KLOE results on light mesons

The KLOE collaboration has recently published new results concerning scalar and pseudoscalar mesons.Here the φ→ a 0 (980)γ→ηπ 0 γ decay analysis and the search for the φ→ K 0 K 0 γ decay are discussed,together with the η→π + π-e + edecay measurements annd the new results for the pseudoscalar mixing angle and gluonium content of the η’ meson.     

Study of q and η' physics at BES-Ⅲ

Decays of both η and η' provide very useful information in our understanding of low-energy QCD,and experimental signatures for these decays would be extremely helpful at BES-Ⅲ.The rare decays of the η and η' mesons could serve as a low-energy test of the Standard Model and its beyond.The sensitivities of the measurements of η and η' decays are discussed at BES-Ⅲ,in which the η and η' mesons are produced in the ψ decays.     

Radial excitations of scalar, η, and η′ mesons in a chiral quark model

First radial excitations of the scalar-meson nonet and of the pseudoscalar mesons η and η′ are described within a nonlocal chiral quark model of the Nambu-Jona-Lasinio type with ′t Hooft interaction. In this model, simple form factors are used, which allows us to describe first radial excitations of the mesons and to retain the gap equations describing spontaneous breakdown of chiral symmetry in the standard form. The external parameters of form factors are fixed by the masses of excited pseudoscalar mesons, and the same form factors are used to predict the masses of excited scalar mesons. The strong decays of excited scalar mesons and of η and η′ mesons are described in satisfactory agreement with experimental data.     

Mixing of pseudoscalar mesons and M1 radiative decays

We discuss the mixing of pseudoscalar mesons, in particular SU(3) breaking effects, based on ideas abstracted from QCD. The admixtures of η and η′ in η_c are calculated and utilized to estimate the M1 radiative decays ψ → ηγ, η′γ. A reasonably consistent picture emerges for these decays as well as others involving only the light quarks.     

Experimental consequences of a small mixture of cc̄ in the η′ and η mesons

We show that a small but significant mixing of η and η′ with the pseudoscalar cc? state may explanin the large η and η′ masses, the small mass of the new 2.8 GeV state, the large rates for ψ′ → ψη, ψ → η′γ and ψ → ηψ, the large number of photons in ψ decay, some of the missing decay modes of ψ′ and ψ and the small K/π ratio in ψ′ and ψ decays. We predict that 20–30% of all ψ and ψ′ decays contain an η′. Other tests and one important difficulty are also discussed.     

Radiative decays of radially excited pseudoscalar mesons in the extended Nambu-Jona-Lasinio model

In the extended NJL model the radiative decay widths of the radially excited states of the pseudo-scalar π, η, and η′ mesons are calculated. The predictions for the decay widths of the processes π(1300) → (ρ⁰, ω)γ, η(1295) → (ρ⁰, ω, φ)γ, and η(1475) → (ρ⁰, ω, φ)γ are given. Nowadays, there are no solid experimental data for these processes. The comparison of the results obtained in the framework of the standard and the extended NJL models for decays of the ground states of mesons is given. It is shown that these calculations correspond to each other and are also in satisfactory agreement with experimental data. This allows one to expect that the extended NJL can give reliable predictions for the excited states of mesons.     

Radial excitation states of η and η′ in the chiral quark model

A chiral quark model is applied to calculate the spectra of pseudoscalar mesons η and η . By analyzing the obtained spectra, we find that the mesons η (2 1 S 0 ), η(4 1 S 0 ), η (3 1 S 0 ) and η (4 1 S 0 ) are the possible candidates of η(1760), X(1835), X(2120) and X(2370). The strong decay widths of these pseudoscalars to all the possible two-body decay channels are calculated within the framework of the 3 P 0 model. Although the total width of η (21S0 ) is compatible with the BES Collaboration’s experimental value for η(1760), the partial decay width to ωω is too small, which is not consistent with the BES result. If X(1835) is interpreted as η(4 1 S 0 ), the total decay width is compatible with the experimental data, and the main decay modes will be πa 0 (980) and πa 0 (1450), which needs to be checked experimentally. The assignment of X(2120) and X(2370) to η (31S0 ) and η (41S0 ) is disfavored in the present calculation because of the incompatibility of the decay widths.     

First observation of η(1405) decays into f(0)(980)π0

The decays J/ψ → γ π+ π- π0 and J/ψ → γ π0 π0 π0 are analyzed using a sample of 225×10(6) J/ψ events collected with the BESIII detector. The decay of η(1405) → f(0)(980)π0 with a large isospin violation is observed for the first time. The width of the f(0)(980) observed in the dipion mass spectra is anomalously narrower than the world average. Decay rates for three-pion decays of the η' are also measured precisely.     

Search for new and an investigation of known resonances using experimental data on photoproduction of η and η′ mesons on nucleons

The dynamical model of photoproduction of pseudoscalar mesons on nucleons constructed earlier is used for more accurate determination of the properties of known resonances. The new, “missing,” resonances are sought using modern precise experimental data on photoproduction of η and η′ mesons on nucleons.     

