Search

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 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 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

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 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

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\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 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 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

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

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

The polarization effects in the one-meson radiative decay of the polarized $\tau$ lepton, $\tau^-\to\pi^-\gamma\nu_{\tau}$, are investigated. The inner bremsstrahlung and structural amplitudes are taken into account. The asymmetry of the differential decay width caused by the $\tau$ lepton polarization and the Stokes parameters of the emitted photon itself, are calculated depending on the polarization of the decaying $\tau$ lepton. The numerical estimation of these physical quantities was done for arbitrary direction of the $\tau$ 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$\chi$T)., Comment: 37 pages,7 figures

Model independent expressions for all polarization observables in $\mu+p\to \mu+p$ elastic scattering are obtained, taking into account the lepton mass and including the two-photon exchange contribution. The spin structure of the matrix element is parametrized in terms of six independent complex amplitudes, functions of two independent kinematical variables. General statements about the influence of the two--photon--exchange terms on the differential cross section and on polarization observables are given. Polarization effects have been investigated for the case of a longitudinally polarized lepton beam and polarized nucleon in the final state., Comment: 28 pages, 3 figures

Expressions for the unpolarized differential cross section and for various polarization observables in the lepton-deuteron elastic scattering, $\ell+D\to \ell+D$, $\ell=e$, $\mu$, $\tau$, have been obtained in one-photon-exchange approximation, taking into account the lepton mass. Polarization effects have been investigated for the case of a polarized lepton beam and polarized deuteron target which can have vector or tensor polarization. Numerical estimations of the lepton mass effects have been done for the unpolarized differential cross section and for some polarization observables and applied to the case of low energy muon deuteron elastic scattering., Comment: 29 pages, 6 figure

The polarization effects in the one-meson radiative decay of the polarized $\tau$ lepton, $\tau^-\to\pi^-\gamma\nu_{\tau}$, are investigated. The inner bremsstrahlung and structural amplitudes are taken into account. The asymmetry of the differential decay width caused by the $\tau$ lepton polarization and the Stokes parameters of the emitted photon itself, are calculated depending on the polarization of the decaying $\tau$ lepton. The numerical estimation of these physical quantities was done for arbitrary direction of the $\tau$ 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$\chi$T)., Comment: 37 pages,7 figures

Model independent expressions for all polarization observables in $\mu+p\to \mu+p$ elastic scattering are obtained, taking into account the lepton mass and including the two-photon exchange contribution. The spin structure of the matrix element is parametrized in terms of six independent complex amplitudes, functions of two independent kinematical variables. General statements about the influence of the two--photon--exchange terms on the differential cross section and on polarization observables are given. Polarization effects have been investigated for the case of a longitudinally polarized lepton beam and polarized nucleon in the final state., Comment: 28 pages, 3 figures

Expressions for the unpolarized differential cross section and for various polarization observables in the lepton-deuteron elastic scattering, $\ell+D\to \ell+D$, $\ell=e$, $\mu$, $\tau$, have been obtained in one-photon-exchange approximation, taking into account the lepton mass. Polarization effects have been investigated for the case of a polarized lepton beam and polarized deuteron target which can have vector or tensor polarization. Numerical estimations of the lepton mass effects have been done for the unpolarized differential cross section and for some polarization observables and applied to the case of low energy muon deuteron elastic scattering., Comment: 29 pages, 6 figure

The possibility in principle of the determining high energy photon circular polarization by the measurement of the created electron polarization in the process of triplet photoproduction $\gamma +e^-\rightarrow e^+e^- +e^-$ is investigated. The respective event number which depend on polarization states of photon and created electron does not decrease with the growth of the photon energy, and this circumstance can ensure the high efficiency in such kind of experiments. We study different double and single distributions of the created electron (or positron), which allow to probe the photon circular polarization and to measure its magnitude (the Stock's parameter $\xi_2$), using the technique of the Sudakov's variables. Some experimental setups with different rules for event selection are studied and corresponding numerical estimations are presented., Comment: 26 pages, 20 figures, submitted to JETP

The possibility in principle of the determining high energy photon circular polarization by the measurement of the created electron polarization in the process of triplet photoproduction $\gamma +e^-\rightarrow e^+e^- +e^-$ is investigated. The respective event number which depend on polarization states of photon and created electron does not decrease with the growth of the photon energy, and this circumstance can ensure the high efficiency in such kind of experiments. We study different double and single distributions of the created electron (or positron), which allow to probe the photon circular polarization and to measure its magnitude (the Stock's parameter $\xi_2$), using the technique of the Sudakov's variables. Some experimental setups with different rules for event selection are studied and corresponding numerical estimations are presented., Comment: 26 pages, 20 figures, submitted to JETP

The dependence of the differential cross section and polarization observables in the $\bar N+N\to \pi +e^++e^-$ 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 $\varphi$ and the virtual-photon parameter $\epsilon$), 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., Comment: arXiv admin note: substantial text overlap with arXiv:1011.4013

It is suggested that proton elastic scattering on atomic electrons allows a precise measurement of the proton charge radius. Very small values of transferred momenta (up to four order of magnitude smaller than the ones presently available) can be reached with high probability., Comment: 4 pages, 4 figures

