Spin and parity measurement of the Λ (1405) baryon
A determination of the spin and parity of the Λ(1405) is presented using photoproduction data from the CLAS detector at Jefferson Lab. The reaction γ+p→K++Λ(1405) is analyzed in the decay channel Lambda(1405)→Σ++π, where the decay distribution to Σ+pi- and the variation of the Σ+ polarization with respect to the Λ(1405) polarization direction determines the parity. The Λ(1405) is produced, in the energy range 2.55 c.m.K+<0.9, with polarization P=0.45±0.02(stat)±0.07(syst). The analysis shows that the decays are in S wave, with the Σ+ polarized such that the Λ(1405) has spin-parity JP=1/2-, as expected by most theories.