Search results for " Polarization"
showing 10 items of 668 documents
Position-space approach to hadronic light-by-light scattering in the muon $g-2$ on the lattice
2016
The anomalous magnetic moment of the muon currently exhibits a discrepancy of about three standard deviations between the experimental value and recent Standard Model predictions. The theoretical uncertainty is dominated by the hadronic vacuum polarization and the hadronic light-by-light (HLbL) scattering contributions, where the latter has so far only been fully evaluated using different models. To pave the way for a lattice calculation of HLbL, we present an expression for the HLbL contribution to $g-2$ that involves a multidimensional integral over a position-space QED kernel function in the continuum and a lattice QCD four-point correlator. We describe our semi-analytic calculation of t…
Towards extracting the timelike pion form factor on CLS 2-flavour ensembles
2016
Results are presented from an ongoing study of the $\rho$ resonance. We use the distillation approach in order to create correlator matrices involving $\rho$ and $\pi\pi$ interpolators. The study is done in a centre-of-mass frame and several moving frames. We are able to extract energy levels by solving the GEVP of those correlator matrices. The initial exploratory study is being done on a CLS 2-flavour lattice with a pion mass of $451$ $\mathrm{MeV}$ using $\mathcal{O}(a)$ improved Wilson fermions. One aim of this work is to extract the timelike pion form factor after applying the L\"uscher formalism. We also plan to integrate this study with the existing Mainz programme for the calculatio…
The radiative return at phi- and B-factories: FSR for muon pair production at next-to-leading order
2004
Muon pair production through the radiative return is of importance for a measurement of the hadronic production cross section in two ways: it provides an independent calibration and it may give rise to an important background for a measurement of the pion form factor. With this motivation the Monte Carlo event generator PHOKHARA is extended to include next-to-leading order radiative corrections to the reaction $e^+e^-\to \mu^+\mu^-\gamma$. Furthermore, virtual ISR corrections to FSR from pions are introduced, which extends the applicability of the generator into a new kinematical regime. Finally, the effect of photon vacuum polarization is introduced into this new version of the generator.
The spin structure of the nucleon
2005
An introduction to deep inelastic scattering experiments investigating the spin structure of the proton and the neutron is given. Discussed are measurements with longitudinally polarized targets to determine the spin structure functiong 1 and sum rules and to do pQCD analyses with inclusive data, while a flavour separation and first extractions of the gluon polarization are performed with semi-inclusive data.
Polarized Structure Functions and the Nucleon Spin
1995
The link between the light-cone momentum distributions of constituent quark models and their corresponding parton distributions is used to study the polarized structure functions g 1 of proton and neutron. The formalism allows to analyze the effects of the structure of the quark model wave function and thus we discuss the SU (6) breaking mechanism associated with the One Gluon Exchange and large D-state admixtures originated in pionic models. We analyze the contribution to these structure functions of the gluon polarization arising from the anomaly.
Nonadiabatic spin-transfer torque of magnetic vortex structures in a permalloy square
2014
The stationary displacement of a magnetic vortex core in a permalloy square caused by an ultrahigh direct current has been measured utilizing scanning electron microscopy with polarization analysis. Data have been analyzed for three different generic states of the Landau structure and up to a current density of $3\ifmmode\times\else\texttimes\fi{}{10}^{11}\mathrm{A}/{\mathrm{m}}^{2}$. This procedure allows for separating the effects caused by the Oersted field, the nonadiabatic, and the adiabatic spin-transfer torque. In addition, the spin polarization of the driving current $P=(65\ifmmode\pm\else\textpm\fi{}4)%$ is independently determined from the spin drift velocity of ${v}_{j}=(4.79\ifm…
A single hologram technique for the determination of absolute retardations in holographic photoelasticity
1975
A method for the determination of the absolute retardations families in photoelasticity. The method, which use real-time holographic interferometry, requires only one hologram for the observation of the absolute retardations over the whole model. This is achieved by viewing in the reconstruction process the loaded model through a polarizer. Where the polarization direction is parallel to one of the principal stresses, only the corresponding family of absolute retardations is observed. As an example of application the absolute retardations and stresses in a deep beam centrally loaded are determined.
The influence of the quarter wave plates in automated photoelasticity
2002
During the last decades, several methods have been proposed to automate photoelastic analyses. Some procedures are based on the circularly polarised light by using quarter wave plates. However, quarter wave plates are typically matched for a specific wavelength, and an error is introduced at different wavelengths. The error of quarter wave plates affects the measurement of isochromatic and isoclinic data. In this paper, the influence of the errors of quarter wave plates in some of the most common automated photoelastic methods is reviewed. The errors in the photoelastic data are given and the procedures to reduce, or eliminate, them are also suggested.
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…
Above threshold ionization of atomic hydrogen inns states with up to four excess photons
2010
In a high-intensity laser field an atom can absorb more photons than the minimum necessary for ionization. It is known as above threshold ionization (ATI). Theoretically it is the most difficult case to handle as we have to consider transitions in continuum. To study ATI we use the perturbation theory and Green's function formalism. We have derived the modified two-term Coulomb Green's function (CGF) Sturmian expansion. In each term explicit summation over all intermediate states is carried out. The transition amplitude may be obtained in a closed form. The generalized cross sections are evaluated for the photoionization of atomic hydrogen in ns states with up to four excess photons. Calcul…