PANDA/FAIR上粲重子产生的理论研究

In the past few years, several new charmed baryons have been observed in electron-positron collision experiments by Belle, BABAR, and CLEO. However, there is a great deal of controversy about their internal structures. The forthcoming experiments by proton-antiproton collisions at PANDA/FAIR will provide a novel and powerful experimental approach for studying these charmed baryons. Faced with this great opportunity, we need to carry out theoretical studies on charmed baryon production at PANDA/FAIR in advance, since theoretical calculations in this respect are still sparse. Based on a meson-exchange model, we will study contributions of various charmed baryons in a couple of proton-antiproton reactions, and give theoretical predictions of various observables for these reactions, such as total cross sections, differential cross sections, momentum and angular distributions, invariant mass spectra and Dalitz plots. Furthermore, we will evaluate the event rate of every channel. It can be anticipated that these results.would provide valuable information for accurate determination of charmed baryon identity at PANDA/FAIR in the future.

近年来，Belle，BABAR和CLEO合作组在正负电子对撞实验中发现了一系列新的粲重子，对于它们内部结构的解释还存在巨大的争议。PANDA/FAIR利用质子—反质子散射为研究这些粲重子提供了一种全新的实验手段。面临这个重大机遇，我们有必要预先对PANDA/FAIR上粲重子的产生进行理论研究，目前这方面的理论计算还较为缺乏。本项目将以介子交换模型为基础研究各种粲重子激发态在几个主要的反质子－质子反应道中的贡献，并且给出关于反应总截面，微分截面，各种动量和角分布以及末态粒子不变质量谱和达立兹图等物理信息的理论预言，大致估计出各个反应道的事例率。可以预计这些结果将为以后在PANDA/FAIR上精确确定各种粲重子激发态的物理特征提供有价值的理论信息。

本项目中我们计算了PANDA/FAIR上粲重子$\Lamda_c(2880)$的产生率。目前的PDG上$\Lamda_c(2880)$的自旋宇称已被确定为$J^P=5/2^+$，据此我们计算了反应$\bar{p}p \to \bar{\Lamda_c}\Lamda_c(2880)$的总截面，发现它可以达到几百个$\mu$b。考虑到PANDA/FAIR的设计亮度大约是$2 \times 10^{32}cm^{-2}/s$，可以预计在PANDA/FAIR上每天产生的$\Lamda_c(2880)$事例数将会达到$10^9$量级。另外，我们还给出了反应$\bar{p}p \to \bar{\Lamda_c}D^0p$的各种末态粒子不变质量谱和Dalitz图，并对其中的背景贡献（相对于$\Lamda_c(2880)$的产生）进行了粗略分析，都表明$\bar{p}p \to \bar{\Lamda_c}D^0p$是一个很好的研究粲重子$\Lamda_c(2880)$的反应场所。这些研究结果为精确确定$\Lamda_c(2880)$的物理特征提供了有价值的信息。