Production mechanism of ϱ0 and f mesons in πN→π+π−N reactions

The production of ?⁰ and f mesons in πN→π⁺π^?N reactions in the momentum range 4 to 17 GeV/c is investigated in a model-independent way by imposing in full the positivity of the density matrix. The results so obtained are used in order to determine the effective Regge trajectories for unnatural and natural parity exchanges and are compared to results obtained in different analyses.     

Continuous phase transitions which should be first order

It is demonstrated that phase transitions predicted to be first order by the Landau symmetry arguments can be continuous for a finite range of the physical parameters. For transitions with a rank-two tensor order parameter it is shown that fluctuations in a phase associated with the anisotropy of the tensor result in a renormalization of the cubic term. This leads to continuous transitions when the coefficient of the bare cubic term is small compared to the coefficient of the quartic term. It is shown that the argument can be extended to more general cases when the order parameter belongs to a multidimensional representation of the broken symmetry group.     

Finite-range effects in pionic atoms

Pionic atom data are refitted in terms of conventional π^? nuclear optical potentials, modified to allow for finite range in the underlying p-wave πN interaction. We find that level shifts and widths in light and medium-weight nuclei cannot distinguish between the various ranges tested. In heavy nuclei, and for reasonable choices of neutron radii, the data tend to exclude ranges of order 0.5 fm and larger.     

Observation of the decay τ → πv

The decay of the heavy lepton τ into πv has been established using the magnetic detector PLUTO. The branching ratio is determined to be BR(τ→πv)=(9.0 ± 2.9)% with an additional systematic uncertainty of 2.5%. This value is in good agreement with the theoretical prediction.     

Heterocyclic synthesis using ethyl carboethoxyformimidate

Ethyl carboethoxyformimidate is shown to be a versatile reagent for the synthesis of a variety of mono- and bicyclic heterocyclic systems.     

Zur elektronenstruktur vicinaler triketone: Bicyclo[3.1.0]hexan-2.3.4-trione

Bicyclo[3.1.0]hexane-2.3.4-trione and its 1.5-dimethyl derivative have been synthesized and investigated by means of photoelectron spectroscopy.