Kaonic hydrogen X-ray measurement in SIDDHARTA

Abstract

Kaonic hydrogen atoms provide a unique laboratory to probe the kaon-nucleon strong interaction at the energy threshold, allowing an investigation of the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. The SIDDHARTA Collaboration has measured the $K$-series X rays of kaonic hydrogen atoms at the DA$\Phi$NE electron-positron collider of Laboratori Nazionali di Frascati, and has determined the most precise values of the strong-interaction induced shift and width of the $1s$ atomic energy level. This result provides vital constraints on the theoretical description of the low-energy $\bar{K}N$ interaction.Comment: 11 pages, 7 figures, Nuclear Physics A (in press) Special Issue on Strangeness Nuclear Physic

K−N amplitudes below threshold constrained by multinucleon absorption

“…Our specific choice follows that by Cieplý et al [3] in their recent pole-content study of six such amplitudes generated in four different models, [16,17,18,19] in chronological order. At NLO, the meson-baryon interaction consists of contact terms, parametrized by low-energy constants (LEC) which are fitted to low-energy K − p scattering and reaction cross sections, to three precisely determined threshold branching ratios, and also to the kaonic hydrogen energy shift and width as measured recently at the DAΦNE e + e − collider in Frascati by the SIDDHARTA Collaboration [1,2]. These NLO fitted LEC are added to the leading-order (LO) Weinberg-Tomozawa (WT) term plus the Born graphs contributions.…”

“…The density dependence of ξ k (ρ)ρ/4 in the denominators of Eq. (5) reduces at threshold to ξ k=0 (ρ)ρ/4 = (3k F /2π) ∝ ρ 1/3 , thereby giving rise to a leading ρ 4/3 Paulicorrelation contribution to the single-nucleon 'tρ' potential [22] The single-nucleon optical potential V (1) K − is often augmented by a phenomenological isoscalar potential V (2) K − of the form…”

“…At threshold, the precise measurement of strong-interaction level shift and width of the 1s state in the kaonic atom of hydrogen by the SIDDHARTA collaboration [1,2] provides an important constraint on the K − p interaction, in addition to three previously known threshold branching ratios. However, as shown recently [3,4] the resulting K − N scattering amplitudes appear to be strongly model dependent when extrapolating to energies below threshold and also with respect to their pole content.…”

“…For the predominantly attractiveKN interaction, theKN energies involved in kaonic atoms are below threshold, leading to a well defined in-medium 'subthreshold kinematics' scheme, as practised in our recent analyses of kaonic atom data [7,8]. For lack of accepted microscopic theory, this approach cannot be applied to the multinucleon part V (2) K − (ρ) of V K − (ρ), which usually consists of phenomenological terms devised to achieve agreement with experiment, as reviewed in Refs. [9,10].…”

Estimation of the Spatial Structure of \(\Lambda \)(1405) with Energy-Dependent Complex \(\bar{K}N\) Potential

“…To estimate the Λ(1405) size, we use the realisticKN potential [14] based on chiral SU(3) symmetry and the recent precise data relating to the K − p scattering length [15][16][17][18]. Here, we have to note that the single-channelKN potential is energy-dependent and complex, because of the elimination of the lower energy πΣ channel.…”