Antikaon-nucleon Interaction Research Articles

Quasibound state in the K¯NNN system

The attractive nature of the antikaon-nucleon interaction suggests that few-body systems of antikaons and nucleons can exist. The author presents a new study of the exotic $\overline{K}\phantom{\rule{0}{0ex}}N\phantom{\rule{0}{0ex}}N\phantom{\rule{0}{0ex}}N$ system. Four-body Faddeev-type equations are used to evaluate the binding energy and the width of the quasi-bound state in the system. The dependence of the results on the two-body antikaon-nucleon and nucleon-nucleon interactions is quantified.

Antikaon-nucleon interaction within three-dimensional approach: Homogeneous and inhomogeneous Lippmann-Schwinger equations

The Λ(1405) resonance below the antikaon-nucleon threshold is studied by solving homogeneous and inhomogeneous Lippmann-Schwinger equations for local K‾N Yukawa and Gaussian potentials within three-dimensional approach. In this method, unlike the partial wave method, in which the number of considered partial waves needs to increase with enhancing energy, the calculations are performed without decomposition into angular momentum components. Also, the behavior of the transition matrix in on-shell, half-off-shell, and fully off-shell modes for various energies is investigated.

Scattering Studies with Low-Energy Kaon-Proton Femtoscopy in Proton-Proton Collisions at the LHC.

The study of the strength and behavior of the antikaon-nucleon (K[over ¯]N) interaction constitutes one of the key focuses of the strangeness sector in low-energy quantum chromodynamics (QCD). In this Letter a unique high-precision measurement of the strong interaction between kaons and protons, close and above the kinematic threshold, is presented. The femtoscopic measurements of the correlation function at low pair-frame relative momentum of (K^{+}p⊕K^{-}p[over ¯]) and (K^{-}p⊕K^{+}p[over ¯]) pairs measured in pp collisions at sqrt[s]=5, 7, and 13TeV are reported. A structure observed around a relative momentum of 58 MeV/c in the measured correlation function of (K^{-}p⊕K^{+}p[over ¯]) with a significance of 4.4σ constitutes the first experimental evidence for the opening of the (K[over ¯]^{0}n⊕K^{0}n[over ¯]) isospin breaking channel due to the mass difference between charged and neutral kaons. The measured correlation functions have been compared to Jülich and Kyoto models in addition to the Coulomb potential. The high-precision data at low relative momenta presented in this work prove femtoscopy to be a powerful complementary tool to scattering experiments and provide new constraints above the K[over ¯]N threshold for low-energy QCD chiral models.

Kaonic deuterium from realistic antikaon-nucleon interaction

We present precise three-body calculations for the spectrum of kaonic deuterium with a realistic antikaon-nucleon interaction. Thanks to the precise measurement of kaonic hydrogen, it is now possible to construct realistic $\bar KN$ interactions which reproduce the whole set of experimental data in the threshold region. Employing such realistic interactions, the energy of the three-body system of kaonic deuterium is determined with the accuracy of eV, by expanding its wave function with a large number of correlated Gaussian basis functions. The level shift and width of the 1S state are found to be 670 eV and 1016 eV, respectively. The improved Deser formulas work reasonably well to estimate the shift and width of kaonic hydrogen, but their application to kaonic deuterium does not give an accurate estimation. It is shown that the result is sensitive to the I = 1 component of the $\bar KN$ interaction, which will be further constrained in future experiments.

A New Silicon Drift Detector System for Kaonic Atom Measurements

The kaonic deuterium measurement at J-PARC and DAΦNE will provide a piece of information still missing to the antikaon-nucleon interaction close to threshold, providing valuable information to answer one of the most fundamental problems in hadron physics today - to the yet unsolved puzzle of how the hadron mass is generated. For this a new X-ray detector system has been developed to measure the shift and width of the 2p → 1s transition of kaonic deuterium with a precision of 60 eV and 140 eV, respectively.

