M. I. Konchatnij

Scanning of hadra]on cross section at DAΦNE by analysis of the initial-state radiative events

The initial-state radiative events in electron-positron annihilation into hadrons at DAΦNE are considered. The corresponding cross section with the full first-order radiative corrections is calculated. The analytical calculations take into account the actual angular acceptance and energy cutoff of the DAΦNE photon detector.The initial-state radiative events in electron-positron annihilation into hadrons at DAFNE have been considered. The coresponding cross-section with the full first order radiative correction has been calculated. The analytical calculations take into account the realistic angular acceptance and energy cut of DAFNE photon detector.

Single-spin asymmetries in the bethe-heitler process e- + p → e- + γ + p induced by loop corrections

The single-spin beam and target asymmetries in the hard electroproduction process e− + p → e− + γ + p induced by the loop radiative corrections to the vertex part of lepton interaction are considered. The physical reason for the appearance of such asymmetries is the nonzero imaginary part of the amplitude (on the level of radiative corrections) caused by diagrams with photon radiation from the outgoing electron. We calculate the single-spin beam and target asymmetries at a longitudinally polarized electron beam or at arbitrary polarizations of the target proton for the CLAS and HERMES experimental conditions.

Polarization effects in radiative decay of a polarized τ lepton

The polarization effects in the one-meson radiative decay of a polarized τ lepton, τ → π−γντ, are investigated. The inner bremsstrahlung and structural amplitudes are taken into account. The asymmetry of the differential decay width caused by the τ-lepton polarization and the Stokes parameters of the emitted photon itself are calculated depending on the polarization of the decaying τ lepton. These physical quantities are estimated numerically for an arbitrary direction of the τ 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 (RχT).

Current tensor with heavy photon for double hard photon emission by a longitudinally polarized electron

The electron current tensor for the scattering of a heavy photon on a longitudinally polarized electron with the emission of two hard real photons is considered. The contributions of collinear and semicollinear kinematics are computed. The result allows one to calculate the corresponding contribution to the second-order radiative correction to the deep inelastic scattering or electron-positron annihilation cross sections with next-to-leading-order accuracy.The electron current tensor for the scattering of heavy photon on longitudinally polarized electron accompanied with two hard real photonsis considered. The contribution of collinear and semicollinear kinematics is computed. The obtained result allows to calculate the corresponding contribution into second order radiative correction to DIS or electron-positron annihilation cross-sections with the next-to-leading accuracy.

Azimuthal distributions in radiative decay of a polarized τ lepton

We investigate various distributions over emitted photon angles, especially over the azimuthal angle, in the one-meson radiative decay of the polarized τ lepton, τ– → π–γντ. In connection with this, the photon phase space is discussed in more detail because it is nontrivial in the case of a polarized τ lepton. The decay matrix element contains both the inner bremsstrahlung and the resonance (structural) contributions. The azimuthal dependence of some observables are calculated. They are the asymmetry of the differential decay width caused by the τ-lepton polarization, the Stokes parameters of the emitted photon itself, and the correlation parameters describing the influence of τ-lepton polarization on the photon Stokes parameters. A numerical estimation is done in the τ-lepton rest frame for an arbitrary direction of the τ-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 (RχT). It is found that the features of the azimuthal distributions allows separating various terms in the spin-dependent contribution. The so-called up–down and right–left asymmetries are also calculated.

Tagged-photon events in polarized deep inelastic scattering

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.Deep inelastic scattering events of a longitudinally polarized electron by a polarized proton with a tagged collinear photon radiated from the 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. The obtained result is applied to the elastic scattering.

Analysis of triplet production by a circularly polarized photon at high energies

The possibility in principle of determining the circular polarization of a high-energy photon by measuring the created electron polarization in the process of triplet photoproduction γ + e− → e+e− + e− is investigated. The respective event number, which depends on polarization states of the photon and the created electron, does not decrease as the photon energy increases, and this circumstance can ensure the high efficiency in such experiments. We study different double and single distributions of the created electron (or positron), which allow probing the photon circular polarization and measuring its magnitude (the Stokes parameter ξ2) using the technique of Sudakov variables. Some experimental setups with different rules for event selection are studied and the corresponding numerical estimations are presented.

QED corrections in the radiative return method during measurement of the e+e−→π+π− cross-section below 1 GeV

We discuss radiative corrections during the measurement of the e+e−→π+π− cross-section by the radiative return method without photon tagging. The radiative corrections to the initial-state radiation process are computed for DAΆNE conditions using the quasireal electron approximation for both the cross-section and the underlying kinematics. The efficiency of experimental rules for event selection by the restrictions on the lost invariant mass and so-called “track mass” is estimated. Some numerical calculations illustrate our analytical results.

Scanning of the e+e− → π+π− cross section below 1 GeV at DAΦNE by radiative events

The tagged photon events for the measurement of the e+e− → π+π− total cross section by the radiative return method at DAΦNE is discussed. The effects caused by the not exactly head-on collision of beams and by the QED radiative corrections are investigated. The essential part consists of the analysis of the event selection rules that ensure the rejection of the 3-pion hadronic state and take the main properties of the multiple purpose KLOE detector into account. The study of the non-head-on effect is performed in the Born approximation by integrating over the tagged photon angles, whereas the radiative corrections are calculated neglecting this effect. Together with the quasireal electron approach, this allows us to derive analytical formulas for the correction to the cross section of the initial-state radiative process. Some numerical calculations illustrate our analytical results.

Compton tensor with heavy photon for longitudinally polarized electron with next-to-leading accuracy

Compton tensor for scattering of a longitudinally polarized electron by a heavy photon is considered. The result obtained can be used for the analysis of electromagnetic corrections to the spin-spin correlation in quasi-elastic and deep inelastic scattering with next-to-leading accuracy.