Track segment finding with CGEM-IT and matching to outer drift chamber tracks in the BESIII detector

The relative differences in coordinates of Cylindrical Gas Electron Multiplier Detector-based Inner Tracker(CGEM-IT) clusters are studied to search for track segments in CGEM-IT for the BESIII experiment.With the full simulation of single muon track samples, clear patterns are found and parameterized for the correct cluster combinations. The cluster combinations satisfying the patterns are selected as track segment candidates in CGEM-IT with an efficiency higher than 99%. The parameters of the track segments are obtained by a helix fitting.Some χ~2 quantities, evaluating the differences in track parameters between the track segments in CGEM-IT and the tracks found in the outer drift chamber, are calculated and used to match them. Proper χ~2 requirements are determined as a function of transverse momentum and the matching efficiency is found to be reasonable.     

Monte Carlo studies of micromegas as a neutron detector and its track reconstruction

In this paper a two dimensional readout micromegas detector with a polyethylene foil as converter was simulated on GEANT4 toolkit and GARFIELD for fast neutron detection.A new track reconstruction method based on time coincidence technology was developed in the simulation to obtain the incident neutron position.The results showed that with this reconstruction method higher spatial resolution was achieved.     

Lagrange multiplier method used in BESⅢ kinematic fitting

In this paper,the kinematic fitting with the Lagrange multiplier method has been studied for BESⅢ experiment.First we introduce the Lagrange multiplier method and implement kinematic constraints.Then we present the performance of the kinematic fitting algorithm.With the kinematic fitting,we can improve the resolution of track parameters and reduce the background.     

Monte Carlo studies of micromegas as a neutron detector and its track reconstruction

In this paper a two dimensional readout micromegas detector with a polyethylene foil as converter was simulated on GEANT4 toolkit and GARFIELD for fast neutron detection. A new track reconstruction method based on time coincidence technology was developed in the simulation to obtain the incident neutron position. The results showed that with this reconstruction method higher spatial resolution was achieved.     

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial reso-lution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.     

Lagrange multiplier method used in BESⅢ

In this paper, the kinematic fitting with the Lagrange multiplier method has been studied for BESⅢ experiment. First we introduce the Lagrange multiplier method and implement kinematic constraints. Then we present the performance of the kinematic fitting algorithm. With the kinematic fitting, we can improve the resolution of track parameters and reduce the background.     

Electrical characterization of polymer matrix — TiO2 filler composites through isothermal polarization / depolarization currents and I–V tests

Specimens of polymer matrix — ceramic TiO₂ filler composites were prepared. The contribution of the filler content on the electrical conductivity and energy storage properties of the samples was examined. I–V and Isothermal Polarization/Depolarization Current (IPC/IDC) measurements were conducted. Dc conductivity values directly calculated from the I–V curves exhibited excellent agreement with corresponding values derived from the IPC/IDC recordings. Standard models were employed for fitting the IPC/IDC data. In specific, the short and the very long depolarization times were fitted by use of power laws of different slopes, while the intermediate depolarization times were fitted as a sum of three exponential decays. The present study reveals a strong dependence of the depolarization and polarization processes, as well as of the dc conductivity, on the filler concentration.     

Preparation for the alignment of the ALICE inner tracking system

Tracking detectors in high-energy physics experiments require an accurate determination of a large number of alignment parameters in order to allow a precise reconstruction of tracks and vertices. In addition to the initial optical survey, the use of tracks in a special software alignment is essential. The methods in use for the alignment of the ALICE Inner Tracking System are presented, starting from residual-based procedure to fitting systems with many thousands of parameters. The two methods are reviewed and the preliminary results showed.     

