北京正负电子对撞机综述

本文简单地介绍了北京正负电子对撞机的建造及初步调束情况。     

北京正负电子对撞机工程

本文介绍北京正负电子对撞机工程的建造目的和意义，工程的主体结构以及对于我国工业技术和高技术所起的促进作用．     

北京正负电子对撞机的建造和调束

本文介绍北京正负电子对撞机的结构特点、工程建设情况以及能在短期内建成的原因．     

北京正负电子对撞机(BEPC)正电子源的优化

本文在模拟计算和粒子跟踪的基础上,进行了BEPC正电子源的优化设计,作了实验检验,说明了实验与理论符合得很好.文中给出了一些重要的结论,如从束斑论证了电子枪流强增加的效果;从产额论证了过渡线圈和长螺线管的磁场强度及匹配磁场的峰值位置的影响;两个最佳注入相位的存在及其重要意义;以及实践证明正、负电子可以不必分离,因而无须使用昂贵、复杂的高频分离器等等.     

北京正负电子对撞机上发现新粒子

新年伊始，北京谱仪国际合作组在北京中国科学院高能物理研究所和美国夏威夷大学同时宣布：北京正负电子对撞机上发现了一个仅存在10-23s的新粒子，科学家猜测，它有可能是在高能物理实验中寻找了几十年的新型粒子，暂时被命名为“X1835”。这个新粒子是在分析J/Ψ粒子(丁肇中因此在1975年获得诺贝尔奖)衰变到一个光子和三个介子的过程中被发现的。它的质量值约为3.3×10-27kg，略低于二倍质子质量值。而且它的寿命也极短，仅为约10-23s，人类的正常知觉根本无法感受到它的存在。最终确定“X1835”粒子的基本结构需要更大量的数据，但是已…     

北京正负电子对撞机中的束束作用偏转效应

 利用静电分离器对正负电子束团在垂直方向上的相对轨道偏差进行了扫描,并用数字示波器对束流轨道的变化进行监视,在北京正负电子对撞机(BEPC)上完成了垂直方向上的束束作用偏转效应的观察与测量。实验过程和实验结果可为北京正负电子对撞机改进工程(BEPCⅡ)的对撞调节提供参考依据。把束团之间相对位置偏差的测量转换为对束流偏转角度的测量是可行的,也是有效克服束流位置探测器分辨率不足的一种方法。     

北京正负电子对撞机重大改造工程

北京正负电子对撞机重大改造工程（BEPCII）的建设目标是对北京正负电子对撞机（BEPC）和北京谱仪（BES）进行重大改造。BEPCII要在BEPC已有隧道内建设国际先进的双环对撞机,采用多束团、水平大交叉角对撞方式,大幅度提高对撞亮度,并建造新的北京谱仪BESIII,适应BEPCII高计数率运行的要求,并大幅度提高测量精度和粒子识别能力,以满足在粲能区进行精确测量,     

北京正负电子对撞机和高能物理

 1988年10月24日上牛,阳光明媚,雨后空气格外清新.位于北京西郊的中国科学院高能物理研究所内,繁花似锦,一派节日气象.取得首次对撞成功的广大科技人员迎来了邓小平、赵紫阳、杨尚昆、李鹏等国家领导人.四年前,就在这片土地上,邓小平同志亲临破土,开始了我国第一台高能加速器--北京正负电子对撞机的建设.在全国几百家工厂、研究所、高等院校上万名科技人员、工人、干部的通力合作下,经过四年的日夜奋战,终于取得了对撞成功.     

