标量介子f0(980)光生过程γp→pf0(980)的研究

轻标量介子性质研究是当今中高能核物理研究中的热点问题之一,特别是质量低于1 GeV的标量介子f₀（980）的内部结构一直存在争议,至今未达成共识。基于前人的研究结果,运用有效拉氏量方法,对f₀（980）粒子的光生过程γp→pf₀（980）进行了更深入的理论研究。探讨了两种传播子形式下得矢量介子ρ和ω交换的贡献,第一种是选择雷吉传播子,第二种是选择普通费曼传播子。第二种形式的微分散射截面理论结果与现有实验数据符合比第一种形式的结果好。基于此,计算了两种形式的总截面,两种形式给出的理论结果相差很大。另外,给出了γp→pf₀（980）→pπ+π-过程的π+π-不变质量分布的理论预言,发现π+π-不变质量分布对于f₀（980）于K-K的耦合常数（g_f0KK）有很强的依赖关系,不同的g_f0KK给出明显不同的π+π-不变质量分布。将来相关实验数据可以验证这些理论预言,并对矢量介子传播子形式和耦合常数g_f0KK做出限制,加深人们对f₀（980）粒子的认识。We study the scalar meson f0(980) in the γp→pf0(980) reaction within an effective Lagrangian approach. Based on previous studies, we calculate the differential cross sections of this reaction. We take two types of the propagators of vector mesons ρ and ω, one is the Regge form, the other one is the normal Feynman propagator. It is found that our theoretical results for the differential cross sections with the Feynman propagator are in agreement with the current experimental data. For the total cross sections, the results with the two types of propagator are much different. On the other hand, we predict the π+π- invariant mass distribution of the γp→pf0(980)→pπ+π- reaction. We find that the π+π- invariant mass distribution depends sensitively on the value of the coupling constant gf0KK. We hope that the future experiments can test our model calculation and give further constraints on the value of gf0KK and also the nature of f0(980).     

闪烁体探测器中光的衰减通式(英文)

闪烁体探测器被广泛应用于当今粒子物理与原子核物理实验中。研究闪烁探测器的光衰减规律（LASD）对时间和能量的准确测量都十分重要,这一点对条形闪烁探测器尤为如此。本文以圆柱闪烁探测器为例,对各向同性的闪烁光进行立体角积分,进而研究不同立体角下光程差异对结果的影响。在数值计算的基础上,导出了描述LASD的通用公式。在一定条件下,公式可以约化为双指数衰减形式。对于DAMPE上PSD的实验数据,该公式能使闪烁体远端的拟合偏差从大约10%降低至2%以下。同时,模型也能够很好地描述Kaiser实验、Gierlik实验和Platino实验的实验数据。Scintillator detectors are widely used in modern nuclear and particle physics experiments. Studying the light attenuation of scintillator detector (LASD) is vitally important for extracting proper measurements of energy and time. In this paper, we integrate the isotropic fluorescence over solid angle to study the influence on overall light-intensity from varying optical path at different angle. Based on numerical results, a universal formula for describing LASD is derived. Under certain condition, our formula can be written as a form of widely-used double-exponential function. The universal formula describes the experimental data of PSD at DAMPE, reducing the maximum deviation at far-side of the scintillator from~10% to less than 2%. Moreover, our model also deciphers Kaiser's experiment, Gierlik's experiment and Platino's experiment successfully.     

A comparison of condensate mass of QCD vacuum between Wilson line approach and Schwinger effect

We studied the condensate mass of QCD vacuum through the duality approach via dilaton wall back-ground in the presence of the parameter c,which represents the condensation in a holographic set up.First,fromWilson line calculation,we found m₀²(i.e.,the condensate parameter in mixed non-local condensation),whose beha-vior mimics that of QCD.The value of m₀²that we found by this approach is in agreement with QCD data.Second we considered the produced mass m via the Schwinger effect mechanism in the presence of the parameter c.We show that vacuum condensation generally contributes the mass dominantly and that the produced mass via Schwing.er effect is suppressed by m₀.     

