We report on an experiment at the Paul Scherrer Institute, Villigen, Switzerland measuring x rays from muon transfer from deuterium to helium. Both the ground-state transfer via the exotic (dmu(3,4)He)(*) molecules and the excited-state transfer from (mud)(*) were measured. The use of charge-coupled device detectors allowed x rays from 1.5 keV to 11 keV to be detected with sufficient energy resolution to separate the transitions to different final states in both deuterium and helium. The x-ray peaks of the (dmu(3)He)(*) and (dmu(4)He)(*) molecules were measured with good statistics. For the D-2+He-3 mixture, the peak has its maximum at (EdmuHe)-He-3=6768+/-12 eV with full width at half maximum (FWHM) Gamma(dmu)(3)He=863+/-10 eV. Furthermore, the radiative branching ratio was found to be kappa(dmu)(3)He=0.301+/-0.061. For the D-2+He-4 mixture, the maximum of the peak lies at (EdmuHe)-He-4=6831+/-8 eV and the FWHM is Gamma(dmu)(4)He=856+/-10 eV. The radiative branching ratio is kappa(dmu)(4)He=0.636+/-0.097. The excited-state transfer is limited by the probability to reach the deuterium ground state, q(1s). This coefficient was determined for both mixtures: q(1s)(3)He=68.9+/-2.7% and q(1s)(4)He=90.1+/-1.5%.

The energy and time distributions of the decay X-rays of excited, metastable, molecular ( d µHe)*-resonances were measured. The comparison of the observed energy spectra with calculated ones suggests that decay from the rotational state J = 1 dominates at the investigated conditions. The muon transfer rates from ground state deuterium to the helium isotopes 3 He and 4 He at low temperatures were determined from the time distributions of these spectra. Additionally, the temperature dependence of the muon transfer rate was clearly established in deuterium / 4 He mixtures.

The scientific program and the experimental setup of the DEAR (DAΦNE Exotic Atom Research) experiment at the new φ-factory DAΦNE of Laboratori Nazionali di Frascati are described. The objective of DEAR is to perform a 1% measurement of the K α line shift due to the strong interaction in kaonic hydrogen. A measurement will also be performed on kaonic deuterium for the first time. The aim is to investigate low-energy \(\overline K N\) physics and to understand SU(3) chiral symmetry breaking. The setup takes advantage of the unique features of the “kaon beam” from the φ decay in DAΦNE; of a low-temperature pressurized gaseous target; and of a detector for soft X-rays – the Charge-Coupled Device (CCD) – characterized by a very good energy (and spatial) resolution and by an unprecedented background rejection capability. The DEAR experiment represents a major effort in the study of low energy \(\overline K N\) interactions and has the potential to produce a breakthrough in the field.

The DEAR (DAΦNE Exotic Atom Research) experiment at the new φ-factory DAΦNE of Laboratori Nazionali di Frascati aims for a 1% measurement of the line shift of the K-complex due to strong interaction in kaonic hydrogen. This presentation is meant to prove that the high statistics and good resolution obtainable with DEAR will be able to disentangle the kaonic hydrogen K-complex lines (a cascade unconstrained fit), obtaining in this way constraints for what concerns the cascade parameters and, consequently, information regarding the physical processes involved in the kaonic hydrogen atomic cascade.

The transfer reaction of negative muons from muonic protium to 3 and 4 in binary and triple gas mixtures was studied. In the binary mixtures the transfer rates to the two helium isotopes were determined from the time distribution of the 7-keV X-rays of the intermediate muonic molecule (pµHe)*. The experimental transfer rate to 4 is in good agreement with theoretical predictions, whereas the rate to 3 is a factor 2 to 3 smaller than the predicted ones. Radiative branching ratios of the (pµHe)8 molecular decay were obtained. Muon transfer from excited states of muonic protium gives the main contribution to the total intensity of the µHe Lyman series in the binary mixtures. Values of q 1s He are determined.

Formation and decay of the (p mu(3)He)* and (p mu(4)He)* molecules have been studied in binary-gas mixtures of H-2 + He-3 and H-2 + He-4 at 30 K. The muon ground-state transfer rates from hydrogen to the two helium isotopes were extracted from the time distribution of the 7-keV decay x rays of the muonic hydrogen-helium molecules, measured with a Ge detector. The obtained transfer rates are lambda(p3He) = (0.46 +/- 0.15) x 10(8) s(-1) and lambda(p4He) = (0.42 +/- 0.07) x 10(8) s(-1). The radiative branching ratios of the decay of the (p mu(3)He)* and (p mu(4)He)* molecules were determined by comparing the yields of the Lyman series of muonic hydrogen with the one of the 7-keV line with charge-coupled-device detectors. The ratios are in agreement with theoretical predictions. Muon transfer from excited states of muonic hydrogen to both helium isotopes was also observed. [S1050-2947(98)07010-3].

