A. Olshevski

Measurement of π−-meson polarizability in pion compton effect

Abstract About 7 × 10 3 events of Compton effect on pion in the reaction π − A → A π − γ st 40 GeV/ c were detected and for the first time the charged pion polarizability was obtained α π = (6.8 ± 1.4) × 10 −43 cm 3 .

Compton-effect on π−-meson

The reaction π−A→Aπ− γ at 40 GeV/c was studied on “Sigma” spectrometer on six different nuclear targets in the region of four-momentum transfer |t|<0.05 (GeV/c)2. A phenomenon of elastic scattering of pions on the nuclear Coulomb field photons was observed, its total and differential cross sections were measured. The cross section of Compton effect on π−-meson was measured.

Scintillation hodoscopes for time-of-flight measurements

Abstract The performances of the TOF scintillation counters used in the SIGMA-AIAKS spectrometer are presented. The counters, made of NE110, are 150, 65 and 10 cm long, 10 cm wide and 1.5 cm thick. The time resolutions for minimum ionizing particles have been measured to be σ t = 0.18 ns, 0.14 ns and 0.11 ns respectively. The main contribution to the resolution is given by the photoe collection statistics determined by the decay time of the scintillator and the difference of the optical paths in the counter. The scintillation counters, assembled into hodoscopes of 1.5 × 3.2 m 2 and 0.65 × 0.8 m 2 are used for identification of particles through the TOF. The algorithms of off-line data processing are also presented.

Some investigations with plastic streamer tubes

Abstract Streamer tubes of two kinds — with and without conductive cover — were investigated. Their main characteristics were measured. It was observed that the induced signal distribution over the tube surface practically depends neither on the readout side, nor on the kind of the tube.

How effective is the weak mixing angle

The usefulness of an effective weak mixing angle to parameterise the electroweak couplings of quarks and leptons measured at LEP is discussed. After a review of the theoretical formalism used to handle the electroweak radiative corrections to LEP processes, some suggestions for procedures to be used to extract the mixing angle are given and the various definitions of the effective weak mixing angle used by the experiments are examined. This is followed by an attempt to extract a coherent set of mixing angle values from the four experiments with the published 1989/90 (and some 1991) measurements of the Z0 line-shapes, asymmetries and τ polarisation. These results are updated with preliminary results from the 1991 data presented at the XXVI International Conference on High Energy Physics, in Dallas, USA, in August 1992, including the preliminary measurement ofALR at the SLC. The average value found for the effective weak mixing angle, defined for leptons, is sin2θefflept=02322±0.0010. The error on sin2θefflept can be further reduced by imposing the constraints between the parameters implicit in the MSM. With the additional constraint αs=0.123±0.006 imposed in the fit, the result is sin2θefflept, where the central value is formH=300 GeV, and the second error is the variation ifmH is changed to 50 GeV (lower error) and 1000 GeV (upper error). Within the MSM, sin2θlepteff is directly related to the top-quark mass, and the corresponding value ismt=153−25−23+22+19 GeV, where the errors have the same meaning as those for sin2θefflept. Finally, the prospects for improved precision are discussed.

Fe-scintillator hodoscopic hadron calorimeter

Abstract A Fe-scintillator hodoscopic hadron calorimeter is described. It consists of independent sections, each containing four total absorption counters 20×20 cm 2 in cross section. The energy resolution for hadrons in the energy range E = 4–40 GeV is σ E / E = 0.02 + 0.52/√ E and the mean space resolution is ∼ 2 cm at 40 GeV.

Determination of the branching ratio ofρ0→+μ− in the coherent dissociation π−→μ+μ−π− and π−→π+π−π−

AbstractIn the diffraction dissociation of π− into μ+μ−π− on a Cu nucleus at 50 GeV/c, the cross section

Experimental Study of the Radiative Scattering π-p → π-pγ at 43 GeV

\sigma _{\mu ^ + \mu ^ - \pi ^ - }