A Study of the Processes of e+e－→e+e－,μ+μ－ at Large Angle and Measured Luminosities

Using the BES data collected at √S=4.03GeV.the QED processes of e⁺e^－→e⁺e^－,μ⁺μ^－ have been studied. Our measurements agree with the QED prediction,and luminosities obtained from these two final states are compatible at a level of 4%.The total integrated luminosity of 23.1pb^－1 was given for all data collected at this energy region from the calculation.     

Nonfactorization in D+→K0K+ Decays

We analyze D⁺→K⁰K⁺decay at the leading order, α s corrections with the QCD factorization approach and the soft-gluon effects with the light cone QCD sum rules. We find the prediction of naive factorization is far from the experimental data, and the QCD factorization result approaches to the experimental data. However, in QCD factorization method, if we consider the soft-gluon effects, then the result is in accordance with the experimental data well. Our calculation shows that the soft-gluon contributions which are firstly calculated in D meson nonleptonic decay are noticeable. So, it can't be neglected in the decay channel.     

D0-MESON DECAYS Γ（D0→K+K-）/Γ（D0→π+π-）

In this paper the nonleptonic D⁰-decays are discussed. Using Gilman and Wise's methods, we derived the effective Hamiltonian for Cabibbo-suppressed nonleptonic D^0*-decays. The rate F(D⁰→K⁺K^-)/Γ(D⁰→π⁺π^-)～1.26 is obtained. Some problems in this method of the calculations are discussed roughly.     

Searching for new physics in D0→μ+μ-, e+e-,μ±e干 at BES and/or the super charm-tau factory

In contrast with B⁰-B⁰, B_s-B_s mixing where the standard model (SM) contributions overwhelm that of the new physics beyond standard model (BSM), a measured relatively large D⁰-D⁰ mixing where the SM contribution is negligible, definitely implies the existence of the new physics BSM. It is natural to consider that the rare decays of D meson might be more sensitive to new physics, and the decay mode D⁰→μ⁺μ^- could be an ideal area to search for new physics because it is a flavor changing process. In this work we look for a trace of the new physics BSM in the leptonic decays of D⁰. Concretely we discuss the contributions of unparticle or an extra gauge boson Z' while imposing the constraints set by fitting the D⁰- D⁰ mixing data. We find that the long-distance SM effects for D⁰→l1 still exceed those contributions of the BSM under consideration, but for a double-flavor changing process such as D⁰→μ^±e⁺, the new physics contribution would be significant.     

Measurement of Inclusive Semileptonic Branching Fractions for D－→e－X and D0→e－X

We report a measurement of the absolutely inclusive semileptonic branching fractions of D^－ and D⁰ mesons, using a data sample of 22.3pb^－1 collected with BES detector at BEPC e⁺e^－ Collider at s=4.03GeV and based on the method of "combinative D⁺ and D⁰ single and double tags". The measured values of the branching fractions for D^－→e^－X and D⁰→e^－X are (21.8±8.5±4.2)% and (8.9±3.0±1,6)%, respectively. The measured ratio of the branching fractions is BF(D^－→e^－X)/BF(D⁰→e^－X)=2.4±1.7±0.8.     

Study of D0→π－l+νl Decay

In this paper, the D⁰→π^－l⁺ν_l decay process is studied by applying light-cone QCD sum rules. The form factor of D→π transition is calculated by choosing a correlation function with a chiral current to eliminate the effect caused by the uncertainty of the twist-3 function of the pion. Therefore the calculated result of the form factor is improved, and the branching ratio of the D⁰→π^－l⁺ν_l decay process is consistent with the new experimental data.     

D介子衰变Γ（D0→K+K-）/Γ（D0→π+π-）

考虑强作用修正对D⁰介子衰变的影响,用Gilman和Wise^[1]的方法,导出ΔC=1的等效哈密顿量,算得Γ（D⁰→K⁺K^-）/Γ（D⁰→π⁺π^-）～1.26,简单讨论了这种计算方法中的一些问题。     

Analytic Approximation for Process e++e－→τ++τ－ Cross Section Near Threshold

In the structure function approach,we calculate the threshold behaviours for e⁺+e^－→τ⁺+τ^－,which including QED radiative corrections from initial correction,vacuum polarization effect,Coulomb effect and final state correction.This theoretical prediction for threshold behaviours of τ-pair production is useful for BES new measurement of lepton τ mass.     

Branching Ratios of J/ψ→π03(π+π－)

The decay mode of J/ψ→π⁰3(π⁺π^－) was studied very little before. There are no informations except branching ratios for this channel in PDG book which based on less than 0.2×10⁶J/ψ events of MARKⅠ. Now, BESⅠ has a data sample of 7.8×10⁶J/ψ events, we can make more accurate results than MARKⅠ. Total of 3290±43 J/ψ→π⁰3(π⁺π^－) events including 1275±86 J/ψ→ω²(π⁺π^－) events are selected. J/ψ→π⁰3(π⁺π^－) and J/ψ→ω²(π⁺π^－) events have been generated with MC simulition for calculating events selection efficiency. BESⅠ result is: Br(J/ψ→π⁰3(π⁺π^－))=(2.52±0.06±0.43)% and Br(J/ψ→π⁰3(π⁺π^－))=(1.31±0.09±0.21)%. Meanwhile, we studied the invariant mass of 4π and ωππ to find interesting signals. It seems that there is a peak at about 1.74GeV in the invarianat mass spectrum of 4π, and a enhancement was also found at about 1.9GeV in the invariant mass spectrum of ωππ. It is not clear whether they are from resonances or background. Therefore, more work in detail is still going on.     

