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Structure near the $$K^- + p + p$$ threshold in the in-flight $$^3$$He$$(K^-,Lambda p)n$$ reaction

Sada, Yuta*; Tanida, Kiyoshi   ; J-PARC E15 Collaboration*; 69 of others*

To search for an $$S = -1$$ di-baryonic state which decays to $$Lambda p$$, the $$^3$$He$$(K^-,Lambda p)n_{rm missing}$$ reaction was studied at 1.0 GeV/$$c$$. Unobserved neutrons were kinematically identified from the missing mass $$M_X$$ of the $$^3$$He$$(K^-, Lambda p)X$$ reaction in order to have a large acceptance for the $$Lambda pn$$ final state. The observed $$Lambda pn$$ events, distributed widely over the kinematically allowed region of the Dalitz plot, establish that the major component comes from a three-nucleon absorption process. A concentration of events at a specific neutron kinetic energy was observed in a region of low momentum transfer to the $$Lambda p$$. To account for the observed peak structure, the simplest $$S$$-wave pole was assumed to exist in the reaction channel, having a Breit-Wigner form in energy and with a Gaussian form factor. A minimum $$chi^2$$ method was applied to deduce its mass, $$M_X = 2355^{+6}_{-8}({rm stat.}) pm 12({rm syst.})$$ MeV/$$c^2$$, and decay width, $$Gamma_X = 110^{+19}_{-17}({rm stat.}) pm 27({rm syst.})$$ MeV/$$c^2$$, respectively. The form factor parameter $$Q_X sim 400$$ MeV/$$c$$ implies that the range of the interaction is about 0.5 fm.



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Category:Physics, Multidisciplinary



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