Matthias Burkardt
The beam charge asymmetry helps to isolate the real part of the deeply virtual Compton scattering (DVCS) amplitude. It is discussed what information can be gained both from the real and imaginary part of the DVCS amplitude.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
继续探索
Status of DVMP, DVCS and GPDs
本文综述了手提袋方法下DVMP的分析及GPD参数化，重点讨论H和E，并展示其在DVCS等硬独家过程及Ji求和规则中的应用。
We describe small-x_Bj deeply virtual Compton scattering measurements at HERA in terms of generalized parton distributions at leading order of perturbation series.
We propose new parameterizations for the border and skewness functions appearing in the description of 3D nucleon structure in the language of Generalized Parton Distributions (GPDs). These parameterizations are constructed in a way to fulfill the basic properties of GPDs, like their reduction to Parton Density Functions and Elastic Form Factors. They also rely on the power behavior of GPDs in the $x \to 1$ limit and the propounded analyticity property of Mellin moments of GPDs. We evaluate Compton Form Factors (CFFs), the sub-amplitudes of the Deeply Virtual Compton Scattering (DVCS) process,…
We review the phenomenological framework for accessing Generalized Parton Distributions (GPDs) using measurements of Deeply Virtual Compton Scattering (DVCS) from a proton target. We describe various GPD models and fitting procedures, emphasizing specific challenges posed both by the internal structure and properties of the GPD functions and by their relation to observables. Bearing in mind forthcoming data of unprecedented accuracy, we give a set of recommendations to better define the pathway for a precise extraction of GPDs from experiment.
We consider deeply virtual Compton scattering (DVCS) on a photon target, in the generalized Bjorken limit, at the Born order and in the leading logarithmic approximation. This leads us to the extraction of the photon anomalous generalized parton distributions (GPDs) \cite{url, DVCSphoton}.
We develop the minimal model of a new leading order parameterization of GPDs introduced by Shuvaev and Polyakov. The model for GPDs H and E is formulated in terms of the forward quark distributions, the Gegenbauer moments of the D-term and the forward limit of the GPD E. The model is designed primarely for small and medium-size values of x_B, x_B \leq 0.2. We examined two different models of the t-dependence of the GPDs: The factorized exponential model and the non-factorized Regge-motivated model. Using our model, we successfully described the DVCS cross section measured by H1 and ZEUS, the m…
We generalize the leading twist theory of nuclear shadowing and calculate quark and gluon generalized parton distributions (GPDs) of spinless nuclei. We predict very large nuclear shadowing for nuclear GPDs. In the limit of the purely transverse momentum transfer, our nuclear GPDs become impact-parameter-dependent nuclear parton distributions (PDFs). Nuclear shadowing induces nontrivial correlations between the impact parameter b and the light-cone fraction x. We make predictions for the deeply virtual Compton scattering (DVCS) amplitude and the DVCS cross section on Pb-208 at high energies. W…
We study incoherent DVCS on $^4$He in the $^4{\rm He}(e,e^{\prime}γp)X$ reaction, which probes medium-modifications of the bound nucleon GPDs and elastic form factors. Assuming that the bound nucleon GPDs are modified in proportion to the corresponding bound nucleon elastic form factors, as predicted in the Quark-Meson Coupling model, we develop an approach to calculate various incoherent nuclear DVCS observables. As an example, we compute the beam-spin DVCS asymmetry, and predict the $x_B$- and $t$-dependence of the ratio of the bound to free proton asymmetries, $A_{\rm LU}^{p^{\ast}}(ϕ)/A_{\…
By assuming factorization of the GPD under the deconvolution integral for the hand-bag diagram, we develop a method of solving this integral beyond the cross-over line. As examples we use explicit models of deeply virtual Compton scattering (DVCS) amplitudes to get solution for relevant GPDs.
The sub-leading power of the scattering amplitude for deeply-virtual Compton scattering (DVCS) off the nucleon contains leading-twist and twist-3 generalized parton distributions (GPDs). We point out that in DVCS, at twist-3 accuracy, one cannot address any individual twist-3 GPD. This complication appears on top of the deconvolution issues familiar from the twist-2 DVCS amplitude. Accessible are exclusively linear combinations involving both vector and axial-vector twist-3 GPDs. This implies, in particular, that the (kinetic) orbital angular momentum of quarks can hardly be constrained by twi…
Within the framework of the Color Glass Condensate model, we evaluate quark and gluon Generalized Parton Distributions (GPDs) and the cross section of Deeply Virtual Compton Scattering (DVCS) in the small-$x_{B}$ region. We demonstrate that the DVCS cross section becomes independent of energy in the limit of very small $x_{B}$, which clearly indicates saturation of the DVCS cross section. Our predictions for the GPDs and the DVCS cross section at high-energies can be tested at the future Electron-Ion Collider and in ultra-peripheral nucleus-nucleus collisions at the LHC.
