Radiative decays and quark content of f 0(980) and φ(1020)

The quark structure of φ(1020) and f ₀(980) is studied on the basis of data on the radiative decays φ(1020) → γπ ⁰, γη, γη′, γ a ₀(980), γ f ₀(980) and f ₀(980) → γγ. The partial widths are calculated under the assumption that all the mesons under consideration are $\bar qq$ states: φ(1020) is a dominantly $s\bar s$ state ( $\eta ' = n\bar nsin\theta + s\bar scos\theta $ component contributes not more than 1%); η, η′, and π ⁰ are standard $q\bar q$ states, $\eta = n\bar ncos\theta - s\bar ssin\theta $ and $\eta ' = n\bar nsin\theta + s\bar scos\theta $ with θ?37°; and f ₀(980) is a e5 meson with the flavor wave function $n\bar ncos\varphi + s\bar ssin\varphi $ . The transition φ → γπ ⁰ specifies the admixture of the $n\bar n$ component in the φ meson: it is on the order of 0.5%. We argue that this order of $n\bar n$ value does not contradict data on the decay φ(1020) → γ a ₀(980). The partial widths calculated for the decays φ → γη, γη? are in reasonable agreement with experimental data. The measured branching-ratio value Br(φ→γf ₀(980))=(3.4±0.4 _?0.5 ^+1.5 ×10^?4) requires 25°≤|?|≤90°. For the decay f ₀(980) → γγ, the agreement with data, Γ(f ₀(980) → γγ)=0.28 _?0.13 ^+0.09 keV, is attained at either ?=85°±8° or ?=?46°±8°. A simultaneous analysis of the decays φ(1020) → γ f ₀(980) and f ₀(980) → γγ favors the solution with the negative mixing angle of ?=?48°±6°, setting f ₀(980) very close to the flavor octet (? _octet=±54.7°).     

B→f0(980)(π,η') decays in the PQCD approach

Based on the assumption of a two-quark structure of the scalar meson f0(980), we calculate the branching ratios and CP-violating asymmetries for the four B→f0(980)π and B→f0(980)η(') decays by employing the perturbative QCD (Pqcd) factorization approach. The leading order Pqcd predictions for branching ratios are, Br(B-→f0(980)π-)～2.5×10-6, Br(B0→f0(980)πo)～2.6×10-7, Br(B0→f0(980)η)～ 2.5×10-7 and Br(B0→f0(980)η')～6.7×10-7, which are consistent with both the QCD factorization predictions and the experimental upper limits.     

Rare kaon decaysK L(S) 0 →π0ℓ+ℓ− in the quark confinement model

K _L(S) ⁰ →π⁰?⁺?^?. The rare decaysK _L(S) ⁰ →π⁰?⁺?^?(?=e or μ) are investigated in the Quark Confinement Model (QCM), a relativistic quark model, based on some assumptions about hadronization and quark confinement. Using the effective electroweak Lagrangian (with QCD corrections), proposed by Gilman and Wise, the matrix elements of kaon transitions to a pion and lepton pair are calculated. The obtained results for the decay widths are in agreement with the experimental data for upper limits on branching ratios and the theoretical predictions calculated by effective chiral Lagrangian method.     

The radiative decay ϕ → γππ in a coupled-channel model and the structure of f0(980)

A coupled-channel model is used to study the nature of the scalar mesons produced in the decay ϕ → γππ. The K molecular picture of f₀(980) is found to be in a good agreement with the recent experimental data from SND and CMD-2. The structure of the light scalar mesons is elucidated by investigating the S-matrix poles and the q spectral density.     

Study of scalar meson f 0(980) from B→f 0(980)K * decays

We show how parton distributions unintegrated over the parton transverse momentum, k _t , may be generated, at NLO accuracy, from the known integrated (DGLAP-evolved) parton densities determined from global data analyses. A few numerical examples are given, which demonstrate that sufficient accuracy is obtained by keeping only the LO splitting functions together with the NLO integrated parton densities. However, it is important to keep the precise kinematics of the process, by taking the scale to be the virtuality rather than the transverse momentum, in order to be consistent with the calculation of the NLO splitting functions.     

