用便携式μ介子探测器观测中层大气动力学
Middle-atmosphere dynamics observed with a portable muon detector
摘要：
在过去的几年里，大型粒子物理学实验表明，在地下实验室中检测到的μ介子速率变化对区域性中层大气温度变化很敏感。潜在的应用包括跟踪短期大气动力学，如平流层突然变暖。我们在这里报告说，这种灵敏度不仅限于高不透明度条件下的大型表面探测器。我们使用便携式μ介子探测器设想μ介子层析成像的地球物理应用，我们研究μ介子率的变化，观察到超过一年的测量在蒙特特里地下岩石实验室，瑞士（不透明度约700米水当量）。我们观察到中层大气季节性温度变化和μ介子率之间的直接相关性。μ子速率变化也对2017年1月至2月的异常大气加热敏感，与平流层突然变暖有关。对我们这种特殊情况的有效温度系数的估计与理论模型和在可比条件下从大型中微子实验中计算的结果一致。因此，便携式μ介子探测器可用于：1）研究季节性和短期中层大气动力学，特别是在缺乏数据的地点，如中纬度地区; 2）改进不同不透明度条件下有效温度系数的校准。此外，我们强调的重要性，评估温度对μ介子速率变化的影响时，考虑地球物理应用。根据纬度和不透明度条件，这种影响可能大到足以掩盖地下水含量变化引起的地下密度变化，因此应从时间序列中删除。
英文摘要：
In the past years, large particle-physics experiments have shown that muon rate variations detected in underground laboratories are sensitive to regional, middle-atmosphere temperature variations. Potential applications include tracking short-term atmosphere dynamics, such as Sudden Stratospheric Warmings. We report here that such sensitivity is not only limited to large surface detectors under high-opacity conditions. We use a portable muon detector conceived for muon tomography for geophysical applications and we study muon rate variations observed over one year of measurements at the Mont Terri Underground Rock Laboratory, Switzerland (opacity of ~700 meter water equivalent). We observe a direct correlation between middle-atmosphere seasonal temperature variations and muon rate. Muon rate variations are also sensitive to the abnormal atmosphere heating in January-February 2017, associated to a Sudden Stratospheric Warming. Estimates of the effective temperature coefficient for our particular case agree with theoretical models and with those calculated from large neutrino experiments under comparable conditions. Thus, portable muon detectors may be useful to 1) study seasonal and short-term middle atmosphere dynamics, especially in locations where data is lacking such as mid-latitudes; and 2) improve the calibration of the effective temperature coefficient for different opacity conditions. Furthermore, we highlight the importance of assessing the impact of temperature on muon rate variations when considering geophysical applications. Depending on latitude and opacity conditions, this effect may be large enough to hide subsurface density variations due to changes in groundwater content, and should therefore be removed from the time-series.
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