在$γp\to p η$的新精确束流不对称PDMATHAAB数据中观测$pη'$尖点
Observation of the $pη'$ Cusp in the New Precise Beam Asymmetry $Σ$ Data for $γp\to p η$
摘要：
在质子光生$η$介子的光束不对称$Σ$的数据报告标记的光子能量从1130到1790 MeV（质量范围从$W=$ 1748 MeV到$W=$ 2045 MeV）。数据覆盖了整个立体角，可以进行精确的力矩分析。对于第一次，一个强大的尖点效应的极化观察已被观察到，是一个在$pη'$阈值[ $E_γ=$ 1447 MeV（$W=$ 1896 MeV）]的分支点奇点的效果。最新的BnGa分波分析包括新的光束不对称性数据，并产生了强烈的指示$N(1895)\frac{1}{2}^-$核子共振，证明了包括所有奇异性的重要性，正确确定分波和共振参数。
英文摘要：
Data on the beam asymmetry $Σ$ in the photoproduction of $η$ mesons off protons are reported for tagged photon energies from 1130 to 1790 MeV (mass range from $W=$ 1748 MeV to $W=$ 2045 MeV). The data cover the full solid angle that allows for a precise moment analysis. For the first time, a strong cusp effect in a polarization observable has been observed that is an effect of a branch-point singularity at the $pη'$ threshold [$E_γ=$ 1447 MeV ($W=$ 1896 MeV)]. The latest BnGa partial wave analysis includes the new beam asymmetry data and yields a strong indication for the $N(1895)\frac{1}{2}^-$ nucleon resonance, demonstrating the importance of including all singularities for a correct determination of partial waves and resonance parameters.
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