Event generators for η/η' decays at BESⅢ

The light unflavoured meson η/η' decays are valuable for testing non-perturbative quantum chromodynamics and exploring new physics beyond the Standard Model. This paper describes a series of event generators, including η/η'→γl~+l~-, η/η'→γπ~+π~-, η'→ωe~+e~-, η→π~+π~-π~0, η/η'→π~0π~0π~0, η'→ηππ andη'→π~+π~-π~+π~-/π~+π~-π~0π~0, which have been developed for investigating η/ηdecay dynamics. For most of these generators, their usability has been validated in BESIII analyses for determining the detection efficiency, and background studies. The consistency between data and Monte Carlo shows that these generators work well in the BESⅢ simulation, and will also be useful for ongoing BESⅢ analyses and other experiments for studying η/η' physics.     

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.     

Measurements of the γγ＊ → π^0 and γγ＊ → ηc transition form factors at BABAR

We present measurements of the γγ＊ → π^0 transition form factor for the momentum transfer range Q^2=4-40 GeV^2 and the γγ＊ → ηc transition form factor for the range Q^2=2-50 GeV^2. The current status of measurements of the meson-photon transition form factors for the η and η＇ mesons is discussed. The results of the measurement of the ηc mass, total and two-photon widths are also presented.     

ηb decay into charmonium in association with cc pair

We calculate the inclusive decay rates of ηb into charmonium via double c~ pairs for S- and P-wave states ηc, J/ψ and XcJ within the framework of non-relativistic QCD （NRQCD） factorization at leading order in αs. Besides calculating the contributions of the color-singlet channels ηb → cc[2s＋1SL^（1）]＋cc, the effects of cc pair in the color-octet configurations are also considered. We find that ηb → cc[3S1^（8）] ＋cc make a small contribution to Br（ηb →J/ψ（ηc）＋cc）. While in the ηb →XcJ ＋cc case, the color octet contributions are significant, for they are of the same a 5 order as the color-singlet processes. We predict Br（ηb →J/ψ（ηc）＋cc） = 2.99（2.75） × 10^-5 Vc for S-wave states J/ψ and ηc, and Br（ηb → XcJ ＋cc） = （4.37, 3.40, 2.83） × 10^-5 （for J = 0,1, 2） for P-wave states XcJ. In the end, we also find Br（ηb → cccc） is almost saturated by ηb decay into charmonium in association with cc pair from the point of view of duality.     

η_b decay into charmonium in association with c pair

We calculate the inclusive decay rates of ηb into charmonium via double c pairs for S-and P-wave states ηc,J/ψ and χcJ within the framework of non-relativistic QCD(NRQCD) factorization at leading order in αs.Besides calculating the contributions of the color-singlet channels ηb→c[2S+1SL(1)]+c,the effects of c pair in the color-octet configurations are also considered.We find that ηb→c[3S1(8)]+c make a small contribution to Br(ηb→J/ψ(ηc)+c).While in the ηb→χcJ+c case,the color octet contributions are significant,for they are of the same αs4vc5 order as the color-singlet processes.We predict Br(ηb→J/ψ(ηc)+c)=2.99(2.75)×10-5 for S-wave states J/ψ and ηc,and Br(ηb→χcJ+c)=(4.37,3.40,2.83)×10-5(for J =0,1,2) for P-wave states χcJ.In the end,we also find Br(ηb→ cc) is almost saturated by ηb decay into charmonium in association with c pair from the point of view of duality.     

Hadro- and photo-production of η′ in quasi-free proton and neutron processes

The η′ photoproduction process on quasi-free proton and neutron and the reaction NN→ η′NN are investigated within a relativistic effective Lagrangian approach to hadronic interactions. Resonances with spins 1/2 and 3/2 are considered together with the nucleonic and t-channel meson-exchange current contributions. In photoproduction processes, the S11 resonance is found to be responsible for the sharp rise of the cross sections near threshold. In pp → η′pp, it is found that the S11 resonance dominates the total cross section over the entire energy region considered. The spin observables, in particular the beam and target asymmetries, are shown to be very sensitive to the reaction mechanism and will help impose more stringent constraints on the model parameters.     

