Experimental confirmation of the Λ ( 1405 ) ansatz from resonant formation of a K ? p quasi-bound state in K ? absorption by 3He and 4He

摘要

TheΣπinvariant-mass spectra in the resonant capture ofK?at rest in4He,3He anddare calculated by a coupled-channel procedure for aK?pquasi-bound state of an arbitrary chosen mass (M) and width (Γ). Aχ2analysis of old4He bubble chamber data shows a dominance of the s-orbit absorption, and yieldedM=1405.5?1+1.4MeV/c2andΓ=24?3+4MeV, where a possible population ofΣ0(1385)and also a small p-orbit capture contribution are taken into account. This result confirms theΛ(1405)ansatz, whereas recent chiral-SU(3) predictions (M～1420MeV/c2) are excluded. A more stringent test by using a3He target is proposed.