Strong interaction effects in exclusive B decays

随着大型强子对撞机（LHC）于2013年首次成功运行，以及大量数据的不断分析和发表，B介子（即含有B夸克的介子）的物理学进入了一个令人兴奋的新时代。大型强子对撞机的四个主要实验之一，即大型强子对撞机实验，专门研究B介子。它们众多的衰变通道提供了对标准模型（SM）进行精确测试的机会，也许更有趣的是，发现标准模型之外的新物理。数据采集将在2015年能量峰值和更高亮度时恢复。在未来5年，LHCb合作将以越来越高的精度测量各种可观测数据，显然需要理论输入来解释数据并指导该领域的未来实验。在本研究中，我们关注的是罕见的B衰变到光介子，即B衰变到特定的最终产物。这种衰变特别吸引人，因为它们相对容易在实验中获得，尤其是在大型强子对撞机这样的环境中。另一方面，这种衰变的理论是具有挑战性的，因为它们涉及到强相互作用效应，这些效应是不能用量子色动力学（QCD）中的微扰理论计算的，量子色动力学是强相互作用的基本现代理论。在我们的研究中，我们通过使用一种相对较新的技术来模拟这些效应，该技术涉及利用物理时空中的QCD与称为反德西特（AdS）空间的高维弯曲空间中的弦理论之间的对应关系。这种对应称为AdS/QCD。同时，我们将在这些罕见的B衰变中研究新的物理信号。这些罕见的衰变有时很容易受到更重的粒子的干扰，这些粒子可能在那里，但尚未被发现。我们提出的研究是为了更好地理解这些干扰，然后与大型强子对撞机的实验数据进行比较。这种比较有望给我们提供一些线索，告诉我们如何将SM扩展成一个更完整的理论。通过我们的研究，我们希望为粒子物理学界在大型强子对撞机上发现新的物理现象做出贡献。与此同时，我们正在测试AdS/QCD，它提供了对强子中夸克约束的未解决问题的见解。

With the Large Hadron Collider (LHC) first run successfully completed in 2013 and a wealth of data being continuously analysed and published, the physics of the B mesons, i.e. mesons containing a b quark, has entered a new exciting era. One of the four main experiments at the LHC, namely the LHCb experiment, is dedicated to the study of the B mesons. Their numerous decay channels offer the opportunity to make precision tests of the Standard Model (SM) and perhaps more interestingly, to discover new physics beyond the SM. Data taking will resume in 2015 at peak energy and higher luminosity. In the next 5 years, various observables will be measured with increasing precision by the LHCb collaboration and theory input will clearly be required to interpret the data as well as to guide future experiments in this field. In this research, we focus on rare exclusive B decays to light mesons, i.e. B decays to specific final products. Such decays are especially appealing because they are relatively easy to access experimentally especially in an environment like the LHC. On the other hand, the theory of such decays is challenging because they involve strong interactions effects which are not computable using perturbation theory in Quantum Chromodynamics (QCD), the fundamental modern theory of strong interactions. In our research, we model these effects by using a relatively new technique which involves exploiting a correspondence between QCD in physical spacetime and a string theory in a higher dimensional curved space called anti de Sitter (AdS) space. This correspondence is called AdS/QCD. At the same time, we will investigate signals of new physics in those rare B decays. These rare decays are sometimes quite susceptible to the interference from much heavier particles that may be out there but have not been discovered yet. Our proposed investigation is to have a better understanding of these interferences which can then be compared with the experimental data from the LHC. This comparison will hopefully give us some clues on how the SM can be extended towards a more complete theory. With our research, we hope to contribute to the efforts of the particle physics community to discover new physics at the LHC. At the same time, we are testing AdS/QCD which offers insights into the unsolved problem of confinement of quarks in hadrons.