论文标题
部分可观测时空混沌系统的无模型预测
First measurement of massive virtual photon emission from N* baryon resonances
论文作者
论文摘要
在第二个共振区域中巴里子类似的电磁结构的第一条信息是从未经准反应中的二电(E+ E-)不变性质量和角度分布的测量中获得的GSI的光谱仪(HADE)使用斜向$ _2 $目标上的斜束。我们找到了一个总截面$ = 2.97 $ \ pm $ 0.07data $ \ pm $ 0.21acc $ \ pm $ 0.31zeff $ $ $ b。在补充包含E+ E通道的分析中,该数据集对Baryon时间样过渡的描述提供了至关重要的测试。基于载体中的介子优势幅度,其中包含直接光子和矢量介子($ρ$)耦合到巴里昂的方法提供了与数据的令人满意的协议。通过电磁时间状的巴属转变形式在协变量的观众夸克模型中也获得了一个良好的描述,这表明中森 - 云效应的主导地位。与真实光子相比,DiElectron角分布表现出虚拟光子($γ^*$)与纵向极化的贡献。虚拟光子角依赖性支持j = 3/2的优势,i = 1/2在$γ^*$ n和$ππ$ n通道中都观察到的贡献。
First information on the time-like electromagnetic structure of baryons in the second resonance region has been obtained from measurements of dielectron (e+ e-) invariant-mass and angular distributions in the quasi-free reaction $π-$ p $\rightarrow$ n e+ e- at $\sqrt{s_{πp}}$ = 1.49 GeV with the High Acceptance Di-Electron Spectrometer (HADES) at GSI using the pion beam impinging on a CH$_2$ target. We find a total cross section $σ$ = 2.97 $\pm$ 0.07data $\pm$ 0.21acc $\pm$ 0.31Zeff $μ$b. In complement to the analysis of the inclusive e+ e- channel, this data set provides a crucial test of the description of baryon time-like transitions. Approaches based on a Vector Meson Dominance amplitude containing direct photon and vector meson ($ρ$) couplings to the baryon provide a satisfactory agreement with the data. A good description is also obtained by electromagnetic time-like baryon transition form factors in a covariant spectator-quark model, pointing to the dominance of meson-cloud effects. The dielectron angular distributions exhibit the contributions of virtual photons ($γ^*$) with longitudinal polarization, in contrast to real photons. The virtual photon angular dependence supports the dominance of J=3/2, I=1/2 contributions observed in both the $γ^*$n and the $ππ$n channels.