Partial transitions in radiative pion capture on light atomic nuclei

The partial transitions in radiative pion capture on light nuclei are studied within the shell model with intermediate coupling. The probabilities of capture from s- and p-states of a mesoatom and the total yield of γ-quanta have been calculated and compared with experimental data.     

Inclusive radiative pion capture by N = Z nuclei in the 1p shell

A study of inclusive radiative pion capture by means of sum rules is given for the case of self-conjugated nuclei in the 1p shell. The sum rules M₀ and M₁ are evaluated for the dominant Kroll-Rudermann term in the effective hamiltonian. Total branching ratios and mean photon energies are determined from the calculated sum rules. These quantities compare reasonably well with experiment.     

Inclusive radiative muon capture in nuclei: A status report

The problems connected to the use of the effective Hamiltonian and to the nuclear excitation spectrum for inclusive radiative muon capture in nuclei are reviewed. Results are presented for⁴⁰Ca.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

Isovector transitions in 1p-shell nuclei induced by radiative pion capture

A systematic study of radiative pion capture transitions in 1p-shell nuclei has been performed. High-resolution photon spectra measured with a pair spectrometer for ⁶Li, ⁷Li, ⁹Be, ¹⁰B, ¹¹B, ¹²C and ¹⁴N targets show transitions to low-lying bound states of ⁶He, ⁷He, ⁹Li, ¹⁰Be, ¹¹Be, ¹²B and ¹⁴C respectively. The observed levels are predominantly analogs of isovector M1 states in the target nucleus. The measured branching ratios are compared to various shell-model calculations using nuclear wave functions constrained to fit other electromagnetic and weak properties of the same levels or their analogs. The data are found to be consistent with existing electron scattering data where they exist.     

Spin dipole excitations in radiative pion capture on 1p shell nuclei

Shell-model calculations for spin-dipole transitions in the (π^?,γ) reaction on ^6,7Li, ⁹Be, ¹¹B, ¹³C and ¹⁴N are compared with experimental data. The gross structure of resonance is discussed in terms of configurational splitting and symmetry considerations. Quantum numbers of resonances, total and partial yields are considered. Selected (π^?, γn) and (gp^?, γnγ′) coincidence experiments are proposed. The role of quadrupole and quasielastic excitation is also briefly discussed.     

Excitation of magnetic dipole states in 1p shell nuclei in radiative pion capture

The systematics of magnetic dipole resonance excitation in radiative pion capture on 1p shell nuclei with A = 6–14 is discussed in terms of the shell model with intermediate coupling. Comparison with the electromagnetic transitions is given.     

RPA correlation effects in radiative pion capture

A sum rule approach to radiative pion capture is given in terms of the energy-weighted and inverse-energy weighted sum rules. They are evaluated with RPA accuracy for Skyrme-like interactions. The static polarizabilities of the dipole, quadrupole and octupole isovector modes turn out to be the relevant quantities to determine the total branching ratios and mean photon energies.     

Importance of momentum dependent terms in radiative pion capture

The contribution of the momentum dependent terms in radiative pion capture from bound atomic orbits is investigated. A shell model calculation for ⁶Li shows that the momentum dependent terms represent ≈ 2% of the 1s capture rate and up to 40% of 2p capture rates.     

Sum rule approach to radiative pion capture: A full hamiltonian calculation for 1p shell nuclei

A sum-rule approach to radiative pion capture is given for the self-conjugated nuclei in the 1p shell. The non-energy-weighted and the energy-weighted sum rules are evaluated for the full effective hamiltonian. Total branching ratios and mean photon energies are determined from these sum rules. A comparison with the Kroll-Rudermann approximation shows that the mean photon energies are practically unaffected, while the total branching ratios increases of the order of 10%.     

Ordinary and radiative muon capture in complex nuclei

The total rates of ordinary and radiative muon capture in natural zirconium and molybdenum are calculated within the quasiparticle random phase approximation. The total ordinary-muon-capture rates calculated with the unquenched weak axial-vector coupling are consistent with the experimental data and weakly depend on the weak pseudoscalar coupling. The calculated radiative-muon-capture rates have a clear dependence on the pseudoscalar coupling, but highly overestimate the experimental data. The text was submitted by the authors in English.     

