Study of Hyperon Resonances below KbarN threshold via the (K-,n) reaction on deuteron†
The Λ(1405) hyperon is a well-known hyperon resonance with the mass, width and spin-parity of 1405.1+1.3-1.0 MeV/c2, 50 MeV, and 1/2-. This state is assigned to be an orbital excited state with L=1, and the &Lambda(1520) state is regarded as its so-called LS partner. However, it is known that the size of the splitting is too large to explain in the quark model. Since the Λ(1405) is located just below the KbarN threshold, there is a long-standing puzzle whether the Λ(1405) is a KbarN bound state or not. The structure of the Λ(1405) has yet to be settled.
We propose an experiment at the J-PARC K1.8BR beam line to study the Λ(1405) hyperon via the (K-,n) reaction on deuteron, where a 1 GeV/c kaon is incident on the deuteron target knocking out a neutron at the forward angle and a recoiled kaon can be scattered with a residual nucleon to form the Λ(1405).
The d(K-,n) reaction populates both the isospin states of I=0 and I=1. All the decay final states of Λ(1405), Σ-π+, Σ+π-, and Σ0π0 are identified in order to decompose the isospin amplitude in the reaction.