近日，法国巴黎高等师范学院物理实验室的María Olalla Olea-Romacho及其研究团队取得一项新进展。经过不懈努力，他们在介子束流收集实验中寻找具有轴向耦合的新型轻规范玻色子。相关研究成果已于2024年7月24日在国际知名学术期刊《高能物理杂志》上发表。
该研究团队提出一种新的U(1)相互作用的形式，包括弱超荷、重子和轻子数，以及在第二个Brout-Englert-Higgs双重态存在下可能的轴对称发生器FA。由此产生的U玻色子在与Z混合后，在广义暗光子、暗Z和轴向耦合规范玻色子之间插入。研究人员特别关注源于FA或与Z混合的轴向耦合，其由标量扇区通过tan β和额外暗单重态的v.e.v等参数确定。
研究人员探索了轴耦合相互作用的独特特征，特别是在超相对论性极限下，U玻色子的行为很像类轴子粒子，与夸克和轻子的相互作用增强。这种增强与未来的μ介子束流收集实验特别相关，因为与电子的类似实验相比，μ介子质量大大增加了有效耦合，比例为2 mμ/mU。
此外，研究人员还分析了U玻色子相互作用与实验几何形态对预期束流排斥效应或探测区域形态的具体影响。他们考虑了不同的情况，尤其是针对U玻色子在抵达探测器之前即发生衰变，或因其耦合强度过弱而无法触发可观测事件的情形。研究人员还比较了矢量耦合玻色子和类轴子伪标量，强调了理解参数空间对未来实验设计和优化的重要性。
附：英文原文
Title: Searching for a new light gauge boson with axial couplings in muon beam dump experiments
Author: Fayet, Pierre, Olea-Romacho, Mara Olalla
Issue&Volume: 2024-07-24
Abstract: We present a formalism for new U(1) interactions involving weak hypercharge, baryon, and lepton numbers, and a possible axial symmetry generator FA in the presence of a second Brout-Englert-Higgs doublet. The resulting U boson, after mixing with the Z, interpolates between a generalised dark photon, a dark Z, and an axially coupled gauge boson. We especially focus on the axial couplings originating from FA or from mixing with the Z, determined by the scalar sector via parameters like tan β and the v.e.v. of an extra dark singlet.
We explore the distinctive features of axially coupled interactions, especially in the ultrarelativistic limit, where the U boson behaves much as an axion-like particle, with enhanced interactions to quarks and leptons. This enhancement is particularly relevant for future muon beam dump experiments, since the muon mass considerably increases the effective coupling, proportional to 2mμ/mU, compared to analogous experiments with electrons.
We also analyse the shape of the expected beam dump exclusion or discovery regions, influenced by U boson interactions and the experiment geometry. Different situations are considered, limited in particular by cases for which the U decays before reaching the detector, or has too small couplings to produce detectable events. We also compare to vectorially coupled bosons and axion-like pseudoscalars, highlighting the importance of understanding the parameter space for future experiment design and optimisation.
DOI: 10.1007/JHEP07(2024)223
Source: https://link.springer.com/article/10.1007/JHEP07(2024)223