Extracting Nucleon Resonance Transition GPDs from $e^- N\to e^-γNπ$ Deeply Virtual Compton Scattering
通过深度虚拟康普顿散射研究核子共振过渡GPDs，揭示其对横截面的贡献及对实验分析的意义。
Deeply virtual Compton scattering (DVCS) attracts a lot of interest due to its sensitivity to generalized parton distributions (GPDs) which provide a rich access to the partonic structure of hadrons. However, the practical extraction of GPDs for this channel requires a deconvolution procedure, whose feasibility has been disputed. We provide a practical approach to this problem based on a next-to-leading order analysis and a careful study of evolution effects, by exhibiting shadow GPDs with arbitrarily small imprints on DVCS observables at current and future experimental facilities. This shows …
We present a new model for generalized parton distributions (GPDs), based on the aligned jet model, which successfully describes the deeply virtual Compton scattering (DVCS) data from H1, ZEUS, HERMES and CLAS. We also present an easily implementable and flexible algorithm for their construction. This new model is necessary since the most widely used models for GPDs, which are based on factorized double distributions, cannot, in their current form, describe the DVCS data when employed in a full QCD analysis. We demonstrate explicitly the reason for the shortcoming in the data description. We a…
Extraction of DVCS amplitudes off the nucleon
本研究通过PARTONS框架，采用机器学习的两种建模方法提取核子上的DVCS振幅，检验GPDs普适性并对比格点QCD的减法常数预测，推动理论与现象学的良性循环。
Prospects for GPDs extraction with Double DVCS
本文基于1980年代的方法提出DDVCS振幅的新计算，使其适合数值模拟，并通过PARTONS软件验证了其正确性，为在LO直接测量 $x\neq\pmξ$ 的 GPDs 提供了前景。
Non-diagonal DVCS and transition GPDs: A unified framework for spinless hadron case $γ^* π\to γππ$
本文提出了无自旋强子非对角深度虚康普顿散射 $γ^*π\toγππ$ 的统一框架，基于 $π\toππ$ 跃迁GPDs，建立软π定理与分波展开，利用色散方法约束GPDs，并在JLab@12 GeV下估算了包含 $ρ(770)$ 共振态的截面及角分布。
Non-diagonal DVCS and studies of hadronic structure with $N \to N^*$ transition GPDs
该研究在跃迁 GPD 框架下描述核子至共振态的非对角 DVCS，回顾相关模型并给出 JLab@12GeV 能区可观测量估计，同时探讨 Froissart-Gribov 投影应用。
Non-diagonal DVCS with spinless hadron-to-two-hadron transition $γ^* π\to γππ$
本文提出了一种无自旋核子到两核子过渡的GPDs形式，通过角分布和Omnès表示法构建了现象学模型，用于研究γ* π→γππ过程。
Double DVCS as a window to the complete mapping of GPDs
本研究提出基于旋量技术的双深度虚康普顿散射（DDVCS）振幅计算方法，所得表达式适配数值模拟，并借助PARTONS和EpIC工具给出多个对撞机实验的预测，为直接测量GPD提供新途径。
Having in mind the well-known limitations of certain models of generalized parton distributions (GPDs), we show that the allegedly universal GPDs, describing both deeply virtual Compton scattering (DVCS) and deeply virtual meson production (DVMP) data, fail to describe measurements of deep inelastic scattering. We present a new global DVCS fit that describes reasonably the world data set, which includes now also new measurements from Hall A and CLAS collaborations. We also explicitly illustrate that Compton form factors (CFFs) cannot be unambiguously extracted from photon electroproduction mea…
We perform a microscopic evaluation of nuclear GPDs for spin-0 nuclei in the framework of the Walecka model. We demonstrate that the meson (non-nucleon) degrees of freedom dramatically influence nuclear GPDs, which is revealed in the non-trivial and unexpected A-dependence of DVCS observables. In particular, we find that the first moment of the nuclear D-term, d_A(0) ~ A^2.26, which confirms the earlier prediction of M.Polyakov. We find that in the HERMES kinematics, contrary to the free proton case, the nuclear meson degrees of freedom in large nuclei enhance the nuclear DVCS amplitude which …
Generalized Parton Distributions (GPDs) offer a new way to access the quark and gluon nucleon structure. We advocate the need to supplement the experimental study of deeply virtual Compton scattering by its crossed version, timelike Compton scattering. We review recent progress in this domain, emphasizing the need to include NLO corrections to any phenomenological program to extract GPDs from experimental data.
