A study of the proton spectra following the capture of K − in 6 Li and 12 C with FINUDA FINUDA Collaboration
/ Authors
M.Agnello, G.Beer, L.Benussi, M.Bertani, H.C.Bhang, S.Bianco, G.Bonomi, E.Botta, M.Bregant, T.Bressani
and 48 more authors
S.Bufalino, L.Busso, D.Calvo, P.Camerini, P.Cerello, B.Dalena, F. Mori, G.D'Erasmo, D. Santo, D’Elia, F.L.Fabbri, D.Faso, A.Feliciello, A.Filippi, V. Filippini, R.A.Fini, E.M.Fiore, H.Fujioka, P.Gianotti, N.Grion, O.Hartmann, A.Krasnoperov, V.Lenti, V. Lucherini, V.Manzari, S.Marcello, T.Maruta, N.Mirfakhrai, O.Morra, T.Nagae, A.Olin, H.Outa, E.Pace, M.Pallotta, M.Palomba, A.Pantaleo, A.Panzarasa, V.Paticchio, S.Piano, F.Pompili, R.Rui, G.Simonetti, H.So, V.Tereshchenko, S.Tomassini, A.Toyoda, R.Wheadon, A.Zenoni
/ Abstract
Momenta spectra of protons emitted following the capture of $K^-$ in $^6$Li and $^{12}$C have been measured with 1% resolution. The $^{12}$C spectrum is smooth whereas for $^6$Li a well defined peak appears at about 500 MeV/$c$. The first observation of a structure in this region was identified as a strange tribaryon or, possibly, a $\bar K$-nuclear state. The peak is correlated with a $\pi^-$ coming from $\Sigma^-$ decay in flight, selected by setting momenta larger than 275 MeV/$c$. The $\Sigma^-$ could be produced, together with a 500 MeV/$c$ proton, by the capture of a $K^-$ in a deuteron-cluster substructure of the $^6$Li nucleus. The capture rate for such a reaction is $(1.62\pm 0.23_{stat} ^{+0.71}_{-0.44}(sys))%/K^-_{stop}$, in agreement with the existing observations on $^4$He targets and with the hypothesis that the $^6$Li nucleus can be interpreted as a $(d+\alpha)$ cluster.