Search

Manifestation of the heavy 3/2-spin lepton $(h^\pm)$, as possible virtual intermediate state in Feynmann diagrams, have been searched in the $e^+\,e^-\to \gamma\,\gamma$ reaction at high energies and large photon angles. The spin-vector field $\Psi_\alpha$ of the 3/2-lepton is described by the Rarita-Schwinger one and phenomenological Lagrangian of $h^\pm\, e^\pm \, \gamma$-interaction is chosen similarly to interaction of $\Delta$ isobar with nucleon and $\gamma$ quant. It is described by two constants with dimension $[M^{-1}]$ and $[M^{-2}].$ The differential cross section and polarization asymmetries have been calculated for the case when both beams are polarized longitudinally along their directions, as well transversally, in the reaction plane, and normally, perpendicularly to it. Numerical estimations are performed in wide diapason of the collision energy and parameters entering phenomenological Lagrangian., Comment: 17 pages, 7 figures

The nonresonant mechanism in the reactions $e^+\,e^-\to \pi^-\,p\,\bar{n}$ and $e^+\,e^-\to \pi^+\,n\,\bar{p}$ is investigated in frame of the one-photon exchange approximation. The description of the hadronic phase space and the invariant amplitude formalism, earlier developed for the neutral pion channel, are applied here. Some modifications are required to fulfill the invariance and to account for an additional contribution due to diagram with the pion pole. Two different variants which lead to dipole and monopole asymptotic behaviour of the pion electromagnetic form factor, are considered. The double and single distributions over the invariant variables as well the total cross section, are obtained. The results are plotted for $s=$5,\,6,\,10,\,16\, GeV$^2$. The calculations are performed for the $\pi^-\,p\,\bar{n}$ channel and the rules to proceed to the $\pi^+\,n\,\bar{p}$ channel are formulated for every distribution., Comment: 30 pages, 9 figures

The differential cross section and polarization observables for the elastic reaction induced by deuteron scattering off electrons at rest are calculated in the one-photon-exchange (Born) approximation. Specific attention is given to the kinematical conditions, that is, to the specific range of incident energy and transferred momentum. The specific interest of this reaction is to access very small transferred momenta. Numerical estimates are given for polarization observables that describe the of single- and double-spin effects, provided that the polarization components (both, vector and tensor) of each particle in the reaction are determined in the rest frame of the electron target., Comment: 39 pages 11 figures, AddedvAcknowledgment section

The dependence of the nucleon polarization in the reaction $e^+ + e^- \to N + \bar{N} +\pi^0 $ over different invariant variables in frame of the non-resonant mechanism, has been derived. The nucleon polarization is expressed in terms of six invariant complex amplitudes, assuming the conservation of the hadron electromagnetic currents and the P-invariance of the hadron electromagnetic interaction. An inclusive experimental setup when the proton (or the antiproton) and the pion are detected in coincidence is considered. Numerical estimations were performed for the so called normal polarization in the energy range from threshold up to $s=16$ GeV$^2$, using a specific parametrization of the nucleon electromagnetic form factors and taking into account the unpolarized differential cross section of the non-resonant mechanism, as previously calculated., Comment: 18 pages, 10 figures

The general analysis of the differential cross section and various polarization observables is performed for the process $e^+ + e^- \to N + \bar N +\pi^0 $ assuming that the annihilation occurs through the exchange of one virtual photon. The dependence of the differential distributions over invariant variables is derived for the reaction $e^+ + e^- \to N + \bar N +\pi^0 $ in the so-called non-resonant mechanism, applying the conservation of the hadron electromagnetic currents and the P-invariance of the hadron electromagnetic interaction. The detection in an exclusive experimental set up where the nucleon (or antinucleon) and pion are detected in coincidence is considered. A number of single and double differential distributions have been calculated analytically and numerical estimates are given for the $p\bar p\pi^0$ and $n\bar n\pi^0$ channels, in the Born (non-resonant) approximation, in the energy range from threshold up to $s=16$ GeV$^2$., Comment: 29 pages, 9 figures

