Time calibration for the end cap TOF system of BESⅢ

The time calibration for end cap TOF system of BESⅢ is studied in this paper.It has achieved about 110 ps time resolution for muons in dimu events.The pulse height correction using electronic scan curve and the predicted time calculated using Kalman filter method are introduced.This paper also describes the study of using electrons and muous as calibration samples.     

Prototype of time digitizing system for BESⅢ endcap TOF upgrade

The prototype of a time digitizing system for the BESⅢ endcap TOF (ETOF) upgrade is introduced in this paper. The ETOF readout electronics has a distributed architecture. Hit signals from the multi-gap resistive plate chamber (MRPC) are signaled as LVDS by front-end electronics (FEE) and are then sent to the back-end time digitizing system via long shield differential twisted pair cables. The ETOF digitizing system consists of two VME crates, each of which contains modules for time digitization, clock, trigger, fast control, etc. The time digitizing module (TDIG) of this prototype can support up to 72 electrical channels for hit information measurement. The fast control (FCTL) module can operate in barrel or endcap mode. The barrel FCTL fans out fast control signals from the trigger system to the endcap FCTLs, merges data from the endcaps and then transfers to the trigger system. Without modifying the barrel TOF (BTOF) structure, this time digitizing architecture benefits from improved ETOF performance without degrading the BTOF performance. Lab experiments show that the time resolution of this digitizing system can be lower than 20 ps, and the data throughput to the DAQ can be about 92 Mbps. Beam experiments show that the total time resolution can be lower than 45 ps.     

Monte Carlo tuning for the BESⅢ time-of-flight system

Using experimental data, Monte Carlo tuning is implemented for performance parameters associated with the scintillation counters and readout electronics of the BESⅢ time-of-flight(TOF) system, as part of the full simulation model. The implementation of the tuning is described for simulations designed to reproduce the performance of a number of TOF system parameters, including pulse height, hit efficiency, time resolution, dead channels and background. In addition, comparisons with experimental data are presented.     

A GEANT4 simulation study of BESⅢ endcap TOF upgrade

A GEANT4-based Monte-Carlo (MC) model is developed to study the performance of endcap time-of-flight (ETOF) at BESⅢ. It's found that the multiple scattering effects, mainly from the materials at the MDC endcap, can cause multi-hit on the ETOF's readout cell and significantly influence the timing property of ETOF. A multi-gap resistive plate chamber (MRPC) with a smaller readout cell structure is more suitable for the ETOF detector due to significantly reduced multi-hit rate (per channel), from 71.5% for currently-used scintillator-based ETOF to 21.8% or 16.7% for MRPC-based ETOF, depending on the readout pad size used. The timing performance of an MRPC ETOF is also improved. These simulation results suggest and guide an ETOF upgrade effort at BESⅢ.     

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%.     

A study of the calibration of wire positions for the BESⅢ drift chamber using physics data without magnetic field

A method to determine precisely three-dimensional wire positions in the BESⅢ drift chamber using physics events is introduced. In part the proposed technique takes advantage of the possibility that the magnetic field can be turned off, thereby providing a huge sample of straight tracks for which effects due to multiple scattering, energy loss and non-uniformity of the magnetic field are minimized during the calibration process. A toy Monte Carlo study is performed to demonstrate the viability of the method. As a result of the calibration process, the rms of the distribution of wire position deviation is reduced from 35μm to 10μm.     

The Monte Carlo Simulation of BESⅢ Ead cap TOF

The End-Cap TOF (ETOF) of Beijing Spectrometer (BESⅢ) consists of 2×48 pieces of trapezoidal scintillator (BC408). Its main physics goal is to realize the 2σ π/k separation at momentum up to 1GeV/c, and to obtain TOF intrinsic time resolution of 80ps.In order to study the effects of several factors on the intrinsic time resolution of ETOF, the Monte Carlo simulation of the detector is carried out by using Geant4 software package. The performance of ETOF at different conditions, such as scintillator covered materials, shapes, and particle hit positions, is simulated and discussed in discussed in detail. The result can provide a reference for the design of ETOF detecor in BESⅢ.     

Calibration study of the X-T relation for the BESⅢ drift chamber

Offline calibration plays an important role in BES offline data processing. In order to achieve good spatial and momentum resolution, it is necessary to implement high precision offline calibration for the BES drift chamber. This paper studies the time-to-distance relations, which are important calibration constants for track reconstruction. The parameterization of the time-to-distance relation, studies of left-right asymmetry and studies of variation with entrance angle are performed. The impact of dead channels on the time-to-distance relation is given special attention in order to reduce the shift in measured momentum for tracks passing near dead cells. Finally we present the resolutions for barrel Bhabha events(|cos θ|< 0.8) from a J/ψ data set taken in 2012. The average spatial resolution is 123 μm and the momentum resolution for 1.548 Ge V/c Bhabha tracks is 11.9 Me V/c.     

