Simulation and photoelectron track reconstruction of soft X-ray polarimeter

The soft X-ray polarimeter(SXP)is a detector with a wide energy range,large area,and large field of view.A SXP will be mounted on the Chinese Space Station and will mainly focus on detecting the polarization of transient soft X-ray(2–10 keV)sources,especially gamma-ray bursts(GRBs).In this work,a polarimeter detector unit is taken as an example,and Geant4 and Garfield++software are used to simulate the detection efficiency and track production.An improved track reconstruction algorithm is proposed and used to reconstruct two-dimensional images of the tracks.In this method,the initial emission angle of photoelectrons is reconstructed from the initial part of the track by shortening or extending the initial part of the track until the remaining track is straight,and the number of pixels is within an adjustable threshold.The modulation factor of the photoelectronic tracks after reconstruction reaches approximately 57%in the photon energy range of 7–10 keV.

Simulation and reconstruction of particle trajectories in the CEPC drift chamber

The circular electron-positron collider(CEPC)is designed to precisely measure the properties of the Higgs boson,study electroweak interactions at the Z-boson peak,and search for new physics beyond the Standard Model.As a component of the 4th conceptual CEPC detector,the drift chamber facilitates the measurement of charged particles.This study implemented a Geant4-based simulation and track reconstruction for the drift chamber.For the simulation,detector construction and response were implemented and added to the CEPC simulation chain.The development of track reconstruction involves track finding using the combinatorial Kalman filter method and track fitting using the tool of GenFit.Using the simulated data,the tracking performance was studied.The results showed that both the reconstruction resolution and tracking efficiency satisfied the requirements of the CEPC experiment.

Track reconstruction using the TSF method for the BESⅢ main drift chamber

We describe the algorithm to reconstruct the charged tracks for BESⅢ main drift chamber at BEPCⅡ, including the track finding and fitting. With a new method of the Track Segment Finder （TSF）, the results of present study indicate that the algorithm can reconstruct the charged tracks over a wide range of momentum with high efficiency, while improving the robustness against the background noise in the drift chamber. The overall performances, including spatial resolution, momentum resolution and secondary vertices reconstruction efficiency, etc. satisfy the requirements of BESⅢ experiment.

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 of low momentum track reconstruction for the BESⅢ main drift chamber

In order to overcome the difficulty brought by the circling charged tracks with transverse momentum less than 120 MeV in the BESⅢ Main Drift Chamber （MDC）, a specialized method called TCurlFinder was developed. This tracking method focuses on the charged track reconstruction under 120 MeV and possesses a special mechanism to reject background noise hits. The performance of the package has been carefully checked and tuned by both Monte Carlo data and real data. The study shows that this tracking method could obviously enhance the reconstruction efficiency in the low transverse momentum region, providing physics analysis with more and reliable data.

Low transverse momentum track reconstruction based on the Hough transform for the BESIII drift chamber

Background The multilayer drift chamber(MDC)is one of the key detectors at the BESIII,which is mainly responsible for the precise measurement of charged particles.High reconstruction efficiency of charged particles with a wide range of momentums is a basic requirement for the MDC reconstruction software.Purpose The purpose is to improve the tracking efficiency at the low transverse momentum region.Methods The Hough transform is a mathematical method that can map hits in a detector to parameter space to find tracks globally.In this paper,we have used it as the basis for developing a new tracking algorithm to find tracks in MDC.In addition,the drift distances of hits are considered when implementing Hough transform.Results This tracking algorithm is implemented in the BESIII offline software system,and its performance is checked using both Monte Carlo and data.The results show that this tracking method improves reconstruction efficiency at the low transverse momentum region.Conclusions The tracking algorithm based on Hough transform is proved to be beneficial for the MDC low transverse momentum tracking,and has been used in BESIII offline data reconstruction .

Track reconstruction based on Hough-transform for nTPC

A GEM-TPC prototype, which will be used as a fast neutron spectrometer based on the recoil proton method, is designed and being constructed in Tsinghua University. In order to derive the recoil angle of the recoil proton, tracks of recoil proton in the TPC sensitive volume must be reconstructed. An algorithm based on Houghtransform for track finding and least square method for track fitting was developed in this paper. Based on the Monte Carlo simulation data given by Geant 4, a detailed track reconstruction process was introduced and the spectrum of induced fast neutron was derived here. The results show that the algorithm was effective and high-performance.With the recoil angle of the proton less than 30°, a 4.4% FWHM neutron energy resolution was derived for 5 Me V induced fast neutron, and the detection efficiency was about 2×10^-4.

Adaptive multitrack reconstruction for particle trajectories based on fuzzy c-regression models

In this paper, an approach to straight and circle track reconstruction is presented, which is suitable for particle trajectories in an homogenous magnetic field （or 0 T） or Cherenkov rings. The method is based on fllzzy c-regression models, where the number of the models stands for the track number. The approximate number of tracks and a rough evaluation of the track parameters given by Hough transform are used to initiate the fuzzy c-regression models. The technique effectively represents a merger between track candidates finding and parameters fitting. The performance of this approach is tested by some simulated data under various scenarios. Results show that this technique is robust and could provide very accurate results efficiently.

