For almost 50 years the structure of the Λ(1405) resonance has been a mystery. Even though it contains a heavy strange quark and has odd parity, its mass is lower than any other excited spin-1/2 baryon. Dalitz and co-workers speculated that it might be a molecular state of an antikaon bound to a nucleon. However, a standard quark-model structure is also admissible. Although the intervening years have seen considerable effort, there has been no convincing resolution. Here we present a new lattice QCD simulation showing that the strange magnetic form factor of the Λ(1405) vanishes, signaling the formation of an antikaon-nucleon molecule. Together with a Hamiltonian effective-field-theory model analysis of the lattice QCD energy levels, this strongly suggests that the structure is dominated by a bound antikaon-nucleon component. This result clarifies that not all states occurring in nature can be described within a simple quark model framework and points to the existence of exotic molecular meson-nucleon bound states.
CITATION STYLE
Hall, J. M. M., Kamleh, W., Leinweber, D. B., Menadue, B. J., Owen, B. J., Thomas, A. W., & Young, R. D. (2015). Lattice QCD evidence that the Λ (1405) resonance is an Antikaon-Nucleon molecule. Physical Review Letters, 114(13). https://doi.org/10.1103/PhysRevLett.114.132002
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