Search

The Born cross section and dressed cross section of $e^+e^-$ to $b\bar{b}$ and the total hadronic cross section in $e^+e^-$ annihilation in the bottomonium energy region are calculated based on the Rb values measured by the BaBar and Belle experiments. The data are used to calculate the vacuum polarization factors in the bottomonium energy region, and to determine the resonant parameters of the vector bottomonium(-like) states, the Y(10750), Upsilon(5S), and Upsilon(6S)., 24 pages, 10 figures. Version appeared in Chinese Physics C

A simulation study of the parallax effect of gaseous detectors using the Garfield program is reported. A method that mainly uses non-uniform cathode potentials to reduce the parallax error of planar type gas detectors is described. By applying it to MWPC and Micro-pattern gas detectors, the method reduces the parallax broadening with very good results. For a 13° incidence track, the width (FWHM) of the parallax broadening is reduced to less than 20% of the normal one after using the special cathode potentials.

A compact facility for cancer therapy has been designed and is presently under construction. A slow beam extraction system using the RF-Knock Out method and 3rd-order resonance is adopted in the synchrotron of this facility. Eight sextupoles are used, four of them are for correcting the chromaticity and the rest for driving the 3rd-order resonance. In order to save the aperture of vacuum chamber, a 3-magnet bump is adopted during the extraction process. The extraction phase space map and the last 3 turns' particle trajectory before extraction are given. The matching betatron functions with HEBT (high energy beam transport) are also presented.

Scenarios for the τ mass measurement at the upgraded Beijing Electron-Positron Collider (BEPC-II) are studied. A nested minimization procedure is used to optimize the data taking plan. It is found that by using five energy points with the total integrated luminosity of 100 pb−1,the τ mass can be determined with a statistical error of 50 keV.

Chinese Spallation Neutron Source (CSNS), one project of the 12th five-year-plan scheme of China, is under construction in Guangdong province. Three neutron spectrometers will be installed at the first phase of the project, where two-dimensional position sensitive thermal neutron detectors are required. Before the construction of the neutron detector, a prototype of two-dimensional 200 mmx200 mm Multi-wire Proportional Chamber (MWPC) with the flowing gas of Ar/CO2 (90/10) has been constructed and tested with the 55Fe X-Ray using part of the electronics in 2009, which showed a good performance. Following the test in 2009, the neutron detector has been constructed with the complete electronics and filled with the 6atm.3He + 2.5atm.C3H8 gas mixture in 2010. The neutron detector has been primarily tested with an Am/Be source. In this paper, some new developments of the neutron detector including the design of the high pressure chamber, the optimization of the gas purifying system and the gas filling process will be reported. The results and discussion are also presented in this paper., 5 pages

A gamma spectrum of a Pu-C source is measured using a p-type HPGe detector, whose three peaks (full energy, single-escape and double-escape peak) can be used as a calibration source for the beam energy measurement system of BEPCII. The effect of fast neutron damage on the energy resolution of the HPGe detector is studied, which indicates that the energy resolution begins to deteriorate when the detector is subject to 2×107 n/cm2 fast neutrons. The neutron damage mechanism and detector repair methods are reviewed. The Monte Carlo simulation technique is utilized to study the shielding of the HPGe detector from the fast neutron radiation damage, which is of great significance for the future commissioning of the beam energy measurement system.

It has been conjectured that the relative phase between strong and electromagnetic amplitudes is universally $-90^{\circ}$ in charmonium decays. $\psi^{\prime}$ decaying into pseudoscalar pair provides a possibility to test this conjecture. However, the experimentally observed cross section for such a process is depicted by the two-fold integral which takes into account the initial state radiative (ISR) correction and energy spread effect. Using the generalized linear regression approach, a complex energy-dependent factor is approximated by a linear function of energy. Taking advantage of this simplification, the integration of ISR correction can be performed and an analytical expression with accuracy at the level of 1% is obtained. Then, the original two-fold integral is simplified into a one-fold integral, which reduces the total computing time by two orders of magnitude. Such a simplified expression for the observed cross section usually plays an indispensable role in the optimization of scan data taking, the determination of systematic uncertainty, and the analysis of data correlation.

The beam energy measurement system at BEPCII is composed of there parts: laser source and optics system, laser-electron interaction system and High Purity Germanium (HPGe) detector system. The special components and construction of each part are introduced, especially about radiation background measurement in the storage ring, which is of great importance for the safe commissioning of HPGe detector.

The calibration algorithm for RPC-based union detector at BESIII has been developed. The calibration method, calibration error and algorithm performance are studied. The primary results of efficiency and noise at layer, module and strip levels have been calibrated with cosmic ray data. The calibration constants are available for simulation and reconstruction timing. The results of Monte Carlo and data are also compared to check the validation and reliability of the algorithm.

The technique details for measuring radiation dose are expounded. The results of gamma and neutron radiation levels are presented and the corresponding radiation shielding is discussed based on the simplified estimation. In addition, the photon radiation level move as background for future experiments is measured by a NaI(Tl) detector.

A track fitting algorithm based on the Kalman filter method has been developed for BESIII of BEPCII. The effects of multiple scattering and energy loss when the charged particles go through the detector, non-uniformity of magnetic field (NUMF) and wire sag, etc., have been carefully handled. This algorithm works well and the performance satisfies the physical requirements tested by the simulation data.

To achieve a high precision tau mass measurement at the high luminosity experiment BESIII, Monte Carlo simulation and sampling technique are utilized to simulate various data taking cases for single and multi-parameter fits by virtue of which the optimal scheme is determined. The optimized proportion of luminosity distributed at selected points and the relation between precision and luminosity are obtained. In addition, the optimization of the fit scheme is confirmed by scrutinizing a variety of fit possibilities.

