Negative meson capture by hydrogen

Abstract

The total ionization cross section and electron energy spectrum have been calculated for negative muons, kaons and antiprotons at incident relative velocities between 0.04 and 1.0 atomic units. The electron energy spectrum has a sharp peak for electron kinetic energies on the order of 10-3 Rvdbergs. The ionization process thus favors the emission of very slow electrons.

The processes of deexcitation and capture of negative mesons and hadrons in atomich'1drogenare investigated. Only slow collisions in which the projectile-atom relative velocity is less than one atomic unit are considered, 8nd the motion of the incident particle is treated classically. For each c18ssical trajectory the probability of ionizing the hydrogen atom is determined, together with the energy spectrum of the emitted electron. Ionization probabilities are calculated using the time-dependent formulation of the perturbed stationary state method. Exact two-center electronic wave functions are used for both bound and continuum states.

Values obtained for the total ionization cross section when the correct classical trajectory is replaced by a straight line are an order of magnitude larger than those obtained for linear trajectories in a previous calculation by Rosenburg (191-1.9). The non-adiabatic effects treated in the perturbed stationary state method were found to be very large even for relative collision energies as low as a few electron volts. For relative velocities less than 8bout 0.2 atomic x units, use of .curvilinear trajectories produces a total cross section which increases monotonically as the projectile velocity decreases. Cross sections computed using curvilinear trajectories are also strongly mass dependent, with negative muons being the most effective ionizers at a specified velocity.

The cross section for ionization with capture of the incident particle was calculated for relative kinetic energies greater than 1.0 Rvdberg. Since ionization was found to occur with the emission of electrons of nearly zero kinetic energy the fraction of ionizing collisions which result in capture decreases very rapidly with projectile kinetic energy. The energy distributions of slowed down muons and hadrons were also computed. These distributions 1~ere used together with the capture cross section to determine the distribution of kinetic energies at which capture takes place. It was found that most captures occur for kinetic energies slightly less than 1.0 Rvdbergs with relatively little capture at thermal energies. The captured particles therefore tend to go into very large and loosely found orbits with binding energies less than 0.1 Rvdbergs.