Search

Measurements of muon-catalyzed dt fusion ( d(mu)t-->4He + n + mu(-)) in solid HD have been performed. The theory describing the energy dependent resonant molecular formation rate for the reaction (mu)t + HD-->[(d(mu)t)pee](*) is compared to experimental results in a pure solid HD target. Constraints on the rates are inferred through the use of a Monte Carlo model developed specifically for the experiment. From the time-of-flight analysis of fusion events in 16 and 37 microg x cm(-2) targets, an average formation rate consistent with 0.897+/-(0.046)(stat)+/-(0.166)(syst) times the theoretical prediction was obtained.

An alternate approach was used to study the reactions of muonic atoms and molecules in solid layers of hydrogen isotopes. Muons stopped in a protium layer with a small admixture of tritium producing \ensuremath{\mu}p atoms. Muon transfer from a proton to a triton generated \ensuremath{\mu}t atoms, which were emitted into a deuterium layer. Subsequent epithermal dt\ensuremath{\mu} molecular formation followed by dt fusion gave a prompt signal for the \ensuremath{\mu}t emission. Fusion time spectra at various tritium concentrations were measured by detecting neutrons and \ensuremath{\alpha} particles and the \ensuremath{\mu}p disappearance rates were determined. The rates of \ensuremath{\mu}p\ensuremath{\rightarrow}\ensuremath{\mu}t transfer and pp\ensuremath{\mu} formation were measured to be ${\ensuremath{\lambda}}_{\mathit{pt}}$=[5.86\ifmmode\pm\else\textpm\fi{}(0.10${)}_{\mathit{stat}}$\ifmmode\pm\else\textpm\fi{}(0.15${)}_{\mathit{syst}}$${(}_{\mathrm{\ensuremath{-}}0}^{+0.30}$${)}_{\mathit{model}}$]\ifmmode\times\else\texttimes\fi{}${10}^{9}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ and ${\ensuremath{\lambda}}_{\mathit{pp}\mathrm{\ensuremath{\mu}}}$=[3.21 \ifmmode\pm\else\textpm\fi{}(0.10${)}_{\mathit{stat}}$\ifmmode\pm\else\textpm\fi{}(0.14${)}_{\mathit{syst}}$${(}_{\mathrm{\ensuremath{-}}0.06}^{+0}$${)}_{\mathit{model}(}$]\ifmmode\times\else\texttimes\fi{}${10}^{6}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, respectively. Comparisons are made with the most recent theoretical values. \textcopyright{} 1996 The American Physical Society.

The MEGA experiment, which searched for the muon- and electron-number violating decay ${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma},$ is described. The spectrometer system, the calibrations, the data taking procedures, the data analysis, and the sensitivity of the experiment are discussed. The most stringent upper limit on the branching ratio, $\mathcal{B}({\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma})l1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$ with $90%$ confidence, is derived from a likelihood analysis.

Excitation functions have been measured for reactions of /sup 3/He, over the energy range E/sup 3/He = 10--40 MeV, and /sup 4/He over the energy range E/sup 4/He = 10--35 MeV, with natural targets of Mg, Al, and Si by detecting ..beta..-delayed ..gamma.. rays.

The magnetic dipole moment of the ..sigma../sup -/ hyperon has been determined from ..sigma../sup -/-atom x-ray transitions in natural lead and tungsten. Negative kaons were stopped in a target which consisted of sheets of W or Pb immersed in liquid hydrogen. The ..sigma../sup -/ resulting from the reaction K/sup -/p..--> sigma../sup -/..pi../sup +/ were tagged by observing the monoenergetic ..pi../sup +/. X rays from ..sigma../sup -/ atoms were detected by intrinsic Ge detectors. The x-ray lines were analyzed for fine-structure splitting and the magnetic moment was determined from the measured splitting. The value obtained for the magnetic moment is ..mu..(..sigma../sup -/) = (-1.105 +- 0.029 +- 0.010)..mu../sub N/ where the first error is statistical and the second systematic. This value is in reasonable agreement with measurements that used precession techniques and with the theoretical predictions of simple quark models.

Cross sections for various reactions induced by beams of $^{1}\mathrm{H}$ and $^{2}\mathrm{H}$ ions on targets of natural Mg, Al, and Si were determined from observations of the radioactive product $\ensuremath{\gamma}$ rays. $^{1}\mathrm{H}$ energies between 14.5 and 27.0 MeV and $^{2}\mathrm{H}$ energies between 8.7 and 18.0 MeV from the University of Colorado cyclotron were used.

