A. A. Solodkov

The results of the partial wave analysis of the diffractive reaction π−A → π+π−π−A at the momentum 36 GeV/c on the scintillator target are presented. A resonance at m = 1.8 GeV with JPC = 0−+ (π(1800)) is clearly seen in this reaction. The characteristics of π(1800) point to the possible exotic nature of this object.

The Dalitz plot of the η′→ηπ+π− decay is studied using the data collected with the VES spectrometer in two different exclusive reactions, π−p→η′n (charge-exchange) and π−N→η′π−N (diffractive-like production). The η mesons from η′ decays were detected in the η→γγ mode. The coefficients for the matrix element squared decomposition are measured on the largest statistics of η′ decays reported so far; there are ∼13.6×103 and ∼6.5×103 decays after background subtraction in charge-exchange and diffractive-like production, respectively.

The isospin symmetry-breaking (ISB) decay f 1(1285) → π+π−π0 has been studied at the VES facility. The branching ratio is measured: $\frac{{BR\left( {f_1 \to \pi ^ + \pi ^ - \pi ^0 } \right)}} {{BR\left( {f_1 \to \eta \pi ^ + \pi ^ - } \right)}} = 0.86 \pm 0.16_{ - 0.20}^{ + 0.70} \%$ . An upper limit for the f 1 decay into ρ(770)π is obtained: BR(f 1(1285) → ρ +−π−+) < 0.31% at 95% CL.

The isospin-violating decay f 1(1285) → π+π-π0 has been studied at the VES facility. This study is based on the statistics acquired in π- Be interactions at 27, 36.6 and 41 GeV/c in the diffractive reaction π- N → (f 1π-)N . The f 1(1285) → π+π-π0 decay is observed. The preliminary ratio of decay probabilities BR(f 1(1285) → π+π-π0) to BR(f 1(1285) → ηπ+π-). BR(η → γγ) is ∼ 2% .

Results obtained in π - Be interactions at 27, 36.6 and 41 GeV/c are presented. Decay f 1 (1285) → π + π - π 0 is observed; the dominant mechanism of the isospin symmetry violation in this decay is the a 0 (980) – f 0 (980) mixing. The intensity of this mixing is measured. An upper limit on possible f 1 (1285) – a 1 (1260) mixing is obtained. Preliminary results of a study of (ωɸ) system are shown. Plans for coming upgrade of the detector are presented.

Studies of various processes relevant to light scalar mesons at the VES facility are reviewed.

The charge-exchange reaction π - p → ω(780)ɸ(1020)n is studied with the VES setup. The (ωΦ) system is observed at relatively low background. Its invariant mass distribution peaks near threshold. The two-particles partial wave analyses shows that the J PC = 0 ++ state dominates. Comparison with scalar wave in ωω system at the comparable mass gives evidence for violation of the OZI rule. Another subject is a search for possible transition f 0 (980) → a 0 (980), which violates the isospin symmetry.

The charge‐exchange reaction π−p→nω(780)φ(1020) is studied with the VES setup. The (ωφ) system is observed at relatively low background. Its invariant mass distribution peaks near threshold. The two‐particles partial wave analyses shows that the Jpc = 0++ state dominates. This wave is compared with 0++ component in the (ωω) system at the comparable mass, which was measured earlier.

ATLAS is a general purpose experiment which will operate at the LHC. In this paper, the detector performance in terms of electrons, photons and muons identification and measurements are presented, combining full GEANT simulation and test beam results. Some of the prominent methods and event samples which will be used in situ to perform the calibration and evaluate the absolute energy scale are described as well. It is finally shown how these performances will allow ATLAS to accurately reconstruct signal mass peaks in several physics benchmark channels.