Atmospheric Muons

Most muons observed at the surface of the Earth are produced by primary cosmic rays in the upper atmosphere. They are the most numerous energetic particles arriving at sea level, with a flux of about 1 muon per square centimeter per minute. This can be compared to a solar neutrino flux of about 5 x 10⁶ per square centimeter per second.

观测到地球表面的大多数缪子是由高层大气中的初级宇宙射线产生的。它们是到达海平面的最丰富的高能粒子，每平方厘米每分钟的通量约为1个缪子。这可以与每平方厘米每秒约5×10⁶个太阳中微子的通量进行比较。

The mean energy of muons reaching sea level is about 4 GeV. Muons, being charged particles, interact with matter by ionizing it. The loss of energy by muons passing throught he atmosphere is proportional to the amout of matter they traverse. The medium is usually characterized by its density (g/cm³) times the distance traveled in centimeters. This is sometimes called the "interaction length" and is measured in g/cm². The energy loss for muons is about 2 MeV per g/cm². The interaction depth of the atmosphere is about 1000 cm², so muons lose about 2 GeV in passing through the atmosphere. With the sea level mean energy of muons detected at the surface = 4 GeV, this suggests an original muon energy in the neighborhood of 6 GeV.

到达海平面的μ子的平均能量约为4 GeV。由于μ子是带电粒子，它们通过 ionizing 物质与物质相互作用。μ子穿过大气层时的能量损失与其穿过的物质量成正比。介质通常通过其密度（g/cm³）乘以以厘米为单位的旅行距离来表征。这有时被称为“相互作用长度”，单位为g/cm²。μ子的能量损失约为每g/cm² 2 MeV。大气的相互作用深度约为1000 cm²，因此μ子穿过大气层时损失约2 GeV。考虑到在海平面检测到的μ子平均能量为4 GeV，这表明原始μ子能量大约在6 GeV左右。

Most muons are thought to be created at altitudes of about 15000 meters and travel with other particles to the Earth in conical showers within about 1° of the trajectory of the primary particle which creates them. Measurement of muon flux at different altitudes is a useful example of relativistic time dilation. With an energy of 4 GeV, the time dilation factor is γ = 38.8 .

大多数μ子被认为是在约15000米的高空产生的，并与其他粒子一起以锥形 shower 的形式向地球运动，其轨迹大约在产生它们的初级粒子轨迹的1°范围内。在不同高度测量μ子通量是相对论性时间膨胀的一个有用例子。当能量为4 GeV时，时间膨胀因子是γ = 38.8。