S.C. Cheng

Mass and magnetic moment of the antiproton by the exotic atom method

Abstract Precision determinations of the mass and magnetic moment of the antiproton were made by the exotic atom method. Antiprotons were stopped in lead or uranium targets. De-excitation X-rays from the antiprotonic atoms were viewed by a high resolution Ge (Li) detector. Six principal transitions of the pPb spectrum (16 → 15 to 11 → 10) were analyzed to deduce a value of the antiproton mass. The fine structure splittings of the 11 → 10 and 12 → 11 transitions of pPb and pU were used to determine a value of the antiproton magnetic moment. Our computed values of the energy eigenvalues of the ( n , l , j ) levels included corrections due to vacuum polarization and higher order radiative terms, electron screening, nuclear finite size and nuclear polarization. In the case of the pU data, an additional shift due to the dynamic E2 mixing of nuclear rotational levels with antiprotonic orbital levels was included. Noncircular transitions were included in the analysis of the data. The values obtained for the antiproton mass and magnetic moment, 938.179±0.058 MeV and − 2.791±0.021 nuclear magnetons, respectively, are compared with the corresponding quantities pertaining to the proton, 938.2796 ± 0.0027 MeV and +2.793 nuclear magnetons, respectively (error 1.1 × 10 −6 nuclear magnetons).

Nuclear excitation in muonic 209Bi

Abstract The hyperfine spectra of muonic L and K X-rays of 209Bi have been reanalyzed by taking into account the resonance processes and the observed isomer shifts in addition to the M1 and the E2 interaction. The M1 and E2 hyperfine structure constants of the 1s, 2p and 3d muonic states and the nuclear static moments of the excited states 15 2 + and 9 2 + are determined from the best fits to the experimental spectra. The hfs constants and the M1 moments are in good agreement with theoretical predictions from the core excitation model. The quadrupole moment of the ground state remains to be 20% higher than that determined by the atomic beam method. A plausible interpretation is that this discrepancy might be due to the deformation of the lead core.

K− mass from kaonic atoms☆

Abstract The energies of the six circular transitions ( n = 13 → n = 12 through n = 8 → n = 7) of the K − Pb exotic atom have been measured to high precision (typically ∼ 50 ppm) using Ge (Li) spectrometers. The data acquisition system was computer controlled and stabilized, the energy calibration spectrum was taken simultaneously with the data spectrum. The experimental energies of the six transitions were corrected for ADC nonlinearities and data-calibration spectrum shifts, as well as the presence of unresolved noncircular transition contaminants. The energies of five of the transitions (13 → 12 through 9 → 8) were computed from quantum electrodynamics, including all significant orders of vacuum polarization, electron screening and nuclear polarization. The mass of the K − was adjusted to achieve a best fit with the experimental energies: the result was m K − = 493.657 ± 0.020 MeV.

Electric quadrupole moments and strong interaction effects in pionic atoms of 165Ho, 175Lu, 176Lu, 179Hf and 181Ta

Abstract The effective quadrupole moments Q eff of the nuclei of 165 Ho, 175 Lu, 176 Lu, 179 Hf and 181 Ta were accurately measured by detecting the pionic atom 5g-4f X-rays of the elements. The spectroscopic quadropole moments, Q spec , were obtained by correcting Q eff for nuclear finite size effect, distortion of the pion wave function by the pion-nucleus strong interaction, and contribution to the energy level splittings by the strong interaction. The intrinsic quadrupole moments, Q 0 , were obtained by projecting Q spec into the frame of reference fixed on the nucleus. The shift, e 0 , and broadening, Γ 0 , of the 4f energy level due to the strong interaction between the pion and the nucleons for all the elements were also measured. Theoretical values of e 0 and Γ 0 were calculated and compared to the experimental values. The measured values of Q 0 were compared with existing results in muonic and pionic atoms. The measured values of e 0 and Γ 0 were also compared with existing values.