Study of f 0(980) and f 0(1500) from B s →f 0(980)π,f 0(1500)π decays

In this paper, we analyze the scalar mesons f ₀(980) and f ₀(1500) from the decays $\bar{B}^{0}_{s}\to f_{0}(980)\pi^{0},\allowbreak f_{0}(1500)\pi^{0}$ within Perturbative QCD approach. From the leading-order calculations, we find that (a) in the allowed mixing angle ranges, the branching ratio of $\bar{B}^{0}_{s}\to f_{0}(980)\pi^{0}$ is about (1.0～1.6)×10^?7, which is smaller than that of $\bar{B}^{0}_{s}\to f_{0}(980)K^{0}$ (the difference is a few times even one order); (b) the decay $\bar{B}^{0}_{s}\to f_{0}(1500)\pi^{0}$ is better to distinguish between the lowest lying state or the first excited state for f ₀(1500), because the branching ratios for two scenarios have about one-order difference in most of the mixing angle ranges; and (c) the direct CP asymmetries of $\bar{B}^{0}_{s}\to f_{0}(1500)\pi^{0}$ for two scenarios also exists great difference. In scenario II, the variation range of the value ${\mathcal{A}}^{\mathrm{dir}}_{CP}(\bar{B}^{0}_{s}\to f_{0}(1500)\pi^{0})$ according to the mixing angle in scenario II is very small, except for the values for mixing angles near 90° or 270°, while the variation range of ${\mathcal{A}}^{\mathrm{dir}}_{CP}(\bar{B}^{0}_{s}\to f_{0}(1500)\pi^{0})$ in scenario I is very large. Compared with the future data for the decay $\bar{B}^{0}_{s}\to f_{0}(1500)\pi^{0}$ , it is easy to determine the nature of the scalar meson f ₀(1500).     

Radiative decays of scalar mesons σ(600), f 0(980) and a 0(980) in the local Nambu-Jona-Lasinio model

The two-photon decay widths of scalar mesons σ(600), f ₀(980) and a ₀(980) as well a ₀ → ju(ω)γ and f ₀ → ju(ω)γ are calculated in the framework of the local Nambu-Jona-Lasinio model. The contributions of the quark loops (Hartree-Fock approximation) and the meson loops (next 1/N _c -approximation where N _c is the number of colors) are taken into account. The values of these contributions, as we show, are of the same order of magnitude. For the f ₀ decay the K-loop contribution plays the dominant role. The results for two-gamma decays are in satisfactory agreement with modern experimental data. The predictions for a ₀ → ju(ω)γ and f ₀ → ju(ω)γ widths are given.     

f 0(980) and a 0(980) resonances near the thresholds of the γγ → K + K − and γγ → K 0 K̇ 0 reactions

High-statistical data on the γγ → K ⁺ K ^? and γγ → K ⁰ K? ⁰ reactions constitute the last missing link in investigations of light scalar mesons f ₀(980) and a ₀(980) in photon-photon collisions. It is expected that the manifestation of the four-quark structure of the f ₀(980) and a ₀(980) resonances in these reactions will be very peculiar. The possibilities of the observation of scalar contributions in the γγ → K ⁺ K ^? and γγ → K ⁰ K? ⁰ reactions near their thresholds at modern colliders have been estimated.     

Isotopic Symmetry Breaking in the η(1405) → f0(980)π0 → π+π–π0. Decay through a $$K\bar K$$ Loop Diagram and the Role of Anomalous Landau Thresholds

Anomalous isotopic symmetry breaking in the η(1405) → f₀(980)π⁰ → π+π–π⁰ decay through a mechanism featuring anomalous Landau thresholds in the form of logarithmic triangle singularities, i.e., through the \(\eta (1405) \to (K*\bar K + \bar K*K) \to ({K^ + }{K^ - } + {K^0}{\bar K^0}){\pi ^0} \to {f_0}(980){\pi ^0} \to {\pi ^ + }{\pi ^ - }{\pi ^0}\) transition, has been analyzed. It has been shown that this effect can be correctly quantified only by taking into account the nonzero K* width. Different scales of isotopic symmetry breaking associated with the K⁺–K⁰ mass difference are compared.     

