We report on a new measurement of the branching ratio B(KL -> pi0 e+ e- gamma) using the KTeV detector. This analysis uses the full KTeV data set collected from 1997 to 2000. We reconstruct 139 ...events over a background of 14, which results in B(KL -> pi0 e+ e- gamma) = (1.62 +/- 0.14 (stat) +/- 0.09 (syst)) x 10^{-8}. This result supersedes the earlier KTeV measurement of this branching ratio.
Phys. Lett. A 297 (2002) 408 The finite nuclear size correction to the bound-electron g factor in
hydrogenlike atoms is investigated in the range Z=1-20. An analytical formula
for this correction ...which includes the non-relativistic and dominant
relativistic contributions is derived. In the case of the 1s state, the results
obtained by this formula are compared with previous non-relativistic analytical
and relativistic numerical calculations.
We study theoretically the nonequilibrium exciton transport in monolayer transition metal dichalcogenides. We consider the situation where excitons interact with nonequilibrium phonons, e.g., under ...the conditions of localized excitation where a "hot spot" is formed. We develop the theory of the exciton drag by the phonons and analyze in detail the regimes of diffusive propagation of phonons and ballistic propagation of phonons where the phonon wind is generated. We demonstrate that a halolike spatial distribution of excitons akin observed in Phys. Rev. Lett. 120, 207401 (2018) can result from the exciton drag by nonequilibrium phonons.
We provide an assessment of the impact of parton distributions on the
determination of LHC processes, and of the accuracy with which parton
distributions (PDFs) can be extracted from data, in ...particular from current and
forthcoming HERA experiments. We give an overview of reference LHC processes
and their associated PDF uncertainties, and study in detail W and Z production
at the LHC. We discuss the precision which may be obtained from the analysis of
existing HERA data, tests of consistency of HERA data from different
experiments, and the combination of these data. We determine further
improvements on PDFs which may be obtained from future HERA data (including
measurements of $F_L$), and from combining present and future HERA data with
present and future hadron collider data. We review the current status of
knowledge of higher (NNLO) QCD corrections to perturbative evolution and
deep-inelastic scattering, and provide reference results for their impact on
parton evolution, and we briefly examine non-perturbative models for parton
distributions. We discuss the state-of-the art in global parton fits, we assess
the impact on them of various kinds of data and of theoretical corrections, by
providing benchmarks of Alekhin and MRST parton distributions and a CTEQ
analysis of parton fit stability, and we briefly presents proposals for
alternative approaches to parton fitting. We summarize the status of large and
small x resummation, by providing estimates of the impact of large x
resummation on parton fits, and a comparison of different approaches to small x
resummation, for which we also discuss numerical techniques.
The magnetic-dipole transition probabilities between the fine-structure levels (1s{sup 2}2s{sup 2}2p) {sup 2}P{sub 1/2}-{sup 2}P{sub 3/2} for B-like ions and (1s{sup 2}2s2p) {sup 3}P{sub 1}-{sup ...3}P{sub 2} for Be-like ions are calculated. The configuration-interaction method in the Dirac-Fock-Sturm basis is employed for the evaluation of the interelectronic-interaction correction with negative-continuum spectrum being taken into account. The 1/Z interelectronic-interaction contribution is derived within a rigorous QED approach employing the two-time Green function method. The one-electron QED correction is evaluated within framework of the anomalous magnetic-moment approximation. A comparison with the theoretical results of other authors and with available experimental data is presented.
Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality and crystal ...symmetry. The family of semiconducting transition metal dichalcogenides is an especially promising platform for fundamental studies of two-dimensional (2D) systems, with potential applications in optoelectronics and valleytronics due to their direct band gap in the monolayer limit and highly efficient light-matter coupling. A crystal lattice with broken inversion symmetry combined with strong spin-orbit interactions leads to a unique combination of the spin and valley degrees of freedom. In addition, the 2D character of the monolayers and weak dielectric screening from the environment yield a significant enhancement of the Coulomb interaction. The resulting formation of bound electron-hole pairs, or excitons, dominates the optical and spin properties of the material. Here recent progress in understanding of the excitonic properties in monolayer TMDs is reviewed and future challenges are laid out. Discussed are the consequences of the strong direct and exchange Coulomb interaction, exciton light-matter coupling, and influence of finite carrier and electron-hole pair densities on the exciton properties in TMDs. Finally, the impact on valley polarization is described and the tuning of the energies and polarization observed in applied electric and magnetic fields is summarized.
Exciton valley Hall effect is the spatial separation of the valley-tagged excitons by a drag force. Usually, the effect is associated with the anomalous velocity acquired by the particles due to the ...Berry curvature of the Bloch bands. Here we show that the anomalous velocity plays no role in the exciton valley Hall effect, which is governed by the side-jump and skew scattering. We develop a microscopic theory of the exciton valley Hall effect in the presence of a synthetic electric field and phonon drag and calculate all relevant contributions to the valley Hall current also demonstrating the cancellation of the anomalous velocity. The sensitivity of the effect to the origin of the drag force and to the scattering processes is shown. We extend the drift-diffusion model to account for the valley Hall effect and calculate the exciton density and valley polarization profiles.
The nonlinear optical and optoelectronic properties of graphene with the emphasis on the processes of harmonic generation, frequency mixing, photon drag and photogalvanic effects as well as ...generation of photocurrents due to coherent interference effects, are reviewed. The article presents the state-of-the-art of this subject, including both recent advances and well-established results. Various physical mechanisms controlling transport are described in depth including phenomenological description based on symmetry arguments, models visualizing physics of nonlinear responses, and microscopic theory of individual effects.
For many applications of intense electron beams, including flash radiography and free-electron lasers, multikiloampere currents and low emittance are required. The report deals with the development ...of an injector ensuring these demands. Design parameters of the injector are 800 keV beam energy, 2...5 kA current, 80 ns pulse flat top and 100 Hz repetition rate. The average power of the series of pulses is 40 kW. The injector contains seven induction modules in series to generate 0.8 MV diode potential. The voltage contributions of seven modules, at 120 kV each, are summed along the cathode stem as it threads through the seven units. The modules use amorphous alloy and permalloy cores. The injector has been designed to provide two modes of operation: with a low and high current electron beam respectively. A velvet cathode and a mesh-less anode are used to produce an electron beam with the current of 2 kA and the brightness of 2.4 10/sup 3/A/(cm rad)/sup 2/ in the first mode. A 800 keV, 5 kA electron beam is derived by a mesh anode in the second mode. The modules of the induction injector and its parameters are described in this report.
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