Hyperon resonances coupled to pseudoscalar- and vector-baryon channels

Abstract

We study hyperon resonances by solving coupled channel scattering equations. The coupled systems include pseudoscalar-and vector-baryon channels. The parameters of the model are restricted by making a χ 2 -fit to the cross section data on processes: K − p → K − p, K − p →K 0 n, K − p → ηΛ,Data on the energy level shift and width of the 1s state of the kaonic hydrogen, as well as some cross-section ratios near the threshold are also considered in the fit. Two types of fits are found as a result. In both cases, the properties of Λ(1405) are well reproduced. In addition to this, a Σ state is also found with mass around 1400 MeV. Cross sections, obtained with one of the two fits, are found to stay close to the data at energies away from the thresholds too, and as a result resonances with higher masses have also been studied. a kanchan.khemchandani@unifesp.br b amartine@if.usp.br c oller@um.es arXiv:1810.09990v2 [hep-ph] 1 Aug 2019 Investigating low-energy meson-baryon interaction, with nonzero strange quantum number, is of great importance to several interrelated topics in nuclear and hadron physics, such as the determination of the nature of the low-lying hyperons [1-10], the existence of kaonic-nuclear bound states, which has motivated several experiments [11-13], studies of kaon producing reactions which are, in turn, useful to understand the interactions of kaons in a dense medium [14], etc. The key motivational idea behind several related works is that the strangeness −1 meson-baryon interaction is attractive in nature, and it is especially interesting in the s-wave since, as now widely accepted, it generates the isoscalar resonance Λ(1405). The list of references on this topic is extensive, but for some of the recent works we refer the reader to Refs. [15-23]. A lot of effort is being put in by the lattice community too, bringing valuable information on the topic [24-30].There exist evidences for the presence of an isovector resonance too in nature, with its origin lying in the meson-baryon dynamics, with a mass similar to Λ(1405) [3,[31][32][33][34][35][36][37]. However, the case is less studied, as compared to Λ(1405), and the properties of the low-lying 1/2 − Σ(s) obtained from different works are different. In Ref. [3], a coupled channel study of pseudoscalar-baryon systems was made using a kernel arising from s-, u-channel exchange of the lightest octet baryon and a contact interaction obtained from the lowest order chiral Lagrangian. The subtraction constant required to calculate the loop function were constrained by fitting relevant data available, namely, the K − p →KN, πΣ, πΛ cross sections and different cross-section ratios among these processes at the K − p threshold, as well as the π + Σ − mass distribution. As a result, in the case of isospin 1, two Σ states were found near thē KN threshold: 1440 − i70 MeV and 1420 − i42 MeV. The work was further extended by considering next-to-leading-order contributions from the chiral Lagrangian [31] and including data on the energy shift and width of the 1s-sta...

Is two-pole’s $$\varLambda (1405)$$ one state or two?

“…With more constraints from the vector-baryon interactions in the ChUA, the two poles were well reproduced in Ref. [60], where one new state of isospin I = 1 was claimed. In a chiral quark model, it was also supported that the Λ(1405) state was aK N bound state and had the two-pole structure in Ref.…”

Photoproduction of $Λ^*$ and $Σ^*$ resonances with $J^P=1/2^-$ off the proton

“…Some studies find evidence for the existence of a J P = 1/2 − Σ state in the mass region of Λ(1405) while others do not [10,[12][13][14][15][16][17][18][19][20]. In a recent article [21], some of the coauthors of the present work studied the strangeness −1 coupled channel interactions by constraining the model parameters through a χ 2 -fit to the relevant experimental data. Besides constraining the parameters, more diagrams were considered in Ref.…”

The decay of $N^*$(1895) to light hyperon resonances

“…We would like to emphasize here that the couplings for all the vertices in Fig. 1 are known from our previous works [9,19] which describe relevant experimental data. In the study of hyperon resonances of Ref.…”

“…The field H * in the above equations represents Σ(1400) or Λ(1405), and the factor √ 3 in the Lagrangians, L N * V B and L V BH * , appears due to the fact that the spin-projected amplitudes were parameterized as Breit-Wigner in Refs. [9,19] when calculating the meson-baryon-resonance couplings.…”

“…With the couplings available from Refs. [9,19] we can also calculate the radiative decay widths of the nucleon/hyperon resonances. Such widths can be useful in the calculation of the diagrams contributing to the photoproduction of Λ(1405)/Σ(1400) (as shown in Fig.…”