BACKGROUND RECONSTRUCTION AND OBJECT EXTRACTION BASED ON COLOR AND OBJECT TRACKING

In YCbCr colorspace, a method is proposed to reconstruct the background and extract moving objects based on the Gaussian model of chroma components. Background model is updated according to changes of chroma components. In order to eliminate the disturbance of shadow, a shadow detecting principle is proposed in YCbCr colorspace. A Kalman filter is introduced to estimate objects＇ positions in the image and then the pedestrian is tracked according to its information of shape. Experiments show that the background reconstruction and updating are successful, object extraction and shadow suppression are satisfactory, and real-time and reliable tracking is realized.

Simulation study of BESⅢwith stitched CMOS pixel detector using AcTs

The reconstruction of the tracks of charged particles with high precision is crucial for HEP experiments to achieve their physics goals.The BESⅢdrift chamber,which is used as the tracking detector of the BESⅢexperiment,has suffered from aging effects resulting in degraded tracking performance after operation for approximately 15 years.To preserve and enhance the tracking performance of BESⅢ,one of the proposals is to add one layer of a thin cylindrical CMOS pixel sensor based on state-of-the-art stitching technology between the beam pipe and the drift chamber.The improvement in the tracking performance of BESⅢwith such an additional pixel detector compared to that with only the existing drift chamber was studied using the modern common tracking software Acts,which provides a set of detector-agnostic and highly performant tracking algorithms that have demonstrated promising performance for a few high-energy physics and nuclear physics experiments.

Simulation and prototype testing of multi-wire drift chamber arrays for the CEE

The building of a large-scale external-target experiment, abbreviated as CEE, in the cooling storage ring at the Heavy Ion Research Facility in Lanzhou has been planned. The CEE is a multi-purpose spectrometer that will be used for various studies on heavy-ion collisions. A multi-wire drift chamber(MWDC) array is the forward tracking detector of the CEE. In this work, GEANT4 simulations were performed for the MWDC forward tracking array with a focus on the track reconstruction algorithm. Combined with the time of flight information,particle identification is achieved. The residue is about 30 μm, while the tracking efficiency is higher than 90%with the current redundancy. In addition, a prototype of the forward tracking system using three MWDCs was assembled and tested using a high-energy proton beam. The firing efficiency of the detector and the reconstruction accuracy of the prototype were derived. The track residue for the protons at about 400 MeV/c is better than 300 μm, meeting the requirements of the CEE. Suggestions for improving the performance of the forward tracking system are given.

Real-time human segmentation by BowtieNet and a SLAM-based human AR system

Background Generally, it is difficult to obtain accurate pose and depth for a non-rigid moving object from a single RGB camera to create augmented reality (AR). In this study, we build an augmented reality system from a single RGB camera for a non-rigid moving human by accurately computing pose and depth, for which two key tasks are segmentation and monocular Simultaneous Localization and Mapping (SLAM). Most existing monocular SLAM systems are designed for static scenes, while in this AR system, the human body is always moving and non-rigid. Methods In order to make the SLAM system suitable for a moving human, we first segment the rigid part of the human in each frame. A segmented moving body part can be regarded as a static object, and the relative motions between each moving body part and the camera can be considered the motion of the camera. Typical SLAM systems designed for static scenes can then be applied. In the segmentation step of this AR system, we first employ the proposed BowtieNet, which adds the atrous spatial pyramid pooling (ASPP) of DeepLab between the encoder and decoder of SegNet to segment the human in the original frame, and then we use color information to extract the face from the segmented human area. Results Based on the human segmentation results and a monocular SLAM, this system can change the video background and add a virtual object to humans. Conclusions The experiments on the human image segmentation datasets show that BowtieNet obtains state-of-the-art human image segmentation performance and enough speed for real-time segmentation. The experiments on videos show that the proposed AR system can robustly add a virtual object to humans and can accurately change the video background.

Track matching study from TPC to PHOS in ALICE

We present a study for matching charged tracks reconstructed from the ALICE tracking detectors with the clusters measured in the photon spectrometer. Matching efficiency and contaminations due to wrong matches have been deduced for charged pions and muons. For electrons, the effect of the material in front of PHOS is discussed.

An extended segment pattern dictionary for a pattern matching tracking algorithm at BES Ⅲ

A pattern matching based tracking algorithm, named MdcPatRec, is used for the reconstruction of charged tracks in the drift chamber of the BESIII detector. This paper addresses the shortage of segment finding in the MdcPatRec algorithm. An extended segment construction scheme and the corresponding pattern dictionary are presented. Evaluation with Monte-Carlo and experimental data show that the new method can achieve higher efficiency for low transverse momentum tracks.

