We report a measurement of the ${\pi }^{-}$ photoproduction beam asymmetry for the reaction $\vec{\gamma }p\to {\pi }^{-}{\mathrm{\Delta }}^{++}$ using data from the GlueX experiment in the photon beam energy range 8.2–8.8 GeV. The asymmetry $\mathrm{\Sigma }$ is measured as a function of four-momentum transfer $t$ to the ${\mathrm{\Delta }}^{++}$ and compared to phenomenological models. We find that $\mathrm{\Sigma }$ varies as a function of $t$: negative at smaller values and positive at higher values of $\left|t\right|$. The reaction can be described theoretically by $t$-channel particle exchange requiring pseudoscalar, vector, and tensor intermediaries. In particular, this reaction requires charge exchange, allowing us to probe pion exchange and the significance of higher-order corrections to one-pion exchange at low momentum transfer. Constraining production mechanisms of conventional mesons may aid in the search for and study of unconventional mesons. This is the first measurement of the process at this energy.

中文翻译：

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Eγ= 8.5GeV时质子上π-Δ++光生的束不对称性的测量

我们报告了对 ${\pi }^{-}$ 反应的光产生束不对称 $\vec{\gamma }p\to {\pi }^{-}{\mathrm{\Delta }}^{++}$使用来自GlueX实验的数据在8.2–8.8 GeV的光子束能量范围内。不对称$\mathrm{\Sigma }$ 被测量为四动量传递的函数 $Ť$ 到 ${\mathrm{\Delta }}^{++}$并与现象学模型进行比较。我们发现$\mathrm{\Sigma }$ 因...而异 $Ť$：值较小时为负，值较高时为正 $\left|Ť\right|$。该反应理论上可以通过$Ť$通道粒子交换需要伪标量，矢量和张量中介。特别是，这种反应需要电荷交换，这使我们能够探究介子交换以及在低动量传递时对一介子交换进行高阶校正的重要性。限制常规介子的生产机制可能有助于寻找和研究非常规介子。这是在此能量下对过程的首次测量。