Excitation function for high-energy (p, 2p) reactions

The excitation functions of the (p, 2p) reaction cross sections for the elements ²⁵Mg, ³⁰Si, ⁵⁷Fe, ⁶⁸Zn, ¹¹⁸Sn, ¹⁴²Ce and ¹⁸⁶W have been calculated in the energy region above 100 MeV. The calculated values are compared with the available experimental results and the agreement between the two is found to be fairly good. The dependence of σ(p,2p) on the target mass number has been explained in terms of the expression derived.     

The strong interaction shift and width of the ground state of pionic hydrogen

The 3p-1s transition in pionic hydrogen was investigated with a high-resolution crystal spectrometer system. From the precisely measured transition energy, together with the (calculated) electromagnetic energy, the strong interaction shift of the 1s state was obtained as ϵ_1s = −7.127 ± 0.028(stat.)± 0.036(syst.) eV (attractive). From the natural line width, measured for the first time, we determine the decaywidth of the 1s state: Γ_1s^(decay) = 0.97 ± 0.10(stat.)± 0.05(syst.) eV. With the recently calculated electromagnetic corrections the s-wave scattering lengths of an isospin symmetric strong interaction are deduced. The scattering length for elastic scattering of a negative pion on a proton is a_{π⁻p→π⁻p}^h = 0.0885±0.00003(stat.)±0.0006(syst.)m_π⁻¹. The scattering lengthe for single charge exchange is found to be a_{π⁻p→π⁰n}^h = −0.136 ± 0.007(stat.) ± 0.003(syst.)m_π⁻¹.The experiment was performed at the Paul Scherrer Institute (PSI) in Switzerland. A focussing crystal spectrometer with an array of bent crystals, the cyclotron trap (a magnetic system designed to increase the particle stop density) and a CCD (charge-coupled device) detector system were employed. The results from the pionic hydrogen experiment — together with those from the pionic deuterium experiment — were used to test the isospin symmetry of the strong interaction. The present data are still consistent with isospin sysmmetry.     

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.     

Study on antiprotonic atoms of light nuclei and isotopes

New data on strong interaction effects in light antiprotonic atoms (N, ¹⁶O, ¹⁸O, S) are presented. For the first time an isotope effect could be observed in p?-¹⁶O/¹⁸O which is used to gain new information about the p?-n interaction in nuclei. A comparison between all existing p?-atomic data and an optical model calculation is performed, yielding a set of fit parameters for the potential.     

Muonic Au: A test of the weak-coupling model

We report the measurement of the energies of various muonic atomic transitions above 500 keV in ¹⁹⁷Au. We have used the weak-coupling model in order to analyze the hyperfine structure of ¹⁹⁷Au. Using transitions to and from the 1s, 2s 2p and 3p levels as well as the fine structure of the 2p states and hyperfine splittings of the 2p, 3p and 3d states we have fitted our data to two deformed Fermi distributions: one with a constant skin thickness, the other with a skin thickness which varies. Both yield equally good fits. We have determined the quadrupole moment of ¹⁹⁷Au to be 0.547±0.016 b. The model dependence of our results is discussed. The weak coupling parameters of de-Shalit Ω_p, Ω₂₂, Ω₂₀ and A² have been determined and are in fair agreement with Coulomb excitation results. There is also good agreement between our results and those of electron scattering.     

Direct measurement of the transfer rate pμ+Ar → p+Arμ at high gas pressure

The transfer rate pμ + Ar → p + Arμ has been directly measured in H₂ gas of 600 atm with 2.03 × 10^3̄ at. % Ar at room temperature using delayed coincidence techniques. The transfer rate reduced to an Ar concentration (atoms per unit volume) corresponding to that of liquid hydrogen was found to be (9.8 ± 1.5) × 10¹¹s^?1, which is considerably higher than previous results obtained at lower pressure.     

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.     