On the radiative Kaon capture by nuclei

The process of the radiative kaon capture by nuclei is considered. The total yields of γ-quanta corresponding to the production of different hyperons are calculated.     

One- and two-nucleon emission following the nuclear radiative pion capture

Decay channels in the radiative pion capture reactions are discussed and their respective yields calculated. Specific consequences of a recently suggested quadrupole excitation mode in the ( ^–,) reaction are found and their experimental investigation is urged. A yield of about 19% of the total decay was estimated for the two-nucleon decay channel even for the light nuclei like¹⁶O.On leave of absence fromthe Institute of Nuclear Physics, Czechosl. Acad. Sci., 250 68 e, Czechoslovakia.We a re grateful to the members of Lausanne-Münich-Zürich collaboration, particularly to C.Joseph, G.Strassner and P.Trüol for supplying us with the experimental results prior to publication. M. G. also thanks them and R.Wünsch for interesting discussions. We are grateful to R. A.Sakaev for his help at an early stage of this work.     

Experimental results on radiative muon capture in complex nuclei

Experimental results for the radiative muon capture branching ratio in several nuclei and the photon-muon spin asymmetry in⁴⁰Ca are reported. For the measurements a two arm Nalspectrometer was used. Apart from²⁶O and⁴⁰Ca, where we confirm previous results of our group, new data on¹²C,²⁶Fe,¹⁶⁵Ho and²⁰⁹Bi are presented. No available theoretical models explain all the data consistently. The preliminary results for the asymmetry measurements, obtained using a stroboscopic method are in agreement with previous measurements and with theoretical calculations.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

The radiative capture of fast protons by medium-mass nuclei

High-energy photon spectra were obtained with moderate resolution for a number of neighboring nuclei: ⁵⁶Fe, ⁵⁹Co, ⁵⁸Ni, ⁶⁰Ni, ⁶¹Ni, ⁶³Cu and ⁶⁴Zn in bombardments with protons (8 to 22 MeV). The shapes, magnitudes and energy dependence of the observed spectra are found to be consistent in most of their essential features with the implications of the semidirect model for fast nucleon capture.     

Towards a better understanding of O nuclear structure: Muon capture and radiative pion capture reactions

Muon capture and radiative pion capture reactions on ¹⁶O have been analysed with the aim to extract more information on the importance of higher components of the A = 16 nuclear ground and excited states. Good agreement with the experimental data for both reactions may be achieved if at least 2p2h components of the nuclear wave functions are taken into account. The positive parity excited states in ¹⁶N are shown to contribute 43 % to the radiative π⁻ capture but only ≈ 10 % to the muon capture rate.     

On the radiative pion decay

A reanalysis of the radiative pion decay together with the calculation of the radiative corrections within chiral perturbation theory (CHPT) is performed. The amplitude of this decay contains an inner Bremsstrahlung contribution and a structure-dependent part, which are both accessible in experiments. In order to obtain a reliable estimate of the hadronic contributions we combine the CHPT result with a large-N_c expansion and experimental data on other decays, which makes it possible to determine the occurring coupling constants. PACS  13.20.Cz; 12.39.Fe     

Form factors in the radiative pion decay

We perform an analysis of the form factors that rule the structure-dependent amplitude in radiative pion decay. The resonance contributions to π→eν_eγ decays are computed through the proper construction of the vector and axial-vector form factors by setting the QCD driven asymptotic properties of the three-point Green functions 〈VVP〉 and 〈VAP〉, and by demanding the smoothening of the form factors at high transfer of momentum. A comparison between theoretical and experimental determination of the form factors is also carried out. We also consider and evaluate the role played by a non-standard tensor form factor. We conclude that, at present and due to the hadronic uncertainties, the search for new physics in this process is not feasible. PACS 11.15.Pg; 12.38.-t; 12.39.Fe