ηb decay into charmonium in association with c(c) pair

We calculate the inclusive decay rates of ηb into charmonium via double cc pairs for S- and P-wave states ηc, J/ψ and χcJ within the framework of non-relativistic QCD (NRQCD) factorization at leading order in αs. Besides calculating the contributions of the color-singlet channels ηb→c(c)[2S+1Sl(1)]+c(c), the effects of c(c) pair in the color-octet configurations are also considered. We find that ηb→c(c)[3S1(8)]+c(c) make a small contribution to Br(ηb→J/ψ(ηc)+c(c)). While in ther ηb→χcJ+c(c) case, the color octet contributions are significant, for they are of the same αs4vc5 order as the color-singlet processes. We predict Br(ηb → J/ψ(ηc)+c(c)) = 2.99(2.75) × 10-5 for S-vrave states J/ψ and ηc, and Br(ηb→χcJ +c(c))= (4.37,3.40,2.83)×10-5 (for J = 0,1,2) for P-wave states χcJ. In the end, we also find Br(ηb → c(c)c(c)) is almost saturated by ηb decay into charmonium in association with cc pair from the point of view of duality.     

On ηc line shape in charmonium transitions

The line shapes to observe ηc in charmonium transitions, i.e., ψ（2S）, J/ψ→γηc, are investigated. The ηc line shapes in exclusive decays or by observing the inclusive photon spectrum are given. The sensitivities to measure the ηc resonance parameters are also evaluated. With more than two thousand ηc events observed, the precision of the ηc decay width measurement will be improved by better than 3%. However, the uncertainties associated with the ηc modified line shapes will dominate the systematic errors and this will prohibit precision mass and width measurements.     

Study of the η’→Ve~+e~- decay with hidden local symmetry model

Within the hidden local symmetry framework, the Dalitz decay η→Ve+e-is studied with the vector meson dominance model. It is found that the partial width Γ(η→ωe+e-)≈40 e V and branching ratio B(η→ωe+e-)≈2×10-4, and Γ(η→ρe+e-)≈10Γ(η→ωe+e-) and B(η→ρe+e-)≈10B(η→ωe+e-). The maximum position of the dilepton distribution is m e+e-≈1.33 Me V. These decays are measurable with the advent of high statistic ηexperiments.     

Study of the η'→Ve~+e~- decay with hidden local symmetry model

Within the hidden local symmetry framework, the Dalitz decay η→Ve+e-is studied with the vector meson dominance model. It is found that the partial width Γ(η→ωe+e-)≈40 e V and branching ratio B(η→ωe+e-)≈2×10-4, and Γ(η→ρe+e-)≈10Γ(η→ωe+e-) and B(η→ρe+e-)≈10B(η→ωe+e-). The maximum position of the dilepton distribution is m e+e-≈1.33 Me V. These decays are measurable with the advent of high statistic ηexperiments.     

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.     

B→ Ds^（＊）η（′） Decays in Perturbative QCD

In this paper, we calculate the branching ratios for B^＋→ Ds^＋η, B^＋→ Ds^＋η′, B^＋→ Ds^（→）η and B^＋ → Ds^＋η′ decays by employing the perturbative QCD （pQCD） factorization approach. Under the two kinds of η - η′ mixing schemes, the quark-flavor mixing scheme and the singlet-octet mixing scheme, we find that the calculated branching ratios agree well with the currently available experimental upper limits. We also consider the so called ＂fDs puzzle＂, by using two groups of parameters about the Ds^（→） meson decay constants, that are fDs = 241 MeV, fDs^→ = 272 MeV and fDs = 274 MeV, fDs^→ = 312 MeV, to calculate the branching ratios for the considered decays. We find that the results change 30%by using these two different kinds of paramters.     

Helicity Amplitude Analysis of ηc Decays into Hyperon-Antihyperon Pairst

The helicity amplitudes for the processes of e^＋e^- →J/ψ→γηc→γYY（Y： hyperon） are presented, together with the joint angular distributions for ηc decays into ∧∧,∑^0 ∑^0, and [1]-[1]＋. The sensitivities to measure the hyperon decay parameters in these decays are evaluated based on the helicity amplitudes. The prospects to test the Bell inequality in experiment using the decay of ηc→∧∧ are discussed.     

D+ → η(')l+νl semileptonic decays in light-cone sum rules

We calculate the D → η transition form factor in light-cone sum rules by taking improved current correlators to avoid the pollution from the twist-3 wave function. We get consistent results of the D⁺ → η^(')l⁺ν_l decays with the experimental data. By comparing the difference between the results of the branching ratios of D⁺ → η^(')l⁺ν_l from a two-pole parameterization model and from a BZ parameterization model, we find that the two-pole model and the BZ model are comparably believable. One way is supposed for the determination of the η-η' mixing angle from the dependence of the branching ratios of D⁺ → η^(')l⁺ν_l decays on the η-η' mixing angle.     

