On extra neutral and charged Higgs bosons at the LHC

The properties of 125 GeV new particle, which was discovered in 2012 at the Large Hadron Collider (LHC), are found to be consistent with those of the Higgs boson in the standard model (SM). Hereafter the new particle is dubbed as SM-like Higgs boson. However there is still spacious room for physics beyond the SM (BSM) due to the limited energy and luminosity of the LHC. With more data, experiments will scrutinize whether the new particle is indeed the SM one or not. At the same time, one believes that discovery of the SM-like Higgs boson is just the start of the new era of particle physics. The predominant topic is whether there are other new Higgs bosons as speculated in various BSM models. In this short review, we will describe the current status of Higgs physics at the LHC and several BSM models which contain more Higgs sectors. In literatures, there are numerous studies on extended Higgs sector and a comprehensive review is beyond the scope of this review. Instead, we will present two latest studies on Higgs physics: (1) how to detect the charged Higgs boson and measure \(\tan \beta \) after including the top polarization information, and (2) how to discover the extra neutral Higgs boson via the pair production of SM-like Higgs boson.     

LHC上的重大进展——发现Higgs粒子

2012年7月,欧洲核子中心CERN的大型强子对撞机（LHC）上的CMS与ATLAS实验组相继宣布发现了质量在125GeV附近的新粒子．其后,基于更多的数据和更深入的分析,CERN于2013年3月14日发表声明：“新的结果表明CERN发现的粒子是Higgs玻色子”．在简要回顾标准模型Higgs的理论以及在LHC之前的寻找结果之后,我们将结合近年来参-9CMS实验及Higgs寻找的工作经历,详细介绍LHC上Higgs玻色子的发现历程,以及对Higgs质量、耦合、自旋、宇称等性质的测量现状．     

在LHC上探测Higgs玻色子的反常规范耦合

探测Higgs玻色子的反常耦合是不依赖于具体模型且无遗漏地探测超出标准模型的新物理效应的有效办法.探测Higgs玻色子的反常规范耦合更有特殊意义,它与电弱对称破缺的机制相关.我们曾提出在LHC上通过WW散射来探测Higgs玻色子反常规范耦合的灵敏方法.本文简要综述这种方法的物理思想及所得结论.     

B_s→μ~+μ~-对LHC寻找Higgs粒子的影响

研究在各种实验限制下CMSSM参数空间,尤其是以双比率R形式探讨Bs→μ+μ-的限制,并讨论了该参数空间的唯象学性质.得出在30fb-1积分亮度下,LHC只能发现一个与标准模型Higgs粒子性质非常相似的粒子(即通常文献所言Lone Higgs Scenario)这一重要结论.     

A precision measurement of the mass of the top quark

The standard model of particle physics contains parameters--such as particle masses--whose origins are still unknown and which cannot be predicted, but whose values are constrained through their interactions. In particular, the masses of the top quark (M(t)) and W boson (M(W)) constrain the mass of the long-hypothesized, but thus far not observed, Higgs boson. A precise measurement of M(t) can therefore indicate where to look for the Higgs, and indeed whether the hypothesis of a standard model Higgs is consistent with experimental data. As top quarks are produced in pairs and decay in only about 10(-24) s into various final states, reconstructing their masses from their decay products is very challenging. Here we report a technique that extracts more information from each top-quark event and yields a greatly improved precision (of +/- 5.3 GeV/c2) when compared to previous measurements. When our new result is combined with our published measurement in a complementary decay mode and with the only other measurements available, the new world average for M(t) becomes 178.0 +/- 4.3 GeV/c2. As a result, the most likely Higgs mass increases from the experimentally excluded value of 96 to 117 GeV/c2, which is beyond current experimental sensitivity. The upper limit on the Higgs mass at the 95% confidence level is raised from 219 to 251 GeV/c2.     

