Pole position of Λ(1405) measured in d(K−,n)πΣ reactions
S. Aikawa, S. Ajimura, T. Akaishi, H. Asano, G. Beer, C. Berucci, M. Bragadireanu, P. Buehler, L. Busso, M. Cargnelli, S. Choi, C. Curceanu, S. Enomoto, Hiroyuki Fujioka, Yuya Fujiwara, Tomokazu Fukuda, C. Guaraldo, T. Hashimoto, R. Hayano, T. Hiraiwa, M. Iio, M. Iliescu, Kentaro Inoue, Y. Ishiguro, S. Ishimoto, Takashi Ishikawa, K. Itahashi, M. Iwai, M. Iwasaki, Koki Kanno, K. Kato, Yuko Kato, Shingo Kawasaki, P. Kienle, Yusuke Komatsu, H. Kou, Y. G., J. Márton, Y. Matsuda, Y. Mizoi, O. Morra, R. Murayama, T. Nagae, H. Noumi, H. Ohnìshì, S. Okada, Zhadyra Omar, H. Outa, K. Piscicchia, Y. Sada, A. Sakaguchi, F. Sakuma, M. Sato, A. Scordo, M. Sekimoto, H. Shi, K. Shirotori, D. Sirghi, F. Sirghi, K. Suzuki, S. Suzuki, Takehiro Suzuki, K. Tanida, H. Tatsuno, A. O. Tokiyasu, Makoto Tokuda, D. Tomono, A. Toyoda, K. Tsukada, O. Vázquez Doce, E. Widmann, T. Yamaga, Toshitsugu Yamazaki, H. Yim, Q. Zhang, J. Zmeskal
Abstract
We measured a set of π ± Σ ∓ , π 0 Σ 0 , and π − Σ 0 invariant mass spectra below and above the K ¯ N mass threshold in K − -induced reactions on deuteron . The measured π Σ mass spectral shape is well reproduced via the two-step mechanism, i . e ., a neutron knocked out at a forward angle from a deuteron by an incident K − , with the K ¯ recoiled backward reacting with the residual nucleon to produce π and Σ. We deduced the S -wave K ¯ N → π Σ and K ¯ N → K ¯ N scattering amplitudes in the isospin 0 channel in the framework of a K ¯ N and π Σ coupled channel. We find that a resonance pole corresponding to Λ ( 1405 ) is located at 1417.7 − 7.4 + 6.0 (fitting errors) − 1.0 + 1.1 (systematic errors) + [ − 26.1 − 7.9 + 6.0 (fitting errors) − 2.0 + 1.7 (systematic errors)] i MeV/ c 2 , closer to the K ¯ N mass threshold than the value determined by the Particle Data Group.