Experimental study of relativistic hypernuclei using the HYBS-spectrometer

The method and the results of an experiment on the study of relativistic Λ 4 H and Λ 3 H production in interactions of 18 GeV/c4He nuclei with CH2 target nuclei are presented. The experiment was performed using the HYBS-spectrometer. The main registering part of the spectrometer is a (2×0.6×1)m3 streamer chamber placed in a magnetic field of 0.9 T. The streamer chamber was triggered when the beam4He nucleus lost one charge unit in the target and then again became double-charged inside the chamber fiducial volume according to the selection criteria for Λ 3,4 H hypernucleus production and its mesonic decay with the He nucleus in the final state. After scanning of the pictures, measurements of two-prong events and careful analysis, events of the decays Λ 4 H→4He+π− and Λ 3 H→3He+π− were identified. The estimates of the Λ 4 H production cross-section (∼0.4 µb) and its mean lifetime (∼2.2·10−10s) were obtained. A comparison with the results of other experiments and theoretical calculations is made. By the way, the cross-section of the charge exchange reaction3H+Ne→3He+π−++...(∼1 mb) was estimated. The work has been performed at the Laboratory of High Energies, JINR, Dubna.