Muon transfer from excited mu p* and mu d* atoms to the three gases nitrogen, neon, and argon is studied. Variations of the experimental conditions such as pressure and relative concentrations on the fractions alpha(pZ) and alpha(dZ) of excited state events in prompt muonic x rays are analyzed. The differences between excited-state transfer from mu p* and mu d* to N-2, Ne, and Ar are discussed. For these elements, capture ratios A(H-2,Z) and A(D-2,Z) are given, from which an indirect value A(H-2,D-2) is deduced.

The present status of research of muon transfer from the ground state of muonic protium to 4He is reviewed. The analysis of a recent measurement in a triple gas mixture of H2+4He+Ne at 15 bar and room temperature is presented and the result is compared to the existing experimental and theoretical rates. The average muon transfer rate from protium to 4He determined from all lifetime measurements is \(\).

The transfer reaction of negative muons from (mu p)(1?(s) atoms to He-3 and He-4 was studied at 30 K, and the transfer rate to He-3 was determined. Germanium detectors were employed to measure the time distribution of muonic neon x rays in triple-gas mixtures H-2 + He-3?(,He-?(4+Ne. The rates for the two helium isotopes, normalized to the atomic density of liquid hydrogen, are determined as lambda(p?(3?(He)=(0.29+/-0.12) x 10(8) s(-?(1) and lambda(p?(4?(He)=(0.55 +/- 0.07)x10(8) s(-?(1). The transfer rate to neon was obtained from binary H-2 + Ne gas mixtures, measured at the same experimental conditions as for the triple-gas mixtures, with the result lambda(pNe)=(0.0677+/-0.0032)x10(11) s(-?(1).

The scientific program and the experimental setup of the DEAR (DAΦNE Exotic Atom Research) experiment on the new ϕ-factory DAΦNE of Laboratori Nazionali di Frascati, are presented. The objective of DEAR is to perform a 1% measurement of the shift, due to the strong interaction, of the K_α line of kaonic hydrogen and a similar precision measurement, performed for the first time, on kaonic deuterium. The aim is to investigate the low-energy KN physics and to understand SU(3) chiral symmetry breaking. DEAR looks as the major effort ever performed to study low energy KN interaction, capable to produce a real breakthrough in the field.

The charge exchange reaction of negative muons from the \((\mu {\text{p}})_{1{\text{s}}} \) atom to oxygen has been measured in gaseous mixtures of H2 + O2. The measurements were performed at three different relative oxygen concentrations ranging from 0.2% to 0.8% and total pressures 3.5–15 bar. A mean transfer rate of \(\lambda _{{\text{pO}}}^{\text{t}} = 0.85(2) \times 10^{11} {\text{s}}^{{\text{ - 1}}} \), describing the transfer from the ground state of thermalized \(\mu {\text{p}} \) atoms to oxygen, was determined. In order to investigate the energy dependence of the transfer rate, Monte Carlo simulations of the \((\mu {\text{p}})_{1{\text{s}}} \) thermalization and the muon transfer were carried out. The comparison of measured and simulated time spectra yielded an epithermal transfer rate \(\lambda _{{\text{pO}}}^{\text{e}} \)=3.9 \(\times \) 1011 s-1 in the energy interval 0.12–0.22 eV. The analysis with the model of “Two components” shows that all measured time spectra can be reproduced with the same set of parameters.

Formation and decay of the $(p{\ensuremath{\mu}}^{3}{\mathrm{H}\mathrm{e})}^{*}$ and $(p{\ensuremath{\mu}}^{4}{\mathrm{H}\mathrm{e})}^{*}$ molecules have been studied in binary-gas mixtures of ${\mathrm{H}}_{2}{+}^{3}\mathrm{He}$ and ${\mathrm{H}}_{2}{+}^{4}\mathrm{He}$ at 30 K. The muon ground-state transfer rates from hydrogen to the two helium isotopes were extracted from the time distribution of the 7-keV decay x rays of the muonic hydrogen-helium molecules, measured with a Ge detector. The obtained transfer rates are ${\ensuremath{\lambda}}_{{p}^{3}\mathrm{He}}=(0.46\ifmmode\pm\else\textpm\fi{}0.15)\ifmmode\times\else\texttimes\fi{}{10}^{8}{\mathrm{}\mathrm{s}}^{\ensuremath{-}1}$ and ${\ensuremath{\lambda}}_{{p}^{4}\mathrm{He}}=(0.42\ifmmode\pm\else\textpm\fi{}0.07)\ifmmode\times\else\texttimes\fi{}{10}^{8}{\mathrm{}\mathrm{s}}^{\ensuremath{-}1}.$ The radiative branching ratios of the decay of the $(p{\ensuremath{\mu}}^{3}{\mathrm{H}\mathrm{e})}^{*}$ and $(p{\ensuremath{\mu}}^{4}{\mathrm{H}\mathrm{e})}^{*}$ molecules were determined by comparing the yields of the Lyman series of muonic hydrogen with the one of the 7-keV line with charge-coupled-device detectors. The ratios are in agreement with theoretical predictions. Muon transfer from excited states of muonic hydrogen to both helium isotopes was also observed.

