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文章阐明微扰色动力学在π介子虚Compton散射过程中的应用性问题.在此过程中,量子色动力学耦合常数除了端点奇点之外还有中心区域的奇点.于是引进一套简单的技术来判断这些奇点的贡献,并认为这些贡献在一定能标上不妨碍微扰色动力学的应用.提出“工作点”判断法来论证微扰色动力学何时对某个遍举过程是适用的.不同的π介子分布振幅的适用性被详细的考察.得到10 GeV2时微扰量子色动力学开始工作;如果放宽限制,工作点将只有4 GeV2. 相似文献
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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. 相似文献
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在α粒子模型下用Glauber理论计算了800MeV的P-40Ca散射微分截面,分析本领和自旋旋转参数,结果与实验较好地符合,文中还分析了p-α振幅中相因子的影响. 相似文献
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计算和比较了26Mg+244Cm, 27Al+243Am和32S+238U3个反应系统的俘获截面和复合核270Hs形成截面. 在俘获截面计算中, 考虑了靶核形变效应. 穿越库仑势垒后, 反应系统由熔合谷进入不对称裂变谷. 只有越过不对称裂变谷中的条件鞍点的事件才进入复合核组态. 我们用考虑中子流动和径向运动的二参量Smoluchowski扩散方程来处理中间阶段的动力学过程. 此外, 还计算了经4n蒸发形成超重核266Hs的截面. 研究表明, 入射道的势垒分布, 中间阶段的条件鞍点高度对俘获截面, 复合核形成几率, 以及最终的超重核形成截面有显著影响. 相似文献
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对整个中能区现有的质子与4He原子核散射的实验数据(微分截面和极化能力)进行了系统的振幅分析,给出了一组参数化的唯象振幅.这些振幅对于利用中能质子研究原子核的α粒子结构问题是必要的输入量. 相似文献
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本文运用量子色动力学微扰理论讨论了γ-p碰撞中质子内胶子分布对康普顿效应的影响。计算结果表明质子中胶子分布函数按幂次变化对康普顿的QED计算影响不大,可以采用方便的胶子分布函效形式来进行估算。 相似文献
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Xian-Ming Liu Zhong-Xu Zhai Kui Xiao Wen-Biao Liu 《The European Physical Journal C - Particles and Fields》2012,72(7):1-9
We study the deeply virtual Compton scattering off a spin-one particle, as the case for the coherent scattering off a deuteron target. We extend our approach, formulated initially for a spinless case, and discuss the role of twist three contributions for restoring the gauge invariance of the amplitude. Using twist three contributions and relations, which emanate from the QCD equations of motion, we derive the gauge invariant amplitude for the deeply virtual Compton scattering (DVCS) off hadrons with spin 1. Using the derived gauge invariant amplitude, the single spin asymmetry is discussed. 相似文献
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D. Amrath M. Diehl J. P. Lansberg 《The European Physical Journal C - Particles and Fields》2008,58(2):179-192
We study deeply virtual Compton scattering on a virtual pion that is emitted by a proton. Using a range of models for the
generalized parton distributions of the pion, we evaluate the cross section, as well as the beam spin and beam charge asymmetries
in the leading-twist approximation. Studying Compton scattering on the pion in suitable kinematics puts high demands on both
beam energy and luminosity, and we find that the corresponding requirements will first be met after the energy upgrade at
Jefferson Laboratory. As a by-product of our study, we construct a parameterization of pion generalized parton distributions
that has a non-trivial interplay between the x and t dependence and is in good agreement with form factor data and lattice calculations. 相似文献
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M. Kuroda D. Schildknecht 《The European Physical Journal C - Particles and Fields》2004,37(2):205-222
Based on the generic two-gluon-exchange dynamical mechanism for deeply inelastic scattering at low
, we stress the intimate direct connection between the total virtual photoabsorption cross section, deeply virtual Compton
scattering and vector-meson electroproduction. A simple expression for the cross section for deeply virtual Compton scattering
is derived. Parameter-free predictions are obtained for deeply virtual Compton forward scattering and vector-meson forward
production, once the parameters in the total virtual photoabsorption cross section are determined in a fit to the experimental
data on deeply inelastic scattering. Our predictions are compared with the experimental data from HERA.
Received: 16 February 2004, Revised: 16 July 2004, Published online: 2 September 2004
Supported by Deutsche Forschungsgemeinschaft, contract number schi 189/6-2.
An erratum to this article is available at . 相似文献
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B. Pasquini D. Drechsel M. Vanderhaeghen 《The European physical journal. Special topics》2011,198(1):269-285
We review recent developments in the theoretical investigation of the nucleon polarizabilities. We first report on the static
polarizabilities as measured in real Compton scattering, comparing and interpreting the results from various theoretical approaches.
In a second step, we extend the discussion to the generalized polarizabilities which can be accessed in virtual Compton scattering,
showing how the information encoded in these quantities can provide a spatial interpretation of the induced polarization densities
in the nucleon. 相似文献
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We formulate the low-energy theorem for virtual Compton scattering off a nucleon and examine its consequences for generalized nucleon polarizabilites. As a result of a new, model-independent definition of the low-energy limit for doubly virtual Compton scattering, all generalized sum rules of the nucleon have a continuous limit for real photons and obtain contributions from the t channel that were not included previously. 相似文献
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We discuss the low-energy behaviour of the virtual Compton scattering amplitude off a spin-zero target. We first compare various
methods of obtaining a low-energy expression based either on the soft-photon approximation or the use of Ward-Takahashi identities.
We point out that structure-dependent terms are defined with respect to a low-energy approximation of the pole terms, which
commonly is separated from the full amplitude. We derive a general expression for the structure-dependent terms in an expansion
in terms of the momenta and of the initial and final virtual photon, respectively, up to and including terms of order . At order two terms appear that are related to the usual electric and magnetic polarizabilities of real Compton scattering. At order
we find nine new structures of which five can only be determined using virtual photons.
Received October 23, 1997; accepted for publication December 29, 1997 相似文献
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We present a calculation of the virtual Compton scattering amplitude for the pseudoscalar meson octet in the framework of chiral perturbation theory at O(p 4). We calculate the electromagnetic generalized polarizabilities and compare the results in the real Compton scattering limit to available experimental values. Finally, we give predctions for the differential cross section of electron-meson bremsstrahlung. 相似文献