Azimuthal asymmetry in polarized leptoproduction and spin-dependent structure functions

Asymmetry in azimuthal angle distribution of hadrons produced in polarized deep-inelastic lepton-nucleon scattering is discussed. Significant polarization effects are predicted. It is pointed out that such effects can be used as another method to measure the spin-dependent structure functions of the nucleons.     

Measurement of the photon asymmetry in capture of polarized neutrons by deuterons

We have looked for parity violation in neutron capture by deuterons. Parity violation would produce an asymmetric angular distribution of the 6.24 MeV photon about the spin direction of the neutron of the form (1 + A cos θ), where θ is the angle between photon momentum and incident neutron spin. We find A = (4.2 ± 3.8) × 10⁻⁶, where the error is the statistical error of counting. If we include an estimate of systematic errors, the error increases to ± 3.9. In addition there is an overall scale error which can be described by multiplying the result by (1 ± 0.15). The value is one standard deviation larger than predictions based on either Cabbibo or gauge theoretical models, which give values of A between 10⁻⁶ and 10⁻⁷.     

Electron–positron pair production by linearly polarized photon in the nuclear field

Process of lepton pair production by polarized photon on nuclei can be used to measure the degree of linear polarization of high energy photon. The differential cross section and the analyzing power are calculated with taking into account higher powers of expansion in Zα. Pure Coulomb and screened potential are considered. The results are illustrated in terms of asymmetry. The screening effect as well as the effect of higher orders expansion in Zα   is shown to vanish in limit of pair emission angles exceeding m/ω$m/\omega$.     

Feasibility of experimental investigation of nonlinear QED processes—photon emission by electrons and pair creation by photons in strong laser field

On the basis of the theory of nonlinear QED processes occurring in collisions of high-energy electrons and γ-quanta with a strong laser pulse [1], the feasibility of their experimental investigation is discussed. The use of existing ⋍100 GeV electron beam accelerators and terawatt lasers of ultrashort pulses enables one to attain optimal values for the parameters and to have fields ⋍F_o=m²c³/ħe act on the electron. The choice and organization of laser system, synchronization of accelerator and laser operation, distributions of created γ-quanta and e⁺e⁻-pairs in different variables and parameters, their dependence on polarization of laser target and incident particles, background problems, and other questions connected with carrying out the experiments are discussed. Translated from preprint No. 11, 1993 of the Lebedev Physics Institute, Moscow, Russia.     

Toward a nonlinear theory of acceleration of charged particles in a linearly polarized EH-ubitron field

The motion of charged particles in a linearly polarized EH-ubitron field with sinusoidal time dependence of the variable component of the magnetic field is investigated. It is shown that, depending on the parameters of the system and the initial conditions of entry of the particle into the EH-field region, three different types of motion are possible: ballistic motion, capture in the vicinity of one of the maxima of the magnetic field, and escape of particles from the EH-field region. An analytical expression is found for the criterion determining the type of motion of the particles, along with analytical solutions for the energy of the particles in the approximation of slow variation of the magnetic field amplitude in time. Peculiarities of the motion of the particles in EH fields with arbitrary rate of change of the magnetic field amplitude in time are investigated numerically. Zh. Tekh. Fiz. 69, 87–93 (January 1999)     

Laser Compton scattering for a linearly polarized laser

Laser Compton light sources are potential candidates for the next generation of high-brightness X or γ-ray sources. When increasing the laser power to obtain intense X-ray laser, nonlinear Compton scattering happens. Nonlinear Compton scattering of linearly polarized laser beam is discussed in this paper. A complete transition probability formula is introduced and the polarization properties of final photons are discussed for different conditions.     

Laser Compton scattering for a linearly polarized laser

Laser Compton light sources are potential candidates for the next generation of high-brightness X or γ-ray sources. When increasing the laser power to obtain intense X-ray laser, nonlinear Compton scattering happens. Nonlinear Compton scattering of linearly polarized laser beam is discussed in this paper. A complete transition probability formula is introduced and the polarization properties of final photons are discussed for different conditions.     

Azimuthal asymmetry of direct photons in intermediate energy heavy-ion collisions

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have presented a first calculation of azimuthal asymmetry, characterized by directed transverse flow parameter F   and elliptic asymmetry coefficient v₂$v_2$, for proton–neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive F   and negative v₂$v_2$ of direct photons are illustrated and they seem to be anti-correlated to the corresponding free proton's flow.     

Optimization of focusing of linearly polarized light

We show that, by adding a π-phase shift to one-half of a linearly polarized beam, the roles of the transversal and longitudinal field components of the focused beam are interchanged, resulting in better focusing of the longitudinal component in the direction perpendicular to the phase jump line. For this component the scheme produces a spot with FWHM >15% smaller than a spot generated with either linearly or radially polarized light for any NA. The scheme has a similar advantage when applied to circularly polarized light, and it holds for both a plane wave and a realistic case of a Gaussian incident beam. This technique may find applications when using recording media responsive to the longitudinal field only, particularly in read/write for optical storage where the resolution in one transverse dimension is most important.     