北京正负电子对撞机重大改造工程圆满完成

历时5年、耗资6．4亿元的北京正负电子对撞机重大改造工程（BEPCⅡ）于2009年5月19日圆满完成。改造后的电子对撞机在1．89GeV能量下,对撞亮度超过3×10^32cm^-2·s^-1,最高达到3．21×10^32cm^-2·s^-1,性能提高30多倍,每秒钟可实现碰撞1亿多次,对撞亮度在一定能量区域里,是美国康奈尔大学的加速器CESR曾创下的世界纪录的4倍以上。建成于1988年的北京正负电子对撞机是世界八大高能加速器中心之一,中国科学家利用这一装置在世界高能物理领域占据了一席之地。2003年,在SARS病毒防治战役中,     

SUSY QCD Impact on Top-Pair Production Associated with a Z^0-Boson at a Photon-Photon Collider

The top-pair production in association with a Z^0-boson at a photon-photon collider is an important process in probing the coupling between top-quarks and vector boson and discovering the signature of possible new physics. We describe the impact of the complete supersymmetric QCD （SQCD） next-to-leading order （NLO） radiative corrections on this process at a polarized or unpolarized photon collider, and make a comparison between the effects of the SQCD and the standard model （SM） QCD. We investigate the dependence of the lowest-order （LO） and QCD NLO corrected cross sections in both the SM and minimal supersymmetric standard model （MSSM） on colliding energy √s in different polarized photon collision modes. The LO, SM NLO, and SQCD NLO corrected distributions of the invariant mass of tt^--pair and the transverse momenta of final Z^0-boson are presented. Our numerical results show that the pure SQCD effects in γγ →tt^- Z^0 process can be more significant in the ＋＋ polarized photon collision mode than in other collision modes, and the relative SQCD radiative correction in unpolarized photon collision mode varies from 32.09% to -1.89% when √s goes up from 500 GeV to 1.5 TeV.     

SUSY QCD Impact on Top-Pair Production Associated with a Z0-Boson at a Photon-Photon Collider

The top-pair production in association with a Z⁰-boson at a photon-photon collider is an important process in probing the coupling between top-quarks and vector boson and discovering the signature of possible new physics. We describe the impact of the complete supersymmetric QCD (SQCD) next-to-leading order (NLO)radiative corrections on this process at a polarized or unpolarized photon collider, and make a comparison between the effects of the SQCD and the standard model (SM) QCD. We investigate the dependence of the lowest-order (LO) and QCD NLO corrected cross sections in both the SM and minimal supersymmetric standard model (MSSM) on colliding energy s^1/2 in different polarized photon collision modes. The LO, SM NLO, and SQCD NLO corrected distributions of the invariantmass of t\bar{t}-pair and the transverse momenta of final Z⁰-boson are presented. Our numerical results show that the pure SQCD effects in γγ→t\bar{t}z⁰ process can be more significant in the + + polarized photon collision mode than in other collision modes, and the relative SQCD radiative correction in unpolarized photon collision mode varies from 32.09\% to -1.89\% when s^1/2 goes up from 500 GeV to 1.5 TeV.     

QCD Factorization of Semi-Inclusive DIS Process at Operator Level

The operator level proof of factorization theorem exhibited in [ar Xiv:hep-ph/1307.4194] is extended to the semi-inclusive deep inelastic scattering process(SIDIS). Factorization theorem can be proved at operator level if there are not detected soft hadrons. The key point is that the initial one-nucleon state is the eigenstate of QCD.     

Precision Calculations for the T-Odd Quark Pair Production at the CLIC e+e- Linear Collider

We perform the precision calculations for the e⁺e^-→q_q_(q_q_=u_u_, c_c_, d_d_,s_s_) processes up to the QCD next-to-leading order (NLO) including full weak decays for the final T-odd mirror quarks in the littlest Higgs model with T-parity (LHT) at the Compact Linear Collider (CLIC). We show the dependence of the leading order (LO) and NLO QCD corrected cross sections on the colliding energy √s, and provide the LO and QCD NLO kinematic distributions of final particles. The results show that the LO cross section can be enhanced by the NLO QCD correction and the K-factor increases obviously when the threshold of the on-shell q_q_-pair production approaches the colliding energy √s. The K-factor value varies in the range of 1.04 ～ 1.41 in our chosen parameter space. We find that a simple approximation of multiplying the LO kinematic distribution with the integrated K-factor is not appropriate for precision study of the e⁺e^-→q_q_(q_q_=u_u_, c_c_, d_d_,s_s_) processes, since the NLO QCD corrections are phase space dependent. It is necessary to calculate the differential cross sections including full NLO QCD corrections to get reliable results.     

