Observation of Cosmic Rays by using a Balloon-Borne Superconducting Magnet Spectrometer

计划进行Bess实验(使用超导磁谱仪的气球搭载实验)，并开发Bess探测器来研究宇宙线反粒子的起源，如反质子和反氦原子核。由于运动学抑制，次级反质子的能谱在1GeV以下非常低。另一方面，来自假设来源的反质子，如中性微子暗物质粒子的湮灭或原始黑洞的蒸发，给出了相当平坦的光谱。因此，低能反质子对这些外来来源非常敏感。探测器系统由一个薄薄的超导螺线管磁体、一个圆柱形喷流漂移室、4层弧形漂移室和飞行时间计数器组成。Bess探测器的圆柱形结构提供了广泛的跟踪体积和较大的几何接受度。Bess的气球飞行于1993年7月在加拿大林恩湖进行。该仪器在36.5公里的高空飞行了14个小时。飞行期间共记录了400万次反质子事件，其中包括0.4次能量低于500 MeV的贝克格德事件，这是对低能反质子的首次正向测量。计算了反质子通量与质子的比值，发现该模型与二次生产的模型是一致的，但该模型仍存在较大的不确定性。

The BESS experiment (Balloon-borne Experiment using a Superconducting magnet Spectrometer) was planned and the BESS detector was developed to investigate an origin of cosmic ray anti-particles such as anti-protons and anti-helium nuclei. The spectrum of secondary anti-protons are extremely low below 1 GeV due to the kinematical suppression. On the other hand, the anti-protons expected from the hypothetical sources such as the annihilation of neutralino dark matter particles or the evaporation of primordial black holes give rather flat spectrum. Therefore low energy anti-protons are sensitive to those exotic origins.The detector system consisted of a thin superconducting solenoidal magnet, a cylindrical jet-drift chamber, 4 layrs of arc-shaped drift chambers and time-of-flight counters. The cylindrical configuration of the BESS detector provided a wide tracking volume and a large geometrical acceptance.The balloon flight of the BESS was carried out at Lynn Lake, Canada, in July 1993. The instrument flew at an altitude of 36.5 km for 14 hours. A total of 4 million events were recorded during the flight.We detected 4 anti-protons including 0.4 events of beckground at energies below 500 MeV.This was the first positive measurement of the low energy anti-protons. The ratio of anti-proton flux to proton was calculated and it was found to be consistent with the model of the secondary production, though the model has still large uncertainties.