小丸内靶靶丸跟踪定位系统的研制

HPLUS (Hadron Physics LanzhoU Spectrometer), which is an internal target experiment, has been planned to be built up at CSRm for hadron physics study. The frozen pellet of liquid hydrogen or deuterium is one of the best candidates as the target because it's capable of providing high luminosity conditions, at the same time minimizing background from secondary reactions. Furthermore, the use of pellet target makes it possible for HPLUS detector to provide nearly full solid angle coverage and precisely reaction production tracking which are important for kinematically complete measurements of multi-particle final states..The basic principle is that gas, e.g. hydrogen, is liquefied by liquid helium in a first stage and small droplets are formed by vibrations with 50~100 kHz. These are in next stage injected into vacuum, in which pellets i.e. a train of frozen micro-spheres are produced by evaporative cooling. Then, the pellet will interact with the circulating ion beam perpendicularly in the reaction chamber. The precise determination of the reaction vertex is very helpful for the reconstruction of the events with short-lived production particles, especially those particles comprise charm quarks. Therefore, we are now planning to develop a pellet tracking system to determine the position of reaction vertex with high precision. This system is composed of 3 positioning planes, on each of them 2 line scanning cameras are recording the X, Z coordination of the pellet. Thus, the pellet trajectory can be reconstructed via 2 or 3 positioning. The accuracy for vertex positioning in the reaction area is expected to reach tens of micrometers.

HPLUS是计划建造在兰州CSRm上用于强子物理研究的内靶实验装置，由于小丸靶能为内靶实验提供足够高的事件率，同时可以配置4π立体角的探测器单元，并能进行准确的径迹构建，因此被确定为HPLUS的主要内靶之一。.小丸内靶是用液氦将某种气体冷却液化，通过外加固有频率的振动形成液滴串，然后通过蒸发冷却形成固体靶丸。靶丸与束流离子在反应室内碰撞发生反应。对于产物粒子寿命非常短的反应，尤其是带有粲夸克产物粒子的反应来说，事例顶点的精确定位对于反应过程的重建就非常重要了。本项目拟研制一套靶丸跟踪定位系统，实现靶丸与束流反应点的精确定位。该系统主要由三组平面定位组成，每组平面定位由两台线扫描相机记录该平面内靶丸的x、z两轴坐标，通过两点或三点定位拟合获得靶丸的整个飞行轨迹。该系统在反应区最终给出的顶点定位精确度最高可达到几十微米量级。

小丸内靶跟踪系统是小丸内靶装置的一套辅助测量系统，该系统用于测量小丸在反应点的位置和时间信息，记录每个小丸的飞行轨迹和时间，配合其它探测器实现反应事例顶点的精确定位，精确度能够达到几十微米量级。在项目执行期间，完成了该系统的前期的测试工作，选定了相机、镜头的型号和光源的功率5.5mW，确定了该系统的最终结构，即相机与光源的夹角为135度；测定了线扫描相机频率为98.0008Khz和镜头M7528-MP最小物距为285mm，此时放大倍率为0.244。确定了该系统可测量的事例定点的精确度为62.5µm。完成了系统的获取程序的编写与调试工作。最后整个系统搭建工作已完成。