Contribution of the inelastic channels K − p → Yπ to the shift of the ground-state energy level of kaonic hydrogen

The contribution of the inelastic channels K ^? p → Yπ, where Yπ = Σ^? π ⁺, Σ ⁺ π ^?, Σ ⁰ π ⁰, or λ⁰ π ⁰, kinematically allowed at the K ^? p threshold to the S-wave scattering length of elastic K ^? p scattering, as well as the shift of the ground-state energy of kaonic hydrogen, is calculated. The result, δa ₀ ^K?p = ?0.037 ± 0.010 fm and δε _1s = 15 ± 4 eV, will be important for the theoretical analysis of the expected data from the experiments scheduled by the DEAR and SIDDHARTA Collaborations at the end of 2006.     

Phenomenological \boldsymbol{\bar{K}N} interaction with isospin-breaking effects

New strong coupled-channel $\bar{K}N - \pi \Sigma$ potential, reproducing all existing experimental data and suitable for using in accurate few-body calculations, is constructed. Isospin breaking effects of direct inclusion of the Coulomb interaction and the use of physical masses in calculations are taken into account. The 1s level shift and width of kaonic hydrogen, consistent with the scattering data, was obtained and the corresponding strong K ^??? p scattering length was calculated. One- and two-pole forms of Λ(1405) resonance were considered.     

Scattering and bound states in the K − d system

We investigated different properties of the K ^? d system. First, the near-threshold elastic amplitudes of K ^? d scattering were calculated from the three-body Alt-Grassberger-Sandhas equations with the coupled channels using four versions of the -KN-πΣ potentials. The potentials reproduce the very recent SIDDHARTA or older KEK experimental data on kaonic hydrogen, data on K ^? p scattering and have one- or two-pole structure of the Λ(1405) resonance. Second, the 1s-level shifts and widths of kaonic deuterium, corresponding to the results on near-threshold antikaon-deuteron scattering, were calculated. The question of existence of a strong quasi-bound state in the K ^? d system was also investigated.     

New precision measurements of the strong interaction in kaonic hydrogen

The DEAR experiment performed at the DAΦNE electron-positron collider (Frascati, Italy) studied the strong interaction shift and width of the 1s state in kaonic hydrogen using X-ray spectroscopy. The repulsive character of the kaon-proton interaction at threshold was confirmed and the most precise values of the shift and width were obtained. However, high precision data at the percent level are highly requested to further develop the theories and thus our understanding of the low-energy antikaon-nucleon interaction. Therefore, a new series of precision experiments on kaonic hydrogen and kaonic deuterium are planned at LNF.     

On extracting information about hadron-nuclear interaction from hadronic atom level shifts

It is argued that adjusting strong potentials directly to observed hadronic atom level shifts may lead to significantly different scattering lengths than those predicted by the Deser formula [1]. By the example of the 1s level shift of kaonic hydrogen it is demonstrated that the usually adopted Deser values deduced from the two recent measurements in KEK [2] and by the DEAR collaboration [3], a _D (KEK) = 0.78–0.49i fm and a _D (DEAR) = 0.47–0.3i fm, should be replaced by a _s (KEK) ? 0.85–0.62i fm and a _s (DEAR) ? 0.49–0.35i fm, correspondingly.     

Isospin mixing \bar{K}N\hbox{-}{\pi}{\Sigma} interaction and \bar{K}NN\hbox{-}{\pi} {\Sigma}N quasi-bound state

A phenomenological isospin-dependent $\bar{K}N\hbox{-}\pi\Sigma$ potential reproducing a medium KEK value of 1s kaonic hydrogen level shift instead of a K ^? p scattering length is constructed. The corresponding three-body $\bar{K}NN\hbox{-}\pi\Sigma N$ calculation using the obtained potential is performed.     

Disentangling the K-complex of kaonic hydrogen with DEAR

The DEAR (DAΦNE Exotic Atom Research) experiment at the new φ-factory DAΦNE of Laboratori Nazionali di Frascati aims for a 1% measurement of the line shift of the K-complex due to strong interaction in kaonic hydrogen. This presentation is meant to prove that the high statistics and good resolution obtainable with DEAR will be able to disentangle the kaonic hydrogen K-complex lines (a cascade unconstrained fit), obtaining in this way constraints for what concerns the cascade parameters and, consequently, information regarding the physical processes involved in the kaonic hydrogen atomic cascade. This revised version was published online in August 2006 with corrections to the Cover Date.     

