论文标题
$γ^*γ\ to m \ bar m $中的运动学高扭校正校正
Kinematical higher-twist corrections in $γ^* γ\to M \bar M $
论文作者
论文摘要
我们将运动运动更高扭曲（扭曲4）校正估计为$γ^*（q_1）γ（q_2）\ to m（p_1）\ bar {m}（p_2）$ a a弹片，$ q^2 = 2 = -q_1^2 $ and $ q_1^2 $ and $ s =（q_1+q_1+q_1+q_2）$ s $ pse strain stalare或m $ pse，已知该过程将导致扭转中心分解为可扰动的可计算系数函数和广义分布幅度（GDA）。考虑到在Belle和Belle II上可以访问的运动学方面，运动学上的$ S/Q^2 $和$ m^2/q^2 $的较高贡献很重要。我们向$γ^*γ\至π^0π^0 $的横截面的数值估计值与从Belle测量值中提取的$ππ$ GDA以及渐近$ππ$ gda提取的$ππ$ gda，作为研究动力学更正幅度的输入。要查看目标$ m^2/q^2 $的目标质量更正如何影响横截面，我们还通过使用型号$ηη$ gda.in进行$γ^*γ\ toη$的计算。由于$ππ$ gdas是访问Pion Energy-Momentum Tensor（EMT）的最佳方法，因此我们的研究表明，对EMT形式的准确评估需要包括运动学更高扭曲的贡献。
We estimate kinematical higher-twist (up to twist 4) corrections to the $γ^*(q_1) γ(q_2) \to M(p_1) \bar{M}(p_2)$ amplitudes at large $Q^2=-q_1^2$ and small $s=(q_1+q_2)^2$, where $M$ is a scalar or pseudoscalar meson. This process is known to factorize at leading twist into a perturbatively calculable coefficient function and generalized distribution amplitudes (GDAs). The kinematical higher-twist contributions of order $s/Q^2$ and $m^2/Q^2$ turn out to be important in the cross section, considering the kinematics accessible at Belle and Belle II. We present numerical estimates for the cross section for $γ^* γ\to π^0 π^0$ with the $ππ$ GDA extracted from Belle measurements and with the asymptotic $ππ$ GDA as inputs to study the magnitude of the kinematical corrections. To see how the target mass corrections of order $m^2/Q^2$ affect the cross section, we also perform the calculation for $γ^* γ\to ηη$ by using a model $ηη$ GDA.In the range $s> 1$ GeV$^2$, the kinematical higher-twist corrections account for $\sim 15 \%$ of the total cross section, an effect which is not negligible. Since $ππ$ GDAs are the best way to access the pion energy-momentum tensor (EMT), our study demonstrates that an accurate evaluation of EMT form factors requires the inclusion of kinematical higher-twist contributions.