The model--independent QED radiative corrections to polarization observables in elastic scattering of unpolarized and longitudinally--polarized electron beam by the deuteron target have been calculated in leptonic variables. The experimental setup when the deuteron target is arbitrarily polarized is considered and the procedure for applying derived results to the vector or tensor polarization of the recoil deuteron is discussed. The basis of the calculations consists of the account for all essential Feynman diagrams which results in the form of the Drell-Yan representation for the cross-section and use of the covariant parametrization of the deuteron polarization state. The numerical estimates of the radiative corrections are given for the case when event selection allows the undetected particles (photons and electron-positron pairs) and the restriction on the lost invariant mass is used., Comment: 43 pages,3 figures. To be published in ZhTEF. revised 14.02.2012. arXiv admin note: text overlap with arXiv:nucl-ex/0002003 by other authors

The dependence of the differential cross section and polarization observables in the $\bar N+N\to \pi +e^++e^-$ 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 $\varphi$ and the virtual-photon parameter $\epsilon$), 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., Comment: arXiv admin note: substantial text overlap with arXiv:1011.4013

The model--independent QED radiative corrections to polarization observables in elastic scattering of unpolarized and longitudinally--polarized electron beam by the deuteron target have been calculated in leptonic variables. The experimental setup when the deuteron target is arbitrarily polarized is considered and the procedure for applying derived results to the vector or tensor polarization of the recoil deuteron is discussed. The basis of the calculations consists of the account for all essential Feynman diagrams which results in the form of the Drell-Yan representation for the cross-section and use of the covariant parametrization of the deuteron polarization state. The numerical estimates of the radiative corrections are given for the case when event selection allows the undetected particles (photons and electron-positron pairs) and the restriction on the lost invariant mass is used., Comment: 43 pages,3 figures. To be published in ZhTEF. revised 14.02.2012. arXiv admin note: text overlap with arXiv:nucl-ex/0002003 by other authors

It is suggested that proton elastic scattering on atomic electrons allows a precise measurement of the proton charge radius. Very small values of transferred momenta (up to four order of magnitude smaller than the ones presently available) can be reached with high probability., Comment: 4 pages, 4 figures

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

The experimental observables for the elastic reaction induced by protons on electrons are calculated in the Born approximation. Model independent expressions are derived for the differential cross section and polarization observables. Numerical estimations are given for spin correlation coefficients, polarization transfer coefficients and depolarization coefficients, in a wide kinematical range. Specific attention is given to the kinematical conditions, i.e., to the specific range of incident energy and transferred momentum., Comment: 26 pages 10 figures 2 tables

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

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

The experimental observables for the elastic reaction induced by protons on electrons are calculated in the Born approximation. Model independent expressions are derived for the differential cross section and polarization observables. Numerical estimations are given for spin correlation coefficients, polarization transfer coefficients and depolarization coefficients, in a wide kinematical range. Specific attention is given to the kinematical conditions, i.e., to the specific range of incident energy and transferred momentum., Comment: 26 pages 10 figures 2 tables

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

The differential cross section and the polarization observables for $\Delta $--isobar production in the deuteron electrodisintegration process, $e^-+d\to e^-+\Delta +N$, 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 $e^-+d\to e^- +\Delta +N$ 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 $\phi$ and $\epsilon$ (linear polarization of the virtual photon) is calculated. A similar analysis is performed for the polarization of the nucleon produced in $\gamma ^*d \to \Delta N$ reaction provided the electron beam is unpolarized or longitudinally polarized. Polarization effects, which are due to the strong $\Delta N-$ interaction in the final state are calculated. The photoproduction of the $\Delta $--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., Comment: 52 pages

A model independent formalism for the electron positron annihilation reaction $e^++e^-\to a_1(1260)+\pi $ 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 $\gamma^*a_1\pi $ 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., Comment: 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 \rho+\rho $. 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 $\gamma^*\rho\rho $ current. The elements of the spin--density matrix of the $\rho -$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., Comment: 19 pages, 2 figures, to appear in Phys Rev C

The aim of this work is to give a pedagogical derivation of polarization observables for the annihilation reaction $e^+ + e^- \to N+ \bar N$. The reaction mechanism is one photon + two photon exchange, the last is described by axial parametrization. After deriving the general expressions for the cross section of a binary process, the matrix element is written in terms of three complex amplitudes. The method to derive polarization observables is detailed and all expressions are given in terms of generalized form factors. The strategy for determining physical form factors in annihilation reactions in presence of two photon exchange is suggested, on the basis of model independent properties of the relevant observables., Comment: 50 pages, one figure, Lecture Notes

