H.J. Leisi

SPECTROSCOPIC QUADRUPOLE MOMENT OF 23Na FROM MUONIC X-RAYS+

Abstract With the crystal spectrometer at muon channel I at SIN we measured the 3 d 5 2 −2 p 3 2 transition in muonic 23Na. The h.f.s. of the 2 p 3 2 level was resolved and the spectroscopic quadrupole moment of the nuclear ground state determined: Q = 0.1006 ± 0.0020 b. Using a collective particle-rotor model description of 23Na which includes small ΔK = 1 admixtures in the wave functions, we find agreement between our measured spectroscopic quadrupole moment and the one derived from measured B(E2) values. Combining the quadrupole moment Q with the quadrupole coupling constant measured in the electronic atom of 23Na, we derive the electric field gradient at the nucleus for two different electronic states: 〈dE/dz〉 = 0.1185(32)ea−30 for the 3 2 P 3 2 state, 〈dE/dz〉 = 0.0410(27)ea−30 for the 4 2 P 3 2 state. The field gradient for the 3 2 P 3 2 state is compared with recent many-body calculations of the hyperfine interaction in alkali atoms.

New precision measurements of the muonic 3d52−2p32 X-ray transition in 24Mg and 28Si: Vacuum polarisation test and search for muon-hadron interactions beyond QED☆

Abstract Motivated by the importance of scalar particles in the current work on gauge theories of fundamental interactions, we have performed an improved muonic-atom experiment to search for long-range muon-hadron interactions. We remeasured the wavelengths of the 3 d 5 2 −2 p 3 2 X-ray transitions in 24Mg and 28Si with the bent-crystal spectrometer at the SIN muon channel. The relative difference between the X-ray wavelength λexp and the theoretical value as obtained from QED calculations, averaged over the two elements, is λ exp -λ QUED /λ QUED = (-0.2 +-3.1) × 10 6 Assuming the validity of the QED calculations, we can put limits on an additional muon-nucleon interaction: If such an interaction were mediated, for example, by a scalar or vector (isoscalar) boson with a mass smaller than about 1 MeV, the corresponding coupling constant is gμgN ⩽ 0.8 × 10−6 × e2. Alternatively, if additional muon-hadron interactions are negligible, our result corresponds to a 950 ppm test of the vacuum polarisation effect in QED. The result can also be interpreted as a 3 ppm measurement of the negative muon mass.

Precision measurement of the 2p-1s transition in muonic 12C: Search for new muon-nucleon interactions or accurate determination of the rms nuclear charge radius☆

The wavelength of the 2p32-ls12 transition in muonic 12C was measured with a crystal spectrometer as 16.473765 (88) pm. With an improved model-independent analysis we deduce an rms charge radius for 12C of 2.4829 (19) fm. A 2.4 standard deviation difference between our rms charge radius and that deduced from recent elastic electron-scattering experiments is tentatively attributed to a short-range additional interaction between muon and nucleons. A comparison is made with other experiments yielding information on such interactions.

Vacuum polarization test and search for muonhadron interactions from muonic X-rays:: Crystal-spectrometer experiments

Abstract We have measured the wavelengths of the 3 d 5 2 −2 p 3 2 and the 3 d 3 2 -2 p 1 2 X-ray transitions in μ - 24 Mg, - 28 Si and - 31 P with the bent-crystal spectrometer at the SIN muon channel. The X-rays are measured relative to the wavelengths of the 84 keV and the 63 keV γ-rays of 170 Tm and 169 Yb which have recently been calibrated to about 1 ppm. The measured X-ray wavelengths λ exp are compared with theoretical values λ th , as obtained from QED calculations. The relative difference, averaged over all six measured transitions, is λ exp −λ th λ th = (2 ± 8) × 10 −6 This result corresponds to a test of the vacuum polarization effect in QED of (0.6 ± 2.4) × 10 −3 . Assuming the QED calculations to be correct, we can use the result to put limits on additional muon-nucleon interactions (as required by gauge theories). If such an interaction is mediated by a scalar, isoscalar boson with a mass smaller than 1 MeV, the coupling constant is found to be g N g μ 4π = (−4 ± 17) × 10 −9 Alternatively, we can deduce from our experiments the most accurate direct value to date for the negative muon mass, m μ - = 105.65906(91) MeV .

Nuclear spectroscopic ground-state quadrupole moments from muonic atoms: The quadrupole moment of 175Lu

Abstract We have measured the quadrupole splittings of the 4f → 3d, 5f → 3d and 5g → 4f X-ray transitions in muonic 175 Lu. These states whose size is large compared to the nuclear dimensions are very much hydrogen-like. Hence the quadrupole splitting is almost exclusively determined by the nuclear spectroscopic quadrupole moment Q . The small corrections due to the finite nuclear size, dynamical nuclear excitation and nuclear polarization, vacuum polarization and the M1 and E4 hyperfine interactions are investigated in detail. The ground-state quadrupole moment of 175 Lu is determined to be Q = +3.49 ± 0.02 b. The prediction of the rigid rotar model is tested by combining Q with recently measured B ( E 2) values. From the h.f.s. of the 3d 5 2 state the hexadecapole moment of 175 Lu is estimated to be Π ≈ 0 ± 0.02 b 2 . The quadrupole structure of the 3d → 2p and 2p → 1s transitions have also been measured. By the method described, precise spectroscopic quadrupole moments from muonic atoms can be obtained.

