微扰QCD对Drell-Yan过程能量损失效应的修正

利用Glauber模型以及DGLAP方程下的核内核子的部分子分布函数, 在次领头阶QCD下计算了Drell-Yan过程中的能量损失效应, 计算表明QCD修正并不能改善理论结果与试验结果的符合, 尤其是p-W与p-Be以x₁为变量的微分截面比. 原因是所用的核内核子部分子的分布函数是以领头阶近似为基础并通过演化方程得到的. 于是利用在次领头阶微扰QCD下得到的核遮蔽效应核内核子的部分子分布函数重新计算了次领头阶QCD修正对Drell-Yan过程能量损失的贡献. 计算结果表明康普顿散射过程与湮没过程中应该有更多的能量损失.     

A Comparative Study of fB within QCD Sum Rules with Two Typical Correlators up to Next-to-Leading Order

The B-meson decay constant f_B is an important component for studying the B-meson decays, which can be studied through QCD sum rules. We make a detailed discussion on f_B from two sum rules up to next-to-leading order, i.e. sum rules I and II, which are derived from the conventional correlator and the correlator with chiral currents respectively. It is found that these two sum rules are consistent with each other. The sum rules II involves less non-perturbative condensates as that of sum rules I, and in principle, it can be more accurate if we know the dimension-four gluon condensate well. It is found that f_B decreases with the increment of m_B, and to compare with the Belle experimental data on f_B, both sum rules I and II prefer smaller pole b-quarkmass, m_b=4.68±0.07 GeV. By varying all the input parameters within their reasonable regions and by adding all the uncertainties in quadrature, we obtain f_B=172^{+23}_{-25} MeV for sum rules I and f_B=214_{-34}^{+26} MeV for sum rules II.     

Dependence of Jet Photoproduction on Scales in Higher Order QCD Corrections at HERA

The dependencies of two-jet cross section on renormalization scale and factorization scales of resolved photon and proton are investigated up to next-to-leading order (NLO) QCD. It is shown that the NLO cross section is quite sensitive to the choice of the renormalization scale and the factorization scales of resolved photon and proton in large invariant mass and large negative. rapidity of the two-jet system.     

On Deeply Virtual Compton Scattering at Next-to-Leading Order

Deeply virtual Compton scattering in the near forward kinematic region is the golden access to Generalized Parton Distributions. We studied the \({\mathcal{O}(\alpha_S)}\) corrections to the scattering amplitude for both spacelike and timelike kinematics relevant respectively to the leptoproduction of a real photon and to the photoproduction of a lepton pair. It turns out that these corrections are phenomenologically important and that the gluonic contributions are by no means negligible, even in the moderate energy range of JLab12 and of the COMPASS-II experiment at CERN.     

Light Hypernuclei Based on Chiral Interactions at Next-to-Leading Order

We present predictions for the binding energies of the light hypernuclei \({^3_\Lambda{\rm H},\, ^4_\Lambda{\rm He}}\) and \({^4_\Lambda{\rm H}}\) based on Faddeev- and Yakubovsky equations in momentum space. We discuss how such results can help to test the existing hyperon–nucleon (Y N) potential models and effective field theory based Y N interactions. Especially, we show results for the chiral interactions at next-to-leading order.     

Non-Perturbative Corrections to the Bound State Equation in QCD

We have taken into account non-partnrbative correctios to the bound atate equation in the effective QCD theory. The Betha-Salpeter equation for the light mesons is solved in the zero-order, approximation, where only gluon condensate is considered. The results are quite reasonable.     

Comments on QCD Corrections to b + sγ Decay

We find some errors in the previous calculation of leading log QCD corrections to b + sγ decay, which include corrections from mto, to M_w in addition to corrections from M_w to m_b. The inclusive decay rate is found to be enhanced more than previous calculations. At m_t = 170 GeV, the running from m_top to M_w results in 13% enhancement, and for m_t = 250 GeV, 16% enhancement is found.     

