【作者】 李会红；

【导师】 刘峰； 李金；

【作者基本信息】 华中师范大学 ， 理论物理， 2003， 博士

【摘要】 高能物理学的发展是理论和实验之间相互渗透、相互影响的结晶。理论固然重要，但必须来源于实践，能够经得起实验的检验，反过来指导实践。高能物理实验一般是先通过加速器来产生高能量的粒子束，然后让粒子束去打靶或让两团粒子束对头碰撞，用探测器来测量碰撞后的产物，最后通过对这些产物的分析研究寻找规律。近几十年来，对撞机在粒子物理领域中崭露头角，已经成为一种占主导地位的高能加速器，对新粒子的发掘大部分来自e⁺e^-对撞机。北京正负电子对撞机BEPC（Beijing Electron Positron Collider）的工作能区是2-5GeV，虽然能量较低，但在粲夸克、τ轻子、低能区R值研究方面具有独特的优势，它处在一系列共振区和产生阈区，具有系统误差小、本底小、测量精度高的特点。北京谱仪BES（BEijing Spectrometer）是运行在BEPC上的唯一大型通用探测器，开展2-5GeV能区的e⁺e^-对撞物理研究，重点是τ-粲物理研究，主要包括J／ψ物理、ψ（2S）物理、τ轻子物理、Ds介子物理、D介子物理、2-5GeV能区的强子产生机制及QCD检验的实验研究等。经过中外科学家的共同努力，在北京谱仪上已作出了包括“τ轻子质量的精密测量”、“2-5GeV能区的R值测量”，以及在J／ψ、ψ（2S）、Ds介子等物理研究中的多项国际领先水平的重要科研成果，引起了国际高能物理界的普遍重视和广泛关注。自1990年至今北京谱仪BES已积累了6700万J／ψ、1700万ψ（2s）事例、10万τ轻子对、22pb^-1的D_s粒子以及2-5GeV的R值扫描数据。本文正是利用2-3GeV的R值扫描数据，对类时过程质子形状因子进行测量研究。 ／飞吕回己广飞 十辽＿I＿一个／干二人十 人祸回二岂入 下Viii了二IH了℃卫二 V拄间臼勺y ＊（：上”口oth卜【川儿卜I门八川（）N一 核子不是点粒子，最直接的证脚自于狄拉克方程，该方程假定核子是点粒子，给出质子的磁矩为1－子，中子磁矩为0，而獭上测得的质子和中子的磁矩是反常的。但目前迈】受有完善的理臼仑能够描述核子复杂的内部结构，只能DfliXi：jilli用电磁形状＿u“”—一’“门““““——’—”口一‘—一‘一‘———“‘”‘“’一口”‘一”””一——一”‘—’一‘一”‘甲因子描写它们的内部电荷和磁矩分布。核子有四个形状因子，分别与质子、中子的电荷和磁矩相对应：质子电形状困子G…淬D磁形状因子GLb勺；中子电形状因子＊k奸D磁形状因子GL…、其中q’是粒子四动量转移平方。质子电磁形状因子的研究最早是在类空过程中开始测量的，并且有大量的实验数据，结果表明偶极公蹦8嘶胁…该过程的质刊状因子。相搂空邂的测量而言，类时过程质子形状因子的测量工作难度大些，由于湮灭道的截面陇小，各实验组获取的数据非常有限。尤其在6．gGe＊2＜s＜8．SGe＊区间，没有实验数据。北京谱仪＊＊SI升级为BESll后，首先开展了R值的细致扫描工作，质。乙能量（必）覆盖了2－SGeV。本文利用2－沈eV的R值扫描数据，对9个质。o能量的，＋。一十pp衰变道的截面和类时过程形状因子进行测量研究。 首先简要介绍了北京正负电子对撞机和北京谱仪。北京正负电子对撞机是专为研究T－M能区物理而设计的。它由202米长的电子直线加速器和周长为240米的储存环组成。正负电子在直线段被加速到1．INI．4GeV，然后沿相反方向分别注入储存环中并被加速到所需要的能量，进行对撞。同时环上的四个高频腔不断补充束流由于同步辐射造成的能量损失，使束流保持在工作能量。BEPC有两个对撞点，实际运行中只有安放在南对撞』点的北京谱仪在工作。北京谱仪是工作在北京正负电子对撞机上的大型通用磁谱仪，用于测量正负电子对撞后产生的遍举末态反应，研究末态粒子的性质及其相互作用的规律。北京谱仪长约6米，宽、高各为7米，重n 摘 要 ／·回蠢包b，又1巾I。上·J二：N； 乙L司回回回一Jy1）（）（D门1）川 卜1厂。t！IMHlyJ — — 约拢0吨。它主要由柬流管；稻草管顶点室；主漂移室；飞行时‘问计数状，联卅计数 器；以子计数器；亮度监测器；磁铁线圈等子探测器构成，还包括气休；触发判巡，电’子学，在线数据获取，离线数据分析等控制系统。 质3＝Mt’g是e＋e－－ PP＄例选择的重点。在2－3GeV能区范围，e”e－－p耳末 态质子和反质子的动量分布较广。低动量的质子和反质子在探测器中的行为表现 出不对称性，主要是困为低动量的反质子易与探测器中的物质发生湮灭。质子和反 质子的这种不对称性随着动量的增加而减小；大动量时两者的行为丛本上是一致 的。对于带电粒子的鉴别；BES的两个子探测器飞行时间计数器(TOF杯主漂移 室（MDC）起着非常重要的作用，可以单独用TOF或dE川X信息对粒子进行鉴别， 也可以将两者的信息联合起来使用。本文充分利用B＊Sll所获取的数据挑选出纯度 较高的各种带电?更多还原

