On the structure observed in the in-flight 3He(K−,Λp)n reaction at J-PARC

Abstract

A theoretical investigation is done to clarify the origin of the peak structure observed near the K − pp threshold in the in-flight 3 He(K − , Λp)n reaction of the J-PARC E15 experiment, which could be a signal of the lightest kaonic nuclei, that is, the KN N (I = 1/2) state. For the investigation, we evaluate the Λp invariant mass spectrum assuming two possible scenarios to interpret the experimental peak. One assumes that the Λ(1405) resonance is generated after the emission of an energetic neutron from the absorption of the initial K − , not forming a bound state with the remaining proton. This uncorrelated Λ(1405)p system subsequently decays into the final Λp. The other scenario implies that, after the emission of the energetic neutron, a KN N bound state is formed, decaying eventually into a Λp pair. Our results show that the experimental signal observed in the in-flight 3 He(K − , Λp)n reaction at J-PARC is qualitatively well reproduced by the assumption that a KN N bound state is generated in the reaction, definitely discarding the interpretation in terms of an uncorrelated Λ(1405)p state.

Few-body approach to the structure of K¯ -nuclear quasibound states

“…We obtain the binding energies at 20-30 MeV, which are consistent with recent experimental measurement of the 3 He(K − , Λp)n reaction by J-PARC E15 [47] and its theoretical analysis [48]. The obtained binding energies with the SIDDHARTA potential are 5-10 MeV larger than the values obtained in Refs.…”

Fully coupled-channels complex scaling method for the K−pp system

“…Spectrum calculation is important for direct comparison with experimental results; this calculation is performed in Ref. [24]. In addition, such a study can be conducted using the fully ccCSM calculation with the completeness relation [16].…”

Experimental results on multi-nucleonic K−absorptions in light nuclei

“…A very interesting result is the prediction of the existence of the kaonic clusters [1] [2] that would mean in practice the trap of a antikaon inside a light nucleus allowing the formation of a very dense cold state of matter. A recent claim of the observation of the ppK − bound state [3] is currently under theoretical investigation [4]. On the strength of the antikaon nucleon potential would depend as well the possibility (currently ruled out by the measurement of 2 solar masses neutron star candidates [5]) of a phase transition that would allow the formation of a kaonic condensate inside neutron stars [6] [7].…”

“…The AMADEUS collaboration [10] [11] study the low-energy K − interactions with light nuclei (H, 4 He, 9 Be and 12 C). The attractive behaviour of the K − -nucleon potential is intimately related to the rather large cross-sections for antikaon absorption processes on nucleons that should be understood quantitatively.…”

“…Out of the total number of kaons interacting in the DC entrance wall, about 81% results to be absorbed in the carbon fibre component and the residual 19% in the aluminium foil. The KLOE DC is filled with a mixture of helium and isobutane (90% in volume 4 He and 10% in volume C 4 H 10 ) and is characterised by excellent position and momentum resolutions. Tracks are reconstructed with a resolution in the transverse R − φ plane of σ Rφ ∼ 150 µm and a resolution along the z-axis of σ z ∼ 2 mm.…”