The radiative decay of the Λ(1405) and its two-pole structure

Abstract

We evaluate theoretically the radiative decay widths into γΛ and γΣ 0 of the two poles of the Λ(1405) found in chiral unitary theories and we find quite different results for each of the two poles. We show that, depending on which reaction is used to measure the Λ(1405) radiative decays, one gives more weight to one or the other pole, resulting in quite different shapes in the γΛ(Σ 0 ) invariant mass distributions. Our results for the high-energy pole agree with those of the empirical determination of the γΛ and γΣ 0 radiative widths (based on an isobar model fitting of the K − p atom data), which are sometimes referred to as "experimental data". We have made a detailed study of the K − p → π 0 γΛ(Σ 0 ) and π − p → K 0 γΛ(Σ 0 ) reactions and have shown that they, indeed, lead to different shapes for the γΛ(Σ 0 ) invariant mass distributions. PACS. 13.40.Hq Electromagnetic decays -14.20.Jn Hyperons -13.75.-n Hadron-induced low-and intermediate-energy reactions and scattering -25.20.Lj Photoproduction reactions

Role of five-quark components in radiative and strong decays of theΛ(1405)resonance

“…The results for R > ∼ 1.0 lead then to two series with respect to the width Γ Λγ ≈100 keV (present work and Ref. [59]) and ≈20 Isobar model 27 ± 8 10 ± 4 0.37 ± 0.18 Burkhardt -Lowe [57] 27 ± 8 23 ± 7 0.85 ± 0.36 Burkhardt -Lowe [57] keV [57,60], while Γ Σγ varies by two orders of magnitude.…”

Dynamically generated resonances from the vector octet-baryon decuplet interaction

“…As an example of new states predicted, one has a second Λ(1405) state [17], right now reconfirmed by all the chiral unitary calculations, and which finds experimental support from the analysis of the K − p → π 0 π 0 Σ 0 reaction [18] done in [19]. It also finds an explanation for the new COSY data on Λ(1405) production in pp collisions [20] as shown in [21]. The work with vector mesons was for some time limited to the study of their interaction with pseudoscalar mesons, which generates the low lying axial vector mesons [22,23] and a second K 1 (1270) state [23], for which experimental evidence is found in [24].…”

The role of the Λ(1405) in the pp → pK+Λ(1405) reaction

“…The factors 2 in Eq. (19) accounts for the possibility of having the Λ(1405) production from either of the two protons.…”

“…To compare with the data, we have multiplied our invariant mass distribution , Eq. (19), with the same factor to obtain the distribution of the πΣ.…”

“…On the other hand, the reaction π − p → K 0 (Σπ) 0 seems to give more weight to the lowenergy pole and thus exhibits a peak around 1390 MeV * E-mail address: lsgeng@ific.uv.es † E-mail address: oset@ific.uv.es in the πΣ invariant mass distributions [18]. Recently, we have shown that the two-pole structure may also lead to quite different radiative decay widths [19].…”