Analysis of Bc→τvτ at CEPC

Precise determination of the Bc → tvt branching ratio provides an advantageous opportunity for under-standing the electroweak structure of the Standard Model,me...     

通过τ→a_1v→π~±π~0π~0v道测量由Z~0衰变的τ的极化不对称性

利用L3合作组1992年和1993年的数据，通过τ→a1v→π±π0π0v道测量了由Z0衰变的τ的极化不对称性A(pol)＝－0．239±0．126±0．100，其中第一项误差为统计误差，第二项误差为系统误差．由此推断有效电弱混合角sin2θw＝0．2197±0．0219．     

τ→π~±2π~0v结构函数的测量

首次对τ→π2π0v衰变的结构函数进行了模型无关的实验测量,并与KS模型、IMR模型和Feindt模型进行了比较,在误差范围内,三种理论模型与实验结果一致．与OPAL组测量的τ→3π±v道的结构函数相比,在0．5＜Q2＜2．75GeV2范围内未发现明显差异．     

神经元网络在τ→ρV_τ极化分析中的应用

在ＬＥＰ／Ｌ３的τ→ρＶτ极化物理分析中，用人工神经元网络法选择事例，获得了比较高的选择效率．详细研究表明，网络本身不会引入明显的系统偏差．使用在Ｚ０能区采集到的８９７７个τ＋τ－对事例，得到τ→ρＶτ道的极化率Ｐτ＝－０．１２９±０．０５０±０．０５０．本文介绍在这一工作中使用的神经网络训练方法和技巧     

e~＋e~－→τ~＋τ~－，τ~－→a_1~－υ_τ，a_1￣－→ρπ过程的角分

给出了过程ｅ＋ｅ－→τ＋τ－，τ－→ａ１－υτ，ａ１－→ρπ的密度矩阵和角分布的螺旋度形式．通过分段拟合把相应于Ｗ－ａ１跃迁和强作用顶点ａ１ρπ形状因子的螺旋度振幅比确定下来，给出了一个确定宽共振态ａ１质量和宽度而与模型无关的方法．     

Upper limit on the branching ratio for the decay τ-→Π-ηvτ

We have searched for the decay τ^-→Π^-ηv_τ using the MARK II detector at the PEP e⁺e^- storage ring. No evidence for the decay is found; the upper limit for the branching ratio is B(τ^-→Π^-ηv_τ)<1.0% at the 95% confidence level.     

τ→πVτ疑难和自旋3/2的τ轻子

本文讨论了τ→πν_r衰变的疑难.和自旋1/2的理论相比,对自旋3/2的重轻子τ和自旋1/2的中微子ν_r,τ→πν_r。道和τ→πν_rν_ll道的比值压低了12/5倍,而其它衰变道没有明显的变动.对自旋3/2重轻子τ在e⁺e^-对撞中的产生也作了讨论.     

Technicolor模型下QCD对衰变B→Xτv_τ的修正

在一代Ｔｅｃｈｎｉｃｏｌｏｒ模型下对内含的半轻子Ｂ衰变的（）阶修正进行了计算。将理论的预言与最近的实验结果比较，得到了荷电的色单态和色八重态赝标量粒子质量的下限：     

Radiative leptonic decay B-c→τ-(v)τγ in the standard model and the two-Higgs-doublet model

We analyze the radiative leptonic Be decay B-→τ-(v)τγ in the Standard Model and the twoHiggs-doublet model using the non-relativistic constituent quark model.The results confirm that this channel is experimentally promising in view of the large number of Bc mesons which are expected to be produced at future hadron facilities.We also find that this decay is sensitive to the parameters of the two-Higgs-doublet model,and it can be tested in future experiments.     

神经元网络在τ→ρVτ极化分析中的应用

在LEP/L3的τ→ρV_τ极化物理分析中,用人工神经元网络法选择事例,获得了比较高的选择效率.详细研究表明,网络本身不会引入明显的系统偏差.使用在Z⁰能区采集到的8977个τ⁺τ^－对事例,得到τ→ρVτ道的极化率P_τ=－0.129±0.050±0.050.本文介绍在这一工作中使用的神经网络训练方法和技巧.     

An Investigation of Signal Kinematical Region to Study Standard Model Higgs Boson Properties in the H → WW* → ℓvℓv Decay Channel in the ATLAS Experiment at the Large Hadron Collider at 13 TeV

A signal kinematical region is analyzed by the Higgs Boson Working Group (HWW) within the framework of a study of the Standard Model Higgs boson properties in the H → WW* → evεv decay channel in the ATLAS experiment on the Large Hadron Collider (LHC). The analysis is based on the full statistics of proton-proton collision data during exposures in 2015–2016 at the center-of-mass energy of 13 TeV. As compared to our previous analysis, the reconstruction software is updated and the simulation accuracy of backgrounds is improved. Events taken at low and high LHC luminosity are studied separately. In addition, the kinematics at the later stages of event selection is investigated in detail and systematic uncertainties are fully estimated. It is shown that the Monte Carlo modeling satisfactorily describes the experimental data at different selection stages. Kinematic distributions for hadron jets are studied also in the Z-boson control region, where the acquired data reach the order of ten million events. As compared to the previous investigation, the modeling accuracy of Z and background processes is noticeably improved, and events at low and high LHC luminosities are studied separately. Furthermore, all systematic uncertainties related to jets are estimated as well. As a whole, good agreement between experimental results and Monte Carlo simulation data is observed. No problems that would be caused by high luminosity are observed.

