大型强子对撞机上的新物理研究

The CERN Large Hadron Collider (LHC) has been operating for over one year. With the physics results produced at the machine, theoretical particle physics has entered an exciting era of LHC. This energy frointier machine is expected to provide direct evidence to probe the physics mechanism behind spontaneous electroweak gauge symmetry breaking and study the consitutes of the cosmic dark matter. There are currently two experimental hints from the LHC released results, a 2-3 sigma excess of 125 GeV Higgs in diphoton and four-lepton channels; possible large direct CP violation in the D-meson decays. In this proposal, we will study the physics models directly relevant to these experimental hints.The first example is supersymmetry. Low energy supersymmetry theory is pushed a small corner in parameter space by the finding of 125 GeV Higgs and the enhanced diphoton production. We will study in more details on these scenarios which predicts 125 GeV Higgs of twice diphoton prediction with respect to the SM one, and on the whether the corresponding scecnarios are consistent with various other constraints like relic abundance of neutralino dark matter or direct search of supersymmetry at colliders including the LHC. The second example is a scenario of electroweak symmetry breaking with enhanced Yukawa couplings like bosonic Technicolor models. We will study its predictions at the LHC in particular the implications over the Higgs searches. We propose to find channels to measure Yukawa coupling only, for instance, ttbar plus Higgs production with Higgs decaying into tau pairs. We will also continue our study on the top quark sector, using top quark as a tool to study new physics models or new physics theory directly related to top quarks. In summary, we will study models that can explain the direct findings at the LHC as well as their phenomenological implications on other experiments or theoretical implications on the ultra-violet theories.

大型强子对撞机已经运行超过一年时间,其提供的各种物理结果,将会对粒子物理理论的发展产生深远的影响。该实验将为研究弱电对称性破缺机制,寻找宇宙暗物质本原等重要问题提供直接的实验检验。本项目研究基于大型强子对撞机实验数据的几类新物理唯象模型如低能超对称，Fermiophobic弱电对称性破缺，顶夸克相关的新物理模型等。现有的两个实验迹象分别是2-3个西格玛在125GeV左右的类似Higgs和超过3个西格玛的D介子衰变中的CP破坏。这两个实验迹象对新物理模型构造都有重要的指导意义。125GeV Higgs的双光子道与四轻子道的数据对低能超对称理论有严格限制，加上宇宙暗物质等限制，可能最终指向bino-stau联合湮灭这个对撞机非常难检验的区间。本项目将研究如何寻找这样的机制。如果W质量起源有fermiophobic成分，现有观测不足以区分。本项目还将研究如何利用测量汤川耦合的过程区分这样的模型。

2013-2016年度正值大型强子对撞机实验的第一次运行阶段，实验在希格斯性质测量，新物理信号寻找等方面积累了大量的数据，我们在基金委的资助下，紧扣大型强子对撞机的数据，分别在希格斯物理，大型强子对撞机物理，中微子物理，重味物理以及暗物质限制等方面开展了工作。希格斯物理方面，我们研究了新物理模型对希格斯双光子衰变的影响，讨论了螺旋度压低的重味物理过程和希格斯汤川耦合修正之间的对应关系。大型强子对撞机物理方面，我们研究由参加强相互作用的亚稳态粒子形成的新强子共振态及其衰变到双光子末态的预言，超对称模型的模拟中引入极化信息的简单方法。中微子模型方面，我们讨论了TeV能标新轻子二重态模型以及纯轻W对测量对其的限制，我们另外又讨论了将未来的正负电子对撞机改成电子电子对撞以研究W-W-的产生确定中微子Majorana性质的潜在可能。另外我们还在重味物理以及自旋3/2的暗物质模型及限制方面开展了工作。