Prototype of time digitizing system for BESⅢ endcap TOF upgrade

The prototype of a time digitizing system for the BESⅢ endcap TOF (ETOF) upgrade is introduced in this paper. The ETOF readout electronics has a distributed architecture. Hit signals from the multi-gap resistive plate chamber (MRPC) are signaled as LVDS by front-end electronics (FEE) and are then sent to the back-end time digitizing system via long shield differential twisted pair cables. The ETOF digitizing system consists of two VME crates, each of which contains modules for time digitization, clock, trigger, fast control, etc. The time digitizing module (TDIG) of this prototype can support up to 72 electrical channels for hit information measurement. The fast control (FCTL) module can operate in barrel or endcap mode. The barrel FCTL fans out fast control signals from the trigger system to the endcap FCTLs, merges data from the endcaps and then transfers to the trigger system. Without modifying the barrel TOF (BTOF) structure, this time digitizing architecture benefits from improved ETOF performance without degrading the BTOF performance. Lab experiments show that the time resolution of this digitizing system can be lower than 20 ps, and the data throughput to the DAQ can be about 92 Mbps. Beam experiments show that the total time resolution can be lower than 45 ps.     

Analysis of the Factors that Influence the Time Resolution of TOF in BESⅢ Detector

In TOF measurement, the factors that can increase the time resolution include noise, amplitude measurement error, and the difference of pulse amplitudes and shapes. This article discusses how these factors affect time resolution, and performs quantitative analysis based on the GEANT4 simulation result of the BESⅢ's TOF detector. The result shows that the discriminator level must be selected carefully. To get better time resolution, pulse waveform digitizing is necessary.     

Absolute photon energy calibration for the BESⅢ EMC

The absolute energy calibration with photons from π0＇s for the BESⅢ EMC is discussed. Using 3 million hadronic events, the preliminary results are presented. Precision of about 1% in the photon energy measurement is obtained from crossing check using photons in ψ（2S）→γχc1,2（1P）.     

Absolute photon energy calibration for the BESⅢ EMC

The absolute energy calibration with photons from π⁰'s for the BESⅢ EMC is discussed. Using 3 million hadronic events, the preliminary results are
presented. Precision of about 1% in the photon energy measurement is
obtained from crossing check using photons in ψ(2S)→γχ_c1,2(1P).     

Significance of absolute energy scale for physics at BESⅢ

The effects of absolute energy calibration on BESⅢ physics are discussed in detail, which mainly involve the effects on τ mass measurement, cross section scan measurement, and generic error determination in other measurements.     

Performance of a 3 mm×3 mm silicon photomultiplier for use on the X-ray calibration system of the SVOM gamma ray monitor

The calibration detector of a gamma ray monitor (GRM) is designed to detect alpha particles from ²⁴¹Am and to send out the coincidence signal to the GRM X-ray detector. The silicon photomultiplier (SiPM), as a novel photon device, is a good candidate to convert alpha-exciting fluorescent photons into electric signals. Three types of SiPMs from SSPM and MPPC, each having an active area of 3 mm×3 mm, were compared in the matter of the spectra from low-intensity light, dark count, crosstalk probability and I-V curve. The temperature coe cient of SSPM-0710G9MM was also characterized. The application of a SiPM on the GRM has been proved to be feasible.     

Study of the efficiency of event start time determination at BESⅢ

A method to estimate the efficiency of event start time determination at BESIII is developed.This method estimates the efficiency at the event level by combining the efficiencies of various tracks(e,μ,π,K,p,γ)in a Bayesian way.Efficiencies results and the difference between data and MC at the track level are presented in this paper.For a given physics channel,event start time efficiency and systematic error can be estimated following this method.     

Monte Carlo tuning for the BESⅢ time-of-flight system

Using experimental data, Monte Carlo tuning is implemented for performance parameters associated with the scintillation counters and readout electronics of the BESⅢ time-of-flight (TOF) system, as part of the full simulation model. The implementation of the tuning is described for simulations designed to reproduce the performance of a number of TOF system parameters, including pulse height, hit efficiency, time resolution, dead channels and background. In addition, comparisons with experimental data are presented.     

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.     

Efficiency calibration of neutron detector array for β decay of exotic nuclei

The research of the in-beam efficiency calibration of Neutron Detector Array of Peking University using ¹⁷N and ¹⁶C beams was introduced in this paper. The efficiency of neutron wall and ball are comparable to the foreign similar devices and neutrons can be detected from low to high energies in high efficiency.     

Tuning of the cosmic-ray test system of the BESⅢ drift chamber

The BESⅢ drift chamber and its subsystems need a cosmic-ray test after the chamber construction to check the chamber construction quality,testing the joint operation of the whole system and the performance of the chamber.The noise performance,drift time and charge measurements,and the scanning of channels were examined specifically.The preliminary results of the test indicate that the whole system works well.