Low energy ground-based cosmic ray air shower experiments generally have energy threshold in the range of a few tens to a few hundreds of TeV. The shower observables are measured indirectly with an array of detectors. The atmospheric absorption of low energy secondaries limits their detection frequencies at the Earth's surface. However, due to selection effects, a tiny fraction of low energy showers, which are produced in the lower atmosphere can reach the observational level. But, due to less information of shower observables, the reconstruction of these showers are arduous. Hence, it is believed that direct measurements by experiments aboard on satellites and balloon flights are more reliable at low energies. Despite having very small efficiency ($\sim$0.1%) at low energies, the large acceptance ($\sim$5 m$^2$sr) of GRAPES-3 experiment allows observing primary cosmic rays down below to $\sim$1 TeV and opens up the possibility to measure primary energy spectrum spanning from a few TeV to beyond cosmic ray knee (up to 10$^{16}$ eV), covering five orders of magnitude. The GRAPES-3 energy threshold for primary protons through Monte Carlo simulations are calculated, which gives reasonably good agreement with data. Furthermore, the total efficiencies and acceptance are also calculated for protons primaries. The ability of GRAPES-3 experiment to cover such a broader energy range may provide a unique handle to bridge the energy spectrum between direct measurements at low energies and indirect measurements at ultra-high energies.

中文翻译：

---

GRAPES-3 EAS 阵列对初级宇宙射线质子的能量敏感性

低能地基宇宙射线风淋实验的能量阈值一般在几十到几百 TeV 之间。淋浴观测值是通过一系列探测器间接测量的。低能量次级物质的大气吸收限制了它们在地球表面的探测频率。然而，由于选择效应，在低层大气中产生的一小部分低能量阵雨可以达到观测水平。但是，由于阵雨可观测信息较少，对这些阵雨的重建十分困难。因此，据信通过卫星和气球飞行的实验直接测量在低能量下更可靠。尽管在低能量下效率非常低（$\sim$0.1%），GRAPES-3 实验的广泛接受（$\sim$5 m$^2$sr）允许观察低于 $\sim$1 TeV 的初级宇宙射线，并开辟了测量从几个 TeV 到更大范围的初级能谱的可能性宇宙射线膝（最高 10$^{16}$ eV），覆盖五个数量级。通过蒙特卡罗模拟计算了初级质子的 GRAPES-3 能量阈值，这与数据具有相当好的一致性。此外，还计算了质子初级的总效率和接受度。GRAPES-3 实验覆盖如此广泛的能量范围的能力可以提供一个独特的处理方法，以在低能量的直接测量和超高能量的间接测量之间架起能谱。