NUCLEON-NUCLEON AND HYPERON-NUCLEON INTERACTIONS

The nucleon-nucleon and hyperon-nucleon interactions are studied by the one-boson-exchange(OBE) potential with the vertex form factor. To make our theory as relativistic as possible, we calculate the OBE-potential in the momentum space and use the Blankenbecler-Sugar equation. We also treat the singularity in the multichannel Blankenbecler-Sugar equation. By these formulations, we analyze the nucleon-nucleon and the hyperon-nucleon scatterings.

A New Energy-dependent Δ Width in Coherent Pion Production

A new derivation for the energy-dependent Δ width inside nuclei is presented which includes the all important, energy-dependent nuclear form factor describing the decay of the Δ particle from its harmonic oscillator, bound state back to a captured nucleon and outgoing pion. Additional improvements include relativistic kinematics, generalisation beyond the static limit in the kinematics, and inclusion of the ΔN Π energy-dependent vertex form factor. The new decay width provides a reasonable cut-off at high pion momenta and gives the correct momentum dependence in the limit of single-particle decay at low momenta. The results of calculations for the energy-dependent widths and their effects on the energy distributions of exclusive coherent pion production for 12 C+ 12 C → 12 C+ 12 C* (T = 1)+ Π 0 at incident energies below and above the pion threshold are shown and discussed. The new energy dependence is compared to the free Δ width used previously and it is seen that the new results give a smoother and more realistic shape to the pion energy distributions.

CONSTRAINTS ON THE ELECTROWEAK UNIVERSAL PARAMETERS AND THE TOP AND HIGGS MASSES FROM UPDATED LEP/SLC DATA

A global analysis is performed using the recent data from LEP and SLC. Constraints on the electroweak universal parameters (S, T, U) and on the masses of the top quark and Higgs boson within the standard model (SM) are investigated. The uncertainties due to the QCD and QED effective couplings, αs(mz) and , [Formula: see text] are examined in detail. Even though the mean value of S is increased to be consistent with zero, the naive Technicolor models are still disfavored due to its reduced error. Within the SM, we find the 90% CL constraints; 133 GeV<mt<190 GeV and 10 GeV<mH< 440 GeV for αs(mz)=0.116 and [Formula: see text]. The experimental constraints on the ZbLbL vertex form factor, [Formula: see text] play an important role in disfavoring the region of large mt(mt~200GeV) and large mH(mH~1000 GeV). If mt is precisely known, the present electroweak data give a rather strict upper bound on the Higgs mass, mH<140(300) GeV at 95% CL, for mt=160(175) GeV and for the above αs(mz) and [Formula: see text].