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Probing new physics through B meson mixing and decays: highly improved lattice QCD calculation of hadronic matrix elements.

通过 B 介子混合和衰变探索新物理：高度改进的强子矩阵元素的晶格 QCD 计算。

基本信息

批准号：
PP/E006957/1
负责人：
Matthew Wingate
金额：
$ 24.51万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=PP%2FE006957%2F1
关键词：
Probing new physics through meson

项目摘要

The Standard Model of elementary particle physics is incomplete at the moment. What is lacking is a satisfactory explanation of why the weak force governing quark flavor decays, the underlying phenomenon behind nuclear beta decay, is so weak. We have a possible explanation which requires the existence of a Higgs boson, which we should discover at the Large Hadron Collider (LHC) in Geneva, Switzerland in a few years. Even if we do find the Higgs, there are further open questions. They mostly surround the value of the Higgs mass: having introduced such a particle into our model, Standard Model dynamics alone would give the Higgs an incomprehensibly large mass. Perhaps the LHC will produce new particles or phenomena which are not described by the Standard Model and point us in the right direction toward an explanation. There are many candidate models for this 'new physics.' Sorting through them is a complicated task, requiring both high energy experiments, like those at the LHC, and high precision experiments. In particular, these new models generically predict deviant modes of quark flavor decays. Already experiments studying the strange, charmed, and beautiful mesons (K, D, and B) tightly constrain the parameters of these new models. Further precision in flavor physics experiments and theoretical calculations is needed, in concert with the LHC and other high energy experiments, to pare down the candidate models of new physics. Our proposal is to implement new techniques to further reduce theoretical uncertainties in flavor decays. Free quarks are never seen; they are only seen within bound states, called hadrons. Experimentalists measure decay rates of hadrons and need accurate calculations to extract from their measurements parameters governing quark decays. The answers can be obtained from the firmly established theory of strong interactions between quarks, QCD; however, solving QCD to get hadronic properties from quark interactions must be done numerically, using supercomputers. We have worked on developing and employing methods which will allow better calculations with present computational resources. Two of these, called automated lattice perturbation theory and moving nonrelativistic QCD (mNRQCD), are now ready to be used to improve lattice calculations of decays of the B meson, in particular semileptonic and radiative decays (in these decays the final state is only one daughter meson and either a W boson -- which quickly decays to an electron or muon and a neutrino -- or a photon). The ability to have a bottom (or beauty) quark which is moving with respect to the lattice rest frame is a new one, and it allows us to better extract functional dependences on the daughter meson's momentum; this is the role of mNRQCD. Other reactions can be used to measure the same fundamental parameters in different ways. Any discrepany, or mismatch, in these measurements signals the underlying presence of 'new physics' which is then needed to resolve the discrepancy. For this to be feasible, accurate experiment and theory are needed. Our theoretical calculations are designed to reduce errors to the level of a few percent to achieve this goal. Careful tuning of the lattice description of the dynamics of the decay processes are necessary prior to computing the full non-perturbative contribution of QCD to these particle reactions. Such tuning calculations are large and technically complex, and are made possible only by the automation of much of the calculation using object-oriented programming. The outcome is a flexible theoretical approach that will keep pace with experiment in the search for new physics beyond the Standard Model.

基本粒子物理学的标准模型目前还不完整。我们所缺乏的是一个令人满意的解释，为什么控制夸克味衰变的弱力，核β衰变背后的基本现象，是如此之弱。我们有一个可能的解释，这需要希格斯玻色子的存在，我们应该发现在大型强子对撞机（LHC）在日内瓦，瑞士在几年内。即使我们真的找到了希格斯粒子，还有更多悬而未决的问题。它们大多围绕着希格斯粒子的质量值：在我们的模型中引入这样一个粒子后，仅标准模型动力学就会给希格斯粒子一个难以理解的大质量。也许大型强子对撞机会产生新的粒子或现象，而这些粒子或现象是标准模型所不能描述的，并为我们指出正确的解释方向。对于这种新物理学，有许多候选模型。“对它们进行分类是一项复杂的任务，既需要像LHC那样的高能实验，也需要高精度实验。特别是，这些新模型一般预测夸克味衰变的偏离模式。研究奇异、迷人和美丽介子（K、D和B）的实验已经严格限制了这些新模型的参数。在味道物理实验和理论计算方面需要进一步的精确性，与LHC和其他高能实验相一致，以帕雷新物理的候选模型。我们的建议是实施新的技术，以进一步减少风味衰变的理论不确定性。自由夸克是永远看不到的;它们只在被称为强子的束缚态中被看到。实验学家测量强子的衰变率，需要精确的计算来从他们的测量中提取控制夸克衰变的参数。答案可以从夸克之间强相互作用的QCD理论中得到;然而，求解QCD以从夸克相互作用中得到强子性质必须使用超级计算机进行数值计算。我们一直致力于开发和采用的方法，这将允许更好的计算与目前的计算资源。其中两个，称为自动晶格微扰理论和移动非相对论性QCD（mNRQCD），现在可以用来改进B介子衰变的晶格计算，特别是半轻子和辐射衰变（在这些衰变中，最终状态只有一个子介子和一个W玻色子-它很快衰变为电子或μ子和中微子-或光子）。底夸克（或美夸克）相对于格点静止标架运动的能力是一种新的能力，它使我们能够更好地提取子介子动量的函数依赖性;这就是mNRQCD的作用。其他反应可以用于以不同的方式测量相同的基本参数。这些测量中的任何差异或不匹配都标志着“新物理学”的潜在存在，然后需要解决这种差异。为了使这一点可行，需要精确的实验和理论。我们的理论计算旨在将误差减少到百分之几的水平，以实现这一目标。在计算QCD对这些粒子反应的全部非微扰贡献之前，需要仔细调整衰变过程动力学的晶格描述。这种调整计算量大且技术上复杂，并且只有通过使用面向对象的编程使大部分计算自动化才有可能。其结果是一种灵活的理论方法，将在寻找标准模型之外的新物理学时与实验保持同步。