The feasibility of extracting generalized parton distributions (GPDs) from deeply-virtual Compton scattering (DVCS) data has recently been questioned because of the existence of an infinite set of so-called ''shadow GPDs'' (SGPDs). These SGPDs depend on the process and manifest as multiple solutions (at a fixed scale $Q^2$) to the inverse problem that needs to be solved to infer GPDs from DVCS data. SGPDs therefore pose a significant challenge for extracting GPDs from DVCS data. With this motivation we study the extent to which QCD evolution can provide constraints on SGPDs. This is possible b…
Using a simple model for nuclear GPDs, we study the role of the neutron contribution to nuclear DVCS observables. As an example, we use the beam-spin asymmetry A_{LU}^A measured in coherent and incoherent DVCS on a wide range of nuclear targets in the HERMES and JLab kinematics. We find that at small values of the momentum transfer t, A_{LU}^A is dominated by the coherent-enriched contribution, which enhances A_{LU}^A compared to the free proton asymmetry A_{LU}^p, A_{LU}^A(ϕ)/A_{LU}^p(ϕ)=1.8-2.2. At large values of t, the nuclear asymmetry is dominated by the incoherent contribution and A_{LU…
Variational autoencoder inverse mapper for extraction of Compton form factors: Benchmarks and conditional learning
本文提出用变分自编码器逆映射器（VAIM）及其约束变体（C-VAIM）从DVCS数据中提取康普顿形状因子，验证了与MCMC方法的一致性，并捕捉不同运动学下的相关性，为GPDs提取奠定基础。
Positron initiated deeply virtual Compton scattering (DVCS) off $^4$He and $^3$He nuclei is described. The way the so-called $d-$term could be obtained from the real part of the relevant Compton form factor is summarized, and the importance and novelty of this measurement is discussed. The measurements addressed for $^3$He targets could be very useful even in a standard unpolarized target setup, measuring beam spin and beam charge asymmetries only. The unpolarized beam charge asymmetries for DVCS off $^3$He and $^4$He are also estimated, at JLab kinematics and, for $^4$He, also at a configurat…
We propose measurements of the deeply virtual Compton amplitude (DVCS), gamma* to H H-bar gamma, in the timelike t = (p_{H} + p_{H-bar})^2 > 0 kinematic domain which is accessible at electron-positron colliders via the radiative annihilation process e+ e- to H H-bar gamma. These processes allow the measurement of timelike deeply virtual Compton scattering for a variety of H H-bar hadron pairs such as pi+ pi-, K+ K-, and D D-bar as well as p p-bar. As in the conventional spacelike DVCS, there are interfering coherent amplitudes contributing to the timelike processes involving C= - form factors.…
We study the deeply-virtual Compton scattering (DVCS) process $e^- N \to e^- γπN$ involving the transition between a nucleon and a nucleon resonance in the $πN$ system, within the framework of generalized parton distributions (GPDs). For the four lowest-lying nucleon resonances, $Δ(1232)$, $P_{11}(1440)$, $D_{13}(1520)$, and $S_{11}(1535)$, we express the DVCS amplitude in the Bjorken limit in terms of corresponding nucleon-to-resonance GPDs. Building upon the knowledge of the well studied electromagnetic nucleon-to-resonance transition form factors, which map the quark charge densities in tra…
The impact of potential future measurements of beam charge asymmetries on the current knowledge of Compton form factors is evaluated. Elaborating on the results of a global neural network fit to deeply virtual Compton scattering data, a Bayesian reweighting analysis quantifies the improved determination of the real part of the Compton form factor $\mathcal{H}$. Such an improvement is particularly relevant for the experimental determination of the proton mechanical properties or for universality studies of generalized parton distributions through analyses of virtual Compton scattering in both s…
The inclusion of QCD corrections to the Born amplitude of deeply virtual Compton scattering in both spacelike (DVCS) and timelike (TCS) regimes modifies the extraction process of generalized parton distributions (GPDs) from observables. In particular, gluon contributions are by no means negligible even in the medium energy range accessible at JLab12. We emphasize the complementarity of spacelike and timelike measurements and raise the question of factorization scale dependence of the O(alpha_S) results.
