Soft-gluon corrections for tqZproduction Nikolaos Kidonakisaand Nodoka Yamanakabc aDepartment of Physics Kennesaw State University

2025-05-03 0 0 315.53KB 10 页 10玖币

侵权投诉

Soft-gluon corrections for tqZ production

Nikolaos Kidonakisaand Nodoka Yamanakab,c

aDepartment of Physics, Kennesaw State University,

Kennesaw, GA 30144, USA

bKobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University,

Furocho, Chikusa, Aichi 464-8602, Japan

cNishina Center for Accelerator-Based Science, RIKEN,

Wako 351-0198, Japan

Abstract

We study soft-gluon corrections for the associated production of a single top quark and

aZboson (tqZ production) at hadron colliders. We ﬁnd that the radiative corrections are

dominated by soft-gluon emission. We calculate the approximate NNLO (aNNLO) cross section

at LHC energies, including uncertainties from scale dependence and from parton distributions.

We also calculate diﬀerential distributions in top-quark rapidity. We show that the aNNLO

corrections are signiﬁcant and they enhance the NLO cross section while decreasing theoretical

uncertainties.

1 Introduction

The production of a single top quark in association with a Zboson, i.e. tqZ production where q

represents a light quark or antiquark, is an interesting process that is being studied at the LHC [1–6].

Searches for the process were already underway at 8 TeV LHC energy [1] with later measurements

following at 13 TeV [2, 3], and eventually leading to the observation of this process at 13 TeV

collisions [4, 5]. Further measurements, including diﬀerential cross sections, were made in [6].

The tqZ production processes allow for the t-Zand W-W-Zcouplings to be studied in a single

interaction. These processes can be aﬀected by physics beyond the Standard Model, including

ﬂavor-changing neutral-current processes with anomalous top-quark couplings, such as t-q-Z[7–11]

and t-q-g[12]. Top partner decays to tZ were considered in [13]. Furthermore, analyses for tqZ

production in the context of SMEFT were presented in [14, 15].

The tqZ processes also probe the anomalous “weak” moments of the top quark, whose interac-

tions are deﬁned as LtZ =Ct¯

tσµν (∂µZν)t+C0

t¯

tσµν (∂µZν)γ5t. These anomalous moments may be

generated by new particles beyond the Standard Model appearing through loop diagrams in a simi-

lar way as the anomalous electromagnetic moments. On the other hand, these moments may also be

probed by low-energy precision-test experiments. For instance, the top-quark weak dipole moment

contributes to the electric dipole moments (EDMs) of light quarks through renormalization group

evolution [16], and ﬁnally to the observable EDMs of the neutron and atoms [17]. However, the

mixing between top-quark weak moments and the electromagnetic moments of light quarks occurs

through the weak interaction, so a signiﬁcant suppression happens. We then expect the direct pro-

duction in accelerator experiments to have an important advantage over low-energy precision tests.

We also note that the coupling between the top quark and the Zboson is larger than that between

the top quark and the photon, so the sensitivity of tqZ production to new physics is potentially

increased compared to tqγ, which is another advantage relative to the latter process.

arXiv:2210.09542v1 [hep-ph] 18 Oct 2022

Theoretical calculations for tqZ production are challenging since already at leading order (LO)

the processes involve three particles in the ﬁnal state, with two of them very massive, and four

colored particles overall in the hard scattering. The next-to-leading-order (NLO) QCD corrections

for tqZ production were calculated in [18]. The NLO electroweak (EW) corrections as well as oﬀ-

shell eﬀects were included in [19], with further work in [20]. The NLO QCD corrections turn out

to be quite signiﬁcant, providing an enhancement of around 16% to the LO cross section at LHC

energies, while the NLO EW corrections are rather small, only 1%. Thus, it is important to consider

further higher-order QCD corrections.