A charged particle veto detector for kaonic deuterium measurements at DAΦNE

The antikaon-nucleon interaction close to threshold provides crucial information on the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. In this context, the importance of kaonic deuterium x-ray spectroscopy has been well recognized, but no experimental results have yet been obtained due to the difficulty of the measurement. To measure the shift and width of the kaonic deuterium 1s state with an accuracy of 30 eV and 75 eV, respectively, an apparatus is under construction at the Laboratori Nazionali di Frascati. A detailed Monte Carlo simulation has shown that an increase of the signal to background ratio by a factor of ten will be required compared to the successfully performed kaonic hydrogen measurement (SIDDHARTA). Three pillars are essential for the newly developed experimental apparatus: a large area x-ray detector system (consisting of Silicon Drift Detectors), a lightweight cryogenic target system and a veto system, consisting of an outer veto detector (Veto-1) for active shielding and an inner veto detector (Veto-2) for charged particle suppression. For both veto systems, an excellent time resolution is required to distinguish kaons stopping in gas from direct kaon stops in the entrance window or side wall of the target. First test measurements on the Veto-2 system were performed. An average time resolution of (54 ± 2) ps and detection efficiencies of ~ 99 % were achieved.

Kaonic deuterium and low-energy antikaon-nucleon interaction

A new evaluation of the 1s level shift and width of kaonic deuterium is presented based on an accurate K̅ NN three-body calculation, using as input a realistic antikaon-nucleon interaction constrained by the SIDDHARTA kaonic hydrogen data. The three-body Schrödinger equation is solved with a superposition of a large number of correlated Gaussian basis functions extending over distance scales up to several hundred fm. The resulting energy shift and width of the kaonic deuterium 1s level are △E ≃ 0:67 keV and Γ ≃ 1.02 keV, with estimated uncertainties at the 10 % level.

Ground-state properties of light kaonic nuclei signaling symmetry energy at high densities**Supported by National Natural Science Foundation of China (11775049, 11275048) and the China Jiangsu Provincial Natural Science Foundation (BK20131286)

A sensitive correlation between the ground-state properties of light kaonic nuclei and the symmetry energy at high densities is constructed under the framework of relativistic mean-field theory. Taking oxygen isotopes as an example, we see that a high-density core is produced in kaonic oxygen nuclei, due to the strongly attractive antikaon-nucleon interaction. It is found that the state energy in the high-density core of kaonic nuclei can directly probe the variation of the symmetry energy at supranormal nuclear density, and a sensitive correlation between the neutron skin thickness and the symmetry energy at supranormal density is established directly. Meanwhile, the sensitivity of the neutron skin thickness to the low-density slope of the symmetry energy is greatly increased in the corresponding kaonic nuclei. These sensitive relationships are established upon the fact that the isovector potential in the central region of kaonic nuclei becomes very sensitive to the variation of the symmetry energy. These findings might provide another perspective to constrain high-density symmetry energy, and await experimental verification in the future.

A New Silicon Drift Detector For Kaonic Deuterium Measurements: On behalf of the E57 collaboration at J-PARC

The interaction of antikaons with nucleons and nuclei in the lowenergy regime is a very active research field in hadron physics. Specially, the antikaon-nucleon interaction close to threshold provides crucial information on the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD and touching one of the fundamental problems in hadron physic today - the still unsolved question of how hadron masses are generated. To study this problem, we have developed a new X–ray detector system and constructed an experimental apparatus to measure the kaonic deuterium 1s ground state shift and width with an accuracy of 60 eV and 140 eV, respectively.

Constraining the K¯N interaction from the 1S level shift of kaonic deuterium

Motivated by the precise measurement of the 1S level shift of kaonic hydrogen, we perform accurate three-body calculations for the spectrum of kaonic deuterium using a realistic antikaon-nucleon (K¯N) interaction. In order to describe both short- and long-range behaviors of the kaonic atomic states, we solve the three-body Schrodinger equation with a superposition of a large number of correlated Gaussian basis functions covering distances up to several hundreds of fm. Transition energies between 1S,2P, and 2S states are determined with high precision. The complex energy shift of the 1S level of kaonic deuterium is found to be ΔE−iΓ/2=(670−i508) eV. The sensitivity of this level shift with respect to the isospin I=1 component of the K¯N interaction is examined. It is pointed out that an experimental determination of the kaonic deuterium level shift within an uncertainty of 25% will provide a constraint for the I=1 component of the K¯N interaction significantly stronger than that from kaonic hydrogen.