Λ resonances studied in K~-p→Σ~0π~0 in a chiral quark model

A chiral quark-model approach is extended to the study of the KN scattering at low energies. The process of K~-p→Σ~0π~0 at P_K≤ 800 MeV/c (i.e. the center mass energy W ≤ 1.7 GeV) is investigated. The A(1405)S_(01) dominates the reactions over the energy region considered here. Around P_K≌400 MeV/c, the A(1520)D_(03) is responsible for a strong resonant peak in the cross section. Our analysis suggests that there exist configuration mixings within the Λ(1405)S_(01) and A(1670)S_(01) as admixtures of the [70,~21,1/2] and [70,~28, 1/2] configurations. The Λ(1405)S_(01) is dominated by [70,~21,1/2], and A(1670)S01 by [70,~28, 1/2]. The non-resonant background contributions, i.e. u-channel and b-channel, also play important roles in the explanation of the angular distributions due to amplitude interferences.     

B→f0（980）（π,η^（＇）） decays in the PQCD approach

Based on the assumption of a two-quark structure of the scalar meson f0（980） ,we calculate the branching ratios and CP-violating asymmetries for the four B → f0（980） π and B → f0（980） η^（＇） decays by employing the perturbative QCD（pQCD） factorization approach. The leading order pQCD predictions for branching ratios are,Br（B^-→ f0（980） π^-） ～ 2.5×10^-6,Br（Bˉ^0 → f0（980） π^0） ～ 2.6×10^-7,Br（Bˉ^0 → f0（980） η） ～ 2.5×10^-7 and Br（Bˉ^0 → f0（980） η ） ～ 6.7×10^-7,which are consistent with both the QCD factorization predictions and the experimental upper limits.     

On the possibility of observing a 0 0 (980)-ƒ 0(980) mixing in the reaction π − p → ηπ 0 n on a polarized target

It is shown that the spin asymmetry in the reaction π ^? p → a ₀ ⁰ (980)n → (ηπ ⁰)S _n is highly sensitive to the mixing of the a ₀ ⁰ (980) and ? ₀(980) resonances. At low momentum transfers (namely, in any of the intervals 0 ≤ ?t ≤ 0.025, …, 0.1 GeV²), the asymmetry normalized in such a way that it takes values between ?1 and 1must undergo a jump close inmagnitude to unity in the region of the ηπ ⁰ invariant masses between 0.965 and 1.01 GeV. A large jump of the asymmetry is due exclusively to a ₀ ⁰ (980)?? ₀(980) mixing. A very high resolution in the ηπ ⁰ invariant mass is not required for observing the jump of the asymmetry. The energy dependence of the polarization effect is expected to be rather weak; therefore, the polarization effect in question can be studied at any high energy—for example, in the range between 8 and 100 GeV.     

Search for e + e − → f 0(600)γ, f 0(980)γ, f 0(1350)γ, and f 2(1270)γ processes in the energy range from 1.05 to 1.38 GeV

In the energy range from 1.05 to 1.38 GeV, the upper limits for the cross sections of e ⁺ e ^? → f ₀(600)γ, f ₀(980)γ, f ₀(1350)γ, and f ₂(1270)γ → π⁰π⁰γ processes have been established. Measurements are performed in accordance with the statistics gathered in experiment with a spherical neutral detector (SND) on the VEPP-2M e ⁺ e ^? collider. The resultant upper limits vary from 6 to 42 pb depending on the energy and the model.     