Soft-gluon resummation [21–31] has long been known to be very important for top-quark pro-

cesses, since the cross section receives large corrections from soft-gluon emission near partonic

threshold due to the large mass of the top quark. This is well known for many 2 →2 top-quark pro-

cesses, including top-antitop pair production [21,22,25,28], single-top production [24,26, 27,29,30],

and even processes beyond the Standard Model, for example involving top-quark anomalous cou-

plings [7, 9, 10, 12] (see e.g. the review in Ref. [32]). More recently, soft-gluon resummation has

been applied to 2 →3 processes [31], in particular tqH production [33] and tqγ production [34]. In

all these processes, as well as tqZ production, the soft-gluon corrections are dominant and account

for the majority of the complete corrections at NLO. Furthermore, the soft-gluon calculations at

next-to-next-to-leading order (NNLO) predicted very well the later complete NNLO results for top-

antitop production and s-channel single-top production (see e.g. the review in Ref. [32]). These

facts, along with the relevance of resummation in the related tZ production via anomalous couplings

in [7, 9, 10], provide very strong motivation for the study of resummation for tqZ production.

In this paper, we use soft-gluon resummation to calculate approximate NNLO (aNNLO) cross

sections for tqZ production. In the next section, we describe the resummation formalism and its

speciﬁc implementation for tqZ production in single-particle-inclusive kinematics. In Section 3, we

provide results for the total cross sections, including theoretical uncertainties, at LHC energies. In

Section 4, we give results for the top-quark rapidity distributions. We conclude in Section 5.

2 Resummation for tqZ production

We begin with the soft-gluon resummation formalism for tqZ production, implementing the theo-

retical framework in [31]. We study the parton-level processes a(pa) + b(pb)→t(pt) + q(pq) + Z(pZ),

and we deﬁne the usual kinematical variables s= (pa+pb)2,t= (pa−pt)2, and u= (pb−pt)2.

With an additional gluon emission in the ﬁnal state, momentum conservation is given by pa+

pb=pt+pq+pZ+pgwhere pgis the gluon momentum. We then deﬁne a threshold variable

s4= (pq+pZ+pg)2−(pq+pZ)2=s+t+u−m2

t−(pq+pZ)2which involves the extra energy from

gluon emission and which vanishes as pg→0.

We write the diﬀerential cross section for tqZ production in proton-proton collisions as a con-

volution,

dσpp→tqZ =X

a,b Zdxadxbφa/p(xa, µF)φb/p(xb, µF)dˆσab→tqZ (s4, µF),(2.1)

where µFis the factorization scale, φa/p and φb/p are parton distribution functions (pdf) for parton

aand parton b, respectively, in the proton, and dˆσab→tqZ is the partonic diﬀerential cross section.

The cross section factorizes if we take Laplace transforms [31], deﬁned by

d˜

ˆσab→tqZ (N, µF) = Zs

ds4

se−Ns4/s dˆσab→tqZ (s4, µF),(2.2)

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

10 玖币 0人已下载

立即下载

摘要：

Soft-gluoncorrectionsfortqZproductionNikolaosKidonakisaandNodokaYamanakab;caDepartmentofPhysics,KennesawStateUniversity,Kennesaw,GA30144,USAbKobayashi-MaskawaInstitutefortheOriginofParticlesandtheUniverse,NagoyaUniversity,Furocho,Chikusa,Aichi464-8602,JapancNishinaCenterforAccelerator-BasedScience,R...

展开>> 收起<<

Soft-gluon corrections for tqZproduction Nikolaos Kidonakisaand Nodoka Yamanakabc aDepartment of Physics Kennesaw State University.pdf

共10页,预览2页

还剩页未读，继续阅读

声明：本站为文档C2C交易模式，即用户上传的文档直接被用户下载，本站只是中间服务平台，本站所有文档下载所得的收益归上传人(含作者)所有。玖贝云文库仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对上载内容本身不做任何修改或编辑。若文档所含内容侵犯了您的版权或隐私，请立即通知玖贝云文库，我们立即给予删除！

Soft-gluon corrections for tqZproduction Nikolaos Kidonakisaand Nodoka Yamanakabc aDepartment of Physics Kennesaw State University

相关推荐

开通VIP享超值会员特权

作者详情

相关内容

热门标签

举报选择: