Pionic X-rays from 12, 13C

The energies and widths of pionic 2p-1s and 3d-2p X-rays have been measured in ^12,13C. Values obtained are

${}^{12}\text{C: 2p-1s E=93.221(55)}\text{keV}\text{, τ=2077(14)}\text{keV}$

$\text{3d-2p E=18.400(6)}\text{keV}\text{, τ=1.17(11)}\text{eV}$

${}^{13}\text{C: 2p-1s E=92.227(27)}\text{keV}\text{, τ=2.59(11)}\text{keV}$

$\text{3d-2p E=18.427(5)}\text{keV}\text{, τ=0.97(10)}\text{eV}$

The muonic 2p-1s X-ray energies in ^12,13C have also been measured. The strong interaction effects are discussed in relation to recent low-energy pion scattering measurements.     

Kaonic Hydrogen atom X-rays

The X-ray spectrum obtained with kaons stopping in liquid hydrogen has been measured. Possible candidates for X-ray lines from kaonic hydrogen atoms have been identified and the results compared with previous experiments and with theoretical predictions. X-ray lines from σ^?p atoms may also have been observed.     

X-rays from antiprotonic helium in helium gas

X-ray transitions to the 4F, 3D, and 2P atomic levels of p?He have been observed with antiprotons stopped in He gas at 4 and 1.1 atm NT. The population by radiative transitions of the 3D level in gas Y_M(4atm) = (28±14)% and Y_M(1.1 atm) = (43±22)% exceeds by more than one order of magnitude that measured in liquid He. The annihilation width of the 3D level Γ^a_3D = 2.8±1.0 × 10^?3eV is determined from the ratio between the numbers of X-rays feeding and depopulating the 3D level. The strong-interaction shift of the 2P level ε(2P) = ?14±6 eV is obtained by inputting the $\text{p}\text{He}$ experimental X-ray yields into a cascade calculation, the results of which are in good agreement with well-established data from muonic, pionic, and kaonic helium.     

Measurement of pionic and muonic X-rays IN B

The energies of muonic 2p-1s X-rays in ¹⁰B and ¹¹B have been measured to be 52217(8) eV and 52279(5) eV, from which the rms nuclear charge radii were calculated to be 2.44(6) fm and 2.38(4) fm. The energies and widths of pionic 2p-1s X-rays have been measured in ¹⁰B to be 65901(13) eV and 1780(30) eV, and in ¹¹B to be 65120(26) and 1720(80) eV. The sensitivity of the strong interaction shift to the neutron matter distributions has been investigated using an optical-model approach. The results of these calculations are not in good agreement with the experimental results when reasonable values of the nuclear matter distributions are used.     

Pionic x-ray transitions in 3He

Pionic ³He atoms have been produced in a gaseous target. Energies and strong absorption broadening of the 2 → 1 and the 3 → 1 transition lines have been measured. The 1s level is shifted by 44 ± 5 eV by the (attractive) strong interaction, and the natural 1s level width is 42 ± 14 eV.     

Pionic X-rays from argon and hydrogen plus argon

Pionic X-ray spectra from argon and hydrogen plus argon have been measured with a high-pressure gas target. Energy and natural width of the 3d?2p)-line were determined to beE=168.88±0.10 keV andΓ=1.17±0.17keV, respectively. An upper limit of 56% at 90% confidence was obtained for the probability of pion transfer from hydrogen to argon.     

Nuclear charge radii from muonic X-ray transitions in F,Na, Al,Si, P,S and K

Energies of muonic X-rays of the Lyman series of seven light natural elements (F, Na, Al, Si, P, S and K) have been determined with an accuracy of between 15 and 30 eV. Equivalent charge radii have been deduced. For μ^?-K, transitions to the 2s state allowed an additional constraint on the Fermi c-t diagram. The results are in good agreement with, and generally of an order of magnitude higher precision than, comparable electron scattering data.     

Measurement of strong interaction effects in kaonic atoms

X-rays produced by kaons stopping in targets of O, Mg, Al, Si, S, Co, Ni, Cu, Ag, Cd, In and Sn have been observed. The shifts, widths and yields of the last observed mesic X-ray due to the effects of the strong interaction have been measured. The results are compared with optical-model predictions.     

Measurements of the polarization of the 2p and 1s states in muonic atoms and the helicity of the muon in pion decay

We have measured the polarization of the 2p and 1s states in muonic selenium (amorphous and metallic modifications), cadmium, palladium and iodine, in order to study the depolarization of muons in the cascading process and to measure the helicity of the μ^?. In the cases of cadmium, palladium and amorphous selenium good agreement between the measurements and cascade calculations is found. There is an unexpected depolarization of the 2p_{$\text{1}\text{2}$} state in metallic selenium. The helicity of the muon after the pion decay was measured to h_μ^? = + 0.99 ± 0.16.     

X-rays from antiprotonic3He and4He

Antiprotonic X-rays from the helium isotopes have been observed at pressures of 36, 72, 375 and 600 mbar. The antiproton beam from LEAR with momenta of 309 and 202 MeV/c has been stopped at these pressures using the cyclotron trap. The X-rays were detected with Si (Li) and intrinsic Ge semiconductor detectors. Absolute X-ray yields were determined and the strong-interaction 2p shifts and the 2p and 3d broadenings measured to be _2p=(–17±4) eV, _2p=(25±9) eV and _3d=(2.14 ±0.18) meV for ¯p³He and _2p=(-18±2) eV, _2p =(45±5) eV and _3d=(2.36±0.10) meV for ¯p⁴He.The efforts of the LEAR staff and the help of P. Gauss from the CERN Cryogenic Group as well as the technical assistance of M. Dröge and M. Stoll are gratefully acknowledged. This work is part of the Ph.D. of one of us (M.S.), University of Karlsruhe (1987), KfK report no. 4222.     