Constraints on the properties of the massive neutron star PSR J0348+0432 from the f0(975) and φ(1020) mesons

The effect of the f ₀(975) and φ(1020) mesons on the properties of the massive neutron star PSR J0348+0432 is examined in the framework of the relativistic mean-field theory by choosing the suitable hyperon coupling constants. It is found that, compared with that without the f ₀(975) and φ(1020) mesons, the radius of the neutron star PSR J0348+0432 increases from R = 12.072 km to R = 12.08 km (i.e. by 0.07%), the central energy density ? _c decreases from 5.6695 fm^?4 to 5.6492 fm^?4 (i.e. by 0.36%), the central pressure decreases from 1.585 fm^?4 to 1.58 fm^?4 (i.e. by 0.32%), the moment of inertia increases from 1.4592 × 10⁴⁵ g · cm² to 1.4615 × 10⁴⁵ g · cm² (i.e. by 0.16%) and the surface gravitational redshift decreases from z = 0.4026 to z = 0.4022 (i.e. by 0.1%). Our results show that the effect of the f ₀(975) and φ(1020) mesons on the properties of the massive neutron star PSR J0348+0432 is very small (i.e. no more than 0.5%) and therefore they do not play a major role.     

Bs →φπ^0 Decay in the Extra Down-Type Quark Model

Using the QCD factorization approach, we investigate the electro-weak penguin dominated process 13~ --, q57r~ in the extra down-type quark （EDQS） model. We calculate the effects of new physics （NP） on the branching fraction and direct CP asymmetry of the decay mode. It is found that the branching fraction can be increased by 15~o points or dropped by 13~o points than the standard model （SM） value, and its direct CP asymmetry can be increased by 35% points or dropped by 37% points than the SM one. The effects of NP on the direct CP asymmetry are more obvious than on the branching fraction. If this decay mode could be measured in the upcoming LHCb experiment, these results we obtain will be useful for further studies of the EDQS model.     

Study of scalar meson a0(980) from B→a0(980)π decays

In this paper, we calculate the branching ratios and the direct CP-violating asymmetries for decays B0 →a00(980)π0, a0+(980)π-, a0-(980)π and B- →a00(980)π-, a0-(980)π0 by employing the perturbative QCD (pQCD) factorization approach at the leading order. We found that (a) the pQCD predictions for the branching ratios are around (0.4 - 2.8) × 10-6, consistent with currently available experimental upper limits; (b) the CP asymmetries of B0→ao(980)π0 and B-→a0-(980)π0 decays can be large, about (70-80)% for α = 100°.     

Study of scalar meson a_0(980) from B→a_0(980)π decays

In this paper,we calculate the branching ratios and the direct CP-violating asymmetries for decays B0 →a00(980)π0,a0+(980)π-,a0-(980)π+ and B- →a00(980)π-,a0-(980)π0 by employing the perturbative QCD(pQCD) factorization approach at the leading order.We found that(a) the pQCD predictions for the branching ratios are around(0.4-2.8)×10-6,consistent with currently available experimental upper limits;(b) the CP asymmetries of B0 →a00(980)π0 and B- →a0-(980)π0 decays can be large,about(70-80)% for α=100-.     

The decaysK S 0 →γγ andK L 0 →γγ in the chiral approach

We calculate theK _S ^Emphasis>0 →γγ decay within the approach of non-linear realization of chiralS U(3)×S U(3). The branching ratio with respect to theπ ⁺ π ^- channel turns out to be 3.5×10^?6 and therefore similar to the result gotten previously by dispersion relation techniques in a non-chiral model. We also discuss theK _L ⁰ →γγ decay by taking into account new results onη ₁-η ₈ mixing from recent measurements of the η→γγ decay.     

Rare decays B_(s,d)~0→e+e~- in a top quark two-Higgs-doublet model

In the framework of T2HDM,we calculated the new physics contributions involving neutral Higgs bosons to the branching ratios of Bs0,d→e+e-(= e,μ) decays.Comparing the theoretical predictions with the experimental upper-limits,we found that(a) The data of Br(B0d →e+e-) give the upper bound on tanβ:tanβ 22,while Br(Bs0 →e+e-) give tanβ 12 for fixed δ = 0°,mH+= 350 GeV,mH0 = 160 GeV,mh0 = 115 GeV and mA0 = 120 GeV;(b) A light neutral Higgs boson mass mh0(mA0) less than 50 GeV(120 GeV) is excluded by the data o...