Abstract : A determination of the spin and parity of the $\Lambda(1405)$ is presented using photoproduction data from the CLAS detector at Jefferson Lab. The reaction $\gamma + p \to K^+ + \Lambda(1405)$ is analyzed in the decay channel $\Lambda(1405) \to \Sigma^+ + \pi^-$, where the decay distribution to $\Sigma^+ \pi^-$ and the variation of the $\Sigma^+$ polarization with respect to the $\Lambda(1405)$ polarization direction determines the parity. The $\Lambda(1405)$ is produced, in the energy range $2.55 < W < 2.85$ GeV and for $0.6 < \cos \theta_{K^+} < 0.9$, with polarization $P = 0.45 \pm 0.02 (\text{stat}) \pm 0.07 (\text{syst})$. The analysis shows that the decays are in $S$ wave, with the $\Sigma^+$ polarized such that the $\Lambda(1405)$ has spin-parity $J^P = 1/2^-$, as expected by most theories.
http://hal.in2p3.fr/in2p3-00945802
Contributor : Emmanuelle Vernay <>
Submitted on : Thursday, February 13, 2014 - 9:09:22 AM Last modification on : Friday, November 27, 2020 - 5:52:10 AM
K. Moriya, R.A. Schumacher, M. Aghasyan, M.J. Amaryan, M.D. Anderson, et al.. Spin and parity measurement of the Lambda(1405) baryon. Physical Review Letters, American Physical Society, 2014, 112, pp.082004. ⟨10.1103/PhysRevLett.112.082004⟩. ⟨in2p3-00945802⟩