探索TeV尺度重中微子：LHC上的矢量玻色子融合新方法

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"在大型强子对撞机上扩大重中微子搜索的范围" 这篇研究集中在探索超出标准模型（SM）的物理现象，特别是中微子的非零质量，这由中微子振荡的观测所证实。研究人员提出了一项在13 TeV LHC（大型强子对撞机）上的可行性研究，旨在寻找具有TeV质量级别的假性马约拉纳中微子（N）。马约拉纳中微子是一种特殊的中微子，它们可能是自己的反粒子，这在粒子物理学中是一个引人入胜的概念。研究聚焦于通过矢量玻色子融合（VBF）过程来探测这些重中微子。VBF是一种高能粒子碰撞中产生新粒子的机制，其中两个弱相互作用的矢量玻色子（如W或Z玻色子）在对撞过程中融合，产生新的粒子。在I型跷跷板机制的最小实现（mTISM）下，中微子和相关重中微子的VBF生成截面在大约1.4TeV时超过了Drell-Yan过程。这里，Drell-Yan过程是另一种常见的新粒子生成方式，通常涉及带电费米子对的产生。研究者特别关注第二代（Nμ）和第三代（Nτ）重中微子的生成，它们会衰变成轻子（μ或τ）和两个喷射。通过利用VBF的独特拓扑，即双链双子叶对，其中包含四个喷射器，可以有效地减少标准模型背景。关键在于识别出两个具有伪快度和显著TeV尺度双喷射质量分离的VBF喷射器。这种方法提高了在13 TeV LHC上搜寻Nℓ的能力。实验假设基于13 TeV LHC数据的100（1000）fb^-1（fb-1是逆 femtobarn，用于衡量对撞机的 luminosity，表示事件的数量），并假设中微子混合矩阵元素的平方|VℓNℓ|² = 1。在这种情况下，可以在95%的置信水平下排除质量低于1.7（2.4）TeV的Nℓ。这项工作是在Physics Letters B 778 (2018) 94–100发表的，并且是开放获取的，这意味着研究结果可供公众免费查阅。它展示了在当前对撞机实验条件下，如何利用创新的分析策略来扩展对重粒子搜索的界限，尤其是那些可能揭示新物理现象的重中微子。通过这样的研究，科学家们希望能更深入地理解宇宙的基本粒子和它们的性质，以及可能存在的超出标准模型的新物理理论。

Physics Letters B 778 (2018) 94–100

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Expanding the reach of heavy neutrino searches at the LHC

Andrés Flórez

b,∗

, Kaiwen Gui

, Alfredo Gurrola

a,∗

, Carlos Patiño

, Diego Restrepo

Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, 37235, USA

Physics Department, Universidad de los Andes, Bogotá, Colombia

Department of Physics, Universidad de Antioquia, Medellín, Colombia

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

Article history:

Received

17 August 2017

Received

in revised form 6 December 2017

Accepted

3 January 2018

Available

online 11 January 2018

Editor: L.

Rolandi

The observation of neutrino oscillations establishes that neutrinos have non-zero mass and provides one

of the more compelling arguments for physics beyond the standard model (SM) of particle physics. We

present a feasibility study to search for hypothetical Majorana neutrinos (N) with TeV scale masses,

predicted by extensions of the SM to explain the small but non-zero SM neutrino mass, using vector

boson fusion (VBF) processes at the 13 TeV LHC. In the context of the minimal Type-I seesaw mechanism

(mTISM), the VBF production cross-section of a lepton () and associated heavy Majorana neutrino (N



)

surpasses that of the Drell–Yan process at approximately m



= 1.4 TeV. We consider second and third-

generation

heavy neutrino (N

or N

, where  = muon (μ) or tau (τ ) leptons) production through

VBF processes, with subsequent N

and N

decays to a lepton and two jets, as benchmark cases to

show the effectiveness of the VBF topology for N



searches at the 13 TeV LHC. The requirement of a

dilepton pair combined with four jets, two of which are identiﬁed as VBF jets with large separation in

pseudorapidity and aTeV scale dijet mass, is effective at reducing the SM background. These criteria

may provide expected exclusion bounds, at 95% conﬁdence level, of m



< 1.7(2.4) TeV, assuming 100

(1000) fb

−1

of 13 TeV data from the LHC and mixing |V

N



= 1. The use of the VBF topology to search

for m



increases the discovery reach at the LHC, with expected signiﬁcances greater than 5σ (3σ ) for



masses up to 1.7 (2.05) TeV using 1000 fb

−1

of 13 TeV data from the LHC.

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

1. Introduction

The discovery of a Higgs boson [1,2] at the Large Hadron Col-

lider

(LHC) has addressed the last missing piece of the standard

model (SM) of particle physics. However, the SM remains an in-

complete

theory. One of the open questions it fails to address is

the non-zero mass of the three generations of neutrinos, which is

implied by the observation of neutrino oscillations [3–5]. It has

been suggested that because neutrinos can be their own anti-

particles

(Majorana fermions), the non-zero mass of light neutri-

nos



could be generated by a see-saw mechanism [6–8], which

would imply the existence of yet unobserved heavier Majorana

neutrino states with TeV scale masses. For example, in the left-

right

symmetric model (LRSM), originally introduced to explain

the non-conservation of parity in weak interactions within the SM,

the introduction of a SU(2)

group, the right-handed analogue of

the SM SU(2)

group, produces three heavy right-handed neutrino

Corresponding authors.

E-mail

addresses: ca.ﬂorez@uniandes.edu.co (A. Flórez),

Alfredo.Gurrola@Vanderbilt.edu (A. Gurrola).

states N



( = electron (e), muon (μ), and tau (τ ) leptons) and

three gauge bosons, V

={W

, Z



The

CMS [9] and ATLAS [10] experiments at the CERN LHC have

a strong physics program to search for heavy right-handed neutri-

nos.

One often used benchmark model in those searches is the

LRSM. Within this context, the CMS and ATLAS searches assume

that N



is lighter than V

: m



< m

and m



< 0.5m



. This

model and mass spectrum is chosen because it gives the largest

possible N



production cross-section at the LHC, resulting in im-

proved



discovery sensitivity. Under the assumption that N



lighter than V

, the dominant N



production mechanism at the

LHC is via resonant W

or Z



production from Drell–Yan (DY)

processes of order α

: qq



→ W

→ N



or q

q → Z



→ N



The strategy pursued in those analyses is to exploit the high

mass scale of V

and target the N



decay to a lepton and two

jets ( j), N



→ W

∗

→  jj (through a virtual W

), by selecting

events containing two high-p

leptons (opposite-sign or like-sign

charge) and two jets that are central in the detector (i.e. pseu-

dorapidity

range |η| < 3.0). Therefore, dilepton triggers can be

used to select signal events with high eﬃciency. Furthermore, be-

cause

DY-like production of resonant W

or Z



is dominant if

https://doi.org/10.1016/j.physletb.2018.01.009

0370-2693/

SCOAP

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