The study of quadrupole hyperfine interactions in pionic atoms of181Ta and165Ho

ConclusionIn Table 3 we have listed the Q values of165Ho and181Ta obtained by the pionic methods from this experiment and the one from Ebersoldet. al. and also the results by the muonic methods.4, 5 They are all in good agreements within the experimental uncertainties around 1%. The large discrepency between the Q values of181Ta from Ref. 5 and Ref. 7 was discussed and explained in detail in Ref. 5.The εo obtained in165Ho is comparable to the εo calculated by using the Kisslingers potential. However, the experimental εo for181Ta from this experiment is 28% larger than the theoretical value by Scheck3 by using the perturbation method.As it was mentioned at the beginning of this paper that the strong interaction quadrupole effect introduces characteristic level broadening to each components of the multiplet. The excellent fit between the calculated composite curve with the observed experimental h.f.s. spectra could be obtained only by varying all three independent parameters Qeff, εo and Γo. Without Γo, or Γ2, no satisfactory fitting could be obtained. That this illustrates the intrigue strong quadrupole effects on each components of a multiplet do behave as predicted by Scheck.3

E2 dynamic mixing in p̄ and k− atoms of 238U☆

Abstract The energies of the lower atomic transitions of the p and the K − atoms of 238 U have been measured. The measured values are significantly higher than the energies calculated from the electromagnetic interactions with the ground state of the 238 U nucleus. It is shown that the dynamic mixing of the first excited quadrupole state can explain such shifts.

Resonance processes and nuclear excitation in muonic 205Tl

Abstract The L and K X-rays of muonic 205Tl have been measured with an enriched (99.8 %) 205Tl target. Two sets of resonance processes were included in the analysis, which led to satisfactory fits to the experimental spectra, and explain the anomalous intensity ratios between the fine structure components of the muonic L and K X-rays. At the same time, the M1 hyperfine structure constants, which show the finite distribution of the nuclear M1 moment, were determined. Also determined were the static nuclear E2 and M1 moments of the excited states.

The Resonance Process and the Intensity Anomaly in Muonic 127I

It has been known for some time that the intensity ratio between the (2p3/2-Is1/2) and (2p1/2-Is1/2) muonic X-rays for 127I is anomalously smaller than the theoretical value 1.95. Several theorists(1),(2),(3) have suggested that this may be explained by nuclear resonance excitation. We have observed the muonic N, M, L and K X-rays from 127I, and have calculated a theoretical spectrum within the framework of a resonance process. The resonance is between the 2p fine structure splitting and the nuclear ground and the first excited states. A satisfactory fit to the experimental data has been obtained. From this fit we have determined the M1 and E2 hfs constants for the is and 2p states, and have obtained a quantitative interpretation of the observed intensity ratios.

Rotational excitations in residual nuclei produced by stopped negative pions on targets of 165Ho, 175Lu, 176Lu, 179Hf, and 181Ta

Abstract Reactions produced by stopped negative pions on targets of 165 Ho, 175 Lu, 176 Lu, 179 Hf, and 181 Ta are investigated by measuring photons coincident with the stopped pions. These photons were detected with an 80 cm 3 Ge(Li) detector and identified as pionic X-rays or rotational γ-rays from the residual nuclei. Pion capture is found to result in the excitation of high-spin states. Yields for the residual nuclei are inferred from the observed γ-transitions and compared to calculations based on the exciton model for pre-equilibrium emission followed by particle evaporation. Preliminary results of a pion stop, γn coincidence experiment are presented and compared to the calculations.

Magnetic dipole hyperfine structure in muonic atoms

Abstract The nuclear finite-size effect in the M1 hyperfine structure of muonic atoms of 93Nb and 139La has been studied experimentally. Systematic differences of the finite-size effect between nuclei in which the spin and the orbital angular momentum of the odd proton are parallel or anti-parallel are discussed.