四顶搜索与新物理：对三顶生产的影响与g2HDM的可能性

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本文主要探讨了在大型强子对撞机(LHC)的四顶夸克(4-top)生产与三顶夸克(triple-top)生产之间的相互关系和影响。在标准模型(SM)中，四顶夸克的生产率约为每平方fb的数量级，这是一个重要的研究目标，因为它为探索可能的新物理现象提供了独特的窗口。尽管三顶夸克的SM预测横截面积相对较小，还未成为主要的研究焦点，但它在新物理模型中的重要性不容忽视。在一般的两希格斯双倍态模型(g2HDM)中，由于缺乏通常的离散Z2对称性，三顶夸克的生产率可以被自然地提升至pb级，这是在SM框架下难以实现的。作者强调了通过分析四顶夸克搜索的数据，特别是那些特定的信号区域，可以用来间接约束三顶夸克的生产，这有助于缩小潜在新物理理论的空间。文章还提到了一项由CMS进行的研究，他们在13 TeV的能量下观察到tt共振的干扰，这在400 GeV处显示出一些活动。这种现象可能在g2HDM中通过额外的顶部Yukawa耦合得到解释，这意味着三顶夸克的观测可能与这些新粒子或效应有关。因此，研究四顶夸克不仅可以推进基本粒子物理学的前沿，而且对于理解可能存在的新物理现象，如g2HDM中的额外粒子，具有关键的启示作用。未来，作者呼吁进行专门针对三顶夸克生产的搜寻，并结合四顶夸克研究的结果，以更全面地探索粒子物理学的未知领域。这一领域的进一步工作将有助于揭示标准模型的边界，以及可能隐藏的理论结构。

Physics Letters B 798 (2019) 134953

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Implications of four-top and top-pair studies on triple-top production

Wei-Shu Hou, Masaya Kohda, Tanmoy Modak

∗

Department of Physics, National Taiwan University, Taipei 10617, Taiwan

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

Article history:

Received

1 July 2019

Received

in revised form 12 September

2019

Accepted

17 September 2019

Available

online 20 September 2019

Editor:

J. Hisano

Multi-top quark production is a staple program at the LHC. Single-top and t

t productions are studied

extensively, while current ef forts are zooming in on four-top search, where the Standard Model (SM) cross

section is at O(10) fb. In contrast, only at the fb level in SM, triple-top production has not been targeted

for study so far . But such a small cross section makes it a unique probe for New Physics. Without the

usual discrete Z

symmetry, the general two Higgs doublet model (g2HDM) can naturally raise the triple-

top

production to pb level. We illustrate how certain signal regions of four-top search can be utilized to

constrain triple-top production, but urge a dedicated search. As an aside, we note that the CMS study

at 13 TeV of scalar t

t resonance interfering with QCD production background indicate some activity at

400 GeV. We comment that this could be explained in principle in g2HDM via the extra top Yukawa

coupling.

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

1. Introduction

The top quark was discovered at the Tevatron via t

t pair pro-

duction [1],

and single-top production was subsequently discov-

ered

in the s-channel [2]. The ATLAS and CMS collaborations

quickly rediscovered t

t production [3,4]in early run of the LHC,

and later on discovered single-top in t- and tW channels, and

have also studied the s-channel [2]. The cross section at 13–14 TeV

for the QCD initiated t

t production is at O(10

) pb, while the va-

lence

quark initiated t-channel single-top production is more than

200 pb. In contrast, triple-top production (tt

t and

tt ) is predicted

at the meager few fb [5]level in the Standard Model (SM), which

is negligible compared to t

t, or even single-top. As a result, none

of the experiments have covered triple-top in their search pro-

grams

so far. Although suppressed by four-body phase-space, the

SM cross section of the QCD initiated four-top (t

t) production,

at O(10) fb, is actually larger than triple-top. Both ATLAS [6] and

CMS [7,8]have searched for four-top production, where the more

recent CMS study exploits the full Run 2 dataset.

The

tiny triple-top cross section makes it a good probe for

beyond SM (BSM) physics. It was shown recently [9](see also

Ref. [10]) that the cross section can reach pb level if one drops

the usual discrete Z

symmetry from the two Higgs doublet model

(2HDM), thanks to the presence of extra top Yukawa couplings ρ

Corresponding author.

E-mail

address: tanmoyy@hep1.phys.ntu.edu.tw (T. Modak).

and ρ

. The additional neutral scalars H or A need to be above

t threshold. Such a general 2HDM (g2HDM) framework allows

the possibility of approximate alignment without decoupling, even

with O(1) Higgs quartic couplings [11]. With ρ

acting in pro-

duction

and ρ

in decay, the cg →tH/tA →tt

t processes (conju-

gate

processes always implied) can enhance triple-top production,

making discovery possible for semileptonic decays of all three top

quarks [9].

this work we illustrate how certain signal regions (SRs) of

the CMS search for SM production of t

t at 13 TeV, based on the

datasets of 35.9 fb

−1

[7] and 137 fb

−1

[8], can be utilized to con-

strain

triple-top production via cg → tH/tA → tt

t, and hence the

parameter space for ρ

and ρ

. It is remarkable that SRs not par-

ticularly

meant for triple-top production can give sensitive probes.

While ATLAS has also searched for four-top production [6]in the

single-lepton and opposite sign dilepton ﬁnal states with Run-2

data, we ﬁnd it less sensitive in our analysis. Our purpose, how-

ever,

is to illustrate the need for a dedicated search for triple-top,

perhaps as an extension of the four-t op search program.

With

QCD-induced t

t pair production well understood, it is of

interest to consider resonant t

t production interfering with this

underlying “background”. It has been emphasized [12] that the rise

and dip pattern for (pseudo)scalar channel makes the experimental

study challenging. With ATLAS [13]leading the way, CMS revealed

recently their result with Run 2 data [14], where there is some hint

of activity. We note that, although it is too early to say, the extra

top Yukawa coupling ρ

could in principle be behind this. The Run

https://doi.org/10.1016/j.physletb.2019.134953

0370-2693/

SCOAP

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