The investigation of Λ(1405) state in the stopped K− reaction on deuterium

Abstract

Nowadays, extensive studies of the problem of the deeply bound $ar{K}$ nuclei stimulate the reconsid eration of Λ(1405) state as the theoretical basis of the binding of $ar{K}$ nuclei, and the old question of the nature of Λ(1405) becomes a modern subject by the new interest. In contrast to one of conventional interpretations of Λ(1405) as the $ar{K}$N quasi-bound state at 1405 MeV/c2 , a two-pole hypothesis, by which Λ(1405) consists of two poles at 1420 and 1390 MeV/c2 couple mainly with $ar{K}$N and Σπ channels, respectively, was proposed recently. On the other hand, a very recent theoretical analysis has clarified that the (Σπ)0 invariant mass spectra after K− absorption in d reflect strikingly resonant formation of Λ(1405) (or Λ(1420)) and thus are capable of distinguishing different Ansatz’s. We have proposed a new experiment by means of the stopped K− reaction on liquid deuterium at J-PARC K1.8BR beamline with E15/E17 experimental devices, so as to give a new precision- and high-statistics-data of (Σπ)0 mass spectra to examine the issue, Λ(1405) or Λ(1420), in the most reliable way, and thus to answer the most fundamental questions of $ar{K}$N interaction and $ar{K}$ nuclei.