Muonic x-ray spectra have been measured for /sup 199/Hg and /sup 200/Hg. From the data we have determined model-independent charge radii and isomer shifts of certain excited nuclear states and have inferred spectroscopic quadrupole moments of excited states for both isotopes. The quadrupole moment of the lowest 5/2/sup -/ state in /sup 199/Hg is found to be positive, in agreement with previous muonic-atom data but in disagreement with a recent Moessbauer study. B(E2) values of low-lying excited states have been determined for /sup 199/Hg. An E1 muonic-nuclear resonance has been discovered in /sup 200/Hg.

The E2 nuclear resonance effect has been studied in the pionic atoms of /sup 48/Ti, /sup 104/Ru, /sup 110/Pd, /sup 111,112/Cd, /sup 125/Te, and /sup 150/Sm. The experimental values of the attenuation for /sup 104/Ru, /sup 110/Pd, and /sup 111,112/Cd agree with the predictions of the theoretical model of Leon. Using the more detailed calculations of Dubach et al., one obtains closer agreement between theory and experiment for /sup 150/Sm and /sup 48/Ti although in the latter case the difference is still more than two standard deviations. Although the same levels are mixed in /sup 125/Te as in /sup 104/Ru and /sup 110/Pd, the theoretical prediction of the attenuation by Leon is nearly two standard deviations greater than the experimental value. A more precise energy for the second (5/2)/sup +/ state in /sup 111/Cd is deduced.

X-ray transition energies of antiprotonic atoms formed in targets of $^{6}\mathrm{Li}$, $^{7}\mathrm{Li}$, C, Si, P, Fe, Y, Zr, Cs, and Yb have been measured. Level shifts and widths due to the strong interaction were determined. A phenomenological fit to the data using an optical-model potential proportional to the nuclear matter density and to an effective $\overline{p}$-nucleus $s$-wave scattering length yielded [$(0.85\ifmmode\pm\else\textpm\fi{}0.38)+i(2.66\ifmmode\pm\else\textpm\fi{}0.28)$] fm for the effective scattering length. In addition, the mass of the antiproton was determined to be 938.229 \ifmmode\pm\else\textpm\fi{} 0.049 MeV from the observed energies of the $\overline{p}$ x-ray transitions unperturbed by the strong interaction.NUCLEAR REACTIONS, hadronic atoms. Measured antiprotonic atom x-ray transition energies; determined strong interaction shifts and widths; deduced effective scattering length; deduced antiproton mass.

The masses of the ${K}^{\ensuremath{-}}$ and ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ have been measured by use of exotic-atom x-ray transitions in Pb and W. The transitions used were free from contaminant nuclear $\ensuremath{\gamma}$ rays and strong-interaction effects. Two ${K}^{\ensuremath{-}}$ transitions and three ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ transitions for each target satisfied these criteria. The results are ${M}_{{K}^{\ensuremath{-}}}=493.636\ifmmode\pm\else\textpm\fi{}0.011$ MeV and ${M}_{{\ensuremath{\Sigma}}^{\ensuremath{-}}}=1197.532\ifmmode\pm\else\textpm\fi{}0.057$ MeV. The precision of these measurements is greater than that of any previous experiment. When combined with previous measurements they form a consistent set.

The quadruple and hexadecapole moments of 165Ho were derived from the hfs of the 3d muonic states. The resulting values are Q0 = 7.44 +/- 0.07 b and II0 = 0.52 +/- 0.10 b2. The parameters of the nuclear charge distribution were determined. An indication for an angular variation of the skin thickness was found.

