First measurement of the K−n →Λπ− non-resonant transition amplitude below threshold

K Piscicchia,M Martini,A Scordo,E De Lucia,M Cargnelli,M Silarski,O Vázquez Doce,V De Leo,A Selce,P Branchini,C Curceanu,G Mandaglio,P Moskal,R Del Grande,S Wycech,M Skurzok,L Fabbietti,J Zmeskal,D Sirghi,P Fermani,S Fiore,Alessandro Di Cicco ,J Márton ,E Czerwiński ,I Tucaković ,E Pérez Del Río ,W Krzemień

doi:10.1016/j.physletb.2018.05.025

Abstract

We present the analysis of K− absorption processes on He4 leading to Λπ− final states, measured with the KLOE spectrometer at the DAΦNE e+e− collider and extract, for the first time, the modulus of the non-resonant K−n →Λπ− direct production amplitude about 33 MeV below the K‾N threshold. This analysis also allows to disentangle the K− nuclear absorption at-rest from the in-flight capture, for K− momenta of about 120 MeV. The data are interpreted with the help of a phenomenological model, and the modulus of the non-resonant K−n →Λπ− amplitude for K− absorption at-rest is found to be |AK−n→Λπ−|=(0.334±0.018stat−0.058+0.034syst)fm.

Highlights

Experiments with low energy negatively charged kaon beams directed on gaseous or solid targets are unique to study the antikaon–nucleon/nuclei interactions, by performing measurements of the kaonic atoms de-excitations, or by detecting the final states following K− absorption processes
The in-flight capture process consists in the kaon propagation through the electron cloud, followed by the nuclear absorption
The measured p π, m π and cos(θ π ) spectra were fitted with calculated distributions expressed in terms of K−n→ π − transition amplitudes: the isospin I = 1 S-wave amplitude and the resonant I = 1 P-wave amplitude which is dominated by the

Summary

Introduction

Experiments with low energy negatively charged kaon beams directed on gaseous or solid targets are unique to study the antikaon–nucleon/nuclei interactions, by performing measurements of the kaonic atoms de-excitations, or by detecting the final states following K− absorption processes. In the case of interactions at-rest the underlying mechanism consists in the capture of the strange meson in a highly excited atomic state and a successive cascade to low-lying states, followed by the K− nuclear capture. The in-flight capture process consists in the kaon propagation through the electron cloud, followed by the nuclear absorption. Let us consider the process: K− A → Yπ R,

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Conclusion