately 3 keV, with $T_e\approx T_i$, and produces up to $2\times {10}^{12}$ thermonuclear deuterium-deuterium neutrons. X-ray emission indicates a hot fuel region with full width at half maximum ranging from 60 to $120\mu \mathrm{m}$ over a 6 mm height and lasting approximately 2 ns. Greater than ${10}^{10}$ secondary deuterium-tritium neutrons were observed, indicating significant fuel magnetization given that the estimated radial areal density of the plasma is only $2\mathrm{mg}/{\mathrm{cm}}^2$.

Magnetizing the fuel in inertial confinement fusion relaxes ignition requirements by reducing thermal conductivity and changing the physics of burn product confinement. Diagnosing the level of fuel magnetization during burn is critical to understanding target performance in magneto-inertial fusion (MIF) implosions. In pure deuterium fusion plasma, 1.01 MeV tritons are emitted during deuterium-deuterium fusion and can undergo secondary deuterium-tritium reactions before exiting the fuel. Increasing the fuel magnetization elongates the path lengths through the fuel of some of the tritons, enhancing their probability of reaction. Based on this feature, a method to diagnose fuel magnetization using the ratio of overall deuterium-tritium to deuterium-deuterium neutron yields is developed. Analysis of anisotropies in the secondary neutron energy spectra further constrain the measurement. Secondary reactions also are shown to provide an upper bound for the volumetric fuel-pusher mix in MIF. The analysis is applied to recent MIF experiments [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] on the Z Pulsed Power Facility, indicating that significant magnetic confinement of charged burn products was achieved and suggesting a relatively low-mix environment. Both of these are essential features of future ignition-scale MIF designs.

Penrose tilings form lattices, exhibiting fivefold symmetry and isotropic elasticity, with inhomogeneous coordination much like that of the force networks in jammed systems. Under periodic boundary conditions, their average coordination is exactly four. We study the elastic and vibrational properties of rational approximants to these lattices as a function of unit-cell size $N_S$ and find that they have of order $\sqrt{N_S}$ zero modes and states of self-stress and yet all their elastic moduli vanish. In their generic form, obtained by randomizing site positions, their elastic and vibrational properties are similar to those of particulate systems at jamming with a nonzero bulk modulus, vanishing shear modulus, and a flat density of states.

We report the experimental reconstruction of the nonequilibrium work probability distribution in a closed quantum system, and the study of the corresponding quantum fluctuation relations. The experiment uses a liquid-state nuclear magnetic resonance platform that offers full control on the preparation and dynamics of the system. Our endeavors enable the characterization of the out-of-equilibrium dynamics of a quantum spin from a finite-time thermodynamics viewpoint.

This Letter presents the first study of $W^{\pm }{W}^{\pm }jj$, same-electric-charge diboson production in association with two jets, using $20.3{\mathrm{fb}}^{-1}$ of proton-proton collision data at $\sqrt{s}=8\mathrm{TeV}$ recorded by the ATLAS detector at the Large Hadron Collider. Events with two reconstructed same-charge leptons ($e^{\pm }{e}^{\pm }$, $e^{\pm }{\mu }^{\pm }$, and ${\mu }^{\pm }{\mu }^{\pm }$) and two or more jets are analyzed. Production cross sections are measured in two fiducial regions, with different sensitivities to the electroweak and strong production mechanisms. First evidence for $W^{\pm }{W}^{\pm }jj$ production and electroweak-only $W^{\pm }{W}^{\pm }jj$ production is observed with a significance of 4.5 and 3.6 standard deviations, respectively. The measured production cross sections are in agreement with standard model predictions. Limits at 95% confidence level are set on anomalous quartic gauge couplings.

This Letter reports a technique for the imaging of acoustic nonlinearity. By contrasting the energy of the diffuse field produced through the focusing of an ultrasonic array by delayed parallel element transmission with that produced by postprocessing of sequential transmission data, acoustic nonlinearity local to the focal point is measured. Spatially isolated wave distortion is inferred without requiring interrogation of the wave at the inspection point, thereby allowing nonlinear imaging through depth.

We report a neutron scattering study of the magnetic order and dynamics of the bilayer perovskite ${\mathrm{Sr}}_3{\mathrm{Fe}}_2{\mathrm{O}}_7$, which exhibits a temperature-driven metal-insulator transition at 340 K. We show that the ${\mathrm{Fe}}^{4+}$ moments adopt incommensurate spiral order below $T_N=115\mathrm{K}$ and provide a comprehensive description of the corresponding spin-wave excitations. The observed magnetic order and excitation spectra can be well understood in terms of an effective spin Hamiltonian with interactions ranging up to third-nearest-neighbor pairs. The results indicate that the helical magnetism in ${\mathrm{Sr}}_3{\mathrm{Fe}}_2{\mathrm{O}}_7$ results from competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions whose strengths become comparable near the metal-insulator transition. They thus confirm a decades-old theoretical prediction and provide a firm experimental basis for models of magnetic correlations in strongly correlated metals.

