Structure near K−K^-+pp+pp threshold in the in-flight 3^3He(K−,Λp)n(K^-,\Lambda p)n reaction

To search for an S= -1 di-baryonic state which decays to $\Lambda p$, the ${\rm{}^3He}(K^-,\Lambda p)n_{missing}$ reaction was studied at 1.0 GeV/$c$. Unobserved neutrons were kinematically identified from the missing mass $M_X$ of the ${\rm{}^3He}(K^-,\Lambda p)X$ reaction in order to have a large acceptance for the $\Lambda pn$ final state. The observed $\Lambda p n$ 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 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 $^{+ 6}_{ - 8}$ (stat.) $\pm 12$ (syst.) MeV/c$^2$, and decay-width $\Gamma_X\ =$ 110 $^{+ 19}_{ - 17}$ (stat.) $\pm 27$ (syst.) MeV/c$^2$, respectively. The form factor parameter $Q_X \sim$ 400 MeV/$c$ implies that the range of interaction is about 0.5Comment: 12pages, 8 figure

A search for the K−pp bound state in the 3He(K−in-flight, n) reaction at J-PARC

We have collected the first physics data of an experimental search for the simplest kaonic nuclear bound state, " K − pp", by the 3He( K − n) reaction at J-PARC. We confirmed that our spectrometer system works as designed and observed clear peak structure composed of the quasi-elastic K − " n " → K − n and the charge-exchange K − " p " → ¯ K 0 n reactions in the forward neutron spectrum

Search for the K− pp bound state via the 3He(K−, n) reaction at 1 GeV/c

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Study of the elementary (K−, n) reactions to search for the K¯NN bound state via the 3He (K−, n) reaction at J-PARC

We have searched for the simplest kaonic nuclear state, K̄NN, using the in-flight 3He (K-, n) reaction at the J-PARC hadron experimental facility. In the semi-inclusive neutron missing-mass spectrum at θnlab=0°, an excess of yield was observed just below the K- pp mass-threshold, which cannot be explained by any elementary reactions [PTEP 2015, 061D01]. To understand the missing-mass spectrum of 3He (K-, n) X, we investigated the elementary (K-, n) reactions using hydrogen and deuterium targets. The p (K-, n) X missing-mass spectrum was well described by the charge-exchange reaction. However, in the d (K-, n) X spectrum, we observed an excess of yield just below the K- p mass-threshold, which was similar to that in the 3He (K-, n) X spectrum

A search for the K−pp bound state in the 3He(K−in-flight, n) reaction at J-PARC

We have collected the first physics data of an experimental search for the simplest kaonic nuclear bound state, “K− pp”, by the 3He(K− n) reaction at J-PARC. We confirmed that our spectrometer system works as designed and observed clear peak structure composed of the quasi-elastic K−“n” → K−n and the charge-exchange K−“p” → ¯̅K0n reactions in the forward neutron spectrum