Study of rare hadronic Lambda_b decays at LHCb.

含有B夸克的重强子的罕见衰变被广泛地用于检验粒子物理的标准模型和寻找新物理的可能效应。利用LHCb实验收集的数据集，标准模型的测试现在也可以用重子衰变进行，但到目前为止，这样的研究相当有限。具体而言，LHC B使用2011年和2012年收集的运行1数据观察到了衰变Lambda_B -> Lambda h h'，其中h和h'是带电的π介子或k介子，并且发现Lambda_B -> Lambda K+ pi-和Lambda_B -> Lambda K+ K-衰变的CP不对称性在很大的不确定性内与零一致。由于早期LHCb结果，在运行2期间收集的数据提供了统计量的大幅增加。此外，LHCb探测器已经升级，计划在未来几年内以大约5倍的瞬时光度运行。在升级过程中，硬件触发器已被移除，以便增加全强子衰变（如Lambda_B -> Lambda h h'）的触发效率。在这个项目中，我们计划利用已经存在的LHC B数据集以及在运行3期间收集的数据来更新Lambda_B -> Lambda h h'衰变的现有测量。除了测量衰变的整个相空间的分支分数和CP不对称性，我们还将探索局部CP不对称性。为此，我们计划通过衰减的振幅分析使用模型无关方法以及模型相关方法。局部CP不对称性提供了更灵敏的方法来测试标准模型，因为可观察到的CP不对称性需要非零强相位，其在衰减的可用相空间上显著变化。本项目的结果将为三体无粲Lambda_B衰变的CP不对称性提供最灵敏的测量，并为b介子衰变的研究提供补充信息。

The rare hadronic decays of heavy hadrons containing b quark have been extensively used to test Standard model of particle physics and search for possible effects of new physics. With datasets collected by the LHCb experiment, tests of the Standard model are now possible also with baryon decays, but up to now such studies are rather limited. Specifically, decays Lambda_b -> Lambda h h' with h and h' being charged pion or kaon has been observed by the LHCb using Run 1 data collected in 2011 and 2012 and CP asymmetry for Lambda_b -> Lambda K+ pi- and Lambda_b -> Lambda K+ K- decays has been found consistent with zero within large uncertainties. Since early LHCb result, data collected during Run 2 provides large increase of statistics. Additionally, the LHCb detector has been upgraded and is planned to run at about 5 times higher instantaneous luminosity over next couple of years. During upgrade, hardware trigger has been removed in order to increase trigger efficiency for fully hadronic decays like Lambda_b -> Lambda h h' . In this project we plan to exploit already existing LHCb dataset together with data collected during Run 3 to update existing measurements on Lambda_b -> Lambda h h' decays. Besides measuring branching fractions and CP asymmetries over whole available phase-space of the decay we will also explore localised CP asymmetries. For this purpose, we plan to use both model independent methods as well as model dependent method through amplitude analysis of the decay. The localised CP asymmetries provide more sensitive way to test the Standard model as the observable CP asymmetry requires non-zero strong phases, which vary significantly over available phase-space of the decay. The results of this project will provide most sensitive measurement of the CP asymmetry in 3-body charmless Lambda_b decays and offer information complementary to that obtained from studies in the b-meson decays.