NOVOSIBIRSK: New detector starts taking data

A new nonmagnetic Spherical Neutral Detector (SND) has started operation at the low energy VEPP- 2M electron-positron collider at the Budker Institute, Novosibirsk. This complements the CMD-2 detector built at Novosibirsk in collaboration with Brookhaven, Yale, Boston and Pittsburgh (November 1994, page 9). SND's main component is a 3.6 ton three-layer electromagnetic calorimeter containing 1680 separate Nal(TI) crystals covering 9 0% of the solid angle. The spherical shape provides uniform response over the solid angle, important for reducing systematic errors. In many respects SND looks similar to the famous Crystal Ball detector (originally used at the SPEAR electron-positron ring at Stanford/SLAC and transferred in 1981 to DORIS at DESY Hamburg), but its three layer structure allows better electron/pion and photon/kaon separation to be achieved and photon directions to be measured. A ten layer drift chamber with charge division readout provides good tracking for events with charged particles, while the outer system facilitates selection between muons and pions. The physics programme of experiments with SND in the collision energy range 0.4 to 1.4 GeV is strongly aimed at the investigation of multiphoton final states and states with both charged particles and photons. This would continue a fruitful series of experiments with the Neutral Detector performed by the same group in 1982-1987 which resulted in precision measurements of magnetic dipole radiative decays of rho, omega and phi into an eta meson and a photon or into a neutral pion and a photon which dominate the current data (Physics Reports, Vol. 202, 1991, p.99). The new detector can improve the precision of these measurements and perform a sensitive search for the decay phi into eta prime and a photon as well as electric dipole radiative decays of rho, omega and phi. For heavier quarkonium these decays have been studied in detail, while for their lightest partners none of these decays have been observed. The predicted branching ratios for the decays of phi into a0(980) or f0(980) plus a photon are in the range 10^-4- 10^-6. Observation of these decays will clarify our knowledge of the lightest scalar states and their possible mixing with four-quark states. Another highlight is a careful study, complementing that of CMD-2 , of hadron production in electronpositron annihilation, which makes important contributions to the anomalous magnetic moment of the muon (g-2), to decay widths and spectra of the tau lepton, and to hadronic vacuum polarization effects at the Z boson, as well as various quarkgluon sum rules