利用M_T2判别暗物质稳定对称性
Using M_T2 to Distinguish Dark Matter Stabilization Symmetries
摘要：
我们研究了利用对撞机区分具有宇称（Z_2）稳定的暗物质（DM）的模型与DM由其他对称性稳定的模型的潜力，将后者作为Z_3对称性进行说明。关键的观察是，一个重的母粒子在Z_3稳定化对称性下充电，可以衰变成一个或两个DM粒子和标准模型（SM）粒子。这可以与在宇称对称下带电的母粒子的衰变形成对比;通常，衰变链中只出现一个DM粒子。在arXiv：1003.0899中，我们中的一些人研究了来自单个这样的母粒子衰变的可见不变质量的分布，以突出Z_3对称与宇称对称稳定的暗物质候选者的独特特征。我们现在描述一个补充的研究，重点是衰变链的两个母粒子，这是必然存在于这些事件。我们还在分析中包括事件中丢失的能量/动量。对于Z_3对称性稳定的母体，所得到的包容末态可以有两个、三个或四个DM粒子。相反，具有Z_2对称性的模型只能有两个。我们发现，M_T2型变量的分布的形状和边缘，以及事件两侧的可见动量/能量的比值，在区分这些不同的情况下是强大的。
英文摘要：
We examine the potential of using colliders to distinguish models with parity (Z_2) stabilized dark matter (DM) from models in which the DM is stabilized by other symmetries, taking the latter to be a Z_3 symmetry for illustration. The key observation is that a heavier mother particle charged under a Z_3 stabilization symmetry can decay into one or two DM particles along with Standard Model (SM) particles. This can be contrasted with the decay of a mother particle charged under a parity symmetry; typically, only one DM particle appears in the decay chain. In arXiv:1003.0899, some of us studied the distributions of visible invariant mass from the decay of a single such mother particle in order to highlight the resulting distinctive signatures of Z_3 symmetry versus parity symmetry stabilized dark matter candidates. We now describe a complementary study which focuses on decay chains of the two mother particles which are necessarily present in these events. We also include in our analyss the missing energy/momentum in the event. For the Z_3 symmetry stabilized mothers, the resulting inclusive final state can have two, three or four DM particles. In contrast, models with Z_2 symmetry can have only two. We show that the shapes and edges of the distribution of M_T2-type variables, along with ratio of the visible momentum/energy on the two sides of the event, are powerful in distinguishing these different scenarios.
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