Strong isospin symmetry breaking in light scalar meson production

Abstract

Siberian Branch of the Russian Academy of Sciences, prosp. Akademika Koptyuga 4, 630090 Novosibirsk, Russian FederationIsospin symmetry breaking is discussed as a tool for studying the nature and production mechanisms of light scalar mesons. We are concerned with isospin breaking effects with an amplitude ∼ √ m d − mu (instead of the usual ∼ m d − mu), where mu and m d are the u and d quark masses, whose magnitude and phase vary with energy in a resonance-like way characteristic of the KK threshold region. We consider a variety of reactions that can experimentally reveal (or have revealed) the mixing of a 0 0 (980) and f0 (980) resonances that breaks the isotopic invariance due to the mass difference between K + and K 0 mesons. Experimental results on the search for a 0 0 (980) − f0(980) mixing in f1(1285) → f0(980)π 0 → π + π − π 0 and η(1405) → f0(980)π 0 → π + π − π 0 decays suggest a broader perspective on the isotopic symmetry breaking effects due to the K + and K 0 mass difference. It has become clear that not only the a 0 0 (980) − f0(980) mixing but also any mechanism producing KK pairs with a definite isospin in an S wave gives rise to such effects, thus suggesting a new tool for studying the nature and production mechanisms of light scalars. Of particular interest is the case of a large isotopic symmetry breaking in the η(1405) → f0(980)π 0 → π + π − π 0 decay due to the occurrence of anomalous Landau thresholds (logarithmic triangle singularities), i.e., due to the η(1405) → (K * K +K * K) → (K + K − + K 0K 0 )π 0 → f0(980)π 0 → π + π − π 0 transition (where it is of fundamental importance that the K * meson has a finite width).

Semileptonic decays D→π+π−e+νe and DsAchasov1, Киселев2, Shestakov3 2020Phys. Rev. D15000View full textAdd to dashboardCite

“…(14) and (15) [taking into account Eq. (16)] coincide with the ππ scattering phase δ 0 0 ðsÞ below the K þ K − threshold where η 0 0 ðsÞ ¼ 1.…”

“…Reviews of the current situation can be found, for example, in Refs. [3,4,15,16]. At the same time, the further expansion of the area of the q 2q2 model validity for light scalars on ever new processes seems to us extremely interesting and important.…”

“…3, but the solid theoretical curves correspond to the model describable by Eqs. (14)-(16). The semileptonic decay D þ → π þ π − e þ ν e .…”

Role of the triangle mechanism in the $Λ_b\rightarrow Λ_cπ^-f_0(980)$ reaction

“…An anomalously large production of the π 0 f 0 (980) decay mode of η(1405/1475), which is forbidden by isospin symmetry, was reported by the BESIII Collaboration [5], and that large amount production and the narrow f 0 (980) lineshape in the ππ distribution, which is the order of the mass difference of the charged and neutral kaons due to the isospin symmetry breaking, are explained well by the triangle mechanism [6][7][8][9] (see also Ref. [10] for a review article). The triangle diagram considered in the work is composed of K * KK and its charge conjugation shown in Fig.…”

Exclusive $f_{1}(1285)$ meson production for energy ranges available at the GSI-FAIR with HADES and PANDA

“…In [68] the f 1 (1285) decays into a 0 (980)π 0 , f 0 (980)π 0 and isospin breaking were studied. An interesting proposal was also discussed in [69,70]: to study the anomalous isospin breaking decay f 1 (1285) → π + π − π 0 in central exclusive production of the f 1 . There is another important decay channel, K Kπ, with branching fraction 9% [44] which can be used for f 1 meson studies in CEP.…”