Electromagnetic form factors of Λ hyperon in the vector meson dominance model

Abstract

We perform an analysis on the electromagnetic form factors of the Λ hyperon in the time-like reaction e + e − → ΛΛ by using a modified vector meson dominance model. We consider both the intrinsic structure components and the meson clouds components. For the latter one, we not only include the contributions from the φ and ω mesons, but also take into account the contributions from the resonance states ω(1420), ω(1650), φ(1680) and φ (2170). We extract the model parameters by combined fit to the time-like effective form factor |G eff |, the electromagnetic form factor ratio |G E /G M | and the relative phase ∆Φ of the Λ hyperon from the BaBar and BESIII Collaborations. We find that the vector meson dominance model can simultaneously describe these observables. Particularly, the inclusion of the resonance states in the model is necessary for explaining the ratio |G E /G M | in a wide range of √ s as well as the large phase angle. With the fitted parameters, we predict the single and double polarization observables, which could be measured in polarized annihilation reactions. Moreover, we analytically continue the expression of the form factors to space-like region and estimate the space-like form factors of Λ hyperon.

Electromagnetic form factors of octet baryons with the nonlocal chiral effective theory

“…Theoretically, though QCD is the fundamental theory to describe strong interactions, it is difficult to study hadron physics using QCD directly. There are many phenomenological models, such as the cloudy bag model [5], the constituent quark model [6], the 1/Nc expansion approach [7], the Nambu-Jona-Lasino (NJL) model [8], the perturbative chiral quark model (PCQM) [9], the extended vector meson dominance model [10], the SU(3) chiral quark model [11], the quark-diquark model [12], and so on. These model calculations are helpful to provide the physical scenario for the hadron structure.…”

The electromagnetic form factors of $$\Lambda _c$$ hyperon in the vector meson dominance model

“…(2) [47,48]. Previously, the VMD model has been widely used to study the EMFFs of the nucleon and the hyperon, showing that it has the advantage to well describe the experimental data in the space-like and the time-like regions [15,28,[49][50][51][52]. Very recently, it has also been applied to investigate the EMFFs for + and − [26].…”

“…In this case, the contributing meson excitations are ψ(1S), ψ(2S), ψ(3770), ψ(4040), ψ(4160), ψ(4415). We also assume that the expression of the form factors from the charmed excitations has the same form as those from the vector mesons ω, φ and their excitations [28,53], and we compare them to ω and φ in light of the magnitude of the mass of the charmed states, and put them into and , namely ω(782) → ψ(1S), φ(1020) → ψ(2S) and so on. The reason to take classification for J/ψ and their excitations is to keep a fixed form for Dirac and Pauli form factors and simplify the structures in our modified model.…”

“…It is found that the vector mesons and their excitations, as the intermediate states of reactions, play important roles in these processes. That is, they could provide an explanation for the threshold enhancement effect of scattering cross section and large ratio between G E and G M [27][28][29].…”

Observation of a structure in e+e−→ϕη′ at s from 2.05 to 3.08 GeV

“…The ϕð2170Þ was discovered in the process e þ e − → ϕf 0 ð980Þ by BABAR [4,5] via the initial-state-radiation (ISR) technique, and was later confirmed by Belle [6], BES [7] and BESIII [8,9]. There are several interpretations of the ϕð2170Þ, including a regular ss meson in a 2 3 D 1 [10] or 3 3 S 1 configuration [11], an ssg hybrid [12,13], a tetraquark state [14][15][16][17][18], a ΛΛ bound state [19][20][21][22], an S-wave threshold effect [23], or a three-meson system ϕK þ K − [24]. The conventional ss meson is predicted to decay with significant fraction into the ss-signature modes ϕη and ϕη 0 [11].…”