LHC Run 2后两体共振探索：新需求与未来策略

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在"JHEP04(2020)030"这篇论文中，作者Jeong Han Kim、Kyoungchul Kong、Benjamin Nachman和Daniel Whiteson探讨了大型强子对撞机（Large Hadron Collider, LHC）运行第二阶段（Run 2）之后以及未来两体共振衰变研究的动机与现状。在高能物理学领域，两体共振衰变作为核心研究议题，对于理解标准模型（Standard Model, SM）粒子的行为至关重要。SM粒子的组合已经进行了广泛的研究，然而仍存在许多未探索的空白区域。当两体中的至少一个是非标准模型粒子时，现有的搜索策略往往无法充分覆盖这些未知情况。这种情况下，搜索的局限性变得尤为明显，因为非SM粒子可能具有全新的性质和相互作用模式，这些模式在标准模型框架下难以预测。论文着重指出，为了填补这一知识空白，有必要进行针对性的搜寻，以寻找那些尚未被现有实验数据触及的两体共振衰变组合。作者们回顾了当前两体搜索的方法和技术，包括但不限于对新物理现象的模型依赖和模型独立搜索。他们强调了将专用搜索技术与模型不确定性分析相结合的重要性，这样可以更全面地探测到各种可能的非标准模型信号。未来的研究计划可能需要设计新的分析策略，以适应这种多样性和复杂性，同时考虑到实验数据的处理和理论预测的准确性。此外，论文还讨论了可能的实验进展，包括对新粒子的寻找、背景噪声的控制，以及如何优化数据分析以提高对潜在共振信号的敏感度。他们指出，尽管目前面临挑战，但随着LHC和其他高能物理实验的进一步升级，以及理论计算和分析技术的不断进步，寻找两体共振衰变的可能性正在逐渐扩大。这篇论文不仅揭示了当前两体共振衰变研究的现状，而且还提出了未来的研究方向和策略，这对于推动高能物理学的边界扩展和新物理模型的探索具有重要意义。

JHEP04(2020)030

The left-upper corner of the table (denoted by Group I) reproduces a group of the

standard 2-body decays, A → BC, where A is a BSM particle and B and C are SM

particles, as covered in ref. [14]. In this subtable, the column and row are a list of SM

particles and each entry corresponds to a mother particle, which would decay into one

particle in the column and one particle in the row in the subtable. We show examples

of theories that populate the entire landscape of 2-body resonances. Z

and W

denote

additional gauge bosons, /R represents R-parity violating supersymmetry (SUSY), L

∗

, Q

∗

are excited leptons and quarks, respectively, and T

and B

are a vector-like top and bottom

quarks, respectively. Z

denotes Kaluza-Klein excitation of SM Z.

We categorize the rest of table 1 in terms of nine additional subtables, which are

denoted by Roman numerals II through X, and present each table in the sequential order.

Note that generally we suppress electric charges of each SM particle and focus on the

diversity of decay products, although we mention a few interesting examples of such kinds.

Similarly we will not distinguish light jets from gluon and generically denote them as j

but occasionally we distinguish them for some interesting decays. We denote the bottom

quark, and top quark by b/

b and by t/

t, respectively. The V represents SM gauge bosons

Z and W

and H is a SM Higgs boson. Throughout the manuscript, a primed particle X

represents a BSM particle, whose properties are similar to the corresponding SM particle X.

Ref. [14] provide a complete list of possible production mechanisms of two body res-

onances, including resonant production mode (via the tree-level decay couplings, loop-

induced processes involving the decay coupling, or the inclusion of additional couplings to

quarks or gluons allowed by the quantum numbers of the resonance), the leading produc-

tion mode in association with one, two, three, or four Standard Model particles (using the

same coupling for production and decay in a four-ﬂavor scheme), the unavoidable existence

of a pair production mode. It also notes a possible choice of resonance quantum numbers

that does not lead to a pair production mode. However, if one or both of the decay prod-

ucts of A is a BSM particle, A will not be produced as a single resonance at the LHC via

the same decay coupling. It requires additional couplings to quarks and gluons, which is

not an issue for our discussion in the rest of this study.

In general, various constraints may be imposed on these resonances and could aﬀect

the possible production and decay modes. In order to maintain the broadest possible

scope, we consider only the most stringent constraints imposed by gauge invariance and

Lorentz invariance, as many experimental constraints are dependent on the details of the

underlying model and may in principle be evaded. Gauge invariance and Lorentz invariance

also dictate the structure of interaction of resonances and SM particles.

Table 2 shows example for A → BC, where A and B are BSM particles and C is a

SM particle, which is the Group II in table 1. We consider two similar SM particles in

the B decays. For example, the jj denotes B decays to two quarks (q¯q, q¯q

or qq), while

`` includes both two opposite-charged leptons (`

−

) and the same-sign charged leptons

and `

−

) and the V V includes the B decays to gg, γγ, γZ, ZZ, W W , or ZW .

The H is the observed Higgs boson, H

and H

are heavy scalars, A is a new pseudo

scalar, and H

denotes a doubly-charged scalar particle. The Q

represents a generic

vector-like quark. X

5/3

and π

4/3

represent a vector-like quark with electric charge 5/3 and

– 3 –

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