Phys. Lett. B

First measurements of the mass and width of the Z 0 performed at the newly commissioned LEP Collider by the DELPHI Collaboration are presented. The measuements are derived from the study of multihadronic final states produced in e + e − annihilations at several energies around the Z 0 mass. The values found for the mass and width are M (Z 0 )=91.06±0.09 (stat) ±0.045 (syst.) GeV and Γ (Z 0 )=2.42±0.21 (stat.) GeV respectively, froma three-parameter fit to the line shape. A two-parameter fit in the framework of the standard model yields for the number of light neutrino species N ν =2.4±0.4 (stat.) ±0.5 (syst.).

Phys.Lett.B

The ratio of the number of ultrarelativistic positronium atoms ( A 2e ) to the photon number in the momentum interval 800–2000 MeV/ c has been measured in pC interactions at E p =70 GeV and at an angle of 8.4° in the laboratory frame. The branching ratio ϱ π =(1.84±0.29)×10 -9 for π 0 decay into a photon and A 2e has been obtained. The parameter ϱ π is determined by the conversion probability ϱ A of a time-like photon into A 2e in radiative decays of elementary particles.

Phys. Rev. Lett.

We have measured the mass of the Z boson to be 91.11±0.23 GeV/c2, and its width to be 1.61−0.43+0.60 GeV. If we constrain the visible width to its standard-model value, we find the partial width to invisible decay modes to be 0.62±0.23 GeV, corresponding to 3.8±1.4 neutrino species.

Nucl. Instrum. Meth. A

Lasing in a wide 2400–6900 Å spectral range (from visible to ultraviolet) was reached in the optical klystron OK-4 installed on the VEPP-3 storage ring. OK-4 is the first FEL operating in UV.

EPL

The pion radiative scattering (π-p → π-pγ) has been studied at 43 GeV in the interval 0.2 < |tp| < 0.4 (GeV/c)2 of the momentum transfer squared to the proton and in the range of photon energy 2 < ω < 40 GeV. Calculations based on Low theorem agree well with measured ω, tp and mπγ (final πγ-invariant mass) differential cross-sections. The results obtained extend the validity of Low approach to the radiative scattering at high energies.

Few Body Syst.

The 0° differential cross sections of the12C(4He,p) and12C(4He,t) reactions have been measured at beam momenta of 4.52 and 2.69 GeV/c/nucleon, respectively. The proton and triton momentum distributions in4He are extracted from the cross sections using a relativistic impulse approximation. Some theoretical models based on realisticN-N potentials are examined for our data.

Theor. Math. Phys.

The partial Jost determinants and the Jost operator on the unit sphere are represented in integral form in terms of the spectral density with respect to the momentum transfer for the resolvent of an elliptic operator on R N. The relationship between the spectral densities for the same potential V(r) but different dimensions rN, N ~ 2, is found. New integral representations for solutions to the Coulomb problem are given.

Nucl.Instrum.Meth.A

Two types of electromagnetic undulators are described. The first one has 33.5 periods with a length of 10 cm and a magnetic field amplitude of 5.3 kG. The other, developed for future FEL experiments, has 39.5 periods with 7 cm length and a magnetic field amplitude of 55 kG.

Nucl. Instrum. Meth. A

A parallel-series readout system for a drift chamber is described. It allows one to considerably reduce the number of time-to-digital converters used. The results of testing the registration electronics setup for a mini drift chamber in a 10 Gev/ c particle beam are given. It is shown that the system can be used to read information from precision drift chambers ( σ ≈ 50 μ m).

Phys. Lett. B

The p¯4He annihilation cross section averaged over the interval 40–50 MeV/ c has been measured using a streamer chamber in a magnetic field. The measured value is 1342±250 mb. It agrees with a behaviour like 1/ p of the annihilation cross section. Our result has been obtained at the lowest momentum achieved till now in measurements of antiproton annihilation in flight.