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.     

KLOE results on scalar and pseudoscalar mesons

The data collected by the KLOE Collaboration at the Frascati φ-factory DAФNE from 2001 to 2006 have been used for extensive studies in meson spectroscopy. The decays of the scalar mesons a0（980） and f0（980） into two pseudoscalar mesons have been exploited to measure the relevant parameters of those resonances. The radiative decays φ →ηγ and η＇γ have been used for the determination of the pseudoscalar mixing angle and to search for a possible gluonium content in the η＇. The dynamics of the η → 3π decay has been studied and the Dalitz Plot parameters have been measured. The large amount of η mesons produced allowed also to study interesting rare η decays.     

Study on the Effects of the Light CP-odd Higgs via the Leptonic Decays of Pseudoscalar Mesons

To explain the anomalously large decay rate of Σ+→ p+μ+μ- , it was proposed that a new mechanism where a light CP-odd pseudoscalar boson of mA10 = 214.3 MeV makes a crucial contribution. Later, some authors have studied the transition π0→e+e- and Υ→γA10 in terms of the same mechanism and their result indicates that with the suggested mass one cannot fit the data. This discrepancy might be caused by experimental error of Σ+→p+μ+μ- because there were only a few events. Whether the mechanism is a reasonable one motivates us to investigate the transitions π0→e+e-; η(η′) →μ+μ- ; ηc→μ+μ- ;ηb→τ+τ- within the same framework. It is noted that for π0→e+e-, the standard model (SM) prediction is smaller than the data, whereas the experimental central value of η→μ+μ- is also above the SM prediction. It means that there should be extra contributions from other mechanisms and the contribution of A10 may be a possible one. Theoretically calculating the branching ratios of the concerned modes, we would check if we can obtain a universal mass for A10 which reconcile the theoretical predictions and data for all the modes. Unfortunately, we find that it is impossible to have such a mass with the same coupling |ge|. Therefore we conclude that the phenomenology does not favor such a light A10 , even though a small window is still open.     

KLOE results on scalar and pseudoscalar mesons

The data collected by the KLOE Collaboration at the Frascati φ-factory DAΦNE from 2001 to 2006 have been used for extensive studies in meson spectroscopy.The decays of the scalar mesons a0(980) and f0(980) into two pseudoscalar mesons have been exploited to measure the relevant parameters of those resonances.The radiative decays φ→ηγ and ηγ have been used for the determination of the pseudoscalar mixing angle and to search for a possible gluonium content in the η.The dynamics of the η→ 3π decay has been studied and the Dalitz Plot parameters have been measured.The large amount of η mesons produced allowed also to study interesting rare η decays.     

Studies of Bs^0 → η＇η＇ Decays in pQCD Approach

We calculate the CP averaged branching ratios and CP-violating asymmetries for Bs^0 → η＇η＇ and η＇η＇ decays in the perturbative QCD （pQCD） approach here. The pQCD predictions for the C P-averaged branching ratios are Br（Bs^0 → ηη）=（14.2-7.5^＋18.0） ×10^-6,Br（Bs^0 → ηη＇）=（12.4-7.0^＋18.2）×10^-6,and Br（Bs^0 → η＇η＇） =（9.2-4.9^＋15.3）×10^-6, which agree well with those obtained by employing the QCD factorization approach and also be consistent with available experimental upper limits. The gluonic contributions are small in size： less than 7% for Bs →ηηand ηη＇ decays, and around 18% for Bs →η＇η＇ decay. The CP-violating asymmetries for three decays are very small： less than 3% in magnitude.     

Single photo and electroproduction of pions at EBAC@JLAB

Within the Excited Baryon Analysis Center we have performed a dynamical coupled-channels analysis of the available p（e,e＇π）N data in the region of W ≤ 1.6 GeV and Q2 ≤1.45 （GeV/c）2. The channels included are γ＊N, π＊N, ηN, and ηN which has π△, pN, and σN components. With the hadronic parameters of the model determined in our previous investigations of πN→ πN reaction, we have found that the available data in the considered W ≤ 1.6 GeV region can be fitted well by only adjusting the bare γ＊N → N＊ helicity amplitudes for the lowest N＊ states in P33, P11, S11 and D13 partial waves. The meson cloud effect, as required by the unitarity conditions, on the γ＊N → N＊ form factors are examined.