F. Entezami

On the models of Coulomb capture of negative particles

Abstract Various models of atomic capture of negative mesonic particles are tested against 321 experimental Coulomb-capture ratios, measured on binary systems: gas mixtures, alloys and simple compounds. The comparison has shown that the general agreement between theory and experiment is not satisfactory. We tried to improve on the models by introducing adjustable parameters to be estimated by fitting the experimental data. The predictions of the model proposed by Schneuwly, Pokrovsky and Ponomarev (SPP) are closest to the atomic capture ratios for alloys and compounds while the data measured in gas mixtures are better approximated by the empirical formula of Vasilyev et al. The theoretical formula of Daniel fails in describing the capture in the light elements.

Spin Spin Correlations and Spin Asymmetries for the Reaction

Abstract Spin-spin correlation parameters A LL , A NN , A SS , A SL and spin asymmetries A NO and A ON have been measured for the reaction p p → pn π + with incident beam energies of 510, 465 and 420 MeV. Clean separation of free proton events from the bound proton background has been achieved. A LL , A SS and A NN , were all found to be large and negative indicating domination by the 1 D 2 partial wave. The spin asymmetries were large. Results are compared to the predictions of Dubach, Kloet and Silbar.

p p \to p n \pi^+

Abstract Using the lifetime technique, atomic capture ratios of negative muons have been measured in 41 oxides. The results, though a little different from the earlier TRIUMF findings, are consistent with the mesic X-ray measurements. It has been noticed that the atomic capture ratios have an approximately linear dependence on density, whereas the Z -dependence is periodic.

at Intermediate-energies

Abstract Including a density dependence, as well as a Z -dependence, an empirical expression was formulated for atomic capture ratios of negative muons in oxides, chlorides and fluorides, using a chi-squared minimization method. The overall chi-square per point produced by this expression is lower than the same obtained from any of the present atomic capture models.

Atomic capture ratios for muons in oxides

No entirely satisfactory model has yet been established for describing the processes of molecular and atomic capture of negative pions in organic materials. One major point of dispute between theories is the manner in which pions captured by hydrogen are transferred to other nuclei. The two suggested mechanisms are tunneling by the pion through the potential barrier to the atom bound to the hydrogen or the collision of the small neutral π− p system with some other nucleus after leaving the parent molecule. Experiments were conducted at TRIUMF to attempt to clarify this point. The nuclear capture of pions by hydrogen were measured using the charge exchange reaction: pπ− → nπ0, π0 →γγ. The coincident γ-rays were detected by two large NaI detectors, TINA and MINA. Measurements were made of acid anhydrides, sugars, simple hydrides and some nitrogen compounds. The implications of these measurements for the various theoretical models are discussed.

Atomic capture of muons and density

Abstract The elastic scattering differential cross-section ratios of 36 S/ 32 S, 34 S/ 32 S and 26 Mg/ 24 Mg have been measured with 48.4 MeV and 43.9 MeV negative pions, respectively, using magnetic spectrometers. The data are analysed with optical potential calculations, using a Fourier-Bessel description for the neutron density of the heavier isotope. Neutron density and rms radius differences between the isotopes are determined and compared to shell-model calculations, and show reasonable agreement.

Gamma-ray coincidence measurements for studies of pion chemistry

Abstract The photon asymmetry (α γ ) and partial branching ratio above 57 MeV ( R k > 57) have been measured for radiative muon capture on 40 Ca in order to determine the magnitude of the induced-pseudoscalar coupling constant, g p . Based on 2500 events a value of α γ = 1.32 +0.57 −0.47 is obtained from a fit to the photon time spectrum; this implies a value for g p g A . For the first time the asymmetry signal is clearly visible and unconstrained multi-parameter fits reproduce the parameters obtained from the decay electron spectrum. The present results are discussed and compared in detail with previous results.