精确探测e-e+对撞机中顶夸克与希格斯玻色子CP违反效应

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"增强对撞机顶夸克汤河相互作用的测量" 这篇论文主要关注的是在电子-正电子(e-e+)对撞机上对顶夸克与汤夸克之间违反CP（电荷宇称守恒）的相互作用进行精确测量的技术方法。CP违反是粒子物理学中的一个重要概念，它涉及到粒子与它们的反粒子在物理过程中的行为差异。在标准模型中，CP违反已经被确认为是宇宙中物质与反物质不对称性的关键因素。然而，标准模型中的CP违反程度不足以解释我们宇宙中观察到的物质主导现象，因此寻找新的CP违反源成为探索超出标准模型的新物理学的重要途径。文章介绍了一种全新的分析策略，该策略无需重建顶夸克就可以探测到顶夸克对和希格斯玻色子关联产生的CP违规效应。这一方法的核心在于利用顶夸克衰变产生的轻子的自旋相关效应来定义可观测量。这些可观测量的形成表达式在任何参考系下都是通用的，这使得分析更具普适性。论文中探讨了两种不同的参考系：上夸克对的剩余框架和希格斯玻色子的剩余框架。在希格斯玻色子的剩余框架中，作者发现对CP奇数和CP偶数可观测量有显著增强，这是在e-e+对撞机上探测CP违规影响的关键。这种增强效应可以提高实验对CP违反的敏感度，从而更有可能揭示电弱尺度以上的新物理现象。此外，文章的发表是在《Physics Letters B》上，这是一个开放获取的期刊，意味着研究结果可以被广大科学社区自由访问和使用。文章经过多次修改和完善，最终于2019年9月被接受并在线发布，编辑由G.F.Giudice担任。总结来说，这篇工作为理解电弱尺度以上的CP违反提供了新的分析工具，对于未来在高能对撞机实验中寻找新物理的线索具有重要意义。通过不依赖于顶夸克重建的方法，以及在特定参考系中增强的CP观测，这项研究为探测和测量顶夸克与希格斯玻色子间的CP违反效应提供了有效手段，有助于推进粒子物理学领域的新发现。

Physics Letters B 797 (2019) 134928

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Enhancing CP measurement of the Yukawa interactions of top-quark

at e

−

collider

Kai Ma

School of Physics Science, Shaanxi University of Technology, Hanzhong 723000, Shaanxi, China

a r t i c l e i n f o a b s t r a c t

Article history:

Received

18 May 2019

Received

in revised form 15 August 2019

Accepted

6 September 2019

Available

online 11 September 2019

Editor:

G.F. Giudice

It is well known that CP-violating coupling of the Yukawa interaction of top-quark is a promising

candidate of a new source of CP violation effect. Precisely measurement of its CP properties is crucial for

understanding new physics above the electroweak scale. In this paper, we introduce a complete analysis

method for probing CP violation effects in the associated production of top-quark pair and Higgs boson

at e

−

collider. Reconstructions of the top-quarks are not needed in our strategy. The observables are

deﬁned based on spin correlation effects of the leptons emerging from decays of top-quarks, and their

formal expressions are universal at any reference frames. Two reference frames, the rest frame of the

top-quark pair and the rest frame of Higgs boson, are examined. Importantly, large enhancement effects

for both CP-odd and CP-even observables are observed in the rest frame of Higgs boson. This can be

essential for probing CP violation effects at future e

−

collider.

(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP

After the long waited era in the elementary particle physics,

a scalar particle with mass ∼ 125 GeV [1]was discovered at LHC

in 2012 [2,3]. However, our knowledge about its physical proper-

ties

can not be less any more to make a judgment that it is really

the Higgs boson who spontaneously breaks the electroweak vac-

uum

and gives masses to the observed vector bosons and fermions,

because so far its self-coupling which is responsible for the sym-

metry

breaking has not been measured [4]. On the other hand,

theoretical extensions of the Standard Model (SM) always possess

more than one Higgs doublet, and hence more scalar particles

with either heavier or lighter masses, but having CP quantum

numbers different from the SM prediction, J

= 0

, are pre-

dicted.

Therefore, the observed mass eigenstate h(125) (we will

use this notation in the rest of this paper) can be potentially a

mixture of the CP eigenstates. As a natural expectation that the

Higgs boson predicted by the SM is at least the dominant compo-

nent

of the observed scalar particle h(125), decisive measurement

on the CP violation effect, which is a promising potential source

of the observed asymmetry between matter and anti-matter in

our universe [5–7], is important and urgent for understanding the

physics above electroweak scale. However, it is challenging in prac-

tice [8].

E-mail address: makainca@yeah.net.

Without loss of generality, we can assume that h(125) is a su-

perposition

of CP-even eigenstate H and CP-odd eigenstate A,

h = H cos ξ + A sin ξ, (1)

where ξ is the Higgs mixing angle that has been assumed to be

real. The story is further complicated by the couplings of H and

A to the observed vector bosons and fermions because what we

measure are usually combinations of those couplings and the mix-

ing

angle ξ . Therefore, in general, channel by channel studies on

the CP violation effects related to h(125) is unavoidable.

Soon

after h(125) was observed, its CP property was stud-

ied

through h → ZZ → 4 by the ATLAS and CMS collaborations

[9–11], and the results disfavor the CP-odd hypothesis by nearly

3σ , which is a rather weak constraint on the mixing angle due

to the complexity mentioned above. On the other hand, while

HVV



couplings usually appear at tree level, the AV V



interac-

tions

are only loop induced, and hence CP violation is heavily

suppressed [12–15]. This drawback absents, theoretically, in the

couplings of H and A to the fermions, where both types of inter-

action

can happen at tree level and hence are promising probes of

CP violation effects [16]. Recently, the decay of h(125) to τ -lepton

pair channel was analyzed by the ATLAS and CMS collabora-

tions [17,18],

and the bound is again rather weak. The optimization

method proposed in Ref. [8]is expected to enhance the sensi-

tivity

to a promising level. However, the precision is still limited

https://doi.org/10.1016/j.physletb.2019.134928

0370-2693/

SCOAP

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