     

在双Higgs模型Ⅲ中研究单举b→sτ+τ-衰变过程

在模型Ⅲ中研究了单举b→sτ+τ-过程的衰变分支比,包括领头阶QCD修正.发现由中性Higgs玻色子传播的树图贡献在一个合理的参数空间范围内是主要的,因此这个过程在将来的B介子实验中有可能被观察到.     

Technicolor模型下QCD对衰变B→Xτvτ的修正

在一代Technicolor模型下对内含的半轻子B衰变的()阶修正进行了计算. 将理论的预言与最近的实验结果比较,得到了荷电的色单态和色八重态赝标量粒子质量的下限:m_p>43GeV, M_P8>77GeV.     

b→cτ■ decay in supersymmetry with R-parity violation

In past years,several hints of lepton flavor universality(LFU)violation have emerged from the b→ct■,and b→sl~+l-data.More recently,the Belle Collaboration has reported the first measurement of the D* longitudinal polarization fraction in the B→D*τV decay.Motivated by this intriguing result,along with the recent measurements of RJ/Ψand τ polarization,we present the study of b→ct■ decays in supersymmetry(SUSY)with R-parity violation(RPV).We consider B→D(*)t■,Bc→ηct■,Bc→J/ψt■ and ∧b→∧ct■ modes and focus on the branching ratios,LFU ratios,forward-backward asymmetries,polarizations of daughter hadrons,and the τ lepton.The RPV SUSY was capable of explaining the RD(*) anomalies at the 2σ level,after taking into account various flavor constraints.In the allowed parameter space,the differential branching fractions and LFU ratios are largely enhanced by the SUSY effects,especially in the large dilepton invariant mass region.Moreover,a lower bound B(B~+→K~+vv)7.37×10~(-6) is obtained.These observables could provide testable signatures at the high-luminosity LHC and SuperKEKB,and correlate with direct searches for SUSY.     

Radiative leptonic decay Bc^-→τ^vτ^-γ in the standard model and the two-Higgs-doublet model

We analyze the radiative leptonic Bc decay Bc^-→τ^vτ^-γ in the Standard Model and the two- Higgs-doublet model using the non-relativistic constituent quark model. The results confirm that this channel is experimentally promising in view of the large number of Bc mesons which are expected to be produced at future hadron facilities. We also find that this decay is sensitive to the parameters of the two-Higgs-doublet model, and it can be tested in future experiments.     

Anomalies in(semi)-leptonic B decays B~±→τ~±ν,B~±→Dτ~±ν and B~±→D~*τ~±ν,and possible resolution with sterile neutrino

The universality of the weak interactions can be tested in semileptonic b→c transitions,and in particular in the ratios R(D~(*)) ≡Γ(B → D(*)τν)/Γ(B → D~(*)lν)(where 1 = μ or e).Due to the recent differences between the experimental measurements of these observables by Ba Bar,Belle and LHCb on the one hand and the Standard Model predicted values on the other hand,we study the predicted ratios R(D~(*))=Γ(B→D~(*)τ+"missing")/Γ(B→D(*)lν)in scenarios with an additional sterile heavy neutrino of mass ～1 Ge V.Further,we evaluate the newly defined ratio R(0)≡Γ(B→τ+"missing")/Γ(B→μν) in such scenarios,in view of the future possibilities of measuring the quantity at Belle-Ⅱ.     

Probing magnetic moment operators in H_γ production and H→τ~+τ~-γ rare decay

The magnetic moment(a_γ) and weak magnetic moment(a_W) of charged leptons and quarks are sensitive to quantum effects of new physics heavy resonances.In effective field theory,a_γ and a_W are induced by two independent operators.Therefore,one has to measure both ay and aw to shed light on new physics.The aw's of the SM fermions are measured at the LEP.In this work,we analyze the contributions from magnetic and weak magnetic moment operators in the processes of pp→H_γ and gg→H→τ~+τ~-γ at the High-Luminosity Large Hadron Collider.We demonstrate that the two processes can cover most of the parameter space that cannot be probed at the LEP.     

Next-to-leading order QCD corrections to bg→tW− at the CERN Large Hadron Collider

The next-to-leading order QCD corrections to the Standard Model process of single top production, bg→tW⁻, for the CERN Large Hadron Collider with $\text{s}\text{=14}$ TeV have been calculated. For renormalization and factorization scales μ=μ₀ (μ₀=m_t+m_W), the NLO hadronic cross section is ∼42 pb, while ∼26.5 pb for tree level. The NLO QCD corrections can enhance the cross section by a factor from 1.4 to 1.7 for μ₀/2<μ<2μ₀.