Color Rearrangement in e+e－→W+W－→h's Process

The probability of Color Rearrangement at partonic level in e⁺e^－→W⁺W^－→h,s process is studied using the Color Effective Hamiltonian. The comparison between our results and those of Gutafson and Sjostrand et al. is also given. It is found that this probability cannot be neglected, and it is pointed out that to investigate the Color Rearrangements, the hadronization models should be developped and improved.     

高能e++e－→e++e－+强子过程中的电弱干涉效应

在这篇文章中, 我们用[2]中的结果讨论了与极化光子结构函数相关的电弱干涉效应, 这个效应提供了对G-W-S(格拉肖-温伯格-萨拉姆)模型作进一步检验的可能并且导致对光子结构函数的更深入的了解.     

The Structures of Colour String for e+e－→qqg and γ→3g

In Lund model,the explanation of e⁺e^－→qqg→3 jets and γ→3g→h's is based on applying Lund string fragmentation model to their assumed structures of colour string for qqg and 3g systems.In this paper,starting from the colour wave functions of qqg and 3g systems,we study these colour string structures by QCD directly.The results reveal the reasonableness and accuracy of Lund string pictures.     

Experimental Searches for the Non-DD Decays of ψ(3770) in e+e－ Collider

The previous experiments which provide information on the ψ(3770) to non-DD decays are reviewed. Three approaches of searching for the non-DD decays are discussed in detail. It is also pointed out that the search for the non-DD decays of the ψ(3770) is very important for the understanding of the dynamics of charmonium decays.     

ELECTROWEAK INTERFERENCE EFFECTS IN THE HIGH ENERGY e++e－→e++e－+ HADRONS PROCESSES

In this paper we examine the electroweak interference effects related to the polarized photon structure functions making use of the results of the ref.[2]. The effects provide the probability of a further test of the G-W-S model and may lead to a deep understanding to the photon structure functions.     

Determination of J/φ Event Number via J/φ→μ+μ- and J/φ→ e+e- at BESIII

The decays of J/φ→μ⁺μ^- and J/φ→ e⁺e^- are studied by Monte-Carlo simulation, based on the Beijing Spectrometer (BES)Ⅲ offline software system. The methods of determination of the J/φ event number via J/φ→μ⁺μ^- and J/φ→ e⁺e^- are presented, respectively. These methods can be used to determine the J/φevent number for the coming BESⅢ J/φ data sample.     

A Rigorous Calculation for the Radiator in e+e－ Process

Using the precise expression of electron,positron distribution function we obtained earlier,we derive the rigorous analytical expression of radiator in e⁺e^－ collision process.This series expression converges rapidly to the precise result required.The comparison with existing approximate expression is also given.Our result benefits the precice calculation for the radiative corrections in e⁺e^－ collision processess.     

Probe the Strength of Annihilation In BS→π＋π－ Decays Within QCD Factorization

Using the method of QCD factorization, we calculate the branching ratio and the CP violation for pure annihilation decay B_S→π^＋π^－ in the Standard Model. Meanwhile, we employ an effective gluon mass resulted in the study of the infrared behaviour of gluon propagators to avoid the soft endpoint divergence. We find that the CP-averaged branching ratio is about 1.24×10^－7, and the penguin diagram contributions is dominant in this process. The direct CP violation parameter is about －0.05, while the mixing-induced CP asymmetry is a quite large number of 0.18. Once these quantities can be measured in the future LHC-b experiments, studying such a process will enrich our knowledge on the dynamics of the charmless hadronic decay of B-meson and the property of gluon.     

Helicity Formalism of the Angular Distributions for the Process e++e－→J/ψ→V+X,X→3P

The helicity formalism of the angular distributions for the process e⁺+e^－→J/ψ→V+X,X→P₁+P₂+P₃(V and stand for vr and psealar meson, respectvely) are given in this paper. It provides the theical formula for determining the spin and parity of the intermediate state X of the above process.     

Event generators for η/η' rare decays into π+π-l+l- and e+e-μ+μ-

Study of the rare and forbidden decays of η/η' offers a sensitive probe to test fundamental symmetries of quantum chromodynamics and search for new physics beyond the Standard Model. To study the rare decays of η/η' to π⁺π^-e⁺e^-, π⁺π^-μ⁺μ^- and e⁺e^-μ⁺μ^- at the BESⅢ detector, we developed several event generators based on the vector meson dominant model with finite-width corrections and the pseudoscalar mesons mixing theory. The various distributions from event generators are in good agreement with the theoretical predictions, which indicates that the event generators work very well after implemention in the BESⅢ Monte Carlo simulation package. In the BESⅢ physics analysis, the performance of the event generators will be improved in accordance with the distributions of different variables of η/η' from data and the improvement on the theoretical calculations.     

THE FRAGMENTATION SCHEMES IN e+e－ ANNIHILATION

The comparison of two fragmentation schemes used in the analysis of e⁺e^－ annihilation are presented in this paper.It is found that the independent fragmentation assumption is strongly disfavored by the data of the final particle multiplicities,and the string fragmentation assumption agrees with experiments.