K. A. Woodle

Low Energy Positron Production at the Livermore Linac

Beams of monoenergetic positrons with energies of a few eV to many keV have been used in experiments in atomic physics, solid state physics and materials science. The results of some of these experiments are given and the production of positron beams from a new source, an electron linac, is described. Intense, pulsed beams of low-energy positrons have been produced by a high-energy beam from an electron linac. The production efficiency for low-energy positrons has been determined for electrons with energies from 60 to 120 MeV. Low-energy positron beams produced with a high energy electron a linac can be of much higher intensity than those beams currently derived from radioactive sources. These higher intensity beams will make possible positron experiments previously infeasable.

Intense Positron Beams: Linacs

Beams of monoenergetic positrons with energies of a few eV to many keV have been used in experiments in atomic physics, solid state physics and materials science. The production of positron beams from a new source, an electron linac, is described.

Flash ADC time‐of‐flight spectrometer

We describe a time‐of‐flight spectrometer based on the direct readout of a 7‐bit, 15‐MHz flash ADC. The wide dynamic range of this device leads to several advantages over conventional time‐of‐flight methods, particularly with regard to noise reduction. The performance of a CAMAC‐based flash ADC/RAM unit for low‐energy electron time‐of‐flight measurements is described.

Measurement of the muonium 1S‐2S transition frequency

Resonant ionization spectroscopy has been employed for measuring the 12S1/2−22S1/2 frequency difference in the hydrogen‐like muonium atom to 2 455 529 002(33)(46) MHz. The 1S‐2S two‐photon transition was induced Doppler‐free using two counter‐propagating laser beams. The 2S state was photo‐ionized by a third photon from the same laser field. The measurement agrees with QED theory within two standard deviations. The mass of the positive muon can be extracted from the isotope shifts in this transition to hydrogen and deuterium to 105.658 80(29)(43) MeV/c2.

A precise microwave spectroscopy measurement of the muonium ground state: hyperfine structure interval and muon magnetic moment

An experiment is in progress at the Los Alamos Meson Physics Facility (LAMPF) to determine with high precision the hyperfine structure interval /spl Delta/v (to /spl sim/10 ppb) and the muon to proton magnetic moment ratio /spl mu//sub /spl mu////spl mu//sub p/(to /spl sim/60 ppb) in the ground state of muonium (/spl mu//sup +/e/sup -/). These precision goals correspond to increases in precision of /spl Delta/v and of /spl mu//sub /spl mu////spl mu//sub p/ by about a factor of 5 compared to present knowledge.

Search for spontaneous conversion of muonium to antimuonium

We have searched for spontaneous conversion of muonium (M) to antimuonium (M) by a method involving detection of high-Z muonic X-rays. A beam of M atoms with keV energies, produced by electron pickup by μ+ from a foil, travels in vacuum and in a magnetic field-free environment to a high-Z target. The events signatures used were a double coincidence of two muonic X-rays of the target material and a triple coincidence that also required detection of secondary electrons ejected when M strikes the target. Partial analysis of our 8 × 106 triggers indicates upper limits on the effective M → M four-fermion coupling constant of GMM ⩽ 30GF (90% C.L.) and GMM ⩽ 8GF (90% C.L.), respectively, from the two signatures. This begins to probe predictions of the left-rightsymmetric theory with a doubly-charged Higgs triplet.