A dispersion theoretical approach to the threshold amplitudes of pion photoproduction

We give predictions for the partial wave amplitudes of pion photoproduction near threshold by means of dispersion relations at fixed t. The free parameters of this approach are determined by a fit to experimental data in the energy range 160 MeV $\le E_{\gamma} \le$ 420 MeV. The observables near threshold are found to be rather sensitive to the amplitudes in the resonance region, in particular to the $\Delta$ (1232) and $N^*$ (1440). We obtain a good agreement with the existing threshold data for both charged and neutral pion production. Our predictions also agree well with the results of chiral perturbation theory, except for neutral pion production off the neutron.Comment: 16 pages LATEX including 4 postscript figure

Control sideband generation for dual-recycled laser interferometric gravitational wave detectors

We present a discussion of the problems associated with generation of multiple control sidebands for length sensing and control of dual-recycled, cavity-enhanced Michelson interferometers and the motivation behind more complicated sideband generation methods. We focus on the Mach–Zehnder interferometer as a topological solution to the problem and present results from tests carried out at the Caltech 40 m prototype gravitational wave detector. The consequences for sensing and control for advanced interferometry are discussed, as are the implications for future interferometers such as Advanced LIGO

Multipole analysis of pion photoproduction based on fixed t dispersion relations and unitarity

We have analysed pion photoproduction imposing constraints from fixed t dispersion relations and unitarity. Coupled integral equations for the S and P wave multipoles were derived from the dispersion relations and solved by the method of Omnes and Muskhelishvili. The free parameters were determined by a fit to the most recent data for \pi^{+} and \pi^{0} production on the proton as well as \pi^{-} production on the neutron, in the energy We have analysed pion photoproduction imposing constraints from fixed t dispersion relations and unitarity. Coupled integral equations for the S and P wave multipoles were derived from the dispersion relations and solved by the method of Omnes and Muskhelishvili. The free parameters were determined by a fit to the most recent data for \pi^{+} and \pi^{0} production on the proton as well as \pi^{-} production on the neutron, in the energy range 160 MeV \leq E_{\gamma} \leq 420 MeV. The lack of high precision data on the neutron and of polarization observables leads to some limitations of our results. Especially the multipole M_{1-} connected with the Roper resonance P_{11}(1440) cannot be determined to the required precision. Our predictions for the threshold amplitudes are in good agreement with both the data and chiral perturbation theory. In the region of the \Delta(1232) we have determined the ratio of electric quadrupole and magnetic dipole excitation. The position of the resonance pole is obtained in excellent agreement with pion-nucleon scattering, and the complex residues of the multipoles are determined with the speed-plot technique.Comment: 46 pages LATEX including 29 postscript figure

Determination of the pion-nucleon coupling constant and scattering lengths

We critically evaluate the isovector GMO sum rule for forward pion-nucleon scattering using the recent precision measurements of negatively charged pion-proton and pion-deuteron scattering lengths from pionic atoms. We deduce the charged-pion-nucleon coupling constant, with careful attention to systematic and statistical uncertainties. This determination gives, directly from data a pseudoscalar coupling constant of 14.11+-0.05(statistical)+-0.19(systematic) or a pseudovector one of 0.0783(11). This value is intermediate between that of indirect methods and the direct determination from backward neutron-proton differential scattering cross sections. We also use the pionic atom data to deduce the coherent symmetric and antisymmetric sums of the negatively charged pion-proton and pion-neutron scattering lengths with high precision. The symmetric sum gives 0.0012+-0.0002(statistical)+-0.0008 (systematic) and the antisymmetric one 0.0895+-0.0003(statistical)+-0.0013(systematic), both in units of inverse charged pion-mass. For the need of the present analysis, we improve the theoretical description of the pion-deuteron scattering length.Comment: 27 pages, 5 figures, submitted to Phys. Rev. C, few modifications and clarifications, no change in substance of the pape

Density Matrix Kinetic Equation Describing a Passage of Fast Atomic Systems Through Matter

The quantum-mechanical consideration of a passage of fast dimesoatoms through matter is given. A set of quantum-kinetic equations for the density matrix elements describing their internal state evolution is derived. It is shown that probabilistic description of internal dynamics of hydrogen-like atoms is impossible even at sufficiently low energies because of the ``accidental'' degeneracy of their energy levels.Comment: 12 pages, LATEX, submitted to J. Phys.

Low-energy Pion-nucleon Scattering

This paper contains the results of an analysis of recent low-energy pion-nucleon scattering experiments. Obtained are phase shifts, the pion-nucleon coupling constant and an estimate of the Sigma term.Comment: 30 pages, 11 figures, LaTe

Chiral Perturbation Theory and the pp -> pp pi0 Reaction Near Threshold

A chiral-perturbative consideration of the near-threshold pp -> pp pi0 reaction indicates that the pion-rescattering term has a substantial energy and momentum dependence. The existing calculations that incorporate this dependence give pion rescattering contributions significantly larger than those of the conventional treatment, and this enhanced rescattering term interferes destructively with the one-body impulse term, leading to theoretical cross sections that are much smaller than the observed values. However, since the existing calculations are based on coordinate-space representation, they involve a number of simplifying assumptions about the energy-momentum flow in the rescattering diagram, even though the delicate interplay between the one-body and two-body terms makes it desirable to avoid these kinematical assumptions. We carry out here a momentum-space calculation that retains the energy-momentum dependence of the vertices as predicted by chiral perturbation theory. Our improved treatment increases the rescattering amplitude by a factor of 3 over the value obtained in the r-space calculations. The pp -> pp pi0 transition amplitude, which is now dominated by the rescattering term, leads to the cross section much larger than what was reported in the approximate r-space calculations. Thus, the extremely small cross sections obtained in the previous chiral perturbative treatments of this reaction should be considered as an accidental consequence of the approximations employed rather than a general feature.Comment: 25 pages,REVTEX, 5 ps figure

X-ray emission during the muonic cascade in hydrogen

We report our investigations of X rays emitted during the muonic cascade in hydrogen employing charge coupled devices as X-ray detectors. The density dependence of the relative X-ray yields for the muonic hydrogen lines (K_alpha, K_beta, K_gamma) has been measured at densities between 0.00115 and 0.97 of liquid hydrogen density. In this density region collisional processes dominate the cascade down to low energy levels. A comparison with recent calculations is given in order to demonstrate the influence of Coulomb deexcitation.Comment: 5 pages, Tex, 4 figures, submitted to Physical Review Letter

Status of the GEO600 gravitational wave detector

The GEO600 laser interferometric gravitational wave detector is approaching the end of its commissioning phase which started in 1995.During a test run in January 2002 the detector was operated for 15 days in a power-recycled michelson configuration. The detector and environmental data which were acquired during this test run were used to test the data analysis code. This paper describes the subsystems of GEO600, the status of the detector by August 2002 and the plans towards the first science run