质子-质子碰撞中的双π产生--实验总截面及其同位旋分解
Two-Pion Production in Proton-Proton Collisions -- Experimental Total Cross Sections and their Isospin Decomposition
摘要：
在CELSIUS上，从阈能到$T_p$ = 1.36 GeV，对pp碰撞中的2 π介子产生进行了专门的测量研究。已经获得了通道$pnπ^+π^0$、$ppπ^+π^-$、$ppπ^0π^0$以及$nnπ^+π^+$的全截面和微分截面。对于中等入射能量$T_p >$ 1 GeV，即在超出Roper激发但在$ΔΔ$激发开始的区域中，总$ppπ^0π^0$截面落后于理论预测，在1.2 GeV附近相差多达一个数量级，而$nnπ^+π^+$截面比预测大五倍。总截面的同位旋分解在Roper激发区域中表现出类似s沟道的能量依赖性，并且除了$Δ(1232)$之外，同位旋3/2共振也有显著贡献。作为可能的候选者，讨论了$Δ(1600)$和$Δ(1700)$。
英文摘要：
The two-pion production in pp-collisions has been investigated at CELSIUS in exclusive measurements from threshold up to $T_p$ = 1.36 GeV. Total and differential cross sections have been obtained for the channels $pnπ^+π^0$, $ppπ^+π^-$, $ppπ^0π^0$ and also $nnπ^+π^+$. For intermediate incident energies $T_p >$ 1 GeV, i.e. in the region which is beyond the Roper excitation but at the onset of $ΔΔ$ excitation, the total $ppπ^0π^0$ cross section falls behind theoretical predictions by as much as an order of magnitude near 1.2 GeV, whereas the $nnπ^+π^+$ cross section is a factor of five larger than predicted. An isospin decompostion of the total cross sections exhibits a s-channel-like energy dependence in the region of the Roper excitation as well as a significant contribution of an isospin 3/2 resonance other than the $Δ(1232)$. As possible candidates the $Δ(1600)$ and the $Δ(1700)$ are discussed.
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