Fermion Corrections to Mass of Scalar Glueball in QCD Sum Rule

Contributions of fermions to the mass of the scalar glueball 0⁺⁺ are calculated at two-loop level in the framework of QCD sum rules. It slightly changes the coefficients in the operator product expansion (OPE) and shifts the mass of glueball to 1.72 ±0.07 GeV.     

Fermion Corrections to Mass of Scalar Glueball in QCD Sum Rule

Contributions of fermions to the mass of the scalar glueball 0^＋＋ are calculated at two-loop level in the framework of QCD sum rules. It slightly changes the coefficients in the operator product expansion （OPE） and shifts the mass of glueball to 1.72 ± 0.07 GeV.     

Next-to-Leading order QCD corrections to charged current charm production and the unpolarized and polarized strange sea at HERA

We discuss fixed target and ISR inclusive photon production and attempt a comparison between theory and experiments. The dependence of the theoretical predictions on the structure functions, and on the renormalization and factorization scales is investigated. The main result of this study is that the data cannot be simultaneously fitted with a single set of scales and structure functions. On the other hand, there is no need for an additional primordial to force the agreement between QCD predictions and experiments, with the possible exception of one data set. Since the data cover almost overlapping kinematical ranges this raises the question of consistency among data sets. A comparative discussion of some possible sources of experimental uncertainties is sketched. Received: 23 November 1998 / Published online: 22 March 1999     

洛伦兹规范条件下对单胶子夸克势的QCD非微扰修正形式

在洛伦兹规范条件下,导出了具有平移不变性的双胶子两点函数真空平均值.利用所获得的双胶子真空期待值,给出了对微扰单胶子交换夸克–夸克势、夸克–反夸克对湮没和夸克–反夸克对激发势的最低阶非微扰QCD修正形式.     

Calculation of a High Order QCD Process-gg to ttgg

We use the permutation group of order 4 to classify the fouith order tree QCD Feynman diagrams, which contribute to the gg to tfgg process. (There are 159 of them.) We also provide new methods to make the color sum, and to check the gauge symmetry of the matrix elements and Feynman parts.     

含QCD修正的p-A碰撞Drell-Yan过程的核效应

在微扰QCD α_s级近似下,采用双重Q²重标度模型,计算了p-A碰撞Drell-Yan截面与p-N碰撞Drell-Yan截面之比,即核效应函数R_QCD(x_A,Q²).计算结果与没有QCD修正的R(x_A,Q²)值比较,在0.03≤x_A≤0.3之间都有不同程度的压低,与实验符合的情况有所改善.说明对核Drell-Yan过程核效应的研究,QCD修正是有一定意义的,并且在计入这种修正后,双重Q²重标度模型仍然是有效的.     

Asymptotics of High Order Noise Corrections

We consider an evolution operator for a discrete Langevin equation with a strongly hyperbolic classical dynamics and noise with finite moments. Using a perturbative expansion of the evolution operator we calculate high order corrections to its trace in the case of a quartic map and Gaussian noise. The asymptotic behaviour is investigated and is found to be independent up to a multiplicative constant of the distribution of noise.     

Order alphas4 QCD corrections to Z and tau decays

Using recently developed methods for the evaluation of five-loop amplitudes in perturbative QCD, corrections of order alphas4 for the nonsinglet part of the cross section for electron-positron annihilation into hadrons and for the decay rates of the Z boson and the tau lepton into hadrons are evaluated. The new terms lead to a significant stabilization of the perturbative series, to a reduction of the theory uncertainly in the strong coupling constant alphas, as extracted from these measurements, and to a small shift of the central value, moving the two central values closer together. The agreement between two values of alphas measured at vastly different energies constitutes a striking test of asymptotic freedom. Combining the results from Z and tau decays we find alphas(MZ)=0.1198+/-0.0015 as one of the most precise and presently only result for the strong coupling constant in order alphas4.