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arXiv 2311.06005hep-phhep-ex
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γ* → M1 M2 γ 中的运动学高扭度修正：带电介子产生

Kinematical higher-twist corrections in $γ^* \to M_1 M_2 γ$: Charged meson production

Bernard Pire, Qin-Tao Song

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12 pages, 10 figures, accepted by Physical Review D
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AI总结：

本文研究正负电子对撞中带电介子产生过程，通过初末态光子发射振幅的干涉提取介子广义分布振幅，并给出包含运动学高扭度修正的完整表达式，数值表明该修正对 BESIII 不可忽略而对 Belle II 很小。

摘要：

介子的广义分布振幅（GDAs）可以通过反应 e⁻ e⁺ → M₁ M₂ γ 来探测，这类反应可在 BESIII 和 Belle II 等正负电子对撞机上实现。在本系列的第一篇论文中讨论了中性介子产生情形之后，本文讨论互补的带电介子（M⁺ M⁻）产生情形，其中可以通过两个竞争过程振幅的干涉来提取关于 GDAs 的完整信息，这两个过程中光子要么在初态发射，要么在末态发射。考虑到带电介子产生的重要性，我们给出了截面干涉项的完整表达式，该干涉项由于其电荷共轭特定性质而在实验上可观测。我们采用两类领头扭度 ππ GDAs 模型来数值估计 e⁻ e⁺ → π⁺ π⁻ γ 过程中干涉项的大小，即一个从 Belle 上 γ* γ → π⁰ π⁰ 的先前实验结果中提取的模型，以及由 QCD 演化方程预言的渐近形式。我们在计算中对螺旋度振幅包含了直到 1/Q² 阶的运动学幂次压低（有时称为运动学高扭度）修正。两类 GDAs 模型均表明，对于 BESIII 上测量的截面干涉项，运动学校正不可忽略，因此若要精确提取 GDAs，有必要将其纳入。另一方面，对于 Belle II 上的测量，运动学校正非常微小，领头扭度-2 的干涉项公式将足以描述微分截面中电荷共轭为奇的部分。

英文摘要：

Generalized distribution amplitudes (GDAs) of mesons can be probed by the reactions $e^- e^+ \to M_1 M_2 γ$, which are accessible at electron-positron colliders such as BESIII and Belle II. After discussing the neutral meson production case in the first paper of this series \cite{Pire:2023kng}, we discuss here the complementary case of the charged meson ($M^+ M^-$) production, where one can extract the complete information on GDAs from the interference of the amplitudes of the two competing processes where the photon is emitted either in the initial or in the final state. Considering the importance of the charged meson production, we present a complete expression for the interference term of the cross section which is experimentally accessible thanks to its charge conjugation specific property. We adopt two types of models for leading twist $ππ$ GDAs to estimate the size of the interference term in the process $e^- e^+ \to π^+ π^- γ$ numerically, namely a model extracted from previous experimental results on $γ^* γ\to π^0 π^0$ at Belle and the asymptotic form predicted by QCD evolution equations. We include in the calculation the kinematical power suppressed (sometimes called kinematical higher-twist) corrections up to $1/Q^2$ for the helicity amplitudes. Both models of GDAs indicate that the kinematical corrections are not negligible for the interference term of the cross section measured at BESIII, thus it is necessary to include them if we try to extract the GDAs precisely. On the other side, the kinematical corrections are very tiny for the measurements at Belle II, and the leading twist-2 formula of the interference term will be good enough to describe the charge conjugation odd part of the differential cross section.

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