【Abstract】 The development of the high energy physics is the result of pervasion and effect between theory and experiment each other. Of course the theory is important, but it must come from practice, can be tested by experiment and instruct practice inversely. In general, the high energy physics experiment is first to use accelerator to generate high energy particle beam, then let particle beam hit the target or two bunches of particle beam collide and detect the generated particles after collision, at last search the discipline by analyzing the products. During the last two decades, colliding-beam machines have become important in the field of particle physics, become the leading high energy accelerator and digging new particles is most from e+e- collider. The Beijing Electron Positron Collider (BEPC) works in 2-5GeV region, although the energy is low, it has its own advantage in the study of charm quart, τ lepton, low energy R value. This energy region includes series of resonance regions and generating threshold regions, so it has the characteristics, such as little systematic error and background, high measurement precision etc. The BEijing Spectrometer (BES) is an only large general purpose solenoidal detector at the BEPC, on which the physics is to study e+e- collide physics in 2-5GeV region , the emphasis is in the τ-charm physics and the topics include J/ψ physics, ψ (2S) physics, T physics, Ds physics, D physics and hadron’s generation mechanism as well as the test of QCD in 2-5GeV. With the cooperation of many domestic and overseas scientists, there are many internationally high level important results, such as "Precise measurement of the mass of the τ lepton", "R value measurement in 2-5GeV", and other studies in J/ψ,ψ (2S), Ds physics. These results bring universal regard and comprehensive attention. From 1990 to the present, BES has accumulated 67 million J/ψ events, 17 million ψ(2s) events, 100 thousand T pairs, 22pb-1events and 2-5 GeV R value scan data. In the paper we study the time-like region form factor of the proton using the 2-3 GeV R value scan data.Nucleon is not pointlike, and the direct evidence is from Dirac equation. If assuming that nucleon is pointlike, from the equation the magnetic moment of the proton is one unit and of the neutron is zero, but their values measured from ex-Vperiment are anomalous. By far there is no perfect theory to describe its complex structure and we can only empirically use electromagnetic form factor to describe its distribution of inner charges and magnetic moments. The nucleon has four form factors. According to proton and neutron’s electron and magnetic moment respectively, there are proton’s electronic form factor GpE(q2) and magnetic form factor GpM(q2); neutron’s electronic form factor GnE(q2) and magnetic form factor GnM/(q2). The early measurements of proton form factor were in the space-like region, and there are a lot of results, which show that empirical dipole formula can work well for proton form factors. While in the time-like region, it is some difficult to measurement proton form factors, because the annihilation cross section is small so that the each experiment group’s data is very limited. Especially for 5.9GeV2 < s < 9GeV2, there is no data at present. Running with updated BESII from BESI was firstly devoted to careful scan of the R value covering the center-of-mas’s energy of 2-5 GeV. Here we use R scan data of 2-3GeV to study the proton form factor of time-like region.Firstly, BEPC and BES are introduced briefly. BEPC is designed specially for the study of T-charm energy region physics. It is composed of 202-meter-long electron linear accelerator and 240-meter-circumference storage ring. In the linear region the electron and positron are accelerated to 1.1 ~ 1.4GeV, then injected to storage ring in the opposite direction and accelerated to needed energy to collide. At the same time four high frequency cavities supply the energy to beam current continuously,which is lost because of synchronous radiation, and keep be更多还原