Search results for "Excitation"
showing 10 items of 1290 documents
New sum rule for the nuclear magnetic polarizability
2015
I extend the well-known photonuclear sum rule that relates the strength of the photoexcitation of the giant dipole resonance in a nucleus to the number of elementary scatterers-nucleons to the case of virtual photons. The new sum rule relates the size of the magnetic polarizability of a nucleus to the slope of the transverse virtual photoabsorption cross section integrated over the energy in the nuclear range. I check this sum rule for the deuteron where necessary data is available, discuss possible applications and connection with other sum rules postulated in the literature.
The Drell-Hearn-Gerasimov sum rule and the constituent quark model
1993
The helicity structure function of the nucleon has been calculated for the constituent quark model and compared to the prediction of the Drell-Hearn-Gerasimov sum rule. The multipole decomposition of the sum rule shows large cancellations between different resonances. The small isoscalar-isovector contribution is related to the admixture of aD-state (“bag deformation”) in the nucleon's wave function. The calculations indicate a relatively slow saturation of this part of the sum rule with excitation energy.
Recent result from the A2 collaboration at MAMI
2016
The A2 Collaboration at the Mainz Microtron MAMI is measuring photon absorption cross section using circularly and linearly polarized photons up to energies of 1.6 GeV. The photons are produced in the ‘Bremsstrahlungs’ process, the energy is determined by a dedicated tagging system. The Crystal Ball-TAPS detector system with its high capability to cope with multi photon final states is used to acquire data with a variety of nonpolarized and spin polarized targets. Physical goals are the investigation of the nucleons excitation spectrum via single and double meson photoproduction and in addition a detailed determination of meson decays in precision experiments. We have started a program to m…
Where Do Diffractive Nucleons Go?
1974
Nucleon and pion-nucleon distributions from the diffractive component in pp collisions are analysed. Diffractive events are assumed to come from a mechanism pp → N*p, in which a proton is diffractively excited to a nova N*. The decay properties of N* are determined by assuming that a Pomeron-proton collision behaves as a proton-proton collision. Correlations within the diffractive component are computed and seen to be numerically small. Even interference with the pionization component does not reproduce the observed pattern of pion (in the plateau)-proton (in the fragmentation region) correlations. This may imply the existence of long-range correlations within the pionization component.
A universal relation for power-law confining interactions
1993
Abstract Power-law ( r α ) confining interactions are considered in the Schrodinger equation with a hyperangular momentum, which corresponds to the lowest order of the hyperspherical harmonic expansion for an N -particle system. It is shown that the product of the first odd-parity excitation energy times the mean square radius is independent of the exponent α of the potential within a few percent. This universal relation is extended to other states.
Excitation and ionization of Rydberg atoms by short half-cycle pulses
1999
Simple semiclassical formulas are derived for the probability of excitation and ionization of Rydberg atoms irradiated by a half-cycle pulse whose duration is shorter than the Kepler period. The calculated ionization probabilities are in good agreement with the experimental data of Jones, You, and Bucksbaum [Phys. Rev. Lett. 70, 1236 (1993)] and with previous calculations.
Transient spatio-temporal domain patterns in permalloy microstructures induced by fast magnetic field pulses
2006
The response of multidomain flux-closure structures (Landau states) in micrometer-scale magnetic thin-film elements upon fast magnetic field pulses leads to the excitation of magnetic eigenmodes and to short-lived domain patterns that do not occur in quasi-static remagnetisation. Such transient spatio-temporal patterns and particular detail features are discussed. Examples are presented for permalloy platelets of various shapes and sizes. Dynamic series of domain patterns with variable delay between field pulse and photon pulse (synchrotron radiation) have been taken using stroboscopic XMCD-PEEM. Precessional remagnetisation starts at the domain boundaries. The damped precessional motion pr…
Robustness of plasmonic angular momentum confinement in cross resonant optical antennas
2015
Using a combination of photoemission electron microscopy and numerical simulations, we investigated the angular moment transfer in strongly enhanced optical near-fields of artificially fabricated optical antennas. The polarization dependence of the optical near-field enhancement has been measured in a maximum symmetric geometry, i.e., excitation by a normal incident planar wave. Finite-difference time-domain simulations for the realistic antenna geometries as determined by high-resolution electron microscopy reveal a very good agreement with experimental data. The agreement confirms that the geometrical asymmetries and inhomogeneities due to the nanoscale fabrication process preserve the ci…
Carrier localization effect in polarized InGaN multiple quantum wells
2005
Carrier localization effects in polarized InGaN/GaN multiple quantum wells (MQWs) were investigated as a function of well width, d, and In content, x. Using photoreflectance (PR), photoluminescence (PL), PL excitation (PLE), selective excitation of PL, PL excitation power, and time-resolved PL spectroscopy, the dominance of the localization effect against the built-in field effect on carrier recombination dynamics in InxGa1–xN MQWs of different well width (d = 2.0–4.0 nm, x ≈ 0.15) and In content (x ≈ 0.22–0.27, d = 2.5 nm) was revealed. Based on the modeling of the PL spectra by Monte Carlo simulation of exciton hopping and the spectroscopic reference provided by PR, increased In content a…
Resonant Rayleigh scattering in quantum well structures
1996
Abstract We report continuous wave experiments on resonant Rayleigh scattering (RRS) performed on high quality GaAs AlGaAs quantum well structures. The simultaneous measurement of the resonant Rayleigh scattering and of the photoluminescence excitation (PLE) allows us to resolve very small differences between the two spectra. We show that, even in very good samples, there is a small but detectable Stokes shift of the RRS profile with respect to the PLE. It is also found that the RRS profile has a smaller linewidth and is sensitive to bound exciton transitions which are not detectable in the PLE. We compare our data with previous findings and discuss possible origins of the Stokes shift.