一种简便的计算层析系统X射线硬化校正方法

以实物拍摄为依据,用一种最简便的修正方法解决计算机X射线层析术成像时由于硬化效应引起的切片图灰度失真问题。用高性能数字X射线机FAXITRON MX-20(射线管焦点20μm,探测板灰度等级16位)对不同厚度的物体进行透射成像,测得对应的透射光强度,并利用新创的指数拟合法得到理想的拟合曲线,由此推导硬化效应的指数校正公式;最后利用实验室的微型计算机层析设备进行扇形束扫描,并逆投影重建生成计算层析断层图像,验证了该校正方法的实用性。该指数拟合法的误差不到常用的二阶多项式拟合法的1/3,对物体计算层析重构,硬化校正以前有明显的“杯状”伪迹,切片灰度不均匀,用指数法修正以后该伪迹消失,切片灰度均匀。     

A 45° PROTOTYPE OF THE CENTRAL DRIFT CHAMBER FOR BES AND RESULTS OF COSMIC RAY TEST

It is described that the function,structure, amplitude characteristics and results of cosmic ray test of a prototype of the central drift chamber for Beijing Spectrometer (BES). It was found that if appropriate high voltage is applied on the field wires homogeneous signal amplitude from different Layer of the chamber can be obtained. The drift velocity deduced by track reconstruction is 5.3cm/μs. The spatial resolution is about 134μm.     

Fast simulation of the forward tracking detector of HPLUS

The necessity of installing a forward tracking detector stack is discussed for the Hadron Physics LanzhoU Spectrometer(HPLUS).A local tracker is developed to solve the multi-track finding problem.The track candidates are searched iteratively via Hough Transform.The fake tracks are removed by a least square fitting process.With this tracker we have studied the feasibility of pp→pp + φ(→K+K-),a typical physical channel proposed on HPLUS.The single track momentum resolution due to the uncertainty of the positioning in FTD is 1.3%.The multiple scattering effect contributes about 20% to the momentum resolution in the FTD coverage.The width and the signal-to-background ratio of the reconstructed φ are 1.51 MeV and 4.36,respectively,taking into account the direct Kaon channel pp→pp+K+K- as background.The geometry coverage of FTD for φ events is about 85.4%.Based on the current fast simulation and estimation,the geometrical configuration of FTD meets the physical requirement of HPLUS under the current luminosity and multiplicity conditions.The tracker is applicable in the full simulation coming next and is extendable to other tracking component of HPLUS.     

用曲线拟合方法测量空气阻尼常量

以物体在气垫导轨上做一维阻尼运动为例,用曲线拟合方法推导出空气的阻尼常量的计算公式,利用与计算机相连的数码照像机采集数据,画出拟合曲线,从而得出了空气的阻尼常量.     

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial resolution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.     

Distributed Brillouin fiber sensing based on spectrum line fitting and wavelet packet denoising

A novel signal processing method is proposed to improve the spatial resolution, frequency resolution and dynamic characteristics of BOTDR. For the BOTDR system with 50 ns pump pulse, by using spectrum line fitting technology based on Levenberg-Marquardt (LM) algorithm, the spatial resolution is improved from 5 m to 5 cm. Combination of LM fitting algorithm, a large frequency scanning interval is adopted without sacrificing measurement accuracy of the BOTDR system. It reduces the number of sampling points of Brillouin spectrum significantly. So, the fitting speed is improved greatly. This is the first time using a large scan interval to increase the spectrum line fitting speed. To improve the fitting speed, the difference between the reference and measured spectrum is used to estimate the variation of Brillouin frequency shift. The measured amplitude of Brillouin spectrum is used to estimate the width of region strain occurred. Finally, by using wavelet packet denoising technology, the spectra containing noise are fitted successfully.     

Computerized Tomography for Sparse-Data Plasma Physics Experiments

Matrix inversion and least squares fitting have been used to recover two dimensional distribution functions from a small number of line integrals taken along chords across them. A self-consistent optimization procedure, free from reliance on comparison with a trial source function, for optimizing the configuration of these chords is described and used to demonstrate that an asymmetric arrangement usually leads to greater reconstruction accuracy than a regular array. Smoothing is incorporated by imposing auxiliary conditions relating to the second derivative ?2f of the source function f, and its effect on reconstruction accuracy and resolution is investigated. These methods are applied to the ten-channel far-infrared interferometer being prepared for use on JET. Electron denisty contour shapes can be identified rather sensitively if the source function contours belong to a predetermined family.     