Pionic and muonic X-ray transitions in liquid helium

Energies and intensities of pionic and muonic X-rays in liquid ⁴He have been measured with a Si (Li) detector. The energy shift due to strong interaction effects of the pionic 1s level in ⁴He was determined to be ?75.7±2.0 eV. The natural line width of this level is 45±3 eV. These values are compared with different theoretical predictions. Cascade calculations, including external Auger effect and sliding transitions, have been performed to reproduce the yields of the muonic and pionic transitions. The pionic 2p level width is deduced: $\text{Γ}{}_{\mathrm{<mtext>2</mtext><mtext>p</mtext>}}\text{= (1.1 ± 0.5) × 10}{}^{12}\text{sec}{}^{\mathrm{?1}}\text{=}\text{(7.2±3.3) × 10}{}^{\mathrm{?4}}\text{eV}$.     

Precision measurement of the 2p-1s transition wavelength in muonic 13C

With the bent-crystal spectrometer at the SIN muon channel we have measured the wavelength of the 2p-1s transition in muonic ¹³C with a precision of 13 ppm. The result for the $\text{2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{-1}\text{S}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ transition is $\text{λ(2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{-1}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{) = 16.46055 ± 0.00021}\text{pm}$; it is interpreted in terms of a short-range muon-nucleon interaction not included in standard QED calculations.     

Measurement of average electron densities in Si and Ge using MeV δ-rays produced by channelled high-energy projectiles

For the first time, average electron densities in silicon and germanium were measured using the channeling effect for 5 and 12 GeV/c protons, π⁺ and π^?. In the investigation, the yield of MeV electrons emitted through the back of the target was measured. Such gd-ray yields are proportional to the local electron density averaged along the path of the projectile in the target. For well-aligned, positive particles, the electron yield is reduced to around 15% of normal yield for germanium and 25% for silicon, whereas negatively charged, channeled projectiles give an increase in yield by a a factor of three compared to normal yield. The experimental results have been compared to yield curves calculated using the Lindhard channeling model in connection with special potential models, and very good agreement is obtained for positive particles when the electron density in the middle of the channels is obtained by summing the contributions from many neighbouring strings. For positive projectiles, this channeling method is most sensitive far away from the strings, where other techniques are weak. The results for negative, channeled particles agree fairly well with simplified theoretical calculations, neglecting dechanneling and the lack of equilibrium in angular momenta in the transverse plane.     

X-rays from pionic 3He

Pionic X-ray energies, lorentzian widths, and relative intensities have been measured for the transitions in liquid ³He. The pion-nucleus interaction is found to result in an attractive shift of the 1s level of 27 ± 5 eV and in a lorentzian width of 65 ±12 eV. The measured K_β to K_α intensity ratio is 1.05±0.07.     

Experimental study of pionic Ca and Ti and examination of the pion-nuclear potential for low-Z nuclei

We report the measurement of the strong interaction shifts and widths of the 3d → 2p transitions in pionic ^{40,42,43,44,48}Ca and ^46,48,50Ti. Using these new data in combination with earlier low-Z pionic data (6 ≦ Z ≦ 16), we have studied, in a purely phenomenological way, the pion-nuclear optical potential. Employing nuclear-structure information from Hartree-Fock calculations and measured charge densities, we have fitted the pion-nuclear potential parameters to the pionic atom data. The effect of adding an isovector dependence to the s- and p-wave two-nucleon terms has been investigated. We have also explored the sensitivity of these data to the value of the Lorentz-Lorenz parameter ξ. A small but definite sensitivity to the latter parameter has been observed with the best fit value of ξ being significantly greater than 1. We have used the phenomenological potentials to determine the neutron radii of the Ca and Ti isotopes and, in fact, find reasonable agreement with Hartree-Fock predictions and with the results of other hadronic probes.     

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

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 p?Pb 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 p?Pb and p?U 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 p?U 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).     

Quark cluster model and the R-matrix theory treatment of NN scattering

A microscopic quark cluster model has been developed for six-quark states consisting of two s³ quark clusters. The consequences of channel nonorthogonality and existence of Pauliforbidden states are investigated explicitly by solving the eigenvalue problem of the resonating group method (RGM) kernel. Since the RGM kernels needed are all available, the form of the six-quark states given in this paper is very suited to detailed RGM calculations. A rigorous treatment based on the R-matrix theory has been carried out to obtain NN phase shifts. The spin-spin term of the quark-quark interaction favors states of higher color-spin symmetry. This explains the larger change caused by the hidden color states in the ³S₁ phase shifts than in the ¹S₀ phase shifts. Phase shifts calculated with inclusion of the delta and hidden color states are still too repulsive. It is pointed out that there arises a subtle problem in adding the one-boson exchange potential by hand to the RGM equation.     

Mass and magnetic moment of Σ− by the exotic atom method

The energies and lineshapes of five circular transitions (n = 15 → n = 14 through n = 11 → = 10) of the Σ^?Pb atom were measured wit of the transitions 15 → 14 through 12 → 11 were determined; these energies were compared with energies calculated from quantum electrodynamics, and the mass of Σ^? was adjusted to achieve a best fit. The result was m_Σ^? = 1197.24 ±0.15 MeV. The lineshape of the 12→11 transition, which is broadened by the fine structure, has been analyzed to extract the magnetic moment of Σ^?. The result was μ_Σ^? = ?1.40_?0.28^+0.41or 0.651_?0.40^+0.28 nuclear magnetons. Comparisons with SU (3) predictions are made.