The fine-structure splittings in atoms formed by stopping antiprotons in Pb and U and $Sigma$$sup -$ hyperons in Pb and Pt have been measured. Since the fine structure is produced through the interaction of the magnetic dipole moment of the anti p or the $Sigma$$sup -$ with the Coulomb field of the nucleus, a value for the magnetic moment can be determined from the splitting. The magnetic moment obtained for the p was (-2.819 +- 0.056) nuclear magnetons, which agrees well with the CPT prediction of -2.793 nuclear magnetons. The magnetic moment derived for the $Sigma$$sup -$ was (-1.48 +- 0.37) nuclear magnetons, which is in agreement with the sign given by simple SU(3) theory, but differs somewhat from the value of -0.9 nuclear magnetons predicted by the theory with no mass breaking. (AIP)

A systematic experimental study of strong interaction shifts, widths, and yields from high-Z kaonic atoms is reported. Strong interaction effects for the K-(8→7) transition were measured in U, Pb, and W, and the K-(7→6) transition in W was also observed. This is the first observation of two measurably broadened and shifted kaonic transitions in a single target and thus permitted the width of the upper state to be determined directly, rather than being inferred from yield data. The results are compared with optical-model calculations.

The 2p-1s atomic transition in pionic hydrogen has been studied with the help of a point-focusing graphite diffraction spectrometer. The transition energy was measured to be E(2p-1s)=2433.5±1.7 eV. From this result a strong interaction shift of -3.9±1.7 eV was derived. The Kα x-ray yield in the 2.7 atm hydrogen target at 40 K was found to be 0.025±0.013 per stopped pion.

The magnetic moment of the ..sigma../sup -/ hyperon has been obtained from measurements of fine-structure splittings of x-ray transitions in ..sigma../sup -/ exotic atoms. The use of targets consisting of sheets of Pb or W immersed in liquid hydrogen, and of a tagging technique utilizing the ..pi../sup +/ emitted in the reaction K/sup -/p..--> sigma../sup -/..pi../sup +/, resulted in improved x-ray signal-to-noise ratio by a factor of 15 over that in previous experiments. The present result is ..mu..(..sigma../sup -/) = (-1.111 +- 0.031 +- 0. 011)..mu../sub N/. .AE

We have measured the 4f ..-->.. 3d pionic x-ray transitions in /sup 148/Nd and /sup 150/Nd in order to determine the strong interaction effect between the pion and these nuclei. The measured transition energies and broadenings of these and all previously measured isotopes, which have appreciably strong interaction effects in the 3d level, were fitted by an optical potential. The isotope shift of the pionic x rays between /sup 150/Nd--/sup 148/Nd was consistent with a change in neutron radius of 45 +- 48 am. The sensitivity of this determination of the change in neutron radius on the assumed form of the neutron distribution is discussed.

A search is described for muonium (..mu../sup +/e/sup -/) conversion to antimuonium (..mu../sup -/e/sup +/) with a coupling strength approximately equal to that of the weak interaction. A silica powder target produced thermal muonium in vacuum. A unique sequence of radioactivity following the capture of a ..mu../sup -/ in tungsten was the signal for conversion. No events were seen, implying an upper limit on the effective four-fermion weak-coupling constant for conversion of 0.88G/sub F/ (90% confidence level), corresponding to a branching ratio of less than 2 x 10/sup -5/ with respect to normal muon decay.

Th 232 and U 238 pionic X ray energies and widths, suggesting anomalous effect for interaction between high-Z nuclei and pion

We have looked for the ${J}^{P}={0}^{+}$ nuclear excitation of ${\mathrm{Zn}}^{68}$ in muonic atoms as suggested by Henley and Wilets. ${\mathrm{Zn}}^{68}$ was chosen because the energy of the ${0}^{+}$ excitation is close to the energy difference of the $2s\ensuremath{-}1s$ muonic levels, thus allowing a dynamic interaction between a muon in a $2s$ state and the nucleus in the ground state. We find that the $2s\ensuremath{-}1s$ level difference is 20 keV less than the nuclear excitation energy and, as a result, the dynamic interaction is too small for us to observe. We measure the ${\mathrm{Zn}}^{66}$-${\mathrm{Zn}}^{68}$ isotope shift to be $\frac{\ensuremath{\delta}R}{\ensuremath{\delta}{R}_{\mathrm{std}}}=0.47\ifmmode\pm\else\textpm\fi{}0.11$.

The $4f\ensuremath{\rightarrow}3d$ pionic x rays in ${\mathrm{Ba}}^{138}$, ${\mathrm{Ce}}^{140}$, and ${\mathrm{Ce}}^{142}$ have been observed in order to measure the effect of the nuclear interaction on a pion in a $3d$ atomic level. The results are used to look for differences in the pion interaction with these nuclei. Within experimental error, we could not detect an isotope shift in the ${\mathrm{Ce}}^{142}$-${\mathrm{Ce}}^{140}$ results. The nuclear isotone shift in the x-ray energy and width for ${\mathrm{Ce}}^{140}$-${\mathrm{Ba}}^{138}$ of 1.59 \ifmmode\pm\else\textpm\fi{} 0.30 and 1.3 \ifmmode\pm\else\textpm\fi{} 1.3 keV agrees with the values of 1.31 and 2.0 keV predicted from an optical-model calculation.