Cosmic-ray data of 90 M events have been collected and used for calibration, alignment as well as detector tuning. A special tracking algorithm for the BESIII muon counter is developed and verified with Monte-Carlo simulation and then further confirmed with the cosmic-ray data. The obtained strip resolutions are in good agreement with the design values. A new alignment approach for the BESIII muon counter is confirmed with the cosmic-ray data and proposed to be used in future analysis of experimental data.

This paper focuses mainly on the vertex reconstruction of resonance particles with a relatively long lifetime such as K0S, Λ, as well as on lifetime measurements using a 3-dimensional fit. The kinematic constraints between the production and decay vertices and the decay vertex fitting algorithm based on the least squares method are both presented. Reconstruction efficiencies including experimental resolutions are discussed. The results and systematic errors are calculated based on a Monte Carlo simulation.

Software alignment is quite important for a tracking detector to reach its ultimate position accuracy and momentum resolution. We developed a new alignment algorithm for the BESIII Main Drift Chamber using the Kalman Filter method. Two different types of data which are helix tracks and straight tracks are used to test this algorithm, and the results show that the design and implementation is successful.

The proposed beam energy measurement system at BEPCII is composed of three parts: the laser source and optics system, the laser-electron interaction system and the HPGe detector system. The working principles of each system are expounded together with the calculation for preliminary design. The normalizations of laser and electron beams are put forth and used for the evaluation of intensity of the backscattering photon. The simulation of HPGe detector is also performed for understanding the working properties.

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%.

The results of a study of event tagging strategies for elementary physics processes in the τ-charm region are presented. The algorithm for online event filtering is optimized by adopting the information provided by different sub-detectors according to their strengths and capacities. The algorithm is tested with various generated physics and background events. The results indicate that the algorithm satisfies the requirements of BESIII physics analysis and its DAQ system.

Material effect of inner-detectors on the performances of the BESIII Electromagnetic Calorimeter (EMC) is investigated. The BESIII Time-Of-Flight counters (TOF) have been utilized to improve the energy resolution and detection efficiency for photons after a careful energy calibration. A matching algorithm between TOF and EMC energy deposits is developed, and the effects of beam-related background are discussed. The energy resolution is improved and the photon detection efficiency can be increased by the combined measurement of EMC and TOF detectors.

A multilayered perceptrons' neural network technique has been applied in the particle identification at BESIII. The networks are trained in each sub-detector level. The NN output of sub-detectors can be sent to a sequential network or be constructed as PDFs for a likelihood. Good muon-ID, electron-ID and hadron-ID are obtained from the networks by using the simulated Monte Carlo samples.

The feasibility of attaining a short-pulse-duration heavy ion beam with a nanosecond pulse length is studied in the main ring of the Heavy Ion Research Facility in Lanzhou (HIRFL). Such a heavy ion beam can be produced by non-adiabatic compression, and it is implemented by fast rotation in the longitudinal phase space. In this paper, the possible beam parameters during longitudinal bunch compression are studied by using the envelope model. The result shows that a shortest heavy ion bunch 238U28+ of 29 ns with energy of 200 MeV/u can be obtained, which can satisfy high energy density physics research.

For MWPCs used for X-ray position detection, simulation studies of the anode wire modulation effect of the detector were carried out using the Garfield program. Different gas mixtures were used as the working gas in the simulation, so as to obtain the influence of the X-ray cross section and electron diffusion coefficient of the working gases on the anode wire modulation effect of an MWPC with anode wire spacing of 2 mm. Results show that, though a working gas with higher X-ray cross section implies a larger average drift distance for the ionized electrons, such gas mixtures are of little use in improving the anode wire modulation effect of MWPCs. It is found that the transverse electron diffusion coefficient is the determining factor for the extent of the anode wire modulation effect in the detector.

A stochastic cooling system is under design and construction at HIRFL-CSRe (Heavy Ion Research Facility in Lanzhou - experimental Cooling Storage Ring), with the aim of cooling secondary particles produced at HIRFL-RIBLL2 (2nd Radioactive Ion Beam Line in Lanzhou). The optical layout of CSRe has been optimized to meet the requirements of a stochastic cooling system. In this paper, a particle tracking method is used to investigate both transverse and longitudinal cooling on the basis of the modified optical layout, demonstrating how it can be used to optimize stochastic cooling parameters. Simulation results indicate that the particle tracking method is an innovative and reasonable method to study stochastic cooling. It also has the advantage of discovering the influence of Twiss parameters at the pickups and kickers, which will be explored in further studies.

The beam energy is measured in the e(+)e(-) collision by using Compton backscattering. The uncertainty of this measurement process is studied by virtue of analytical formulas, and the special effects of variant energy spread and energy drift on the systematic uncertainty estimation are also studied with the Monte Carlo sampling technique. These quantitative conclusions are especially important for understanding the uncertainty of the beam energy measurement system.

We have examined the parametrization of the e+e− → ωπ0 cross section in the vicinity of the resonance and the extraction of the branching fraction of the isospin violating process → ωπ0 from experimental data. We found that there are two possible solutions of the branching fraction: one is 4 × 10−5, and the other is 7 × 10−3. The latter is two orders of magnitude higher than the former, which is the commonly accepted one.

Stripping injection is one of the crucial stages in the accumulation process of the hadron therapy synchrotron HITFiL (Heavy Ion Therapy Facility in Lanzhou). In order to simulate the stripping injection process of carbon ions for HITFiL, the interactions between carbon ions and foil has been studied, and simulated with a code developed by ourselves .The optimized parameters of the injecting beam and the scheme of the injection system have been presented for HITFiL., 6 pages, 9 figures