The triplet-like QED processes $\gamma + \ell_i \to \ell^+_j \ell^-_j + \ell_i$ with $i\neq j,$ and $i=e, \mu,$ $j=e, \mu,\tau$ has been investigated as the reactions where a dark photon, $A'$, is produced as a virtual state with subsequent decay into a $\ell^+_j \ell^-_j-$-pair. This effect arises due to the so-called kinetic mixing and is characterized by the small parameter $\epsilon$ describing the coupling strength relative to the electric charge $e$. The main advantage of searching $A'$ in these processes is that the background to the $A'$ signal is pure QED. Concerning $A'$, we consider its contribution in the Compton-type diagrams only since, in this case, the virtual dark photon has time-like nature and its propagator has the Breit-Wigner form. So, near the resonance, $A'$ can manifest itself. The contribution of $A'$ in the Borsellino diagrams is negligible since, in this case, the virtual dark photon is space-like, the $A'$ propagator does not peak and the effect is proportional, at least, to $\epsilon^2$. We calculate the distributions over the invariant mass of the produced $\ell^+_j \ell^-_j-$ pair and search for the kinematical region where the Compton-type diagrams contribution is not suppressed with respect to the Borsellino ones. The value of the parameter $\epsilon$ is estimated as a function of the dark photon mass for a given number of events., Comment: 27 pages, 13 figures, accepted for publication in Phys Rev D

The polarization effects in the one-meson radiative decay of the polarized $\tau$ lepton, $\tau^-\to\pi^-\gamma\nu_{\tau}$, have been investigated. We present the analytical results for the $t-$distribution of the partial differential widths, which responsible for different polarization phenomena, in the case of the photon energy cut: $\omega>X$. These quantities depend on the invariant mass squared $t$ of the pseudoscalar meson and photon and the photon energy cut $X.$ Our analytical formulae, in terms of the weak vector and axial-vector form factors, describing the structure-dependent part of the decay amplitude, are valid also for the decay $\tau^{\pm}\to K^{\pm}\,\nu_\tau\,\gamma$ after trivial substitutions of the corresponding constants. We demonstrate the essential decrease of the inner bremsstrahlung contribution in comparison with the structural one with increase of the photon cut energy. In numerical calculations the vector and axial-vector form factors are determined using the chiral effective theory with resonances (R$\chi$T)., Comment: 20 pages, 5 figures

General expressions for the unpolarized differential cross section and for various polarization observables in the coherent pseudoscalar meson photo- and electroproduction on the deuteron target have been obtained in one-photon-exchange approximation. The spin structure of the matrix element is explicitly derived in terms of structure functions. The correspondence with the helicity amplitudes is given. The polarization effects have been investigated for the case of a longitudinally polarized electron beam and vector or tensor polarized deuteron target. The polarization (vector or tensor) of the scattered deuteron for the case of unpolarized or a longitudinally polarized electron beam is also considered. In the case of the photoproduction reaction, we consider linearly, circularly or elliptically polarized photon beam. Numerical estimations have been done for the unpolarized differential cross section and for some polarization observables., Comment: 40 pages, 5 figures. arXiv admin note: substantial text overlap with arXiv:0812.3522, arXiv:hep-ph/0412112

The differential cross section for elastic scattering of deuterons on electrons at rest is calculated taking into account the QED radiative corrections to the leptonic part of interaction. These model-independent radiative corrections arise due to emission of the virtual and real soft and hard photons as well as to vacuum polarization. We consider an experimental setup where both final particles are recorded in coincidence and their energies are determined within some uncertainties. The kinematics, the cross section, and the radiative corrections are calculated and numerical results are presented., Comment: 18 pages, 10 figures, 3 tables. arXiv admin note: substantial text overlap with arXiv:1612.02139

The process of the triplet production on a free electron, $\gamma e^-\to e^+e^-e^-$, has been investigated as a reaction where a dark photon, $A'$, is produced as a virtual state with subsequent decay into a $e^+e^-$-pair. This effect arises due to the so-called kinetic mixing and is characterized by the small parameter $\epsilon$ describing the coupling strength relative to the electric charge e. The search of $A'$ in this process has advantage because the background to the $A'$ signal is pure QED. This QED background is described by eight Feynman diagrams taking into account the identity of final electrons. As concern $A'$, we leave its contribution in Compton-like diagrams only since, in this case, the virtual dark photon is time-like and its propagator has the Breit-Wigner form. So, near the resonance $A'$ can manifest itself. The contribution of $A'$ in Borsellino diagrams is negligible since, in this case, the virtual dark photon is space-like, the $A'$ propagator does not peak and effect is proportional at least to $\epsilon^2$. We calculate the distributions over the invariant masses of the both produced $e^+e^-$ pairs and search for the kinematical region where the Compton-like diagrams contribution is not suppressed as compared with the Borsellino one. We estimate what value of the parameter $\epsilon$, as a function of the dark photon mass, can be obtained at given number of the measured events., Comment: 24 pages, 7 figures

