Measurement of the e+e-→W+W- cross section and W decay branching fractions at LEP

From a total data sample of 701.1 pb^-1 recorded with e⁺e^- centre-of-mass energies of 161–209 GeV with the OPAL detector at LEP, 11693 W-pair candidate events are selected. These data are used to obtain measurements of the W-pair production cross sections at 10 different centre-of-mass energies. The ratio of the measured cross sections to the standard model expectation is found to be: , where the uncertainties are statistical, experimental systematics and theory systematics respectively. The data are used to determine the W boson branching fractions, which are found to be consistent with lepton universality of the charged current interaction. Assuming lepton universality, the branching ratio to hadrons is determined to be 67.41±0.37(stat.)±0.23(syst.)%, from which the CKM matrix element |V_cs| is determined to be 0.969±0.017(stat.)±0.012(syst.). The differential cross section as a function of the W^- production angle is measured for the qqeν and qqμν final states. The results described in this paper are consistent with the expectations from the standard model. This paper is dedicated to the memory of Ben Shen.     

e+e－→W+W－→h's过程中的色重组

用色等效哈密顿研究了e⁺e^－→W⁺W^－→h＇s过程中部分子阶段的色重组几率,并与Gustafson和Sjostrand等人的结果作了分析比较,发现色重组几率不能被忽略,并指出研究色重组对发展强子化模型提出了新的要求.     

Determination of the resonant parameters of excited vector strangenia with e+e-→ηφ data

We determine the resonant parameters of the vector states φ(1680) and φ(2170) by performing a combined fit to the e⁺e^-→ηφ cross sections from the threshold to 2.85 GeV measured by the BaBar,Belle,BESⅢ,and CMD-3 experiments.The mass(1678_-3⁺⁵±7) MeV/c² and width(156±5±9) MeV are obtained for φ(1680),and the mass(2169±5±6)MeV/c² and width(96_-14⁺¹⁷±9)MeV are obtained for φ(2170).The statistical significance ofφ(2...     

Quartic gauge couplings and the radiation zero in?pp→l±νγγ?events at the LHC

We report a study of the process pp→l^±νγγ at CERN’s Large Hadron Collider, using a leading order partonic-level event generator interfaced to the Pythia program for showering and hadronisation and a with a generic detector simulation. The process is sensitive to possible anomalous quartic gauge boson couplings of the form WWγγ. It is shown how unitarity-safe limits may be placed on these anomalous couplings by applying a binned maximum likelihood fit to the distribution of the two-photon invariant mass, M _γγ, below a cutoff of ∼1 TeV. Assuming 30 fb⁻¹ of integrated luminosity, the expected limits are two orders of magnitude tighter than those available from LEP. It is also demonstrated how the Standard Model radiation zero feature of the q[`(q)]^￠?Wupgammaupgammabar{mathrm{q}}^{prime}tomathrm {W}upgammaupgamma process may be observed in the difference between the two-photon and charged lepton pseudo-rapidities.     

Expected H →μ+μ-measurement precision with e+e-→Z(q■)H production at the CEPC

A search for the dimuon decay of the Standard Model Higgs boson is performed using Monte Carlo simulated events to mimic data corresponding to an integrated luminosity of 5.6 ab^-1 collected with the Circular Electron-Positron Collider detector in e⁺e^-collisions at■GeV.This study investigates thee⁺e^-→ZH,Z→q■,H→μ⁺μ^-process,and the expected significance considering only the statistical uncertainty in the data for a backgro...     

Measurement of the strong coupling αS from four-jet observables in e+e- annihilation

Data from e⁺e^- annihilation into hadrons at centre-of-mass energies between 91 GeV and 209 GeV collected with the OPAL detector at LEP, are used to study the four-jet rate as a function of the Durham algorithm resolution parameter y_cut. The four-jet rate is compared to next-to-leading order calculations that include the resummation of large logarithms. The strong coupling measured from the four-jet rate is in agreement with the world average. Next-to-leading order fits to the D-parameter and thrust minor event-shape observables are also performed for the first time. We find consistent results, but with significantly larger theoretical uncertainties.     

