Tests of the fundamental symmetries in eta meson decays

Patterns of chiral symmetry violation and tests of the conservation of the fundamental C, P and CP symmetries are key physics issues in studies of the pi0, eta and eta' meson decays. These tests include searches for rare or forbidden decays and searches for asymmetries among the decay products in the not-so-rare decays. Some examples for the rare decays are eta-->2pi, eta-->4pi0 (CP tests), decays into an odd number of photons (e.g., eta-->3g) and the decay eta-->pi0e+e- (C tests). The experimental studies of the pi0, eta and eta' meson decays are carried out at four European accelerator research facilities: KLOE/KLOE-2 at DAFNE (Frascati), Crystal Ball at MAMI (Mainz), WASA at COSY (J\"ulich), Crystal Barrel at ELSA (Bonn).Comment: 9 pages, 2 figures, proceedings of Symposium on Prospects in the Physics of Discrete Symmetries, DISCRETE 2010, 6 - 11 December, Rome; v2: added reference

Convergence properties of η→3π\eta\to 3\pi decays in chiral perturbation theory

Theoretical efforts to describe and explain the $\eta\to 3\pi$ decays reach far back in time. Even today, the convergence of the decay widths and some of the Dalitz plot parameters seems problematic in low energy QCD. In the framework of resummed CHPT, we explore the question of compatibility of experimental data with a reasonable convergence of a carefully defined chiral series, where NNLO remainders are assumed to be small. By treating the uncertainties in the higher orders statistically, we numerically generate a large set of theoretical predictions, which are then confronted with experimental information. In the case of the decay widths, the experimental values can be reconstructed for a reasonable range of the free parameters and thus no tension is observed, in spite of what some of the traditional calculations suggest. The Dalitz plot parameters $a$ and $d$ can be described very well too. When the parameters $b$ and $\alpha$ are concerned, we find a mild tension for the whole range of the free parameters, at less than 2$\sigma$ C.L. This can be interpreted in two ways - either some of the higher order corrections are indeed unexpectedly large or there is a specific configuration of the remainders, which is, however, not completely improbable. Also, the distribution of the theoretical uncertainties is found to be significantly non-gaussian, so the consistency cannot be simply judged by the 1$\sigma$ error bars.Comment: 57 pages, 5 figure

Recent results from the Crystal Barrel experiment

The Crystal Barrel experiment has been constructed and installed at the Low Energy Antiproton Ring (LEAR) at CERN. It has been fully operational since late 1989. In this talk, recent results of meson spectroscopy in p{bar p}-annihilations are presented. The main emphasis is on all-neutral annihilations, the study of the strange quark content of the proton, and the investigation of the decay mode of il particles. A 2{sup ++} resonance decaying into {pi}{degrees}{pi}{degrees}at a mass of 1515 {plus_minus} 10 MeV with a width of 120 {plus_minus} 10 MeV has been seen in a 3{pi}{degrees} final state

Coupled channel analysis of

A partial wave analysis of antiproton–proton annihilation data in flight at 900 $$\mathrm {MeV/}c$$ into $${\pi ^0\pi ^0\eta }$$, $${\pi ^0\eta \eta }$$ and $${K^+K^-\pi ^0}$$ is presented. The data were taken at LEAR by the Crystal Barrel experiment in 1996. The three channels have been coupled together with $$\pi \pi$$-scattering isospin I = 0 S- and D-wave as well as I = 1 P-wave data utilizing the K-matrix approach. Analyticity is treated using Chew–Mandelstam functions. In the fit all ingredients of the K-matrix, including resonance masses and widths, were treated as free parameters. In spite of the large number of parameters, the fit results are in the ballpark of the values published by the Particle Data Group. In the channel $${\pi ^0\pi ^0\eta }$$ a significant contribution of the spin exotic $$I^G=1^-$$ $$J^{PC}=1^{-+}$$ $$\pi _1$$-wave with a coupling to $$\pi ^0 \eta$$ is observed. Furthermore the contributions of $$\phi (1020) \pi ^0$$ and $$K^*(892)^\pm K^\mp$$ in the channel $${K^+K^-\pi ^0}$$ have been studied in detail. The differential production cross section for the two reactions and the spin-density-matrix elements for the $$\phi (1020)$$ and $$K^*(892)^\pm$$ have been extracted. No spin-alignment is observed for both vector mesons. The spin density matrix elements have been also determined for the spin exotic wave

Two photon physics at LEP2

The working group on two photon physics concentrated on three main subtopics: modelling the hadronic final state of deep inelastic scattering on a photon; unfolding the deep inelastic scattering data to obtain the photon structure function; and resonant production of exclusive final states, particularly of glueball candidates. In all three areas, new results were presented.Comment: 23 pages, 27 figures. Report of the working group on two photon physics at Phenomenology Workshop on LEP2 Physics, Oxford, 14-18 April 199