Inelastic final-state interaction

The final-state interaction in multichannel decay processes is sytematically studied with application to B decay in mind. Since the final-state inteaction is intrinsically interwoven with the decay interaction in this case, no simple phase theorem like "Watson's theorem" holds for experimentally observed final states. We first examine in detail the two-channel problem as a toy-model to clarify the issues and to remedy common mistakes made in earlier literature. Realistic multichannel problems are too challenging for quantitative analysis. To cope with mathematical complexity, we introduce a method of approximation that is applicable to the case where one prominant inelastic channel dominates over all others. We illustrate this approximation method in the amplitude of the decay B to pi K fed by the intermediate states of a charmed meson pair. Even with our approximation we need more accurate information of strong interactions than we have now. Nonethless we are able to obtain some insight in the issue and draw useful conclusions on general fearyres on the strong phases.Comment: The published version. One figure correcte

Measurements in the Turbulent Boundary Layer at Constant Pressure in Subsonic and Supersonic Flow. Part 2: Laser-Doppler Velocity Measurements

A description of both the mean and the fluctuating components of the flow, and of the Reynolds stress as observed using a dual forward scattering laser-Doppler velocimeter is presented. A detailed description of the instrument and of the data analysis techniques were included in order to fully document the data. A detailed comparison was made between the laser-Doppler results and those presented in Part 1, and an assessment was made of the ability of the laser-Doppler velocimeter to measure the details of the flows involved

Spin Dependence of Massive Lepton Pair Production in Proton-Proton Collisions

We calculate the transverse momentum distribution for the production of massive lepton-pairs in longitudinally polarized proton-proton reactions at collider energies within the context of perturbative quantum chromodynamics. For values of the transverse momentum Q_T greater than roughly half the pair mass Q, Q_T > Q/2, we show that the differential cross section is dominated by subprocesses initiated by incident gluons, provided that the polarized gluon density is not too small. Massive lepton-pair differential cross sections should be a good source of independent constraints on the polarized gluon density, free from the experimental and theoretical complications of photon isolation that beset studies of prompt photon production. We provide predictions for the spin-averaged and spin-dependent differential cross sections as a function of Q_T at energies relevant for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven, and we compare these with predictions for real prompt photon production.Comment: 34 pages, RevTeX including 17 figures in .ps file

Universal features in sequential and nonsequential two-photon double ionization of helium

We analyze two-photon double ionization of helium in both the nonsequential and sequential regime. We show that the energy spacing between the two emitted electrons provides the key parameter that controls both the energy and the angular distribution and reveals the universal features present in both the nonsequential and sequential regime. This universality, i.e., independence of photon energy, is a manifestation of the continuity across the threshold for sequential double ionization. For all photon energies, the energy distribution can be described by a universal shape function that contains only the spectral and temporal information entering second-order time-dependent perturbation theory. Angular correlations and distributions are found to be more sensitive to the photon energy. In particular, shake-up interferences have a large effect on the angular distribution. Energy spectra, angular distributions parameterized by the anisotropy parameters, and total cross sections presented in this paper are obtained by fully correlated time-dependent ab initio calculations.Comment: 12 pages, 8 figure

Testing draft horses

“When animals are viewed from the standpoint of machines they are wonderful mechanisms. Not only are they self-feeding, self-controlling, self-maintaining and self-reproducing, but they are far more economical in the energy they are able to develop from a given weight of fuel material, than any other existing form of motor. While they are like the steam engine in requiring carbonaceous fuel, oxygen and water for use in developing energy; these are made to combine in the animal body at a much lower temperature than is possible in the steam engine, and a much smaller proportion of the fuel value is lost in the form of heat, when work is being done.

Probing Electron Correlation via Attosecond XUV Pulses in the Two-Photon Double Ionization of Helium

Recent experimental developments of high-intensity, short-pulse XUV light sources are enhancing our ability to study electron-electron correlations. We perform time-dependent calculations to investigate the so-called "sequential" regime (photon energy above 54.4 eV) in the two-photon double ionization of helium. We show that attosecond pulses allow to induce and probe angular and energy correlations of the emitted electrons. The final momentum distribution reveals regions dominated by the Wannier ridge break-up scenario and by post-collision interaction.Comment: 4 pages, 5 figure