Measurement of the Kaonic Hydrogen X-Ray Spectrum

Abstract

The DEAR (DANE 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 and the width ÿ of the 1s state due to the K ÿ p strong interaction are 1s ÿ193 37 (stat) 6 (syst) eV and ÿ 1s 249 111 (stat) 30 (syst) eV, the most precise values yet obtained. The pattern of the kaonic hydrogen K-series lines, K , K , and K , was disentangled for the first time. DOI: 10.1103/PhysRevLett.94.212302 PACS numbers: 13.75.Jz, 25.80.Nv, 36.10.Gv Over 40 years, chiral symmetry breaking has been recognized as the essential aspect of nuclear low-energy phenomena. The outline of how the breaking plays a vital role is well known, yet its detailed dynamics is uncertain. The existence of the eight pseudoscalar mesons (; K; ) is believed to arise from spontaneous symmetry breaking of the flavor global symmetry represented by the group SU3 L SU3 R , which generates the mesons as Nambu-Goldstone bosons, leaving the vacuum only SU(3) symmetric [1]. Furthermore, the mass spectrum of these mesons reflects the explicit breaking of this symmetry [2]. In the quark model, the squares of the meson masses are proportional to the small current quark masses with the multiplicative factors of the chiral quark condensate in vacuum. The large mass difference between the mesons and the current quarks then suggests that the condensate is playing a significant role in the structure of the mesons [3].A similar situation is expected to occur in the structure of baryons and to be manifested in the baryon-pseudoscalar meson interaction [4]. In this case, the corresponding relation is that the baryon sigma terms are proportional to the current quark masses with the factors of the chiral quark condensate for the baryons [3]. The sigma terms thus serve as the measure of the significance of the condensate in the structure of the baryons. Especially of interest here is how the SU(3) flavor symmetry is realized in this aspect of the nucleon structure, but more specifically, how high is the strangeness content of the nucleon. The resolution of these issues depends quite sensitively on the value of the kaonnucleon (KN) sigma terms [5]. As the basic symmetry of QCD is SU(3), the KN sigma terms play the central role in various nuclear phenomena, such as strangeness production in heavy-ion collision and chiral restoration in nucleon matter, a topic of astrophysical interest [6].The KN sigma terms are closely related to the lowenergy KN and antikaon-nucleon (KN) scattering amplitudes [7], but the value of the KN sigma terms continues to remain with a large uncertainty [6,7] in spite of the recent efforts in lattice [8] and chiral perturbation [9] calculations, where the information on the KN and KN scattering lengths is vital. In this work, we report an accurate measurement of the ground-state x-ray transitions in kaonic hydrogen atoms. The shift and width of the atomic ground state is known to provide the most accurate information of the K ÿ -proton scattering l...

On the strangeness -1 S-wave meson-baryon scattering

“…Each channel is labelled by its position (1 to 10) in the previous list. We denote the CHPT amplitudes at O(p) by T (1) χ ij and at O(p 2 ) by T…”

“…Unless the opposite is stated, we also include in the fits the DEAR measurement of the shift and width of the 1s kaonic hydrogen level [1], ∆E = 193 ± 37(stat) ± 6(syst.) eV, Γ = 249 ± 111(stat.)…”

“…[21] was the first chiral fit to be in agreement with the recent and accurate kaonic hydrogen data from ref. [1] and the scattering data of section 3. Nonetheless, since the fits in table 3 are also able to provide a good reproduction of the new precise data from refs.…”

“…Experimentally, we have new exciting data like the increasing improvement in the precision of measurement of the α line of kaonic hydrogen accomplished recently by DEAR [1], and its foreseen better determination, with an expected error of a few eV, by the DEAR/SIDDHARTA Collaboration [2]. This has established a challenge to theory so as to match such precision.…”

Poles and resonances in the coupled channels model for $\bar{K}N$ interaction

“…The simplest TW1 model incorporates only the leading TomozawaWeinberg term of the chiral Lagrangian whereas the NLO30 and CS30 models include the leading (LO) plus the next-to-leading (NLO) orders of the underlying Lagrangian. The free parameters of the models were fitted to the available experimental data on the low energyKN interaction, namely: the K − p cross sections (see references collected in [3]), K − p threshold branching ratios [4] and the kaonic hydrogen characteristics reported by the DEAR [5] and SIDDHARTA [6] collaborations. While the fresh SIDDHARTA data were used for the TW1 and NLO30 models, the CS30 model [7] and IHW [8].…”