A remark on the Primakoff effect

The coherent-nuclear reaction a + A -> a* + A is in the small-angle region dominated by the one-photon-exchange mechanism, often referred to as the Primakoff effect. In this region information about the electromagnetic decay a* -> a + gamma can be obtained. Well-known examples are the two-photon decays of the pi- and eta-mesons. Also decays of charged hadrons can be studied. For charged hadrons the one-photon-exchange amplitude comes with a Coulomb-phase factor and a Coulomb-form factor, which depend on the ratio between transverse- and logitudinal-momentum transfers, the latter being fixed. At the peak of the cross-section distribution, where the two momentum transfers are equal, the form factor could cut down the cross-section value by as much as 40 %. Consequently, a determination of a radiative-decay rate that relies on the peak value becomes sensitive to a proper treatment of the Coulomb-form factor.Comment: 5 pages, 2 figure

Coulomb-nuclear interference in pion-nucleus bremsstrahlung

Pion-nucleus bremsstrahlung offers a possibility of measuring the structure functions of pion-Compton scattering from a study of the small-momentum-transfer region where the bremsstrahlung reaction is dominated by the single-photon-exchange mechanism. The corresponding cross-section distribution is characterized by a sharp peak at small momentum transfers. But there is also a hadronic contribution which is smooth and constitutes an undesired background. In this communication the modification of the single-photon exchange amplitude by multiple-Coulomb scattering is investigated as well as the Coulomb-nuclear interference term.Comment: 21 pages, 5 figures. Eqs.(51,52) corrected; some new figure

Comparison of the Near-Threshold Production of eta- and K-Mesons in Proton-Proton Collisions

The pp -> pp eta and pp -> pLambda K^+ reactions near threshold are dominated by the first and second S_11 resonance respectively. It is shown that a one-pion-exchange model exciting these isobars reproduces well the ratio of the production cross sections. The consequences for this and other channels are discussed.Comment: 10 pages, LaTeX2e, 1 eps-figur

Eta and eta-prime meson production in the reaction pn -> dM near threshold

The two-step model with pi-, rho- and omega- exchanges taken into account is applied to investigate the reactions pn -> d eta and pn -> d eta-prime. The existing experimental data on the reaction pn -> d eta are analysed and predictions for the cross section of the reaction pn -> d eta-prime are presented. It is found that pi- as well as rho exchange yield significant contributions in both reactions. The effect of the final state interaction is also studied.Comment: 15 pages, 4 figure

Cross section and analyzing power of pol{p}p -> pn pi+ near threshold

The cross section and analyzing power of the pol{p}p -> pn pi+ reaction near threshold are estimated in terms of data obtained from the pol{p}p -> d pi+ and pp -> pp pi0 reactions. A simple final state interaction theory is developed which depends weakly upon the form of the pion-production operator and includes some Coulomb corrections. Within the uncertainties of the model and the input data, the approach reproduces well the measured energy dependence of the total cross section and the proton analyzing power at a fixed pion c.m. angle of 90deg, from threshold to T_p = 330 MeV. The variation of the differential cross section with pion angle is also very encouraging.Comment: 20 pages, Latex including 4 eps figure

Empirical Determination of Threshold Partial Wave Amplitudes in pp→ppωp p \to p p \omega

Using the model independent irreducible tensor approach to $\omega$ production in $pp$ collisions, we show theoretically that, it is advantageous to measure experimentally the polarization of $\omega$, in addition to the proposed experimental study employing a polarized beam and a polarized target.Comment: 6 pages, 1 Table, Latex-2

Meson production in high-energy electron-nucleus scattering

Pseudoscalar mesons can be produced and studied in high-energy electron-nucleus scattering. We review and extend our previous analysis of meson production in the nuclear Coulomb field. The $P\rightarrow \gamma \gamma$ decay rates are most directly determined for mesons produced in the double-Coulomb region where both photons are nearly real, and provided the background-hadronic contribution remains small. The larger the mass of the meson the higher the electron energy needed to assure such a condition.Comment: 19 pages, 2 figure

Cross sections for low-energy π−γ\pi^-\gamma reactions

We review the cross sections for low-energy $\pi^- \gamma$ reactions in the framework of chiral perturbation theory. Charged pion Compton scattering, $\pi^- \gamma\to \pi^-\gamma$, is considered up to one-loop order where the pion's internal structure enters through the difference of the electric and magnetic pion polarizability, $\alpha_\pi - \beta_\pi$. The ongoing COMPASS experiment aims at measuring this important structure constant with high statistics using the Primakoff effect. In the same way, the reaction $\pi^- \gamma \to \pi^- \pi^0$ serves as a test of the QCD chiral anomaly (via the $\gamma 3\pi$-coupling constant $F_{\gamma3\pi}$). Furthermore, we calculate the total cross sections for neutral and charged pion-pair production, $\pi^- \gamma \to \pi^- \pi^0\pi^0$ and $\pi^- \gamma \to \pi^-\pi^+\pi^-$, which are governed by the chiral $\pi\pi$-interaction. Finally, we investigate the radiative (correction) process $\pi^- \gamma \to \pi^- \gamma \gamma$ and calculate the corresponding two-photon mass spectrum. This information will be useful for analyzing the $\pi^-$ Primakoff scattering events with photons in the final state.Comment: 14, pages, 10 figures, submitted to EPJ

Eta-Helium Quasi-Bound States

The cross section and tensor analysing power t_20 of the d\vec{d}->eta 4He reaction have been measured at six c.m. momenta, 10 < p(eta) < 90 MeV/c. The threshold value of t_20 is consistent with 1/\sqrt{2}, which follows from parity conservation and Bose symmetry. The much slower momentum variation observed for the reaction amplitude, as compared to that for the analogous pd->eta 3He case, suggests strongly the existence of a quasi-bound state in the eta-4He system and optical model fits indicate that this probably also the case for eta-3He.Comment: LaTeX, uses elsart.sty, 10 pages, 3 Postscript figures, Submitted to Physics Letters

Strangeness Production Process pp→nK+Σ+pp \to nK^ + \Sigma ^ + within Resonance Model

We explore production mechanism and final state interaction in the $pp \to nK^ + \Sigma ^ +$ channel based on the inconsistent experimental data published respectively by COSY-11 and COSY-ANKE. The scattering parameter $a> 0$ for $n\Sigma ^ +$ interaction is favored by large near-threshold cross section within a nonrelativistic parametrization investigation, and a strong $n\Sigma ^ +$ interaction comparable to $pp$ interaction is also indicated. Based on this analysis we calculate the contribution from resonance $\Delta ^* (1920)$ through $\pi ^ +$ exchange within resonance model, and the numerical result suggests a rather small near-threshold total cross section, which is consistent with the COSY-ANKE data. With an additional sub-threshold resonance $\Delta ^*(1620)$, the model gives a much better description to the rather large near-threshold total cross section published by COSY-11.Comment: 10pp + 4figs, published versio