Discovery of a narrow resonance at 1070 MeV in the system of two K S mesons

Results are presented that were obtained by studying the previously unknown narrow resonance of mass about 1070 MeV. This state was discovered in the system of two K _S mesons. The experimental data subjected to the analysis here come from the 6-m spectrometer created at the Institute of Experimental and Theoretical Physics (ITEP, Moscow) and irradiated with a 40-GeV beam of negatively charged pions from the U-70 accelerator at the Institute for High Energy Physics (IHEP, Protvino) with the aim of studying π ^? p and π ^?C interactions. At the respective maximum, there are 69 events, the statistical significance being not less than six standard deviations. The mass and width of the observed meson are M = 1072.4 ± 0.8 MeV and Γ = 3.5 _+1.5 ^?1.0 MeV, respectively, the product of the cross section for its formation and the relevant branching ratio being not less than 20 nb. The preferable J ^PC assignment for this resonance is 0⁺⁺. Its extraordinary small width has no satisfactory theoretical explanation.