Spin and parity measurement of the Λ ( 1405 ) baryon

• Published in: Physical review letters Vol. 112; no. 8
• Main Authors: Moriya, K., Schumacher, R. A., Aghasyan, M., Amaryan, M. J., Anderson, M. D., Anefalos Pereira, S., Ball, J., Baltzell, N. A., Battaglieri, M., Bellis, M., Biselli, A. S., Bono, J., Boiarinov, S., Briscoe, W. J., Brooks, W. K., Burkert, V. D., Carman, D. S., Celentano, A., Chandavar, S., Charles, G., Cole, P. L., Collins, P., Contalbrigo, M., Cortes, O., Crede, V., D’Angelo, A., Dashyan, N., De Vita, R., De Sanctis, E., Dey, B., Djalali, C., Dugger, M., Dupré, R., Egiyan, H., El Alaoui, A., El Fassi, L., Elouadrhiri, L., Eugenio, P., Fedotov, G., Fegan, S., Fleming, J. A., Gilfoyle, G. P., Giovanetti, K. L., Girod, F. X., Gohn, W., Golovatch, E., Gothe, R. W., Guidal, M., Griffioen, K. A., Hafidi, K., Hakobyan, H., Hicks, K., Holtrop, M., Ilieva, Y., Ireland, D. G., Ishkhanov, B. S., Isupov, E. L., Jo, H. S., Joo, K., Keller, D., Khandaker, M., Kim, W., Koirala, S., Kubarovsky, V., Kuleshov, S. V., Lenisa, P., Lu, H. Y., MacGregor, I. J. D., Markov, N., McCracken, M., McKinnon, B., Mestayer, M. D., Meyer, C. A., Mirazita, M., Mokeev, V., Montgomery, R. A., Moutarde, H., Munevar, E., Nadel-Turonski, P., Niccolai, S., Niculescu, I., Osipenko, M., Pappalardo, L. L., Pasyuk, E., Peng, P., Phillips, J. J., Pisano, S., Pogorelko, O., Pozdniakov, S., Price, J. W., Procureur, S., Puckett, A. J. R., Raue, B. A., Rimal, D., Ripani, M., Ritchie, B. G., Rizzo, A., Rosner, G., Roy, P., Sabatié, F.
• Format: Journal Article
• Language: English
• Published: United States American Physical Society 28-02-2014; American Physical Society (APS)
• Subjects: High Energy Physics - Experiment; Nuclear Experiment; Physics; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.112.082004

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.