Three-Body Antikaon–Nucleon Systems

The paper contains a review of the exact or accurate results achieved in the field of the three-body antikaon–nucleon physics. Different states and processes in $$\bar{K}NN$$ and $$\bar{K}\bar{K}N$$ systems are considered. In particular, quasi-bound states in $$K^- pp$$ and $$K^- K^- p$$ systems were investigated together with antikaonic deuterium atom. Near-threshold scattering of antikaons on deuteron, including the $$K^- d$$ scattering length, and applications of the scattering amplitudes are also discussed. All exact three-body results were calculated using some form of Faddeev equations. Different versions of $$\bar{K}N$$ , $${\varSigma }N$$ , $$\bar{K}\bar{K}$$ , and NN potentials, specially constructed for the calculations, allowed investigation of the dependence of the three-body results on the two-body input. Special attention is paid to the antikaon–nucleon interaction, being the most important for the three-body systems. Approximate calculations, performed additionally to the exact ones, demonstrate accuracy of the commonly used approaches.

Three-body calculations for the K−pp system within potential models

We present three-body nonrelativistic calculations within the framework of a potential model for the kaonic cluster K−pp using two methods: the method of hyperspherical harmonics in the momentum representation and the method of Faddeev equations in configuration space. To perform numerical calculations, different NN and antikaon–nucleon interactions are applied. The results of the calculations for the ground-state energy for the K−pp system obtained by both methods are in reasonable agreement. Although the ground-state energy is not sensitive to the pp interaction, it shows very strong dependence on the K−p potential. We show that the dominant clustering of the system in the configuration Λ (1405) + p allows us to calculate the binding energy to good accuracy within a simple cluster approach for the differential Faddeev equations. The theoretical discrepancies in the binding energy and width for the K−pp system related to the different pp and K−p interactions are addressed.

On the pole content of coupled channels chiral approaches used for the [formula omitted] system

Several theoretical groups describe the antikaon–nucleon interaction at low energies within approaches based on the chiral SU(3) dynamics and including next-to-leading order contributions. We present a comparative analysis of the pertinent models and discuss in detail their pole contents. It is demonstrated that the approaches lead to very different predictions for the K−p amplitude extrapolated to subthreshold energies as well as for the K−n amplitude. The origin of the poles generated by the models is traced to the so-called zero coupling limit, in which the inter-channel couplings are switched off. This provides new insights into the pole contents of the various approaches. In particular, different concepts of forming the Λ(1405) resonance are revealed and constraints related to the appearance of such poles in a given approach are discussed.

Antikaon–nucleon interaction and Λ(1405) in chiral SU(3) dynamics

The properties of the Λ(1405) resonance are key ingredients for determining the antikaon–nucleon interaction in strangeness nuclear physics, and the novel internal structure of the Λ(1405) is of great interest in hadron physics, as a prototype case of a baryon that does not fit into the simple three-quark picture. We show that a quantitative description of the antikaon–nucleon interaction with the Λ(1405) is achieved in the framework of chiral SU(3) dynamics, with the help of recent experimental progress. Further constraints on the K¯N subthreshold interaction are provided by analyzing πΣ spectra in various processes, such as the K−d→πΣn reaction and the Λc→ππΣ decay. The structure of the Λ(1405) is found to be dominated by an antikaon–nucleon molecular configuration, based on its wavefunction derived from a realistic K¯N potential and the compositeness criteria from a model-independent weak-binding relation.

Topics in low-energy QCD with strange quarks

Recent developments and pending issues in low-energy strong interaction physics with strangeness are summarized. Chiral SU(3) effective field theory has progressed as the appropriate theoretical framework applied to antikaon- and hyperon-nuclear systems. Topics include antikaon-nucleon interactions and the Λ(1405), \(\bar {K}NN\) systems, recent developments in hyperon-nucleon interactions and strangeness in dense baryonic matter with emphasis on new constraints from neutron star observations.

Measurement of the Strong Interaction Induced Shift and Width of the 1$s$ State of Kaonic Deuterium at J-PARC

The antikaon-nucleon interaction close to threshold provides crucial information on the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. In this context the importance of kaonic deuterium X-ray spectroscopy has been well recognized, but no experimental results have yet been obtained due to the difficulty of the measurement. We propose to measure the shift and width of the kaonic deuterium 1s state with an accuracy of 60 eV and 140 eV respectively at J-PARC. These results together with the kaonic hydrogen data (KpX at KEK, DEAR and SIDDHARTA at DAFNE) will then permit the determination of values of both the isospin I=0 and I=1 antikaon-nucleon scattering lengths and will provide the most stringent constraints on the antikaon-nucleon interaction, promising a breakthrough. Refined Monte Carlo studies were performed, including the investigation of background suppression factors for the described setup. These studies have demonstrated the feasibility of determining the shift and width of the kaonic deuterium atom 1s state with the desired accuracy of 60 eV and 140 eV.