Top夸克，实验测量与唯象研究（Ⅱ）

本文计算了对辐射修正因子△ｒ的０（αα＿３）和０（α￣２）双圈贡献，并把包含了双圈贡献的△ｒ理论值和△ｒ的实验测定值（△ｒ）＿（ｅｘｐ）进行了机会，导出了对Ｔｏｐ夸克质量Ｍｔ的限制，然后根据几率分布计算得到了对Ｍｔ比较严格的上限限制：当Ｈｉｇｇｓ粒子质量Ｍ＿Ｈ＝１５０ＧｅＶ时，Ｍｔ＜１７７ＧｅＶ（９５％Ｃ．Ｌ）。     

探索质量起源与2013年诺贝尔物理学奖

 本文首先介绍1964年Peter Higgs及Francois Englert等提出的Higgs机制及其在电弱标准模型的建立中所起的重要作用,说明为什么2012年实验上发现一个Higgs玻色子后,2013年的诺贝尔奖就颁给Englert和Higgs。然后指出,接下来重要的是在实验上进一步探测这个Higgs玻色子对标准模型预言的偏离,和探索可能的新物理。LHC的升级实验和将来的高能对撞机对实现这个目标至关重要。最后展望粒子物理的发展前景。     

新的规范玻色子和直线对撞机上顶夸克对产生的自旋修正

在非对角基下,研究了3-3-1模型所预言的中性规范玻色子Z′对顶夸克对产生的自旋相关过程的修正.结果表明Z′的改变可以对t↑-t↓和t↓-t↑散射截面产生主要修正,而且在非对角基下散射截面在相同自旋态下是不为零的.因此我们希望,Z′对顶夸克对产生的自旋结构的贡献可以在未来的ILC实验上探测到,并且可以区别不同的3-3-1模型.     

Has the Higgs boson been discovered?

The standard model of particle physics describes the strong and electroweak interactions of fermions (spin-1/2), gauge bosons (spin-1) and a final vital ingredient--the spin-0 Higgs boson, which gives masses to the other particles. But the Higgs boson has yet to be discovered, and its own mass is not specified by the theory. There is some evidence (although statistically not very significant) for its detection at a mass of about 115 GeV/c2, from electron-positron interactions at LEP (the Large Electron Positron collider). Indirect methods can also be used to constrain the mass of the Higgs boson, because it affects other observable quantities (for example, the mass of the W boson and some measurable properties of the Z boson). An indirect determination of the Higgs boson mass from the most recent measurements of such quantities yields a value compatible with 115 GeV/c2, but with some important caveats arising from inconsistencies in the present data.     

SU(3)简易群模型和直线对撞机上顶夸克对产生的自旋修正

在SU（3）简易群模型的框架下,研究了在直线对撞机上质心能量为800GcV时顶夸克对通过e^＋ e^→tt产生的自旋修正．结果表明新的规范玻色子ZH对t↑t↓ 态和 t↓t↑态的产生截面能产生明显的修正;当1TeV≤MZH≤2TeV和cosθ〈0时,相对修正参数的值R（t↑t↓ ）和（ t↓t↑）分别在18．16%-3．45％和47．6%-3．4%的范围．因而在大部分参数空间内,新的规范玻色子也对顶夸克对产生的自旋修正影响应该可以在未来的高能直线对撞机上被观测到．     

标准模型下γγ→tH过程的散射截面的树图级计算

笔者在标准模型下计算了两个光子的碰撞过程中产生top夸克对和一个附带的中性Higgs粒子的最低阶的散射截面.该过程从理论上可以在新一代的线性对撞机上实现.ttH的产生是探索中性Higgs粒子和Top夸克耦合与Higgs粒子质量关系的唯一的直接途径.讨论该过程对于理解higgstop耦合具有重要的意义.通过理论计算得到的结果是当质心能量的取值在0.5～2TeV之间,而Higgs粒子的质量在120～200GeV时,其散射截面大致在1～3fb之间.在实验条件达到相应的条件时,利用理论计算结果能为实验上寻找Higgs粒子提供帮助.     

TC理论与B—混合

本文应用动力学破缺理论讨论了B_d—B_d混合效应。动力学破缺弱电理论是指具有夸克与复合脣Goldstone(P.G)玻色子之间唯象耦合的最小Technicolor(TC)理论。PG玻色子对混合效应的贡献被QCD色因子所加强。PG玻色子的贡献在参数的较广范围内起着支配的作用。若KM矩阵元不取最小允许值,在PG玻色子质量及t夸克质量的一定取值范围内PG,玻色子与W玻色子的贡献之和可以对观测到的混合值给出满意的解释。     

t夸克圈对TC理论中P~（0a）_3→gγ衰变宽度的影响

考虑到ｔ夸克圈的影响后，我们推出了ＴＣ理论的中性格尔斯通粒子Ｐ￣（０ａ）＿３与光子、胶子的反常耦合拉氏量，计算结果表明ｔ夸克圈有效地增加这种反常耦合强度从而增大了Ｐ￣（０ａ）＿３→ｇγ的衰变宽度，有利于在ＨＥＲＡ中探测Ｐ￣（０ａ）＿３粒子。     