高Q2电子原子核单举准弹性散射截面的计算方法

电子与原子核碰撞实验是通过中高能探针探测原子核结构的方法。本文提供了一个高Q2单举准弹性电子原子核散射截面的计算方法,此方法是基于核子-核子短程关联的经验公式与弱束缚近似下的氘核散射截面模型。在弱束缚近似下,氘核可以看成是由近似自由质子与中子组成,质子与中子的短程关联可以忽略,氘核结构函数可以写成质子与中子结构函数线性组合,从而可以得到氘核的散射截面。根据氘核散射截面以及短程关联的经验公式,可以得到考虑短程关联的原子核A > 2的散射截面。我们将计算得到的散射截面与已有的实验和及Bosted拟合方法的结果比较,发现本文的方法在大x和Q2 > 2 GeV2区域得到的结果与实验结果符合得较好并且对于一些重原子核,尤其是4He核,明显优于Bosted方法的结果。The electron nucleus collision experiments are approaches measuring the structure of nuclei by using intermediate and high energy probe. This paper shows a calculation method of inclusive electron nucleus quasielastic scattering cross section at high Q2 which based on a empirical formula of Nucleon-Nucleon Short Range Correlation (NN-SRC) and a model of electron deuteron quasi-elastic cross section in Weak-Binding Approximation (WBA). In WBA, the deuteron can be regarded as the combination of quasi-free proton and neutron and the short range correlation between them can be ignored. Therefore the structure function of deuteron can be written as the linear combination of that of proton and neutron, then one can get the cross section of deuteron. According to the cross section of deuteron and the empirical formula, one can obtain the cross section of nuclei A > 2 which considers NN-SRC effect. We compare our calculation results with existing experiments and the results calculated by Bosted' fit method, then find that our results match the experiments at high x and Q2 > 2 GeV2 and better significantly than the Bosted's results for some heavier nucleus, especially 4He.     

小型宇宙射线探测仪的模拟和测量

介绍了一款小型宇宙射线探测仪。该仪器具有宇宙射线科普演示功能,主要用于实时测量μ子射线并显示计数,以及长时间尺度下（年）稳定地对不同角度的次级宇宙线通量进行监控记录。简要地展示了探测器的硬件构造和探测效率的模拟计算。探测仪单个探测器的探测效率为93.1%,两个探测器符合测量的探测效率为86.6%。根据探测器的计数率以及模拟计算的探测效率,估计了次级宇宙射线垂直地面方向的通量,为J=29±3 m-2 sr-1 s-1。另外,利用该宇宙射线探测仪,测量了兰州市区的次级宇宙射线的天顶角分布。其结果很好地满足I（θ）=IH+I₀ cosα θ经验公式,其中的角度依赖参数α=2.42±0.52。A small cosmic ray device is introduced in this paper.It has the demonstration function for popularization of science,and can be used mainly to display the μ counts in a real-time measurement,and to monitor the secondary cosmic ray flux at different angles in a very long time scale (years).We briefly show the hardware of the device and the detecting efficiency calculation by simulation.The detecting efficiency for one detector of the device is 93.1%,and the detecting efficiency is 86.6% for the coincidence measurement of two detectors.Based on the count rate by the detector and the simulated efficiency,the secondary cosmic ray flux perpendicular to the ground surface is measured,which is J=29±3 m-2sr-1 s-1.Moreover,with an application of the device,we measured the angular distribution of the secondary cosmic ray rate in Lanzhou City.The resulting angular distribution agrees well with the empirical formula as I(θ)=IH+I₀ cosα θ,in which the parameter for the angle-dependence is α=2.42±0.53.     

3π强子物理和实验

在强子物理研究中,3π产生的理论和实验有非常重要的意义,是目前世界上很多大型实验设备的重要研究对象。3π强子物理包含丰富的物理内容,可以作为探索低能区强相互作用的有力工具。同时,3π产生过程是寻找奇特轻介子态的主要途径之一。另外,通过研究3π产生反应道还可以寻找“失踪”共振态和重子激发态之间的级联衰变。介绍了目前国际各大高能物理实验室的3π产生过程的实验、理论研究以及分波分析技术现状,重点介绍了美国杰弗逊国家实验室（Jefferson Lab,简称JLab）的CLAS（CEBAF Large Acceptance Spectrometer）实验上的3π反应过程。最后,指出了3π强子物理研究的意义和未来的研究方向。Three pion productions off nucleon are of significance in the research of hadron physics. Meanwhile it is the subject of many big experimental apparatus in the world. Due to the variety of three pion productions, it can be applied as an effective tool to study QCD in low energy region. Three pion productions is one of the main reactions in searching light exotic meson state. Moreover, it is possible to find out the "missing" baryon resonance and the cascaded decay process between baryon excited states. We introduce present experiments and theories of three pion productions as well as the partial wave analysis technique. The emphasis is on the CLAS (CEBAF Large Acceptance Spectrometer) experiment at JLab (Jefferson Lab). In the end, we point out the significance of studying the three-pion hadron physics at JLab.     