Study on Background Radiation at Beijing Electron Positron Collider and Radiation Damage of High-Z Scintillation Crystals

A systematic study of radiation backgrounds in the interaction region at the Beijing e⁺e^－ Collider BEPC is carried out for the first time to the needs of particle physics experiment.An effective method to study dynamically the radiation environment of the collider is successfully developed which allows the measurement of the instantaneous radiation dose rate and is distribution for different beam conditions and as a function of time during a quiet luminosity run.The radiation sensitivity of domestic BGO and BaF₂ crystals in the BEPC environment is examined.     

Collider physics at HERA

From 1992 to 2007, HERA, the first electron-proton collider, operated at cms energies of about 320 GeV and allowed the investigation of deep-inelastic and photoproduction processes at the highest energy scales accessed thus far. This review is an introduction to, and a summary of, the main results obtained at HERA during its operation.     

Reconstruction of physics objects at the Circular Electron Positron Collider with Arbor

After the Higgs discovery, precise measurements of the Higgs properties and the electroweak observables become vital for the experimental particle physics. A powerful Higgs/Z factory, the Circular Electron Positron Collider (CEPC) is proposed. The Particle Flow oriented detector design is proposed to the CEPC and a Particle Flow algorithm, Arbor is optimized accordingly. We summarize the physics object reconstruction performance of the Particle Flow oriented detector design with Arbor algorithm and conclude that this combination fulfills the physics requirement of CEPC.     

Calculation of Partition Function of QCD at Finite Chemical Potential

In equilibrium statistical field theory, the partition function has fundamental importance. In this paper we propose a direct and general method for calculating the partition function and equation of state of QCD at finite chemical potential. It is found that the partition function is totally determined by the dressed quark propagator at finite chemical potential up to a multiplicative constant. From this a criterion for the phase transition between the Nambu and the Wigner phases is obtained. This general method is applied to two specific cases： the free quark theory and QCD with a model dressed quark propagator having confinement features. In the first case, the standard Fermi distribution at T = 0 is reproduced. In the second case, we apply the conclusion in previous works to obtain the dressed quark propagator at finite chemical potential and find the unphysical result that the baryon number density vanishes for all values of chemical potential. The reason for this result is discussed.     

Simulation of neutron-tagged deep inelastic scattering at EicC

Measuring the pionic structure function is of high interest, as it provides a new area for understanding the strong interaction among quarks and testing QCD predictions. To this end, we investigate the feasibility and expected impact of a possible experiment at EicC(Electron-ion collider in China). We show the simulation results on the statistical precision of an EicC measurement, based on the model of leading neutron tagged DIS process and the parton distribution functions of the pion from JAM18 global analysis. The simulation shows that at EicC, the kinematics cover the x π range from 0.01 to 1, and the Q~2 range from 1 to 50 GeV~2, within the acceptable statistical uncertainty. Assuming an integrated luminosity of 50 fb~(-1), in the low-Q~2 region( 10 GeV~2), the Monte Carlo data show that the suggested measurement in the whole x π range reaches very high precision( 3%). To perform such an experiment, only the addition of a far-forward neutron calorimeter is needed.     

Ultimate parameters of the photon collider at the international linear collider

At linear colliders, the e ⁺ e ⁻ luminosity is limited by beam-collision effects, which determine the required emittances of beams in damping rings (DRs). In γγ collisions at the photon collider, these effects are absent, and so smaller emittances are desirable. In the present damping ring designs, nominal DR parameters correspond to those required for e ⁺ e ⁻ collisions. In this note, I would like to stress once again that as soon as we plan the photon collider mode of ILC operation, the damping ring emittances are dictated by the photon collider requirements — namely, they should be as small as possible. This can be achieved by adding more wigglers to the DRs; the incremental cost is easily justified by a considerable potential improvement of the γγ luminosity. No expert analysis exists as of now, but it seems realistic to obtain a factor five increase of the γγ luminosity compared to the ‘nominal’ DR design.