Determination of the hadronic width of the ground state in pionic hydrogen

In a new high-precision experiment at the Paul Scherrer Institut (PSI), the hadronic shift (ε _1s) and width (Γ_1s) of the ground state of pionic hydrogen, which are directly connected to the pion-nucleon isospin scattering lengths, were remeasured (PSI-Experiment R-98-01 Gotta et al. 1998). The results can be confronted with recent work of effective field theories defined in the low-energy limit of quantum chromodynamics (QCD), such as, e. g., chiral perturbation theory (ChPT). In addition, Γ_1s is connected to the pion-nucleon coupling constant f _πN. A precisely known value for f _πN allows an accurate determination of the Goldberger-Treiman discrepancy, which constitutes a measure of chiral symmetry breaking. This contribution is mainly devoted to describe a method for an accurate extraction of the hadronic width from the π ^??H data.     

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.     

On the eigenperiods in the Tyrrhenian Sea level oscillations

Summary In this paper the eigenperiods of the Tyrrhenian Sea are examined by a hydrodinamical model in two dimensions. The knowledge of these eigenperiods is important to evaluate the seiches that often appear, in some point or circumstance, stronger than the tides. This investigation is performed by energizing the basin through the Sardinia channel, in the same way as it was already done for the tides. This excitation simulates a large set of waves inducing oscillations inside the basin. The periods of the waves are narrow and their amplitude equal. An analogous method of investigation is that of the fluorescence. In addition, the results are compared with those previously obtained leaving the basin swinging, after having increased the sea level by a uniform displacement. The response of the bidimensional model agrees with that of a monodimensional one as far as possible; thus the last one can give useful information, also for a sea that does not have a channel shape, like the Tyrrhenian Sea. Nevertheless, this basin has other openings, besides the Sardinia channel, it seems that they do not influence the eigenperiod behaviour. This has been confirmed by performing the same computations over a sea 500 m less deep: the uniform lowering of the sea surface is equivalent to close the four minor openings. The results carried out in this case agree with the previous one. Among all the periods pointed out by our investigation, one is always exhibited in every point and by each system. The period is that of 5.70 h and it can be considered a fundamental mode of the Tyrrhenian Sea.     

Optical potential calculations for the 1s level in pionic atoms

The Ericson-Ericson optical potential for theπ-nucleuss-wave interaction was extended to be applicable also for light nuclei. In particular, terms of order A^?1 were evaluated and the (π2N) dispersion was considered. From comparison with experimental data we found that considerable improvement could be achieved by introducing terms of order A^?1. The (π2N) dispersion was found to be repulsive and of the same magnitude as the absorption. The (πN) scattering lengths were deduced to be α₃?α₁=0.258±0.008m _π ^?1 and α₁+2α₃=?0.018±0.008m _π ^?1 .     

Sea level oscillations in the gulf of Trieste, the role of the atmospheric-pressure forcing and the tidal effect in the pressure and wind behaviour

Summary This paper is divided into three parts. The first one takes some cases of sea level perturbation (the tides being removed) at Trieste into account. The spectral analysis shows the occurring of the principal seiches of the Adriatic Sea together with oscillations believed as forced oscillations. In the second part the pressure oscillations have been examined and the same periods forcing the sea level have been found. Such oscillations appear very evident and stable, mostly in the summer months. In the third part of the work the tidal effect on the wind, derived from the atmospheric pressure, is tested. In the summer situations prevailing breezes are present and the spectral analysis of the records points out clearly the occurrence of some ?wind tides? both in the diurnal and semi-diurnal range.