Muonic x-ray transition energies have been measured in $^{120}\mathrm{Sn}$, $^{138}\mathrm{Ba}$, $^{140}\mathrm{Ce}$, $^{142}\mathrm{Ce}$, and $^{206}\mathrm{Pb}$ using a high-efficiency Ge(Li) detector. Precise measurements and relative-intensity measurements have made it possible to identify transitions to and from the $2s$ state in each of these targets. There is good agreement between theoretical and experimental relative intensities for these transitions, except for the $^{206}\mathrm{Pb}$ nucleus. These transition energies, together with those from the $2p\ensuremath{-}1s$, $3d\ensuremath{-}2p$, and $4d\ensuremath{-}2p$ transitions are used to deduce sets of nuclear charge parameters. It has been found that for each target except $^{120}\mathrm{Sn}$, the best agreement between theory and experiment is obtained by applying the theoretical nuclear polarization corrections to all levels with $ng1$, and varying the nuclear polarization induced by the muon in the $1s$ state. The nuclear polarization values determined were 5.8 \ifmmode\pm\else\textpm\fi{} 1.5 keV for $^{120}\mathrm{Sn}$, 6.7 \ifmmode\pm\else\textpm\fi{} 1.4 keV for $^{138}\mathrm{Ba}$, 6.5 \ifmmode\pm\else\textpm\fi{} 1.3 keV for $^{140}\mathrm{Ce}$, 7.0 \ifmmode\pm\else\textpm\fi{} 1.4 keV for $^{142}\mathrm{Ce}$, and 5.5 \ifmmode\pm\else\textpm\fi{} 1.7 keV for $^{206}\mathrm{Pb}$. These results are in fair agreement with the most recent theoretical predictions.

Antiprotons were brought to rest in targets of gaseous ${\mathrm{H}}_{2}$ and gaseous He at temperatures of 30 K and also in a target of liquid ${\mathrm{H}}_{2}$. High-resolution x-ray detectors were used to measure the energies of x rays from $\overline{\mathrm{p}}$-He and to search for x rays from $\overline{\mathrm{p}}$-H. The $\overline{\mathrm{p}}$-He data are compared with similar measurements at different densities and with the theoretical predictions of Landua and Klempt. The $\overline{\mathrm{p}}$-H data provide upper limits for the yields of $\mathrm{nP}\ensuremath{\rightarrow}1S$ x rays in liquid and gaseous hydrogen.

A new and more precise measurement of the magnetic moment of the ..sigma../sup -/ hyperon is reported. The result of (-1.48 +- 0.37)..mu../sub N/ is in agreement with the sign given by simple SU(3) theory, but differs somewhat from the value of -0.9..mu../sub N/ predicted by the theory with no mass breaking. 2 figures.

Correlations are noted in the variation with atomic number of kaonic, pionic, and muonic x-ray yields, and positron-annihilation lifetimes in annealed metals, These variations are believed to be due to the variation with Z of the electron density in the outer part of the target atoms. (AIP)

>We calculated x-ray energy-level shifts, widths, and relative x-ray transition yields for antiproton and SIGMA - atoms throughout the Periodic Table. An optical potential was used and the relationship to experimental determinations is discussed. (auth)

We have measured fine-structure splittings in atoms formed by antiprotons with both lead and uranium. Since the fine structure is produced by an interaction between the magnetic moment of the antiproton and the Coulomb field of the nucleus, a value for the magnetic moment can be derived from the observed splitting. We find a magnetic moment of - 2.83 \ifmmode\pm\else\textpm\fi{} 0.10 nuclear magnetons which agrees with the $\mathrm{TCP}$ prediction.

Using a local $K$-nucleus optical potential, we calculated x-ray energy-level shifts and widths and relative x-ray transition yields for kaonic atoms throughout the Periodic Table. We made a detailed study of the determination of the nuclear density parameters from level-shift and width data.