A position resolution MRPC for muon tomography

Muon tomography is a promising method in the detection and imaging of high Z material. In general, considering the quality of track reconstruction in imaging, a detector of good position resolution, high efficiency and large area is required. This paper presents the design and study of a prototype of position sensitive MRPC with 0.15 mm narrow gas gap and 2.54 mm strip readout. Through a cosmic-ray experiment, the performance of MRPC module is carefully observed and each channel is calibrated. Through an X ray experiment with a narrow slit, the position resolution is studied. The results show that the time resolution of the module can reach 61ps and the spatial resolution can reach 0.36 mm.     

Geometry optimization of a barrel silicon pixelated tracker

We have studied optimization of the design of a barrel-shaped pixelated tracker for given spatial boundaries. The optimization includes choice of number of layers and layer spacing. Focusing on tracking performance only,momentum resolution is chosen as the figure of merit. The layer spacing is studied based on Gluckstern's method and a numerical geometry scan of all possible tracker layouts. A formula to give the optimal geometry for curvature measurement is derived in the case of negligible multiple scattering to deal with trajectories of very high momentum particles. The result is validated by a numerical scan method, which could also be implemented with any track fitting algorithm involving material effects, to search for the optimal layer spacing and to determine the total number of layers for the momentum range of interest under the same magnetic field. The geometry optimization of an inner silicon pixel tracker proposed for BESIII is also studied by using a numerical scan and these results are compared with Geant4-based simulations.     

基于高斯拟合的条纹管成像激光雷达目标重构

为得到更为精细的三维重构,提出一种基于信赖域法高斯拟合的峰值探测法,对每帧图像单时间通道的回波进行高斯建模,建模结果可有效减小噪声干扰,具有唯一峰值,该结果作为新的回波波形,再对其进行峰值探测,并基于空中目标实验数据对本文方法进行验证.实验结果表明,基于高斯拟合的峰值探测法可将特征数据的提取误差降至10%以内;利用该方法提取特征数据进行目标三维重构,可实现探测深度方向上最小30cm的空间分辨力,提高了条纹管激光雷达的三维成像精度.     

Enhanced resolution for EPR imaging by two-step deblurring

The broad spectrum of spin probes used for electron paramagnetic resonance imaging (EPRI) result in poor spatial resolution of the reconstructed images. Conventional deconvolution procedures can enhance the resolution to some extent but obtaining high resolution EPR images is still a challenge. In this work, we have implemented and analyzed the performance of a postacquisition deblurring technique to enhance the spatial resolution of the EPR images. The technique consists of two steps; noniterative deconvolution followed by iterative deconvolution of the acquired projections which are then projected back using filtered backprojection (FBP) to reconstruct a high resolution image. Further, we have proposed an analogous technique for iterative reconstruction algorithms such as multiplicative simultaneous iterative reconstruction technique (MSIRT) which can be a method of choice for many applications. The performance of the suggested deblurring approach is evaluated using computer simulations and EPRI experiments. Results suggest that the proposed procedure is superior to the standard FBP and standard iterative reconstruction algorithms in terms of mean-square-error (MSE), spatial resolution, and visual judgment. Although the procedure is described for 2D imaging, it can be readily extended to 3D imaging.     

应用Kalman filter建立时间投影室的径迹重建算法

建立直线径迹模型,详细验证将其用于Kalman filter小型时间投影室径迹重建算法的正确性.结果表明径迹参数在一定的击中点下能够收敛到真实值.实际的径迹重建程序在MarlinTPC框架下实现.通过合理地选择径迹重建参数,程序能够有效地对噪声进行甄别并重建出径迹.本算法对大型时间投影室的径迹重建有借鉴意义.