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Riassunto Questo lavoro si articola in tre parti. Nella prima parte sono mostrati alcuni casi in cui il livello del mare a Trieste è perturbato da forti oscillazioni extramareali. I grafici della marea meteorologica registrati negli intervalli temporalit(1)…t(14) possono tipicizzare queste situazioni, essi riportano l'evoluzione del livello dopo che le maree sono state eliminate con calcoli di filtraggio dei dati osservati. Da queste serie temporali sono stati eseguiti gli spettri di ampiezza col metodo dei minimi quadrati. In questi si vedono due picchi, sempre presenti sui periodi di circa 11 e 21 ore che sono, mediamente e arrotondando, i periodi delle sesse principali (longitudinali) dell'Adriatico. Quando il livello è perturbato queste ultime sono sempre presenti, pur con ampiezza diversa, assieme ad altre di origine locale. Si rilevano anche onde forzate da oscillazioni barometriche. La seconda parte del lavoro esamina alcune onde barometriche forzanti. Si trova che le piú stabili onde barometriche presenti nell'evoluzione della pressione atmosferica a Trieste sono le cosiddette maree atmosferiche. Alcune considerazioni sono presentate su questo fenomeno. Data la persistenza delle maree atmosferiche nella pressione, un sincrono effetto viene cercato nel vento. Nella terza parte del lavoro si esamina questo effetto trovando che effettivamente, in regime di brezza, periodicità ?mareali? si trovano anche nell'evoluzione del vento. In altri regimi ?le maree del vento? sono completamente mascherate da altri effetti, come le maree marine quando si sovrappongono forti perturbazioni di carattere extramareale.

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Резюме Эта статья делится на три части. В первой части рассматриваются некоторые случаи колебания уровня моря (влияние прилива исключается) в заливе Триеста. Спектральный анализ показывает существование главных сейшей Адриатического моря вместе с другими осцилляциями, которые рассматриваются как вынужденные колебания. Во второй части исследуются осцилляции давления и обнаружены колебания уровня моря с такими же периодами. Такие осцилляции являются заметными и устойчивыми, особенно в летние месяцы. В третьей части работы исследуется влияние приливов на ветер, порожденный атмосферным давлением. В летний период превалируют бризы и спектральный анализ показывает в явном виде существование некоторых ?ветровых приливов? в суточных и полусуточных диапазонах измерений.

     

Stark width and shift dependence on the ionization potential

Analytic relations between the Stark widths and shifts and the ionization potential of the corresponding emitters have been found and are discussed.     

Resonant Scattering of Muonic Hydrogen Atoms and Dynamics of the Muonic Molecular Complex

Resonant scattering of muonic hydrogen atoms via back decay of the molecular complex, a key process in the understanding of epithermal muonic molecular formation, is analyzed. The limitations of the effective rate approximation are discussed and the importance of the explicit treatment of the back decay is stressed. An expression of the energy distribution for the back-decayed atoms is given. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of p̄p pionic annihilation in the momentum range 403 to 670 MeV/c

Exclusive p?p pionic annihilation reactions in the momentum range of 403 to 670 MeV/c were analysed in terms of intermediate states involving resonances. The fractions of the various intermediate states showed no significant dependence on the incident momentum. They were compared with a statistical model incorporating SU(3) symmetry. The agreement between the model and data was moderate and qualitative. The exclusive as well as topological cross sections were compared with the same statistical model and a potential model incorporating quark rearrangement. The agreement with the latter model was better than with the first in general, but it was still mostly qualitative.     

Low pressure broadening and shift of the 2p 53p-2p 56s neon spectral lines

Natural radiative lifetimes in the perturbed 6s n s ¹ D ₂ (n=12?30) sequence of barium have been measured using the PUMOLS (PUlse-MOdulated Laser Spectroscopy) method, which incorporates pulse-modulation of a CW dye-laser beam and delayed coincidence techniques. Principal perturbers are the 5d 7d ³ F ₂ and¹ D ₂ states. Lifetimes were also measured for these shortlived valence states, which through configuration mixing cause drastic decreases in lifetime values in the region of perturbation of the 6s n d ¹ D ₂ sequence. Two-step laser excitation from the ground 6s ^{2 1} S ₀ state via the 6s 6p ¹ P ₁ state was employed. Special care was taken to determine the influence of black-body radiation transitions on the measured lifetimes.