AI 中文总结
研究标准模型\(U(1)_{B - L}\)扩展框架下，通过轻标量衰变产生重中性轻子的情况。利用FCC - hh的FPF和SHIP束流卸料实验，考虑多种因素估计灵敏度，发现可显著扩展轻标量和重中微子发现范围，为相关物理研究提供有力探测。
AI 中文摘要
中微子质量的观测有力地推动了标准模型的\(U(1)_{B - L}\)扩展，其中重中性轻子通过自发的\(U(1)_{B - L}\)对称性破缺获得马约拉纳质量，并通过跷跷板机制产生轻中微子质量。在此框架下，负责对称性破缺的单态标量与标准模型希格斯玻色子混合，使其能在罕见介子衰变中产生。我们研究了一种情形，即这种轻标量迅速衰变成一对长寿命重中微子，重中微子随后在提议的FCC - hh的前向物理设施（FPF）和SHIP束流卸料实验中通过轻 - 重中微子混合衰变成可见带电轻子和强子。考虑实际探测器几何形状、衰变概率和可见分支比，我们估计了对标量 - 希格斯混合角作为标量质量函数以及对轻 - 重中微子混合作为重中微子质量函数的预期灵敏度。我们发现FPF和SHIP能显著扩展轻标量和长寿命重中微子的发现范围，超越现有实验限制，为中微子质量产生和隐藏扇区物理提供有力且互补的探测。
英文摘要
The observation of neutrino masses strongly motivates $U(1)_{B-L}$ extensions of the Standard Model, in which heavy neutral leptons acquire Majorana masses through spontaneous $U(1)_{B-L}$ symmetry breaking and generate light neutrino masses via the seesaw mechanism. In this framework, the singlet scalar responsible for symmetry breaking mixes with the SM Higgs boson, allowing it to be produced in rare meson decays. We investigate a scenario in which this light scalar promptly decays into a pair of long-lived heavy neutrinos that subsequently decay into visible charged leptons and hadrons through light-heavy neutrino mixing inside the proposed Forward Physics Facility (FPF) at the FCC-hh and the SHiP beam-dump experiment. Taking into account realistic detector geometries, decay probabilities, and visible branching fractions, we estimate the projected sensitivities to the scalar-Higgs mixing angle as a function of the scalar mass and to the light-heavy neutrino mixing as a function of the heavy neutrino mass. We find that FPF and SHiP can significantly extend the discovery reach for both light scalars and long-lived heavy neutrinos beyond existing experimental limits, providing powerful and complementary probes of neutrino-mass generation and hidden-sector physics.
Comments15 pages, 6 figures, 1 table