The emission of the hard photon by the initial state is considered. The nucleon polarization and the differential cross sections for some experimental conditions have been calculated. The case of the emission of the collinear (with respect to the direction of the electron beam momentum) photon is considered separately. The differential cross section, the nucleon polarization, the correlation coefficients for both polarized nucleons (provided the electron beam is unpolarized or longitudinally polarized), the transfer polarization from the longitudinally polarized electron beam to the nucleon have been calculated. The photon energy distribution for the reaction $e^+e^-\to h_1h_2\gamma $, where $h_1 $ and $h_2$ are some hadrons for the case of the collinear photon, emitted in the initial state, has been calculated. As $h_1h_2$ final state we considered some channels, namely: two spinless mesons (for example, $\pi^+\pi^-, K^+K^-$), two spin--one particles (for example, $\rho^+\rho^-, d\bar d$), the $\pi a_1(1260)$ and $\Delta(1232)\bar N$ channels. The photon energy distributions are calculated in terms of the form factors of the $\gamma^*\to h_1h_2$ transition ($\gamma^*$ is the virtual photon)., Comment: 24 pages, 1 figure, typos corrected, added references

The differential cross section for elastic scattering of protons on electrons at rest is calculated taking into account the QED radiative corrections to the leptonic part of interaction. These model-independent radiative corrections arise due to emission of the virtual and real soft and hard photons as well as to vacuum polarization. We analyze an experimental setup when both the final particles are recorded in coincidence and their energies are determined within some uncertainties. The kinematics, the cross section, and the radiative corrections are calculated and numerical results are presented., Comment: 27 pages, 10 figures. The title of the article has been changed. Improved the quality of figures. An article without an appendix is approved for publication in the Phys.Rev.C

Polarized and unpolarized observables in the process of the triplet photoproduction on a free electron, $\gamma +e\to e+e+e$, have been calculated in the laboratory system. These observables are calculated in the approximation when the Borsellino and $\gamma -e$ diagrams are taken into account. Using the method of the invariant integration over the produced electron-positron pair variables, the different distributions were obtained in the analytical form. We obtain the double distribution over the $q^2$ (the square of the four-momentum transfer to the recoil electron) and $Q^2$ (the created $e^+e^-$-pair invariant mass squared) variables, and single distributions over $q^2$ or $Q^2$ variables. We consider the following cases: unpolarized particles, the photon beam is linearly polarized and circularly polarized photon beam interacts with a polarized electron target. The influence of the $\gamma -e$ terms on the calculated observables has been investigated. The possibility to use this process for the measurement of the circular polarization of the high-energy photon beam is also considered. The numerical estimations of various polarization observables have been done., Comment: 34 pages,11 figures, new version with minor changes

Various distributions over the angles of the emitted photon, especially over the azimuthal angle, in the one-meson radiative decay of the polarized $\tau$ lepton, $\tau^-\to\pi^-\gamma\nu_{\tau}$, have been investigated. In connection with this, the photon phase space is discussed in more detail since in the case of the polarized $\tau$ lepton it is not trivial. The decay matrix element contains both the inner bremsstrahlung and the resonance (structural) contributions. The azimuthal dependence of some observables have been calculated. They are the asymmetry of the differential decay width caused by the $\tau$ lepton polarization, the Stokes parameters of the emitted photon itself and the correlation parameters describing the influence of $\tau$-lepton polarization on the photon Stokes parameters. The numerical estimation was done in the $\tau$ lepton rest frame for arbitrary direction of the $\tau$ lepton polarization 3-vector. The vector and axial-vector form factors describing the structure-dependent part of the decay amplitude are determined using the chiral effective theory with resonances (R$\chi$T). It was found that the features of the azimuthal distributions allows to separate various terms in the spin-dependent contribution. The so-called up-down and right-left asymmetries are also calculated., Comment: 29pages, 12 figures. To be published in JETP