论文标题
$γp\至π^0π^0 p $反应的目标和梁目标不对称
Target and beam-target asymmetries for the $γp \to π^0 π^0 p$ reaction
论文作者
论文摘要
背景：Pion Pairs的光生源可通过激发中间状态研究核子共振的顺序衰减。这样的衰减很重要，例如对于夸克模型中振荡器既激发振荡器又在两步过程中取消兴奋的状态。但是，对多及最终状态的分析非常困难，并且需要比未脱光化的横截面测量值更多。目的：鉴于反应$γp\至π^0π^0 p $的目标和梁目标极化的共振贡献的实验研究和模型分析。方法：研究的靶标（单）和梁目标（双重）极化不对称，以依赖几个参数。实验是使用圆极化光子束和横向极化的固态丁醇靶标在Mainz Microtron（MAMI）上进行的。用水晶球和水龙头探测器分析反应产物。结果：所研究的是极化可观察的PY（非极化束，目标极化）和PX（圆极化的束，靶向X方向的靶极化），它们类似于T（目标不对称）和F（梁靶向不对称）的单个pion产生。用三种独立方法分析了不对称性，揭示了系统的不确定性。
Background: Photoproduction of pion pairs allows to study sequential decays of nucleon resonances via excited intermediate states. Such decays are important e.g. for states which in the quark model have both oscillators excited and de-excite them in a two-step process. However, analyses of multi-meson final states is difficult and requires more than unpolarized cross section measurements. Purpose: Experimental study and model analysis in view of resonant contributions of target and beam-target polarization observables for the reaction $γp \to π^0 π^0 p$. Methods: Investigated were target (single) and beam-target (double) polarization asymmetries in dependence of several parameters. The experiments were performed at the Mainz Microtron (MAMI) using circularly polarized photon beams and transversally polarized solid-state butanol targets. The reaction products were analyzed with the Crystal Ball and TAPS detectors. Results: Studied were the polarization observables Py (unpolarized beam, target polarized in y direction) and Px (circularly polarized beam, target polarized in x direction), which are similar to T (target asymmetry) and F (beam-target asymmetry) for single pion production. The asymmetries were analyzed with three independent methods, revealing systematic uncertainties.
