Experimental transition probability for theE1 intercombination transition in Be-like Xe50+

The 2s^{2 1}S₀ — 2s2p³P°₁ intercombination transition in Be-like Xe⁵⁰⁺ has been observed and the intensity decay with time has been measured using a foil-excited fast ion beam. The transition wavelength value is found to be λ = (9.81±0.05) nm and the upper level lifetime to be τ = (0.47±0.05) ns. Both values agree with recent theoretical predictions.     

Target-thickness dependence of inner shell excitation in 1.4 MeV/u Pb-Pb collisions

For 1.4 MeV/u Pb³⁰⁺ → Pb collisions the impact parameter dependence of theK andL x-ray emission is measured for two thin target foils (30 and 300 µg/cm²). Unexpectedly, theK excitation probability at small impact parameters (<300 fm) is smaller for the thicker foil. We attempt to explain this behaviour by a blocking of exit channels for direct excitation caused by steady state projectile excitation in the thicker target.     

Quark gluon scattering at higher orders in QCD

The infrared evolution equation which sums up leading logarithmic terms is solved for the partonic reactionqgqX in the elastic case i.e.M _X0. The results of the exactO( _s ³ ) calculation are reproduced.     

Evolution of Concentrated Vortices in a Viscous Fluid

Evolution of the vortices of monopole and dipole types in a viscous fluid is considered numerically. Theory and numerical results are compared for some particular exact solutions. A good agreement is obtained for the dipole vortices (viscous Chaplygin-Lamb vortices) moving with variable velocities due to viscosity. For the monopole type vortices, the agreement is more or less good only at an initial stage of their evolution; while in the long-lime asymptotics the law of vorticity decay other than the theoretical one is discovered. The reason for such a discrepancy is discussed. The interactions of dipole vortices with each other and with rigid boundaries are studied too. The stability of dipole vortices with complex internal structures is considered briefly.     

High Rydberg resonances in dielectronic recombination of pb(79+)

Dielectronic recombination resonances of Pb (79+) associated with 2s(1/2)-->2p(1/2) excitations were measured at the heavy-ion storage ring ESR at GSI. The fine structure of the energetically lowest resonance manifold Pb (78+)(1s(2)2p(1/2)20l(j)) at around 18 eV could partially be resolved, and rate coefficients on an absolute scale were obtained. A comparison of the experimental data with results of a fully relativistic theoretical approach shows that high-angular-momentum components up to j=31/2 significantly contribute to the total resonance strength demonstrating the necessity to revise the widespread notion of negligible high-angular-momentum contributions at least for very highly charged ions.     

Radiative electron capture into theK-, L- andM-Shell of decelerated,hydrogenic Ge projectiles

Radiative Electron Capture (REC) in 4 to 12 MeV/u Ge³¹⁺→H₂ collisions has been studied using an X-ray/particle coincidence technique. This technique allowed a systematic investigation ofK-shell REC as well as a separation of REC into the projectileL- andM-shells. The cross sections are discussed within a general scaling picture based on the reduced projectile velocity.     

Quantum electrodynamics in strong electric fields: the ground-state Lamb shift in hydrogenlike uranium

X-ray spectra following radiative recombination of free electrons with bare uranium ions (U92+) were measured at the electron cooler of the ESR storage ring. The most intense lines observed in the spectra can be attributed to the characteristic Lyman ground-state transitions and to the recombination of free electrons into the K shell of the ions. Our experiment was carried out by utilizing the deceleration technique which leads to a considerable reduction of the uncertainties associated with Doppler corrections. This, in combination with the 0 degree observation geometry, allowed us to determine the ground-state Lamb shift in hydrogenlike uranium (U91+) from the observed x-ray lines with an accuracy of 1%. The present result is about 3 times more precise than the most accurate value available up to now and provides the most stringent test of bound-state quantum electrodynamics for one-electron systems in the strong-field regime.     

A Formal Chevalley Restriction Theorem for Kac–Moody Groups

Let G be a symmetrizable Kac–Moody group over a field of characteristic zero, let T be a split maximal torus of G. By using a completion of the algebra of strongly regular functions on G, and its restriction on T, we give a formal Chevalley restriction theorem. Specializing to the affine case, and to the field of complex numbers, we obtain a convergent Chevalley restriction theorem, by choosing the formal functions, which are convergent on the semi-groups of trace class elements G ^trG resp. T ^trT.