The general spin structure of the matrix element, taking into account the two--photon exchange contribution, for the elastic electron (positron) --deuteron scattering has been derived using general symmetry properties of the hadron electromagnetic interaction, such as P--, C-- and T--invariances as well as lepton helicity conservation in QED at high energy. Taking into account also crossing symmetry, the amplitudes of $e^{\mp}d-$scattering can be parametrized in terms of fifteen real functions. The expressions for the differential cross section and for all polarization observables are given in terms of these functions. We consider the case of an arbitrary polarized deuteron target and polarized electron beam (both longitudinal and transverse). The transverse polarization of the electron beam induces a single--spin asymmetry which is non--zero in presence of two--photon exchange. It is shown that elastic deuteron electromagnetic form factors can still be extracted in presence of two photon exchange, from the measurements of the differential cross section and of one polarization observable (for example, the tensor asymmetry) for electron and positron deuteron elastic scattering, in the same kinematical conditions., Comment: 28 pages

Hadron electromagnetic form factors contain dynamical information on the intrinsic structure of the hadrons. The pioneering work developed at the Kharkov Physical-Technical Institute in the 60's on the relation between the polarized cross section and form factors triggered a number of experiments. Such experiments could be performed only recently, due to the progress in accelerator and polarimetry techniques. The principle of these measurements is recalled and the surprising and very precise results obtained on proton are presented. The actual status of nucleon electromagnetic form factors is reviewed, with special attention to the basic work done in Kharkov Institute., Comment: 10 pages, 2 figures, prepared for the QEDSP2006 conference, Kharkov, Ukraine, September 19-23, 2006

Hadron electromagnetic form factors contain dynamical information on the intrinsic structure of the hadrons. The pioneering work developed at the Kharkov Physical-Technical Institute in the 60's on the relation between the polarized cross section and form factors triggered a number of experiments. Such experiments could be performed only recently, due to the progress in accelerator and polarimetry techniques. The principle of these measurements is recalled and the surprising and very precise results obtained on proton are presented. The actual status of nucleon electromagnetic form factors is reviewed, with special attention to the basic work done in Kharkov Institute., Comment: 10 pages, 2 figures, prepared for the QEDSP2006 conference, Kharkov, Ukraine, September 19-23, 2006

The general spin structure of the matrix element, taking into account the two--photon exchange contribution, for the elastic electron (positron) --deuteron scattering has been derived using general symmetry properties of the hadron electromagnetic interaction, such as P--, C-- and T--invariances as well as lepton helicity conservation in QED at high energy. Taking into account also crossing symmetry, the amplitudes of $e^{\mp}d-$scattering can be parametrized in terms of fifteen real functions. The expressions for the differential cross section and for all polarization observables are given in terms of these functions. We consider the case of an arbitrary polarized deuteron target and polarized electron beam (both longitudinal and transverse). The transverse polarization of the electron beam induces a single--spin asymmetry which is non--zero in presence of two--photon exchange. It is shown that elastic deuteron electromagnetic form factors can still be extracted in presence of two photon exchange, from the measurements of the differential cross section and of one polarization observable (for example, the tensor asymmetry) for electron and positron deuteron elastic scattering, in the same kinematical conditions., Comment: 28 pages

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

We study the asymptotic behavior of the ratio of Pauli and Dirac electromagnetic nucleon form factors, $F_2/F_1$, in time-like region for different parametrizations built for the space-like region. We investigate how fast the ratio $F_2/F_1$ approaches the asymptotic limits according to the Phragm\`en-Lindel\"of theorem. We show that the QCD-inspired logarithmic behavior of this ratio results in very far asymptotics, experimentally unachievable. This is also confirmed by the normal component of the nucleon polarization, $P_y$, in $e^++e^-\to N+\bar{N}$ (in collisions of unpolarized leptons), which is a very interesting observable, with respect to this theorem. Finally we observe that the 1/Q parametrization of $F_2/F_1$ contradicts this theorem., Comment: 9 pages, 1 figure

We derive, in model independent way, the spin structure of the matrix element for the reaction of associative $\Theta^+$ pentaquark production, $\pi^{\pm}+D\to \Theta^+ +\Sigma^{\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 $\Theta^+ .$ We have proved that such reaction can be used for a model independent determination of the P-parity of $\Theta^+$ only by measuring the $\Theta^+$ polarization. Other polarization observables, such as the dependence of the $\Sigma^{\pm}$ polarization on the vector and tensor deuteron polarizations, are insensitive to the $\Theta^+$ parity in the considered kinematical conditions. All linear and quadratic relations between polarization observables in $\pi^{\pm}+\vec D\to \Theta^+ +\vec\Sigma^{\pm}(\Theta^+ $ is unpolarized) do not depend on the parity of the $\Theta^+$ pentaquark., Comment: 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

We study the asymptotic behavior of the ratio of Pauli and Dirac electromagnetic nucleon form factors, $F_2/F_1$, in time-like region for different parametrizations built for the space-like region. We investigate how fast the ratio $F_2/F_1$ approaches the asymptotic limits according to the Phragm\`en-Lindel\"of theorem. We show that the QCD-inspired logarithmic behavior of this ratio results in very far asymptotics, experimentally unachievable. This is also confirmed by the normal component of the nucleon polarization, $P_y$, in $e^++e^-\to N+\bar{N}$ (in collisions of unpolarized leptons), which is a very interesting observable, with respect to this theorem. Finally we observe that the 1/Q parametrization of $F_2/F_1$ contradicts this theorem., Comment: 9 pages, 1 figure

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