大型强子对撞机上的CMS实验

CMS探测器是大型强子对撞机（LHC）上的四个实验之一,位于日内瓦附近的欧洲核子中心（CERN）法国一侧地下100米处。它的全称是“紧凑“子螺线管”（Compact Muon Solenoid）。     

考虑旋转中心标定误差的中子偏置计算机断层扫描成像方法

中子偏置CT(computed tomography)扫描是一种有效的大尺寸样品层析检测方法,但投影数据截断会导致较大的CT系统转台旋转中心标定误差,严重影响成像质量。基于投影数据对称性原理,提出了一种计算旋转中心左侧和右侧投影数据和之间方差的偏置CT扫描旋转中心精确标定算法。设计了对称补数据重建算法和投影数据预处理重建算法,验证得到,对称补数据重建算法对旋转中心标定误差更为敏感,较小的误差值会导致补齐后投影数据出现拼接缝以及拼接错位问题。提出了一种中子投影数据噪声仿真方法,设计的三维仿真模体验证了所提标定算法与投影数据预处理重建算法在不同旋转中心偏置大小以及不同强度投影噪声条件下的性能优势。基于反应堆中子源开展了中子偏置CT扫描成像验证实验,获得了样品清晰的内外部结构细节,中子CT成像系统的成像视野扩大了31.4%。     

L3实验单W产生截面及反常耦合常数的测量

使用1996和1997年在L3探测器上获得的数据,对单W粒子产生过程e⁺e^－→e^－ν_eW⁺和e⁺e^－→e⁺νe W^－的反应截面做出了测量,并根据测量结果给出WWγ三玻色子耦合的反常耦合常数为:－0.65<△κ_γ,<0.82,－1.37<λ_γ<0.92.实验结果在误差范围内是与标准模型的理论值一致的,没有发现反常耦合常数存在的迹象.     

利用椭圆投影测量锥束CT系统投影坐标原点新方法

In order to determine the projected coordinate origin in the cone-beam CT scanning system with respect to the Feldkamp-Davis-Kress （FDK） algorithm, we propose a simple yet feasible method to accurately measure the projected coordinate origin. This method was established on the basis of the theory that the projection of a spherical object in the cone-beam field is an ellipse. We first utilized image processing and the least square estimation method to get each major axis of the elliptical Digital Radiography （DR） projections of a group of spherical objects. Then we determined the intersection point of the group of major axis by solving an over-determined equation set that was composed by the major axis equations of all the elliptical projections. Based on the experimental results, this new method was proved to be easy to implement in practical scanning systems with high accuracy and anti-noise capability.     

两种CT成像环状伪影校正方法

探测器探元响应的不一致性导致计算机层析成像(CT)图像产生环状伪影,使得像质下降,影响了缺陷的判读以及图像的后续处理与量化分析.提出了两种CT成像环状伪影校正方法:基于特征识别的校正方法和基于B样条曲线拟合的校正方法.前者针对单个独立探元或者少数几个相邻探元存在突出响应不一致的情况.该方法首先识别出响应不一致探元的位置,然后在该位置执行局部中值滤波以消除正弦图中的竖直条纹.后者针对多个连续探元同时存在微小响应不一致的情况.该方法用B样条曲线拟合的方法确定各个探元的归一化增益系数,进而对探元的响应不一致性进行校正.两种方法各有特点,互为补充,共同组成较为完备的环状伪影校正体系.实验结果验证了两种方法的有效性.     

AMS02电磁量能器三维重建

研究了AMS02电磁量能器簇射三维重建, 发展出一个新的三维重建程序, 并用 蒙特卡罗模拟以及2002年束流测试数据对其进行了检验．该程序应用两次方向 重建、结合光纤衰减修正、横向以及纵向能量泄漏补偿, 完整地对事例进行了 重建, 得到了较为理想的能量分辨率和角度分辨率．     

铅-闪烁光纤夹层电磁量能器的角分辨研究

深入讨论了如何提高铅--闪烁光纤夹层电磁量能器角分辨的分析方法. 用MC方法模拟量能器对不同能量光子事例的响应, 得到了量能器电磁簇射位置测量误差函数; 通过量能器束流测试数据分析, 证明用每层所有测量单元计算该层重心、所有18层做方向重建、并运用误差函数来拟合入射方向, 能够从分析角度显著地改善量能器的角分辨.     

均匀取样电磁量能器能量纵向泄漏的修正

研究对铅-闪烁光纤夹层电磁量能器能量纵向泄漏的纠正.对AMS02电磁量能器2002年束流测试的数据进行了分析,用Γ函数拟合的方法和末层沉积能量法对量能器的能量纵向泄漏进行了修正.经过修正后的能量线性变好,能量分辨率显著提高.末层沉积能量法对于能量分辨率的提高效果更为明显.     

Angular reconstruction of a lead scintillating-fiber sandwiched electromagnetic calorimeter

The Neighbor Cell Deposited Energy Ratio(NCDER) is a new method that is proposed to reconstruct incidence position in a single layer for a 3-dimensional imaging electromagnetic calorimeter(ECAL).This method was applied to reconstruct the ECAL test beam data for the Alpha Magnetic Spectrometer-02(AMS-02).The results show that this method can achieve an angular resolution of 7.36±0.08°/E~(1/2)(?)0.28±0.02o in the determination of the photon's direction,which is much more precise than that obtained with the commonly-adopted Center of Gravity(COG) method(8.4±0.1°/E~(1/2)(?)0.8±0.3o).Furthermore,since it uses only the properties of electromagnetic showers,this new method could also be used for other type of fine grain sampling calorimeters.     

Automatic calibration method of voxel size for cone-beam 3D-CT scanning system

For a cone-beam three-dimensional computed tomography （3D-CT） scanning system, voxel size is an important indicator to guarantee the accuracy of data analysis and feature measurement based on 3D-CT images. Meanwhile, the voxel size changes with the movement of the rotary stage along X-ray direction. In order to realize the automatic calibration of the voxel size, a new and easily-implemented method is proposed. According to this method, several projections of a spherical phantom are captured at different imaging positions and the corresponding voxel size values are calculated by non-linear least-square fitting. Through these interpolation values, a linear equation is obtained that reflects the relationship between the voxel size and the rotary stage translation distance from its nominal zero position. Finally, the linear equation is imported into the calibration module of the 3D-CT scanning system. When the rotary stage is moving along X-ray direction, the accurate value of the voxel size is dynamically exported. The experimental results prove that this method meets the requirements of the actual CT scanning system, and has virtues of easy implementation and high accuracy.