(η−η′−ι)-mixing,decay and production mechanisms

We present a phenomenological model for meson-glueball mixing and apply it to the mixing of the pseudoscalar mesons η and η′ with the ι(1440)-particle as the prime candidate for a 0^?+-glueball. Using the MIT bag model framework, our model incorporates, among other elements, configuration mixing effects due to virtually excited states, as well as mixing of quark and gluon components. We evaluate the portions of quark antiquark and two-gluon admixtures in η,η′ and ι. The results are used to study various decay and production processes involving these particles. In particular, we calculate the radiative and the 2γ-decay widths of the light mesons and make predictions for the widths of the ι in these channels. Furthermore, production mechanisms of the light mesons in electromagnetic and hadronicJ/ψ-decays are used to evaluate the branching ratios for the production of the ι in variousJ/ψ-transitions. Our results are generally in reasonable agreement with experimental data. Especially we predict a rather large width for the decay ι→ργ and a sizable production rate for the ι in the transitionJ/ψ→ωι.     

Strong Decays of Charm Mesons D1*(2680), D3*(2760), D2*(3000)

In this article, we assign the higher charm mesons D₁^*(2680), D₃^*(2760) and D₂^*(3000) to be the 2S 1^-, 1D 3^- and 1F 2⁺ states, respectively, and study the two-body strong decays to the ground state charm mesons and light pseudoscalar mesons with the heavy meson effective theory. We obtain the ratios among the strong decays, which can be confronted to the experimental data in the future and shed light on the nature of those higher charm mesons.     

Weinberg-Salam model and chiral symmetry of mesons

Weinberg-Salam model is considered in the light of SU(4) × SU(4) chiral symmetry for mesons. The Higgs doublet and the pseudoscalar mesons mix in this framework. Consequences of this mixing for the Higgs decays and the nonleptonic decays of the mesons are explored.     

Photon production in heavy-ion collisions at SPS energies

Single photon spectra in heavy-ion collisions at SPS energies are studied in the relativistic transport model that incorporates self-consistently the change of hadron masses in dense matter. We separate the total photon spectrum into “background” arising from the radiative decays of π⁰ and η mesons, and the “thermal” one from other sources. For the latter we include contributions from radiative decays of ρ, ω, η′, and a₁, radiative decays of baryon resonances, as well as two-body processes such as ππ → ργ and πρ → πγ. It is found that more than 95% of all photons come from the decays of π⁰ and η mesons, while the thermal photons account for less than 5% of the total photon yield. The thermal photon spectra in our calculations with either free or in-medium meson masses do not exceed the upper bound set by the experimental measurement of the WA80 Collaboration.     

Further insights into the “ρπ puzzle”

Based on a systematic investigation of J/ψ(ψ) → VP,where V and P stand for light vector and pseudoscalar mesons,we identify the role played by the electromagnetic(EM) transitions and intermediate meson loop transitions,which are essential ingredients for understanding the J/ψ and ψ couplings to VP.We show that on the one hand,the EM transitions have relatively larger interferences in ψ→ρπ and K*K+c.c.as explicitly shown by vector meson dominance(VMD).On the other hand,the strong decay of ψ receives relatively larger destructive interferences from the intermediate meson loop transitions.By identifying these mechanisms in an overall study of J/ψ(ψ)→VP,we provide a coherent understanding of the so-called "ρπ puzzle".     

Electromagnetic transition form factors of light vector mesons

The decays of narrow light vector mesons into pseudoscalar mesons and dileptons are calculated to leading order in a recently proposed scheme which treats pseudoscalar and vector mesons on equal footing. Since all required parameters have been determined by other reactions the presented approach gains predictive power for the considered processes. The decay of the ω-meson into pion and dimuon agrees reasonably well with the available experimental data concerning form factor, single-differential decay width and partial decay width. As well do the partial decay width of the ω-meson into a pion and a dielectron and of the ?-meson into an η-meson and a dielectron. The decay properties of the ω-meson into η-meson and dimuon or dielectron and of the ?-meson into η-meson and dimuon are predicted.     

Neutral decays of the η-meson

The partial widths of η-meson decays η→2γ, η→3π⁰ and η→π⁰γγ have been measured in a high accuracy experiment made at the IHEP accelerator with the hodoscope electromagnetic spectrometer GAMS-2000. An upper limit has been determined for the 3γ channel. The Dalitz plot of the η decay into 3π⁰ shows that the matrix element does not depend on the pion energy.     

Anomalous Ward identities and ψ→γη(η′), ψ′ →ψπ0(η) decay rates

Anomalous Ward identities saturated with one-particle pseudoscalar states, together with π⁰, η and η′ → 2γ decay amplitudes and Γ(ψ → η′γ)/Γ(ψ → ηγ), Γ(ψ′ → ψπ⁰)/Γ(ψ′ → ψη) branching ratios, provide a set of equations which can be solved for the axial-vector couplings and the topological charge components.     

D→PP衰变过程的末态相互作用

利用单粒子交换方法,研究了D介子衰变到两个赝标粒子中的末态相互作用.通过实验数据中抽取的强相角来分析末态相互作用的效应     

Pseudoscalar mixing in J/ψ and ψ(2S)decay

Based on the branching fractions of J/ψ(ψ(2S))→ VP from different collaborations, pseudoscalar mixing is extensively discussed with a well established phenomenological model. The mixing angle is determined to be -14° by fitting to the new world average if only quark content is considered. After taking into account the gluonic content in η and η' simultaneously, the investigation shows that η favors only consisting of light quarks, while the gluonic content of η' is Z2η', = 0.30±0.24.