Observation of nuclear rotational spectra in pion capture on 165Ho and 175Lu

Abstract In X-ray spectra of pionic atoms of 165 Ho and 175 Lu we observed nuclear γ-rays of Dy and Yb isotopes, respectively, arising from the pion capture reactions 165 Ho(π − , x n 165−x Dy ∗ , and 175 Lu(π − x n 175− Yb ∗ , where x = 1, 3, 5, 7, 9, 11.

Monopole and quadrupole strong interaction effects in pionic atoms of 175Lu and 165Ho

Abstract We have measured the strong-interaction monopole energy shift e0 and width Γ0, and the quadrupole splitting of the 4f level in pionic 175Lu and 165Ho. The monopole results are: e0(Lu) = 597 ± 70eV, e0(Ho) = 295 ± 80 eV, Γ0(Lu) = 200 ± 70eV and Γ0(Ho) = 190 ± 40eV. The monopole shift in the case of lutecium deviates from the value obtained with a standard optical potential description of the pion-nucleus interaction. Using the (electromagnetic) quadrupole moment as measured recently in an experiment on muonic 175Lu, we find for the strong-interaction quadrupole constant of the 4f state in 175Lu e2 = − 89 ± 29 eV. The ratio e 2 e 0 is in good agreement with theoretical predictions. We relax the usual assumption in the optical potential of a homogeneous mixture of neutrons and protons and show that e0 and e2 are mainly given by the generalized moment 〈rκe−αr〉 (κ = 3.93, α = 0.21 fm−1) of the monopole and the quadrupole density of the neutrons, respectively. We deduce from the measured monopole shifts the ratio R between the generalized monopole moment above and the value of the same moment if neutrons and protons are homogeneously mixed (the latter is taken from muonic atom data). The results are R(Lu) = 1.34 ± 0.16 and R(Ho) = 1.14 ± 0.26. The deviation of R(Lu) from unity may be interpreted in two ways: the optical potential in the present form is not sufficient for the analysis of the 4f level shift in π-175Lu, or there is a difference between the neutron and proton monopole density distributions in this nucleus.

Spectroscopic quadrupole moments of 25Mg and 27Al from muonic X-rays

Abstract With the crystal spectrometer at Muon Channel I at SIN we measured the 3d 5 2 -2p 3 2 X-ray transitions in muonic 25Mg and 27Al. The h.f.s. of the 2p 3 2 was resolved and the spectroscopic quadrupole moment of the nuclear ground states determined: Q( 25 Mg ) = +0.201 ± 0.003 b , Q( 27 Al ) = +0.150 ± 0.006 b . We find agreement between the intrinsic quadrupole moment value derived from Q( 25 Mg ) with those calculated from measured B(E2) values. This indicates that for 25Mg the strong-coupling limit of the rotational model with an axially symmetric charge distribution is realized in the lower part of the ground-state rotational band. We combine the quadrupole moments Q with the quadrupole coupling constants measured in electronic atoms of 25Mg and 27Al and derive the electric field gradients at the nucleus (in units of e · a0−3, where a0 is the Bohr radius): 〈 d E d z 〉 = 0.339± 0.005 for the 3P2 state of 25Mg, 〈 d E d z 〉 = 0.54± 0.02 for the 2P 3 2 state of 27Al. From Hartree-Fock calculations of the 2P 3 2 state of Al we derive values for the Sternheimer correction factor R and compare them with calculated values.

Precision measurement of the wavelengths and natural line widths of 3d-2p pionic X-ray transitions in low-Z atoms

Abstract The wavelengths and the natural line widths of the 3d-2p transitions in the pionic atoms of 12 C, 16 O, 18 O, 24 Mg, 26 Mg, 28 Si and 30 Si have been measured at SIN with a bent-crystal spectrometer. The precision reached in the transition wavelengths ranges from 4 to 18 ppm, and in the widths from 2 to 14%.

Spectroscopic quadrupole moment of holmium from pionic X-ray measurement☆

Abstract From the observed quadrupole splitting of the 5g-4f X-ray transition in π-165Ho we determine the spectroscopic quadrupole moment of 165Ho to be Q = 3.47±0.11 b. The strong interaction shift and the width of the 4f level are found to be ϵ0 = 0.35±0.08 keV and Γ0 = 0.21±0.04 keV, respectively.