Azimuthal asymmetry of direct photons in high energy nuclear collisions

We show that a sizable azimuthal asymmetry, characterized by a coefficient nu2, is to be expected for large pT direct photons produced in noncentral high energy nuclear collisions. This signal is generated by photons radiated by jets interacting with the surrounding hot plasma. The anisotropy is out of phase by an angle pi/2 with respect to that associated with the elliptic anisotropy of hadrons, leading to negative values of nu2. Such an asymmetry, if observed, could be a signature for the presence of a quark gluon plasma and would establish the importance of jet-plasma interactions as a source of electromagnetic radiation.     

Measurements of the QED structure of the photon

The structure of both quasi-real and highly virtual photons is investigated using the reaction , proceeding via the exchange of two photons. The results are based on the complete OPAL dataset taken at centre-of-mass energies close to the mass of the Z boson. The QED structure function and the differential cross-section for quasi-real photons are obtained as functions of the fractional momentum x from the muon momentum which is carried by the struck muon in the quasi-real photon for values of ranging from 1.5 to 400 GeV. The differential cross-section for highly virtual photons is measured for GeV and GeV, where and are the negative values of the four-momentum squared of the two photons such that . Based on azimuthal correlations the QED structure functions and for quasi-real photons are determined for an average of 5.4 GeV. Received: 8 February 1999 / Published online: 28 September 1999     

Motion invariants for a charge in a linearly polarized wave field

Six motion integrals for a relativistic charge in the field of a transverse linearly polarized electromagnetic wave propagating with an arbitrary phase velocity u>c were obtained by solving the canonical equations of motion. On the basis of these integrals, the charge trajectory as a function of the wave phase is analyzed in a fixed coordinate system. The coordinates, time, and phase are related by elliptic functions.     

Topological phase for spin systems in a linearly polarized RF field

The Permsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 3, pp. 342–344, March, 1991.     

Natural orbitals of helium in linearly polarized laser fields

Practicable equations of motion for the natural orbitals of a spin-singlet helium atom in a linearly polarized laser field are presented. The cylindrical symmetry of the two-electron problem with quantum number M = 0 is shown to yield a sparse expansion of natural orbitals in spherical harmonics. This optimization facilitates the propagation of renormalized natural orbitals of the helium atom. As a demonstration, the equations of motion are solved for a high-harmonic-generation process. In addition to the expected plateau from the single-active-electron picture, the spectrum of emitted radiation features a second plateau at higher harmonic orders.     

Astrophysically relevant processes in Lorentz-violating QED

We consider quantum electrodynamics with violation of Lorentz in-variance. We calculate the rates of photon decay along with the cross sections of electron-positron pair production on background radiation and in the Coulomb field. The latter process is essential for detection of photon-induced air showers in the atmosphere. The results of this work are written in [1] in details.     

Azimuthal asymmetry of coherent Cherenkov radiation from a tilted bunch

Modern accelerator technologies may provide electron beams consisting of ultrashort bunches with transverse sizes, which are much larger than longitudinal sizes. The spectral-angular characteristics of coherent Cherenkov radiation (CChR) produced by such bunches have thus been considered. We simulated the characteristics of CChR and those from a single charge on the basis of the polarization current model, which allowed us to consider finite sizes for the Cherenkov radiator. We calculated the angular distribution of the CChR from a bunch tilted by angle ψ, with respect to the velocity direction, with the assumption of a 3-D Gaussian charge distribution in the bunch. Contrary to the azimuthally symmetrical distribution of conventional ChR, a strong azimuthal asymmetry was observed in the CChR from the tilted bunch. The maximal yield of the CChR may be achieved if the tilt angle ψ coincides with the Cherenkov angle ${\mathrm{\Theta }}_{\text{ch}}=\arccos ?(1/n\beta )$, βc is the charge velocity and n is the refraction index.     

Coherent effects in multiple scattering of linearly polarized light

Comparing the stochastic Monte Carlo technique with the iteration procedure for solving the Bethe-Salpeter equation in the framework of numerical simulation, the time correlation function and the interference component of the coherent backscattering of a linearly polarized light wave in a multiply scattering medium are calculated. The results of the simulation agree well with theoretical results obtained by generalizing the Milne solution, as well as with experimental data.     

L波段高功率线极化径向线阵列天线理论分析与数值模拟

探索了L波段的高功率线极化径向线阵列天线。基于三角形栅格形式实现了径向线圆形平面阵列天线,分析并给出了径向线并联馈电网络,并以同轴馈电的水平单圆环线极化天线为基础,利用径向线并联馈电网络设计出了间距小于一个波长下L波段高功率线极化径向线阵列天线。研究结果表明：这种结构实现径向线阵列天线的线极化辐射是可行的,该天线在中心频率1.57 GHz下,增益为19.97 dBi,轴比为-52.06 dB,反射系数为0.105 2;在1.37～1.77 GHz的频率范围内增益大于18.64 dBi,轴向轴比值小于-46.45 dB。