A method is proposed for investigating muon transfer from excited muonic hydrogen atoms to an element Z>2, and is applied to argon measurements. It makes use of a comparison between the muonic x-ray intensity patterns of the Lyman series of this element measured in mixtures with and without hydrogen. The analysis of the data taken in two gas mixtures H-2 + Ar at 15 bar with argon concentrations of 2% (0.3%), yields consistent results. In both mixtures, two thirds of the prompt argon x rays proceed from transfer from excited mu p* states. The Coulomb capture ratio determined in both mixtures yields a mean value of A(H-2,Ar) = 0.21(2), and agrees with the corresponding pionic ratio.

The yields of muonic x rays of the Lyman series of nitrogen, neon and argon have been analysed to determine capture ratios A(Z1,Z2) in about thirty gaseous mixtures under different experimental conditions. In addition, capture ratios A(Z,H) have been determined in hydrogen mixtures by taking into account transfer processes from muonic hydrogen to elements Z. The influence of the spectral flux density of the muons on capture ratios has been analysed. Our per-atom ratios form a coherent set and confirm the value A(Ar,Ne) = 1. 262(10).

Muon transfer from the ground state of muonic deuterium to a helium atom proceeds mainly via the formation of a muonic molecule in an excited state. A large number of decay X rays (∼ 6.8 keV) from these (dµHe)* molecules were observed for the4He as well as for the3He case. The time distributions of these X rays allow the determination of the ground state transfer rate. The simultaneous employment of Ge/Si-detectors and CCDs for the same target conditions allows the determination of the branching ratio of radiative to nonradiative decay for the first time.

To investigate the energy dependence of muon transfer to oxygen, we performed measurements in gaseous mixtures of hydrogen and oxygen. The time distributions of the muonic oxygen X-rays showed the same structure as the one observed earlier in H2+SO2 mixtures. In the delayed part of these distributions, one can distinguish a short-time and a long-time component. From the latter, we deduced the transfer rates from thermalized muonic protium, respectively deuterium, to oxygen. The short-time component can be interpreted as being due to muon transfer from epithermal muonic hydrogen atoms. The time parameters are characteristic for the deceleration process as well as for energy-dependent transfer rates. With results of recent research on the formation and the thermalization of muonic hydrogen, we performed Monte Carlo simulations in order to test the hypothesis of an energy-dependent transfer rate.

Several experiments performed by our group in recent years have put into evidence the complex structure of the time distributions of the muonic X-rays following transfer from muonic hydrogen isotopes to heavier elements. Simulations have shown that a substantial fraction of the µp atoms in the ground state have epithermal energies. Therefore, an energy dependence of the transfer rate seems a reasonable assumption for the explanation of the complex time structure.

Negative muons were trapped in gaseous mixtures of hydrogen and oxygen. The time distributions of the muonic oxygen X-rays showed a clear deviation from a single exponential structure. From these time distributions we evaluated the transfer rate from thermalized muonic hydrogen atoms to oxygen. In order to test the hypothesis of an energy-dependent transfer rate to oxygen we performed Monte Carlo simulations of the thermalization and the transfer process. We report on the present status of our investigations.

Muon transfer from hydrogen isotopes to helium is of importance in muon-catalyzed fusion and serves as a unique tool for the direct observation of the mesomolecular ion (pµHe)*. During two data-taking runs in 1994 and 1995 at PSI, measurements of the transfer from protium to helium were carried out using CCD's and Ge-diodes as independent X-ray detectors to obtain information on the time distribution and intensity of the 7 keV decay X-ray of the mesomolecular ion. Dual1H2 +4 He and triple1H2 + Ne +3,4He gas mixtures at low temperatures were investigated to extract transfer rates. Protium of high purity was available. For the first time a transfer rate from muonic protium to3He was measured. A general survey of our measurements and preliminary analysis is presented.