The nature of near-surface spin canting within ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles is highly debated. Here we develop a neutron scattering asymmetry analysis which quantifies the canting angle to between 23° and 42° at 1.2 T. Simultaneously, an energy-balance model is presented which reproduces the experimentally observed evolution of shell thickness and canting angle between 10 and 300 K. The model is based on the concept of $T_d$ site reorientation and indicates that surface canting involves competition between magnetocrystalline, dipolar, exchange, and Zeeman energies.

We use large-scale lattice simulations to compute the rate of baryon number violating processes (the sphaleron rate), the Higgs field expectation value, and the critical temperature in the standard model across the electroweak phase transition temperature. While there is no true phase transition between the high-temperature symmetric phase and the low-temperature broken phase, the crossover is sharp and located at temperature $T_c=(159.5\pm 1.5)\mathrm{GeV}$. The sphaleron rate in the symmetric phase ($T>T_c$) is $\mathrm{\Gamma }/T^4=(18\pm 3){\alpha }_W^5$, and in the broken phase in the physically interesting temperature range $130\mathrm{GeV}<T<T_c$ it can be parametrized as $\log (\mathrm{\Gamma }/T^4)=(0.83\pm 0.01)T/\mathrm{GeV}-(147.7\pm 1.9)$. The freeze-out temperature in the early Universe, where the Hubble rate wins over the baryon number violation rate, is $T_{*}=(131.7\pm 2.3)\mathrm{GeV}$. These values, beyond being intrinsic properties of the standard model, are relevant for, e.g., low-scale leptogenesis scenarios.

A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment’s unique configuration of multiple baselines from six 2.9 ${\mathrm{GW}}_{\mathrm{th}}$ nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the ${10}^{-3}{\mathrm{eV}}^2<|\mathrm{\Delta }{m}_{41}^2|<0.3{\mathrm{eV}}^2$ range. The relative spectral distortion due to the disappearance of electron antineutrinos was found to be consistent with that of the three-flavor oscillation model. The derived limits on ${\sin }^{2}2{\theta }_{14}$ cover the ${10}^{-3}{\mathrm{eV}}^2\lesssim |\mathrm{\Delta }{m}_{41}^2|\lesssim 0.1{\mathrm{eV}}^2$ region, which was largely unexplored.

We introduce a rigorous framework for the quantification of coherence and identify intuitive and easily computable measures of coherence. We achieve this by adopting the viewpoint of coherence as a physical resource. By determining defining conditions for measures of coherence we identify classes of functionals that satisfy these conditions and other, at first glance natural quantities, that do not qualify as coherence measures. We conclude with an outline of the questions that remain to be answered to complete the theory of coherence as a resource.

Quantum cryptography promises levels of security that are impossible to replicate in a classical world. Can this security be guaranteed even when the quantum devices on which the protocol relies are untrusted? This central question dates back to the early 1990s when the challenge of achieving device-independent quantum key distribution was first formulated. We answer this challenge by rigorously proving the device-independent security of a slight variant of Ekert’s original entanglement-based protocol against the most general (coherent) attacks. The resulting protocol is robust: While assuming only that the devices can be modeled by the laws of quantum mechanics and are spatially isolated from each other and from any adversary’s laboratory, it achieves a linear key rate and tolerates a constant noise rate in the devices. In particular, the devices may have quantum memory and share arbitrary quantum correlations with the eavesdropper. The proof of security is based on a new quantitative understanding of the monogamous nature of quantum correlations in the context of a multiparty protocol.

Line intensities and oscillator strengths for the controversial $3C$ and $3D$ astrophysically relevant lines in neonlike ${\mathrm{Fe}}^{16+}$ ions are calculated. A large-scale configuration-interaction calculation of oscillator strengths is performed with the inclusion of higher-order electron-correlation effects, suggesting that these contributions cannot explain existing discrepancies between theory and experiment. Then, we investigate nonlinear dynamical effects, showing that, for strong x-ray sources, the modeling of the spectral lines by a peak with an area proportional to the oscillator strength is not sufficient. The dynamical effects give a possible resolution of discrepancies of theory and experiment found by recent measurements, which motivates the use of light-matter interaction models also valid for strong light fields in the analysis and interpretation of astrophysical and laboratory spectra.