44 research outputs found
Microscopic Calculation of Total Ordinary Muon Capture Rates for Medium - Weight and Heavy Nuclei
Total Ordinary Muon Capture (OMC) rates are calculated on the basis of the
Quasiparticle Random Phase Approximation for several spherical nuclei from
90^Zr to 208^Pb. It is shown that total OMC rates calculated with the free
value of the axial-vector coupling constant g_A agree well with the
experimental data for medium-size nuclei and exceed considerably the
experimental rates for heavy nuclei. The sensitivity of theoretical OMC rates
to the nuclear residual interactions is discussed.Comment: 27 pages and 3 figure
Electromagnetic Form Factors of the Nucleon in an Improved Quark Model
Nucleon electromagnetic form factors are studied in the cloudy bag model
(CBM) with center-of-mass and recoil corrections. This is the first
presentation of a full set of nucleon form factors using the CBM. The center of
mass motion is eliminated via several different momentum projection techniques
and the results are compared. It is found that the shapes of these form factors
are significantly improved with respect to the experimental data if the Lorentz
contraction of the internal structure of the baryon is also appropriately taken
into account.Comment: revtex, 28 pages, 8 ps figs include
Is the Unitarity of the quark-mixing-CKM-matrix violated in neutron -decay?
We report on a new measurement of neutron -decay asymmetry. From the
result \linebreak = -0.1189(7), we derive the ratio of the axial vector
to the vector coupling constant = = -1.2739(19). When
included in the world average for the neutron lifetime = 885.7(7)s, this
gives the first element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix . With this value and the Particle Data Group values for and
, we find a deviation from the unitarity condition for the first row of
the CKM matrix of = 0.0083(28), which is 3.0 times the stated error
Radiative corrections to the cross section of and the crossed processes
Born cross section and the radiative corrections to its lowest order are
considered in the frame work of QED with structureless nucleons including the
emission of virtual and real photons. Result is generalized to take into
account radiative corrections in higher orders of perturbation theory in the
leading and next-to leading logarithmic approximation. Crossing processes are
considered in the leading approximation.Comment: 11 pages, 1 figur
Equation of State of an Interacting Pion Gas with Realistic -- Interactions
Within the finite-temperature Greens-function formalism we study the equation
of state of a hot interacting pion gas at zero chemical potential. Employing
realistic meson-exchange interactions we selfconsistently calculate
the in-medium single-pion selfenergy and the scattering amplitude in
the quasiparticle approximation. These quantities are then used to evaluate the
thermodynamic potential, (T), from which the state variables:
pressure-, entropy- and energy-density can be derived. In contrast to earlier
calculations based on the low-energy Weinberg Lagrangian we find an overall
increase as compared to the free-gas results. We also consider the possibility
of a dropping -meson mass as suggested by the 'Brown-Rho Scaling' law.Comment: 30 pages LaTeX, 3 postscript figures appended as uuencoded fil