SOME DISCUSSIONS OF POSSIBLE MECHANISM OF Z0→l+l-γ

The possible mechanisms for anomalous decay Z⁰→l⁺l^-γ are discussed. The mechanism with anomaious ZZ_Y vertex is investipted indetail. It is pointed out that this vertex may appear via some effective Lagrangian which can be derived from an SU(2)×U (1) gauge invariant effective Lagrangian after the spontaneous symmetry breaking. The predictions based on this mechanism are consistent with recent experiments and can be verified experimentally. This mechanism is consistent with a composite model of Z⁰ with radius 10^-15 cm.     

Measurement of the absolute branching fraction of D+→K0e+ve via K0→π0π0

By analyzing 2.93 fb^-1 data collected at the center-of-mass energy √s=3.773 GeV with the BESIII detector, we measure the absolute branching fraction of the semileptonic decay D⁺→K⁰e⁺v_e to be B(D⁺→K⁰e⁺v_e)=(8.59±0.14±0.21)% using K⁰→K_S⁰→π⁰π⁰, where the first uncertainty is statistical and the second systematic. Our result is consistent with previous measurements within uncertainties..     

Electroweak radiative corrections toe + e −→γZ 0

We calculated the explicit analytic expressions for the electroweak radiative corrections to the differential cross sectione ⁺ e ^?→γZ ⁰ to one-loop in the framework of the Glashow-Salam-Weinberg model. Special attention is payed to the dependence on the Higgs and top quark masses.     

Radiative Z0 production: A method for neutrino counting in e+e− collisions

Radiative Z⁰ production in e⁺e^? collisions is analyzed as a method of measuring the partial width of the Z⁰ for decay into neutrinos and thus determining if there exist low mass neutral leptons beyond the three now known (ν_e,ν_μ,ν_τ). The conditions for observing the $\text{γν}\text{ν}$ final state are analyzed and background cross sections are determined. We conclude that the experiment is feasible and requires relatively modest apparatus.     

The Analytical Helicity Amplitudes for Z → 3γ, γγ → γZ and γZ → γγ via W-Loop,Charged Scalar-Loop

The analytic helicity amplitudes of Z → 3γ, γγ → γZ and γZ → γγ via W-loop and charged scalar-loop are presented. There is some difference between our results and those in Z. Phys. C60 (1993) 175 (E.W.N. Glover and A.G. Morgan) for Z → 3γ via W-loop and fermion-loop, which has different physical meanings.     

A 4 → 0 cross-over transition in Pb

A 4⁺ → 0⁺ cross-over γ-ray decay in ²⁰⁴Pb has been detected. The branching ratio of this transition to the 4⁺ → 2⁺ → 0⁺ cascade has been measured to be (0.012 ± 0.002)%.     

The Decay H0 → W+W- in the Two-Higgs-Doublet Model

The additional weak corrections at one-loop level to process H₀ → W⁺W^- in the two-fliggsdoublet model are calculated. The corrections from the extra Higgs sector depend strongly on the masses of Higgs sectors and the ratio of vacuum expectation values tanβ. It is shown that the general two-Higgs-doublet model admits flexibility in adjusting the one-loop corrections for the decay. In particular, for the heavy Ho boson the additional corrections imply a 5~14% reduction, when M_Ho < 1 TeV, due to relative light H₁ mass and heavy H₂, Φ masses which we used.     

Z′ search in e+e− annihilation

Expectations for constraints on extra Z bosons are derived for LEP2 and future linear e⁺e^? colliders. For typical GUTs, a Z′ with M_Z′ ≤ 3 to $6sqrt {s}$ may cause observable effects. The Z′ discovery limits are dominated by statistical errors. However, if a Z′ signal is observed, the discrimination between different models becomes much worse if systematic errors are taken into account. Discrimination between models is possible for $M_{Z^{?ime}} < 3sqrt {s}$. A determination of Z′ff couplings independently of models becomes attractive with future colliders. Anticipated bounds are determined.     

CHARGE ASYMMETRY AND THE Z0 BOSON MASS IN UNPOLARIZED e+e-→μ+μ- REACTION

Department of Physics, Zhongshan University, Guangzhou, China     

Hard photon next-to-leading corrections to two-fermion production in e + e − collisions above the Z 0 peak

A complete next-to-leading order calculation of the initial-state O (α) photonic corrections to hadron and lepton-pair production in e ⁺ e ^?. collisions is presented. The impact of the next-to-leading order corrections on the twofermion cross section and forward-backward asymmetry is studied in detail for several event selections, with special emphasis on hard photon effects at LEP1.5 and LEP2 energies. It is shown that for typical realistic event selections, initial-state next-to-leading order corrections in the soft approximation can be safely extrapolated to energies above the Z ⁰ peak without significant loss of precision.     

Detailed W0 effects in e+e− → e+e−

The predicted cross section for the reaction e⁺e^?→e⁺e^? is presented assuming one photon and W⁰ exchange. Pure W⁰ terms and the W⁰ width are included.     

Second order electromagnetic radiative corrections toe + e −→γ*Z 0→μ+μ−

We derive a compact expression for the cross sectione ⁺ e ^?→μ⁺μ^?, containing a full treatment of the electromagnetic radiative corrections from both initial and final states. By using a formulation in terms of evolution equations, we obtain an expression for the cross-section to theO(α²) which includes soft and hard photons and resums to all orders dominant and non-dominant logarithmic contributions. Comparisons with previous results are made.     

Probability of Color Singlet String States in e + e- → qq + ng at Large Nc Limit

We use the method of color effective Hamiltonian to calculate the probability of color singlet string states at the large N_c limit. We show that a qq + ng system produced from e + e^- annihilation is definitely in color singlet string states when N_c → ∞, i.e., color,singlet string states account for 100% of all possible color singlet states. This justifies the approximation that the hadronization mechanism of each color-neutral flow piece connecting two color-adjacent partons is assumed to be the same as an independent qq singlet system.