Quasi-classical trajectory study of the stereodynamics of a Ne+H2+→NeH++H reaction

We have carried out a quasi-classical trajectory calculation for the reaction of Ne + H₂⁺ (v=0, j=1) → NeH⁺ + H on the ground state (1²A') using the LZHH potential energy surface constructed by Lü et al. [Lü S J, Zhang P Y, Han K L and He G Z 2010 J. Chem. Phys. 132 014303]. Differential cross sections at many collision energies indicate that the reaction is dominated by forward-scattering. In addition, the NeH⁺ product shows rotationally hot and vibrationally cold distributions. Stereodynamical results indicate that the products are strongly polarized in the direction perpendicular to the scattering plane and that the products rotate mainly in planes parallel to the scattering plane.     

Search for heavy charged particles and for particles with anomalous charge in e+e? collisions at LEP

Using the OPAL data accumulated in 1991–1993 amounting to 74 pb^–1 of integrated luminosity, corresponding to 1.64×10⁶ selected multi-hadronic events, a search has been performed for charged particles with unusual mass or unusual charge. The mass was determined from a combination of momentum and ionization energy loss measurements. No isolation criteria were applied to the tracks examined, so that both isolated particles and particles produced in jets were valid candidates. For particles with chargeQ/e=–1, one candidate with a mass of approximately 4.2 GeV/c² was found, which is compatible with the background rate expected according to a Monte Carlo simulation. The implications of this search for the mass limits of a conjectured stable or quasi-stable charged gluino composite are discussed. Limits are also presented for the production of fractionally-charged particles withQ/e=±2/3 and ±4/3 as well as for particles withQ/e=±2.     

高能e+e-物理成就与展望（二）

 六、发现τ轻子餐夸克发现以后,在物质的两类基本组成单元--夸克和轻子之间形成了一个对称的图象:两对轻子,即电子和电子型中微子(v_?)、μ子和μ子型中微子（v_μ）,对应于两对夸克,即上（μ）和下（d）、粲（c）和奇异（s）.它们可以分为两“代”:第一代是u,d,e,v_a,第二代是c,s,μ,v_μ.两代成员依次一一对应,对应的成员具有相同性质,区别主要表现在质量上面,第二代的比第一代的大.     

Measurement of the photon structure functionF2γ in the reactione+e?→e+e?+hadrons at LEP

We present measurements of the hadronic photon structure functionF ₂ (x), in twoQ ² ranges with mean values of 5.9 GeV² and 14.7 GeV². The data were taken by the OPAL experiment at LEP, with close to theZ ⁰ mass and correspond to an integratede ⁺ e ^– luminosity of 44.8 pb^–1. In the context of a QCD-based model we find the quark transverse momentum cutoff separating the vector meson dominance (VMD) and perturbative QCD regions to be 0.27±0.10 GeV. We confirm that there is a significant pointlike component of the photon when the probe photon hasQ ²>4 GeV². Our measurements extend to lower values ofx than any previous experiment, and no increase ofF ₂ (x) is observed.     

LH模型与高能e+e-对撞机上ZH的产生

在最小Higgs模型(LH)框架内讨论了Higgs粒子产生过程e⁺e^-→ZH.结果表明,对该过程的修正效应主要来自重光子A′,但如果自由参数c取值范围为0.85—1,则重规范玻色子Z′的贡献就不能忽略.在LH模型大部分参数空间内,过程e⁺e^-→ZH的总产生截面σtot与标准模型(SM)相应值的偏差大于5%,应该能在未来的高能e+e–对撞机(LC)实验中观测到     

Study of parity violation in Λc+→φp and Λc+→ωp decays

CP violation in baryonic decays has not been significantly observed.With large data events accumulated a te⁺e^- colliders or the Large Hadron Collider,charmed baryon decays would provide a promising laboratory to test CP symmetry.In this study,we formulate Λ_c⁺→φp and Λ_c⁺→ωp decays for the measurement of their asymmetry parameters in weak decays at the BESIII or LHCb experiments.The polarization transfer is analyzed in the two proce...     

