标题： 寻找长寿命粒子的自由中子实验 显示英文标题

标题： Searching for Long-Lived Particles in Free Neutron Experiments

摘要： 我们研究了自由中子衰变为奇异长寿命粒子的衰变过程，这些粒子的衰变可能在下一代自由中子实验中被探测到。 我们表明，只要这种奇异粒子与中子高度质量简并，从而避免大体积探测器的排除，这种可能性就是可行的。 我们估计了可观察事件的数量，并从理论和实验的角度识别了最有可能的最终状态。 我们的分析强调了欧洲散裂源（European Spallation Source）上的HIBEAM-NNBAR实验的独特能力，可以探测这一未被探索的参数空间区域，为探索超出标准模型的物理打开了新的途径。 我们估计，在NNBAR实验中每年可能会观测到几个事件。 显示英文摘要

摘要： We explore the decay of free neutrons into exotic long-lived particles, whose decays could be detected in the next-generation free neutron experiments. We show that such a possibility is viable as long as the exotic particle is highly mass-degenerate with the neutron, avoiding exclusion by large-volume detectors. We estimate the number of observable events and identify the most promising final states from both theoretical and experimental perspectives. Our analysis highlights the unique capability of the HIBEAM-NNBAR experiment at the European Spallation Source to probe this unexplored region of parameter space, opening a new avenue for exploring physics beyond the Standard Model. We estimate that several events per year could be observed in the NNBAR experiment.