Faddeev Treatment of the Quasi-Bound and Scattering States in the {\bar{K}NN - \pi\Sigma N} System: New Results

A chiral-motivated \({\bar{K}N - \pi\Sigma - \pi\Lambda}\) potential was constructed and used in Faddeev calculations of different characteristics of \({\bar{K}NN - \pi\Sigma N}\) system. First of all, binding energy and width of the K ^? pp quasi-bound state were newly obtained. The low-energy K ^? d scattering amplitudes, including scattering length, together with the 1s level shift and width of kaonic deuterium were calculated. Comparison with the results obtained with the phenomenological \({\bar{K}N - \pi\Sigma}\) potential demonstrates that the chiral-motivated potential gives more shallow K ^? pp state, while the characteristics of K ^? d system are less sensitive to the form of \({\bar{K}N}\) interaction.     

Observation of kaonic hydrogen atom X-ray

We successfully observed clear K-series kaonic hydrogen X-rays for the first time taking advantage of two charged pions tagging technique and a gaseous hydrogen target. The strong-interaction energy shift and width of 1s state of K ⁻p atom were determined to be ΔE _1s = -323 ± 63 (statistical) ± 11 (systematic) eV and Г_1s = 407 ± 208 ± 100 eV. Our result means that the K ⁻p strong interaction near threshold is repulsive and the long-standing kaonic hydrogen puzzle is solved. This revised version was published online in August 2006 with corrections to the Cover Date.     

Precision measurements of kaonic atoms at DA ΦNE and future perspectives

The DAΦNE electron-positron collider at the Frascati National Laboratories has made available a unique “beam" of negative kaons providing unprecedented conditions for the study of the low-energy kaon-nucleon interaction, a field still largely unexplored. The DEAR (DAΦNE Exotic Atom Research) experiment at DAΦNE and its successor SIDDHARTA (SIlicon Drift Detector for Hadronic Atom Research by Timing Application) aim at a precision measurement of the strong-interaction shift and width of the fundamental 1s level, via the measurement of the X-ray transitions to this level, for kaonic hydrogen and kaonic deuterium. The aim is to extract the isospin-dependent antikaon-nucleon scattering lengths and to contribute to the understanding of aspects of chiral symmetry breaking in the strangeness sector.     

On kaonic hydrogen. Quantum field theoretic and relativistic covariant approach

We study kaonic hydrogen, the bound K ^- p state A _{K p} . Within a quantum field theoretic and relativistic covariant approach we derive the energy level displacement of the ground state of kaonic hydrogen in terms of the amplitude of K ^- p scattering for arbitrary relative momenta. The amplitude of low-energy K ^- p scattering near threshold is defined by the contributions of three resonances , and and a smooth elastic background. The amplitudes of inelastic channels of low-energy K ^- p scattering fit experimental data on the near-threshold behaviour of the cross-sections and the experimental data by the DEAR Collaboration. We use the soft-pion technique (leading order in Chiral Perturbation Theory) for the calculation of the partial width of the radiative decay of pionic hydrogen and the Panofsky ratio. The theoretical prediction for the Panofsky ratio agrees well with experimental data. We apply the soft-kaon technique (leading order in Chiral Perturbation Theory) to the calculation of the partial widths of radiative decays of kaonic hydrogen and . We show that the contribution of these decays to the width of the energy level of the ground state of kaonic hydrogen is less than 1 .Received: 7 October 2003, Revised: 29 November 2003, Published online: 22 June 2004PACS: 11.10.Ef Lagrangian and Hamiltonian approach - 13.75.Gx Pion-baryon interactions - 21.10.-k Properties of nuclei; nuclear energy levels - 36.10.-k Exotic atoms and molecules (containing mesons, muons, and other unusual particles)A.N. Ivanov: Permanent address: State Polytechnical University, Department of Nuclear Physics, 195251 St. Petersburg, Russian FederationN.I. Troitskaya: Permanent address: State Polytechnical University, Department of Nuclear Physics, 195251 St. Petersburg, Russian Federation.     

