Direct Determination of the Total Width of the Η Meson Using the Cosy–11 Apparatus

Inputs for the phenomenological desription of Quantum Chromo-Dynamics in the non-perturbative regime [1] can be provided from studies of the η meson production [2] and its decays [3]. Such investigations are of interest on its own account and are planned to be conducted with WASAat-COSY [4], KLOE-2 [5] and CBall-at-MAMI [6] experiments. In addition, precise determinations of the partial widths for the η decay channels will be helpful for the development of the Chiral Perturbation Theory as constrains for the calculations. However, regardless of the branching ratios of the η meson decays which are typically known with an accuracy better than 1.5%, the total width is established about 10 times less accurate [7] and cause that the experimental precision of the partial width for various decay channels – where only the branching ratio is known or will be measured – is governed by the precision in the knowledge of the total width. In the last issue of the Review of Particle Physics a value of (0.205±0.015) MeV/c is given for the total width of the η meson (Γη′) resulting