Mechanism of hyperfragment formation in K − capture

Abstract

In an attempt to understand the mechanism of hyperfragment production, a sample of 63 parent stars of hyperfragment production has been studied. These were selected to have a fast pion or proton accompanying the HF emission. The pion charges and energy distributions as well as the proton spectrum are used to establish the HF production process. Hyperfragments are emitted preferentially opposite to the direction of emission of associated pions or fast proton. The energy spectrum of the negative pions emitted from the K −-capture stars in association with hyperfragments can be separated into two groups, the one of lower energy being larger. On the other hand, the fact that all the π + mesons have energies typical of the lower-energy group confirms the assumption that the π + must originate in association with Σ − hyperons. We thus deduce that a majority (71 %) of the Λ's originate in Σ-conversion processes. We evaluate the frequency of π 0 emission in association with hyperfragment production. The reactions for the production of Λ's by K − absorption on one or two nucleons are discussed. Attempts to separate K − captures in C, N, or O from those in Ag or Br are almost completely successful. We estimate that less than 20 % of the multinucleon absorption occurred in heavy elements.