基于Bagging 算法的神经网络在粒子鉴别中的应用

分析了神经网络方法和bagging 算法在实验高能物理和核物理数据分析中的应用现状。分别对神经网络方法和bagging 算法的基本原理进行了介绍。以蒙特卡罗产生器产生的夸克胶子喷注样本为例,详细讨论了神经网络方法以及bagging 算法与神经网络结合对粒子鉴别中信号和背景区分问题的应用过程,并对结果进行了讨论和分析。实验结果表明,应用bagging 算法后,神经网络能够较大幅度地提高实验高能物理和核物理数据分析中粒子鉴别的精度,以及能够得到较高的信噪比。The paper presents the application of neural network and bagging algorithm in experimental high-energy physics and nuclear physics data analysis. Paper also introduces the basic principles of neural network method and bagging algorithm. We use the data samples of quark-gluon jets, which are generated by Monte Carlo generator, to solve the problem of discriminating signal events and background events by the combined algorithm of bagging algorithm and neural network. Experimental results show that, to apply bagging algorithm, neural networks can greatly improve the accuracy of the identification of particles in the experiments of high energy physics and nuclear physical data analysis,and also obtains a larger SNR (Signal to Noise Ratio).     

基于共轭梯度优化算法的BP神经网络在高能粒子鉴别等领域中的应用

人工神经网络方法已被引入高能物理实验领域并被广泛地应用于夸克胶子喷注的鉴别、电子强子分辨、顶夸克和Higgs粒子的寻找等等。本文采用了一种改良的共轭梯度优化算法并应用于高能物理实验中粒子的鉴别。在该应用中,此算法既能实现每步迭代时在搜索方向上获得最优步长,又能避免目标函数陷入局部收敛点,从而使目标函数快速收敛,提高了算法的有效性。分析结果表明,我们改进后的BP算法显著地提高了粒子物理数据分析中的粒子鉴别能力。     

Production of hidden-charm and hidden-bottom pentaquark states in electron-proton collisions

Electro-production of several pentaquark states is investigated in this study.The eSTARlight package is adapted to study the electro-production of J/ψand γ(1S)via pentaquark P_cand P_bresonance channels in ep→eJ/ψp and ep→eγ(1S)p scattering processes at the proposed electron-ion colliders(EICs).The results obtained in this study are compared to those of non-resonance t-channels,which are described in the pomeron exchange model developed in our studies.Some pseudo-rapidity and rapidity distributions of J/ψand γ(1S)are presented for the proposed EICs,including EicC and EIC-US.It is found that EicC is a good platform to identify P_b states in the future.     

Production of vector mesons in pentaquark state resonance channel in p-A ultraperipheral collisions

Ultraperipheral collisions(UPCs) of protons and nuclei are important for the study of the photoproduction of vector mesons and exotic states.The photoproduction of vector mesons in the pentaquark resonance channel in p-Au UPCs at the Relative Heavy Ion Collider(RHIC) and p-Pb UPCs at the Large Hadron Collider(LHC) is investigated by employing the STARlight package.The cross sections of vector mesons via the pentaquark state resonance channel are obtained using the effective Lagrangian method.The pseudo-rapidity and rapidity distributions of J/Ψ and γ(1 S) are given for p-Au UPCs at the RHIC and p-PbUPCs at the LHC.It is found that the RHIC is a better platform for discovering pentaquark states than the LHC.Moreover,Pb(11080) is easier to identify than PC(4312) because the background of γ(1 S) is weaker than that of J/Ψ in the t-channel at the RHIC.