Search

The general analysis of the differential cross section and various polarization observables is performed for the process $e^+ + e^- \to N + \bar N +π^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 +π^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 $p\bar pπ^0$ and $n\bar nπ^0$ channels, in the Born (non-resonant) approximation, in the energy range from threshold up to $s=16$ GeV$^2$., 29 pages, 9 figures

The dependence of the nucleon polarization in the reaction $e^+ + e^- \to N + \bar{N} +π^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., 18 pages, 10 figures

The polarization effects in the one-meson radiative decay of the polarized $��$ lepton, $��^-\to��^-����_��$, 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: $��>X$. 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 $��^{\pm}\to K^{\pm}\,��_��\,��$ 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$��$T)., 20 pages, 5 figures

The triplet-like QED processes $��+ \ell_i \to \ell^+_j \ell^-_j + \ell_i$ with $i\neq j,$ and $i=e, ��,$ $j=e, ��,��$ 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 $��$ 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 $��^2$. 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 $��$ is estimated as a function of the dark photon mass for a given number of events., 27 pages, 13 figures, accepted for publication in Phys Rev D

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 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 $e^+e^-\to h_1h_2��$, 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, $��^+��^-, K^+K^-$), two spin--one particles (for example, $��^+��^-, d\bar d$), the $��a_1(1260)$ and $��(1232)\bar N$ channels. The photon energy distributions are calculated in terms of the form factors of the $��^*\to h_1h_2$ transition ($��^*$ is the virtual photon)., 24 pages, 1 figure, typos corrected, added references

Various distributions over the angles of the emitted photon, especially over the azimuthal angle, in the one-meson radiative decay of the polarized $��$ lepton, $��^-\to��^-����_��$, have been investigated. In connection with this, the photon phase space is discussed in more detail since in the case of the polarized $��$ 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 $��$ lepton polarization, the Stokes parameters of the emitted photon itself and the correlation parameters describing the influence of $��$-lepton polarization on the photon Stokes parameters. The numerical estimation was done in the $��$ lepton rest frame for arbitrary direction of the $��$ 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$��$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., 29pages, 12 figures. To be published in JETP

The polarization effects in the one-meson radiative decay of the polarized $��$ lepton, $��^-\to��^-����_��$, are investigated. The inner bremsstrahlung and structural amplitudes are taken into account. The asymmetry of the differential decay width caused by the $��$ lepton polarization and the Stokes parameters of the emitted photon itself, are calculated depending on the polarization of the decaying $��$ lepton. The numerical estimation of these physical quantities was done for arbitrary direction of the $��$ lepton polarization 3-vector in the rest frame. 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$��$T)., 37 pages,7 figures

The dependence of the differential cross section and polarization observables in the $\bar N+N\to ��+e^++e^-$ reaction on the polarizations of the proton target and antiproton beam (the produced electron may be unpolarized or longitudinally polarized) have been derived in a general form using hadron electromagnetic current conservation and $P-$ invariance of the hadron electromagnetic interaction. The analysis was done for the case of an exclusive experimental setup where the produced electron and pion are detected in coincidence. The explicit dependence of all polarization observables on two, from five, kinematic variables (the azimuthal angle $��$ and the virtual-photon parameter $��$), have been obtained assuming one-photon-exchange. The application to the particular case of a mechanism which contains information on time-like proton form factors in the unphysical region is considered in the Born approximation., arXiv admin note: substantial text overlap with arXiv:1011.4013

The annihilation reaction $e^++e^-\rightarrow \bar ��+��$ is considered. The constraint on time-like $��$-meson form factors from the measurement done by the BaBar collaboration at $\sqrt{s}=10.5$ GeV is analyzed., 10 pages 3 figures

The expressions for the differential cross section and of the polarization observables for the reaction $\bar p+p\rightarrow e^++e^-$ are given in terms of the nucleon electromagnetic form factors in the laboratory system. Radiative corrections due to the emission of virtual and real soft photons from the leptons are also calculated. Unlike the center-of- mass system case, they depend on the scattering angle. Polarization effects are derived in the case when the antiproton beam, the target and the electron in the final state are polarized. Numerical estimations have been done for all observables for the PANDA experimental conditions using models for the nucleon electromagnetic form factors in the time-like region. The radiative corrections to the differential cross section are calculated as function of the beam energy and of the electron angle., Comment: 18 pages, 8 figures

We extend previous calculations of polarization observables for the annihilation reaction $\bar p +p\to \ell^{-}+\ell^{+}$ to the case of heavy leptons, such as the $\tau$-lepton. We consider the case when the beam and/or the target are polarized, as well as the polarization of the outgoing leptons. We give the dependence of the unpolarized cross section, angular asymmetry, and various polarization observables on the relevant kinematical variables in the center of mass and in the laboratory system, with particular attention to the effect of the mass induced terms., Comment: 25 pages, 8 figures

A general formalism is developed to calculate the cross section and the polarization observables for the reaction $\bar N+N\to ��+\ell^++\ell^-$. The matrix element and the observables are expressed in terms of six scalar amplitudes (complex functions of three kinematical variables) which determine the reaction dynamics. The numerical predictions are given in frame of a particular model in the kinematical range accessible in the PANDA experiment at FAIR., 19 pages, 4 figures