Double DVCS amplitudes including kinematic twist-3 and 4 corrections
本研究计算了（赝）标量靶上包含至运动学twist-4修正的DDVCS振幅，为未来EIC、JLab实验中相关过程的测量及GPDs精确提取提供支撑，并给出π介子靶的初步数值估计。
Systematic description of hadron's response to non-local QCD probes: Froissart-Gribov projections in analysis of deeply virtual Compton scattering
本研究重新探讨Froissart-Gribov投影在深度虚康普顿散射分析中的应用，首次建立自旋1/2靶的该投影与广义部分子分布的关联，结合实验数据给出首个数值估计，为强子对非定域QCD探针响应的系统描述提供方法支撑。
Can we measure Double DVCS at JLab and the EIC?
本文评估在 JLab 和 EIC 上测量 DDVCS 的可行性，通过多种 GPD 模型和 EpIC 模拟表明非极化与极化轻子束可观测量敏感且事件数可观。
Deeply Virtual Compton Scattering at Future Electron-Ion Colliders
本文通过模拟EicC和EIC上的DVCS过程，并参照HERMES方法比较模型与不对称性伪数据，给出了质子中上、下夸克总角动量的模型依赖约束。
The measurement of nuclear generalized parton distributions (GPDs) in hard exclusive processes, such as deeply virtual Compton Scattering (DVCS), will be one of the main achievements of a new generation of experiments at high luminosity, such as those under way at the Jefferson Laboratory (JLab) with the 12 GeV electron beam and, above all, those planned at the future Electron Ion Collider. The CLAS collaboration at JLab has recently demonstrated the possibility to disentangle the two different channels of nuclear DVCS, the coherent and incoherent ones, a first step towards the measurement of …
Recently, coherent deeply virtual Compton scattering (DVCS) off $^3$He nuclei has been proposed to access the neutron generalized parton distributions (GPDs). In Impulse Approximation (IA) studies, it has been shown, in particular, that the sum of the two leading twist, quark helicity conserving GPDs of $^3$He, $H$ and $E$, at low momentum transfer, is dominated by the neutron contribution, so that $^3$He is very promising for the extraction of the neutron information. Nevertheless, such an extraction could be not trivial. A technique, able to take into account the nuclear effects included in …
It has been recently proposed to study coherent deeply virtual Compton scattering (DVCS) off 3He nuclei to access neutron generalized parton distributions (GPDs). In particular, it has been shown that, in Impulse Approximation (IA) and at low momentum transfer, the sum of the quark helicity conserving GPDs of 3He, H and E, is dominated by the neutron contribution. This peculiar result makes the 3He target very promising to access the neutron information. We present here the IA calculation of the spin dependent GPD tilde-H of 3He. Also for this quantity the neutron contribution is found to be t…
Sensitivity of Double Deeply Virtual Compton Scattering observables to GPDs
本文研究极化电子/正电子束轰击极化质子靶时DDVCS可观测量对螺旋度守恒质子GPDs的敏感性，并基于VGG与GK19模型评估CEBAF和EIC的测量前景。
We study the exclusive photoproduction of an electron-positron pair on a neutron target in the Jefferson Lab energy domain. The reaction consists of two processes: the Bethe-Heitler and the Timelike Compton Scattering. The latter process provides potentially access to the Generalized Parton Distributions (GPDs) of the nucleon. We calculate all the unpolarized, single- and double-spin observables of the reaction and study their sensitivities to GPDs.
Generalized Parton Distributions offer a new way to access the quark and gluon nucleon structure. We review recent progress in this domain, emphasizing the need to supplement the experimental study of DVCS by its crossed version, timelike Compton scattering (TCS), where data at high energy should appear thanks to the study of ultraperipheral collisions at the LHC. This will open the access to very low skewness quark and gluon GPDs. Our leading order estimates show that the factorization scale dependence of the amplitudes is quite high. This fact demands the understanding of higher order contri…
We compute the structure function, transverse momentum dependent parton distributions (TMDs), and generalized parton distributions (GPDs) for the physical photon from the light-front quantum electrodynamics (QED) Hamiltonian, determined for its constituent bare photon and electron-positron Fock components within the Basis Light-Front Quantization framework. After performing nonperturbative renormalization, we obtain a good quality description of the perturbative QED properties of the photon, as well as good agreement with the experimental data for the photon's structure function. We also inves…
Transversity Generalized Parton Distributions of $Δ$ with the Diquark Spectator Model
首次利用双夸克旁观者模型计算了$Δ^+$同位异重素的夸克张量广义部分子分布（GPDs），预测了张量电荷，并探讨了其在深度虚康普顿散射等实验过程中的研究前景。
扫码添加微信好友，提出您的宝贵建议 👇
💡 备注请填写：网站反馈
发表机构由 AI 从论文文本抽取，如发现错误，欢迎反馈修正建议。