Preliminary study of kaonic deuterium X-rays by the SIDDHARTA experiment at DAΦNE

The study of the system at very low energies plays a key role for the understanding of the strong interaction between hadrons in the strangeness sector. At the DAΦNE electron–positron collider of Laboratori Nazionali di Frascati we studied kaonic atoms with and , taking advantage of the low-energy charged kaons from Φ-mesons decaying nearly at rest. The SIDDHARTA experiment used X-ray spectroscopy of the kaonic atoms to determine the transition yields and the strong interaction induced shift and width of the lowest experimentally accessible level (1s for H and D and 2p for He). Shift and width are connected to the real and imaginary part of the scattering length. To disentangle the isospin dependent scattering lengths of the antikaon–nucleon interaction, measurements of and of are needed. We report here on an exploratory deuterium measurement, from which a limit for the yield of the K-series transitions was derived: and (CL 90%). Also, the upcoming SIDDHARTA-2 kaonic deuterium experiment is introduced.

Development of a liquid 3He target for experimental studies of antikaon–nucleon interaction at J-PARC

A liquid 3He target system was developed for experimental studies of kaonic atoms and kaonic nuclei at J-PARC. 3He gas is liquefied in a heat exchanger cooled below 3.2K by decompression of liquid 4He. To maintain a large acceptance of the cylindrical detector system for decay particles of kaonic nuclei, efficient heat transport between the separate target cell and the main unit is realized using circulation of liquid 3He. To minimize the amount of material, a vacuum vessel containing a carbon fiber reinforced plastic cylinder having an inside diameter of 150mm and a thickness of 1mm was produced. A target cell made of pure beryllium and beryllium–aluminum alloy was developed not only to minimize the amount of material but also to obtain high X-ray transmission. During a cooling test, the target cell was kept at 1.3K at a pressure of 33mbar. The total estimated heat load to the components including the target cell and heat exchanger cooled by liquid 4He decompression, was 0.21W, and the liquid 4He consumption rate was 50L/day.

Chiral SU(3) theory of antikaon–nucleon interactions with improved threshold constraints

$\bar{K}$-nucleon interactions are investigated in the framework of coupled-channels dynamics based on the next-to-leading order chiral SU(3) meson-baryon effective Lagrangian. A recent determination of the 1s shift and width of kaonic hydrogen enables us to set accurate constraints on the coupled-channels meson-baryon amplitudes in the strangeness $S=-1$ sector. Theoretical uncertainties in the subthreshold extrapolation of the coupled-channels amplitudes are discussed. Using this framework, we give predictions for $K^-$-neutron interactions and for the spectrum of the $\Lambda(1405)$ resonance. A simplified, effective three-channel model using leading order chiral SU(3) meson-baryon interactions is also constructed for convenient application in $\bar{K}$-nuclear few-body calculations.

Strangeness production in antiproton-nucleus collisions

Antiproton annihilations on nuclei provide a very interesting way to study the behaviour of strange particles in the nuclear medium. In low energy \(\bar p\) annihilations, the hyperons are produced mostly by strangeness exchange mechanisms. Thus, hyperon production in \(\bar p A\) interactions is very sensitive to the properties of the antikaon-nucleon interaction in nuclear medium. Within the Giessen Boltzmann–Uehling–Uhlenbeck transport model (GiBUU), we analyse the experimental data on Λ and \(K^{0}_S\) production in \(\bar p A\) collisions at p lab = 0.2 − 4 GeV/c. A satisfactory overall agreement is reached, except for the \(K^{0}_S\) production in \(\bar p+{^{20}}\)Ne collisions at p lab = 608 MeV/c, where we obtain substantially larger \(K^{0}_S\) production rate. We also study the Ξ hyperon production, important in view of the forthcoming experiments at FAIR and J-PARC.