The differential cross section and the polarization observables for $��$--isobar production in the deuteron electrodisintegration process, $e^-+d\to e^-+��+N$, are calculated in a general formalism based on structure functions. The obtained expressions have a general nature, hold for one--photon--exchange, assuming P--invariance of the electromagnetic interaction and the conservation of the hadron electromagnetic current. The dependence of the differential cross section of the $e^-+d\to e^- +��+N$ reaction on the vector and tensor polarizations of the deuteron target with unpolarized and longitudinally polarized electrons is considered. The general dependence of the asymmetries on two of five kinematic variables, the azimuthal angle $��$ and $��$ (linear polarization of the virtual photon) is calculated. A similar analysis is performed for the polarization of the nucleon produced in $��^*d \to ��N$ reaction provided the electron beam is unpolarized or longitudinally polarized. Polarization effects, which are due to the strong $��N-$ interaction in the final state are calculated. The photoproduction of the $��$--isobar on the deuteron target has been considered in detail, as a particular case. The differential cross section and various polarization observables have been derived in terms of the reaction amplitudes. The polarization observables due to the linear and circular polarizations of the photon, when the deuteron target is arbitrarily polarized have been derived in terms of the reaction amplitudes. The polarization of the final nucleon is also considered., 52 pages

Using a general parametrization of the spin structure of the matrix element for the elastic $e^-+^4He$ scattering and for the annihilation $e^++e^-\to ��^++��^-$ reactions in terms of two complex amplitudes, we derive general properties of the observables in presence of two--photon exchange. We show that this mechanism induces a specific dependence of the differential cross section on the angle of the emitted particle. We reanalyze the existing experimental data on the differential cross section, for elastic electron scattering on $^4He$, in the light of this result., 15 pages 1 figure

A model independent formalism for the electron positron annihilation reaction $e^++e^-\to a_1(1260)+��$ has been derived. The differential and total cross sections and the elements of the spin--density matrix of the $a_1$-meson were calculated in terms of the electromagnetic form factors of the corresponding $��^*a_1��$ current. Simple models of $a_1$ form factors have been fitted to the available cross section data and they allow to give numerical predictions for the different observables., 19 pages, 6 figures Added formulas for axial meson decay in 3 pions Modified version to appear in PRC

The electron positron annihilation reaction into four pion production has been studied, through the channel $e^++e^-\to \bar ��+��$. The differential (and total) cross sections and various polarization observables for this reaction have been calculated in terms of the electromagnetic form factors of the corresponding $��^*����$ current. The elements of the spin--density matrix of the $��-$meson were also calculated. Numerical estimations have been done, with the help of phenomenological form factors obtained in the space--like region of the momentum transfer squared and analytically extended to the time-like region., 19 pages, 2 figures, to appear in Phys Rev C

Polarization observables for the reaction $\bar p+p\to e^++e^-$ are given in terms of three independent complex amplitudes, in presence of two photon exchange. General expressions for the differential cross section and the polarization observables are given and model independent properties are derived. Polarization effects depending on the polarization of the antiproton beam, the target and of the electron in the final state, have been calculated., Comment: 15 pages

We derive, in model independent way, the spin structure of the matrix element for the reaction of associative $��^+$ pentaquark production, $��^{\pm}+D\to ��^+ +��^{\pm}, $ in the threshold region and in collinear kinematics. The expressions for the polarization observables in this reaction are found assuming spin 1/2 and different parities for $��^+ .$ We have proved that such reaction can be used for a model independent determination of the P-parity of $��^+$ only by measuring the $��^+$ polarization. Other polarization observables, such as the dependence of the $��^{\pm}$ polarization on the vector and tensor deuteron polarizations, are insensitive to the $��^+$ parity in the considered kinematical conditions. All linear and quadratic relations between polarization observables in $��^{\pm}+\vec D\to ��^+ +\vec��^{\pm}(��^+ $ is unpolarized) do not depend on the parity of the $��^+$ pentaquark., 5 pages, 1 figure

General properties of the differential cross section and of the polarization observables are derived for the $e^++e^-\to N+\bar N$ reaction, in presence of two--photon exchange. Polarization effects are investigated for longitudinally polarized electron and polarized antinucleon and/or polarized nucleon in the final state. The single--spin asymmetry induced by the transverse polarization of the electron beam is also discussed., Comment: 18 pages

The coplete analysis of the model-independent leading radiative corrections to cross-section and polarization observables in semi-inclusive deep-inelastic electron-nucleus scattering with detection of a proton and scattered electron in coincidence has been performed. The basis of the calculations consists of the Drell-Yan like representation in electrodynamics for both spin-independent and spin-dependent parts of the cross-section in terms of the electron structure functions. The applications to the polarization transfer effect from longitudinally polarized electron beam to detected proton as well as to scattering by the polarized target are considered., Comment: 18p, to be published in JETP

Deep-inelastic events for the scattering of the longitudinally polarized electron by polarized proton with tagged collinear photon radiated from initial-state electron are considered. The corresponding cross-section is derived in the Born approximation. The model-independent radiative corrections to the Born cross-section are also calculated. Obtained result is applied to the case of elastic scattering., Comment: 14 pages, 2 figures, submitted to JETP