Results of search for narrow diproton structures in the pn->pp pi(-) reaction at 1.98 GeV/c

The effective mass spectrum of two protons from the reaction p + n --> pp + pi(-)(backward) was investigated. The work was carried out at ITEP using a 3-meter magnet spectrometer and a proton beam of 1.98 GeV/c momentum. Liquid deuterium was used as a target. The presented mass spectrum includes about 34000 events. No statistically significant signals from narrow dibaryons were found in the mass reg;ion 1.89 - 2.17 GeV/c(2); the upper limits on narrow dibaryon production cross-section are given. At a mass of 1.8775 GeV/c(2) a narrow enhancement was found. A more detailed investigation of the observed phenomenon is needed.