Study of new boson W±1 in the Minimal Higgsless Model at the LHC

The Minimal Higgsless Model predicts the existence of new vector gauge boson W1^±, By the process PP →W1^±qq →W^±Z^0qq, Z^0→ 1^＋1^-, W^±→ qq （1=e,μ; q is hadronized to be jets）, we study the sensitivity of searching for this possible vector gauge boson in the level of generator events of signal and backgrounds, then give integrated luminosity required to discover 5σ signal as a function of W1^± mass. The generator for the signal PP → W1^±qq →W^±Z^0qq at tree level is developed with the Minimal Higgsless Model and then interfaced with PYTHIA for the patton showers and hadronization. The backgrounds are produced with MadGraph and PYTHIA.     

场流关系和π+→e++ν+γ的衰变过程

本文应用由复合场场论或场代数导出的轴矢流的场流恒等式计算了π介子的辐射衰变π⁺→e⁺+ν+γ过程。计算结果与目前的实验大致相合。     

A study of the reactions π+p→ K+∑+ and K−p→π−∑+ at 10 GeV/c

For the first time, the reactions π⁺p→K⁺∑⁺ and K^?p→π^?∑⁺ have been studied in the same apparatus. This has been done at an adequately high momentum (10.1 GeV/c) to allow a check of the prediction of exchange degeneracy, that the differential cross sections should be converging at high energy. We have measured the cross section for momentum transfers t between t_min and t = ?0.3 (GeV/c)². We find that for both reactions the differential cross section shows an exponential fall, with no deviations right in to t =t_min (where some other experiments have shown a dip in the cross section). Furthermore, we find the magnitude of the differential cross sections to be closely similar at t = 0, with a ratio

$\text{R=}\text{(}\text{d}\text{σ}\text{d}\text{t)}{}_{\mathrm{t=0}}\text{(}\text{K}{}^{\mathrm{?}}\text{p}\text{→π}{}^{\mathrm{?}}\text{∑}{}^{\mathrm{+}}\text{)}\text{(}\text{d}\text{σ}\text{d}\text{t)}{}_{\mathrm{t=0}}\text{(π}{}^{\mathrm{+}}\text{p}\text{→}\text{K}{}^{\mathrm{+}}\text{∑}{}^{\mathrm{+}}$

However, the slope for the positive reaction is about 19% steeper than that for the negative reaction.     

Electromagnetic structure of W± bosons in the e–e+ → W+W– reaction

A model-independent analysis of anomalous gauge coupling constants of W ^± bosons is presented and the corresponding restrictions on them and on the electromagnetic characteristics of W ^± bosons following from the experiments on measuring the e⁺ e^- ? W⁺ W^- ? ( e

标准模型中两类中性玻色子混合圈链图传播子的重整化及其e+e-→μ+μ-反应截面

采用电弱统一标准模型, 对光子γ和中间玻色子Z₀ 混合圈链图传播子的构架方式及其重整化问题作了详细分析与讨论, 并完成了有关解析计算, 获得了由参与电弱相互作用的各种混合圈构成的γ和Z₀的重整化链图传播子的解析计算结果. 此外, 我们还将此结果应用于高能物理中备受关注的一类轻子反应e⁺e^-→μ⁺μ^-中, 获得了在γ和Z₀所构架出的重整化混合圈链图传播中e⁺e^-→μ⁺μ^-反应截面的解析计算结果, 并将本文所获得的这一理论计算结果与实验观测值作了对比分析, 发现本文理论计算结果与实验观测值符合非常好, 并由此也获得了有关辐射修正的重要信息. 本文研究结果也可为探讨一般复杂传播子的理论研究与应用提供某些参考. 关键词： 标准模型 链图传播子 重整化 辐射修正