New gauge boson and spin correction of top quark pair production at ILC

Based on the SU（3） simple group model , we study the spin correction of the top quark pair production at the high energy linear e＋ecollider （ILC） with a center-of-mass energy √s=800GeV. Our numerical results show that the gauge boson Z. exchange generates very small corrections to the spin correction observable in all the parameter space, which can not be detected in the future ILC experiments.     

2016年粒子物理学热点回眸

 盘点了2016年粒子物理学的研究热点,在希格斯物理、新物理直接搜索方面提高了测量精度,积累了大量数据;中微子物理方面θ₁₃的测量精度提高到了4%;低能强相互作用物理方面确认了5夸克态的存在,同时发现多个可能的4夸克态;暗物质搜索方向全面压低WIMP粒子及其他类型暗物质粒子同普通物质相互作用的截面。     

希格斯粒子与暴涨宇宙

希格斯(Higgs)粒子是迄今为止发现的第一个标量粒子.在粒子物理标准模型中,希格斯粒子起到了非常重要的作用.另一方面,在宇宙暴涨时期,使宇宙加速膨胀的往往是也一个标量场,或者标量粒子,被称为暴涨子.由于能标的不同,希格斯粒子不能直接作为暴涨子,但通过一些间接的手段,暴涨子却有可能是希格斯粒子在高能标时的另一种表现形式.本文作者回顾了希格斯暴涨模型,并且着重讨论了宇宙学常数在暴涨中所起到的作用.     

HTC在大型强子对撞机上对顶夸克对产生过程的修正

TC2模型是高能物理研究热点之一,而top-Higgs粒子是TC2模型的一个特征粒子.文章对top-Higgs为中间态的在欧洲核子中心的大型强子对撞机上顶夸克对产生过程进行了计算.研究结果表明,在一些数合理的参数空间内,这个过程的散射截面和标准模型顶夸克对产生截面的比值达到了1％的量级,修正效果比较明显.因此,这个反映...     

Quadratic Yukawa coupling and matrix Yukawa coupling in the large N expansion

In this article, we study three types of new Yukawa couplings (the boson field is coupled to the fermion field). Two of them are quadratic Yukawa couplings (the boson field is in the form of a vector), and the other one is the matrix Yukawa coupling (the boson field is in the form of a matrix). Based on the above three couplings, we introduce the Higgs mechanism, and find out the properties of the generated mass for the fermions with multiple flavors. For the matrix boson, we introduce its coupling with non-Abelian gauge field. It turns out that the generated mass of the gauge field through the Higgs mechanism is unique. In the large N limit, using the method of auxiliary field, we study the dynamical behaviors of the quadratic Yukawa couplings, including the poles of some dressed propagators.     

HTM模型中带电希格斯玻色子在ILC上的联合产生

希格斯三重态模型(HTM)预言了类标准模型的中性希格斯玻色子h,还预言了单电荷和双电荷希格斯玻色子(H~±,H~(±±))的存在.主要研究了在高能光子对撞机上的两个三体产生过程:γγ→hH~+H~-和γγ→hH~(++)H~(--).计算结果表明,在合理的参数空间内,两种过程的产生截面分别达到几十fb和一百多fb,分析了主要的标准模型背景并计算了信噪比.由于较低的标准模型背景,在未来的高能直线对撞机上实验中可以通过这些过程探测到带电标量粒子H~±和H~(±±)的信号.     

LHC Pb-Pb碰撞过程中的光生SUSY Higgs

计算了ＬＨＣ条件下的超对称中心Ｈｉｇｇｓ玻色Ａ＾０,ｈ＾０以及Ｈ＾０在Ｐｂ－Ｐｂ碰撞过程中,质心系能量为√ｓ＝６３００Ａ ＧｅＶ时的光生截面,结果表明Ｈｉｇｇｓ光生截面在相应的质量区域内大到足可以被测出。