The stopping of slow75As recoil atoms in He,Ne and H2

Recent measurements of the 2p—1s X-ray line in theK ^? p atom indicate that the 1s level shift is very different from the theoretical prediction based on the extrapolation from theK ^? p scattering data. Deloff and Law have suggested that an anomalously large Coulomb effect could be responsible for this discrepancy. We examine this possibility by carrying out an explicit model calculation, using the method by which Sauer demonstrated the possible existence of an anomalously large Coulomb effect in the proton-proton system. Our conclusion is that if there exists an anomalous Coulomb effect which explains theK ^? p atomic level shift result, then the same effect would cause a serious conflict with theK ^? p scattering data above threshold.     

Surprises in threshold antikaon-nucleon physics

Low energy KN interactions are studied within unitary chiral perturbation theory at next-to-leading order with ten coupled channels. We pay special attention to the recent precise determination of the strong shift and width of the kaonic hydrogen 1s state by the DEAR Collaboration that has challenged our theoretical understanding of this sector of strong interactions. We typically find two classes of solutions, both of them reproducing previous data, that either can or cannot accommodate the DEAR measurements. The former class has not been previously discussed.     

A test of the validity of the extraction ofK − π− scattering in the reactionK − p →K −π−Δ++ in the framework of the one-pion-exchange model

In a study of the reactionK ^? p →K ^-π^?π⁺ p at 10 and 16 GeV/c the one-pion-exchange model was tested by attempting to extract on this basis the angular distributions for π⁺ p elastic scattering and comparing to real π⁺ p scattering. In thes-channel frame high order moments already appeared at relatively low mass. In general there are large discrepancies in both thes- andt-channel frames which remain after extrapolation to the pion pole and are related toQ ^? production. The structure of the decay angular distribution of theK ^? K ^- π^- system produced in association with Δ⁺⁺ is dominated by proton diffractive dissociation into Δ⁺⁺π^-.     

Decay of kaonium in a chiral approach

The decay of the K⁺K⁻ hadronic atom kaonium is investigated non-perturbatively using meson-meson interaction amplitudes taken from leading order chiral perturbation theory in an approach adapted from that proposed by Oller and Oset (1997) [18]. The Kudryavtsev-Popov eigenvalue equation is solved numerically for the energy shift and decay width due to strong interactions in the 1s state. These calculations introduce a cutoff ∼1.4 GeV in O(4) momentum space that is necessary to regulate divergent loop contributions to the meson-meson scattering amplitudes in the strong-interaction sector. One finds lifetimes of (2.2±0.9)×¹⁰−18 s for the ground state of kaonium.     

The DEAR case

The scientific program and the experimental setup of the DEAR (DAΦNE Exotic Atom Research) experiment at the new φ-factory DAΦNE of Laboratori Nazionali di Frascati are described. The objective of DEAR is to perform a 1% measurement of the K _α line shift due to the strong interaction in kaonic hydrogen. A measurement will also be performed on kaonic deuterium for the first time. The aim is to investigate low-energy physics and to understand SU(3) chiral symmetry breaking. The setup takes advantage of the unique features of the “kaon beam” from the φ decay in DAΦNE; of a low-temperature pressurized gaseous target; and of a detector for soft X-rays – the Charge-Coupled Device (CCD) – characterized by a very good energy (and spatial) resolution and by an unprecedented background rejection capability. The DEAR experiment represents a major effort in the study of low energy interactions and has the potential to produce a breakthrough in the field. This revised version was published online in August 2006 with corrections to the Cover Date.     

Results of the search forK-series X-rays from kaonic hydrogen

The X-ray spectrum associated withK ^? stopping in liquid hydrogen was measured with high resolution Si(Li) detectors. The totalK X-ray yield is not larger than 8×10^?4 per stoppedK ^? assuming no line broadening. A weak line pattern was found, which was tentatively ascribed to theK ^? HK-series X-rays. The shift and width of the 1s level, deduced from this pattern, are ε_1s =+270±80 eV andΓ=560±260 eV, respectively.     

Measurement of the kaonic hydrogen x-ray spectrum

The DEAR (DAPhiNE exotic atom research) experiment measured the energy of x rays emitted in the transitions to the ground state of kaonic hydrogen. The measured values for the shift epsilon and the width Gamma of the 1s state due to the K(-)p strong interaction are epsilon(1s)=-193 +/- 37 (stat) +/- 6 (syst) eV and Gamma(1s)=249 +/- 111 (stat) +/- 30 (syst) eV, the most precise values yet obtained. The pattern of the kaonic hydrogen K-series lines, K(alpha), K(beta), and K(gamma), was disentangled for the first time.