Two-particle Mass Research Articles

Properties of nuclei in the nobelium region studied within the covariant, Skyrme, and Gogny energy density functionals

We calculate properties of the ground and excited states of nuclei in the nobelium region for proton and neutron numbers of 92≤Z≤104 and 144≤N≤156, respectively. We use three different energy-density-functional (EDF) approaches, based on covariant, Skyrme, and Gogny functionals, each with two different parameter sets. A comparative analysis of the results obtained for quasiparticle spectra, odd–even and two-particle mass staggering, and moments of inertia allows us to identify single-particle and shell effects that are characteristic to these different models and to illustrate possible systematic uncertainties related to using the EDF modelling.

Symmetry of two-particle mass shell and its impact on e-e-scattering

A proof is presented, based on the geometry of the two-electron mass hyperboloid, of Wyler's formula for the electromagnetic fine-structure constant. This proof provides evidence that the two-electron state space in e-e-scattering matches an irreducible two-particle representation of the Poincaré group. Electromagnetic scattering, as described by perturbative quantum electrodynamics, then has to be understood as a sequence of iterated transitions between pure (separable) product states and entangled two-electron states of an irreducible representation of the Poincaré group.

Study of the reactions γp → K+ Σ± π∓ at photon energies up to 2.6 GeV

The reactions γp → K+ Σ± π∓ were studied with the SAPHIR detector using a tagged photon beam at the electron stretcher facility ELSA in Bonn. The decays Σ− → nπ− and Σ+ → nπ+, pπ0 were fully reconstructed. Reaction cross-sections were measured as a function of the photon energy from threshold up to 2.6 GeV with considerably improved statistics compared to a previous bubble chamber measurement. The cross-sections rise monotonically with increasing photon energy. The two-particle mass distributions of Σ±π∓ and K+π− show substantial production of resonant states.

Relativistic two-particle mass spectra from time-asymmetric Fokker action

The relativistic two-particle system with field-type time-asymmetric interactions is considered within the framework of manifestly covariant Hamiltonian formalism with constraints. In the second-order approximation in a coupling constant the mass-shell constraint is presented as a relation between one of the generators of SO(2, 1) and the total mass squared of the system. An algebraic quantization of the classical problem is proposed and the relativistic mass spectra for a wide range of the field-type interactions are obtained.

Analytic methods from finite to infinite volumes

We shall review the analytic methods that have been developed over the past few years to understand the volume dependence of field theories on a torus, which is the geometry relevant for lattice gauge theories. First we start in small to intermediate volumes, below one cubic fermi, and discuss the results for the low-lying spectrum of pure SU(3) gauge theory. Then we assume a mass gap is formed in the infinite volume and show how this leads to a precise asymptotic expression for the volume dependence of the stable one-particle masses, due to polarization effects and for the two-particle masses, due to scattering processes in the finite volume. The latter is first illustrated in the two dimensional O(N) model, using the exact S-matrix. The generalization to four (or any) dimensions for the relation between the two-particle masses in a finite volume and the scattering phase shifts, based on a very recent analysis by Lüscher, will be discussed. In the near future this will make a careful study of resonances in a finite volume feasible. Finally we discuss how the Bethe Ansatz for the two dimensional O(N) model can be used to calculate the infinite volume mass gap, providing an important test for lattice Monte Carlo studies to extract this quantity.

The dispersion relation for mass spectrometric fragmentation processes

A dispersion relationship is presented and the characteristic equation determined for two-particle mass spectrometric fragmentation processes.

Computer study of ergodicity and mixing in a two-particle, hard point gas system

Computer experiments performed on the unequal-mass, two-particle hard point gas are discussed and shown to provide evidence for ergodic and mixing behavior when the two-particle mass ratio ( m 2 m 1 ) in cos θ = [l − ( m 2 m 1 )]/[1 + ( m 2 m 1 ] is such that θ is an irrational multiple of π. Although this system appears to be ergodic and mixing, it is certainly not a C-system.