Light-front holographic QCD and exclusive B decays

光前全息 QCD 和独特的 B 衰变

• 批准号: SAPIN-2017-00031
• 负责人: Sandapen, Ruben
• 金额: $ 1.09万
• 依托单位: Mount Allison University
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=675584
• 关键词: Light; front; holographic; QCD; exclusive

The Standard Model (SM) of particle physics has successfully withstood decades of intensive testing culminating in the long-awaited discovery of the Higgs boson in 2012 at the LHC. Yet, we know that the SM is incomplete since it does not accommodate gravity and neither does it account for neutrino oscillations, dark matter and for the matter/antimatter asymmetry. Despite intensive efforts, to this date no New Physics (NP) discoveries have been made at the LHC. However, an intriguing number of anomalies, i.e. discrepancies between the data and SM predictions, have been reported in rare exclusive B decays. These are decays of the B meson (containing a heavy b quark) to a lighter meson (no b quark) accompanied by a photon or a pair of leptons. These exclusive decays are relatively clean to measure experimentally but the theory behind them is challenging. There are two reasons for this: first, although we are able to compute (using perturbation theory) the underlying b-quark decay in the SM, our final predictions for observables have a residual dependence on an energy scale called the renormalization scale thus introducing a systematic uncertainty. Secondly, quarks and gluons are permanently confined into mesons and this has to be carefully accounted for using non-perturbative methods.******The LHC Run II has started in 2015 and in the next five years, the precision of the data is expected to at least double. These more precise LHC data will be complemented by independent measurements from the Belle II detector at the SuperKEKB collider in Japan scheduled to start taking data in 2017. Clearly theory input will be essential to interpret the forthcoming data as well as to guide future experiments. In this research, we aim to increase the reliability of our theoretical predictions for the rare exclusive B decays in two ways. First, we are applying a new theoretical procedure, the so-called Principle of Maximum Conformality, to reduce the renormalization scale uncertainty. Thus, our research can help to identify unambiguously NP signals in these rare decays. Secondly, we are using an alternative (and complementary) non-perturbative method, known as light-front holography, to account for the confinement of quarks and gluons in mesons.******Besides its phenomenological applications, light-front holography in itself is worth investigating. It is an example of what are known as holographic dualities, i.e. mathematical equivalences between strongly-coupled quantum theories in physical spacetime and weakly-coupled gravitational theories in higher dimensional spaces. It may well be that these dualities have a deeper physical meaning aside from being mere mathematical tools. In this research, we also aim to explore the underlying links between light-front holography and another standard non-perturbative method. This will help to understand better the unsolved problem of quark confinement in hadrons.

粒子物理学的标准模型 (SM) 已成功经受了数十年的密集测试，最终于 2012 年在大型强子对撞机上发现了期待已久的希格斯玻色子。然而，我们知道 SM 是不完整的，因为它不能容纳重力，也不能解释中微子振荡、暗物质和物质/反物质不对称性。尽管付出了巨大的努力，迄今为止大型强子对撞机尚未取得任何新物理学（NP）发现。然而，在罕见的独家 B 衰变中报告了大量有趣的异常现象，即数据与 SM 预测之间的差异。这些是 B 介子（包含重 b 夸克）到较轻介子（无 b 夸克）的衰变，并伴随着一个光子或一对轻子。这些独特的衰变通过实验测量相对干净，但其背后的理论具有挑战性。造成这种情况的原因有两个：首先，虽然我们能够计算（使用微扰理论）SM 中潜在的 b 夸克衰变，但我们对可观测量的最终预测对称为重整化尺度的能量尺度具有剩余依赖性，因此引入了系统的不确定性。其次，夸克和胶子被永久限制在介子中，必须使用非微扰方法仔细考虑这一点。******LHC Run II 于 2015 年开始，在接下来的五年中，数据的精度预计至少翻倍。这些更精确的大型强子对撞机数据将得到日本 SuperKEKB 对撞机 Belle II 探测器的独立测量的补充，该探测器计划于 2017 年开始采集数据。显然，理论输入对于解释即将到来的数据以及指导未来的实验至关重要。在这项研究中，我们的目标是通过两种方式提高我们对罕见的独家 B 衰变的理论预测的可靠性。 首先，我们应用一种新的理论程序，即所谓的最大共形原理，来减少重正化尺度的不确定性。因此，我们的研究可以帮助明确识别这些罕见衰变中的 NP 信号。其次，我们正在使用另一种（和补充的）非微扰方法，称为光前全息术，来解释夸克和胶子在介子中的限制。******除了其现象学应用之外，光前全息术本身就值得研究。这是所谓的全息对偶性的一个例子，即物理时空中的强耦合量子理论与高维空间中的弱耦合引力理论之间的数学等价。除了纯粹的数学工具之外，这些对偶性很可能具有更深层次的物理意义。在这项研究中，我们还旨在探索光前全息术和另一种标准非微扰方法之间的潜在联系。这将有助于更好地理解强子中尚未解决的夸克禁闭问题。