Development of a 6D Kalman filter for charged particle tracking in time projection chamber without magnetic field

Background Track reconstruction is necessary for time projection chamber(TPC),because TPCs usually face the measure-ment error that impedes gaining precise spacial and angular resolution.Purpose Kalman filter is a well-performed and applicable algorithm to denoise and reconstruct the event track.Methods In this paper,we develop a six-dimensional Kalman filter to reconstruct the particle track in high-energy physics experiments,while the most common form of Kalman filter used in many research fields is four-dimensional.The modelisation is based on a gaseous TPC,and the whole reconstruction process is first tested by a toy Monte Carlo simulation.Results The results show the Kalman filter can effectively reduce the noise and improve the detector resolution.Then,the performance of the Kalman filter is also verified with the data produced by the Geant4 toolkit.

Determination of event start time at BESⅢ

The principle of the method for the BESⅢ event start time determination and the code construction are described. The investigation of influence of the noise, the method of rejecting noise and the performance checking by the Monte Carlo physics data sample are also presented. The preliminary results got from the Monte Carlo simulation are presented, the reconstruction efficiency of J/ψ → anything events at noise level 0 - 60% can achieve above 99%, and the error rate is below 1%.

Performance study of a novel sampling TPC prototype detector based on THGEM

Introduction Time projection chamber(TPC)with micropattern gaseous detectors(MPGDs)as readout has been one of the research hotspots in recent years.MPGD-based TPC has been applying to many experiments due to its high spatial and energy resolutions in 3D track measurement.Purpose A novel sampling TPC detector based on thick gaseous electron multiplier(THGEM)was developed to measure the low-energy electron tracks online from 0.1 to 50 MeV with a 100μm spatial resolution in a vacuum tank.The tracks will be extrapolated to determine the hit positions on a target about 200mm behind the TPC.Methods and materials A new type of self-developed THGEM detector was chosen as the TPC readout unit.The field cage has two 50×50mm2 windows welded by Gold-plated tungsten wires for low-energy electrons passing through.The front-end electronics was designed with a self-developed application specific integrated circuit chip,i.e.,CASA-GEM.Seven columns of readout pads were used to equidistantly sample the electron tracks in a length of 75mm.Each column has 72 pads of 0.56×0.56mm2 and two additional strips along each column for drift time measurement.Both Geant4 and Garfield++were chosen to simulate and optimize the detector,such as the penetration efficiency,electric field in field cage and operating gas pressure.Results The design and the preliminary performances of the TPC detector were verified by beam test andβsource test.A drift velocity of 3.415±0.103 cm/μs was measured at 125 V/cm in Ar+iC4H10(97:3)forπ−.The electron detection efficiency is about 88%forβsource.And the gain of the double THGEM reached more than 1.0×10^(4).

Performance study of the neutron-TPC

Fast neutron spectrometers will play an important role in the future of the nuclear industry and nuclear physics experiments, in tasks such as fast neutron reactor monitoring, thermo-nuclear fusion plasma diagnostics,nuclear reaction cross-section measurement, and special nuclear material detection. Recently, a new fast neutron spectrometer based on a GEM（Gas Electron Multiplier amplification）-TPC（Time Projection Chamber）, named the neutron-TPC, has been under development at Tsinghua University. It is designed to have a high energy resolution,high detection efficiency, easy access to the medium material, an outstanding n/γ suppression ratio, and a wide range of applications. This paper presents the design, test, and experimental study of the neutron-TPC. Based on the experimental results, the energy resolution（FWHM） of the neutron-TPC can reach 15.7%, 10.3% and 7.0% with detection efficiency higher than 10^-5 for 1.2 Me V, 1.81 Me V and 2.5 Me V neutrons respectively.

A simulation study of a high-resolution fast neutron imaging detector based on liquid scintillator loaded capillaries

Background At present,the highest spatial resolution of a fast neutron imaging detector,mainly determined by the range of secondary particles generated by fast neutrons,is about hundreds of microns.In view of the above inherent spatial resolution limitation,a capillary-based scintillation detector that can improve the spatial resolution of fast neutron imaging by recording and reconstructing the recoil proton track was developed.Purpose The purpose of this paper is to develop a detector for recognizing recoil proton events,reconstructing particle track and improving the position resolution with track reconstruction method to reconstruct the position of interaction.Methods The proposed detector consists of a 1000×1000 array of glass capillaries loaded with a high refractive index liquid scintillator.Each glass capillary was 10μm in diameter and 5 cm in length.The recoil protons generated by the incident neutrons move within the detector and produce scintillation light within each capillary that they traverse.The light emitted from the capillary array can be recorded by employing an intensified CCD camera.We used Geant4 to simulate the detector performance and CERN ROOT analysis framework to record physical information of recoil proton,including position,energy deposition in each capillary and track length.Based on Hough transform,a rapid,computerized and efficient proton track reconstruction procedure was developed.Conclusion The recoil proton events display a continuous extended structure.The track reconstruction algorithms can reconstruct individual track precisely,and when the counting rate was relatively low,the track reconstruction results were in good agreement with simulation data.Moreover,for intensive overlap conditions,this algorithm also reconstructs periphery tracks with high rate of accuracy.