Studies of deep inelastic scattering at ep collider HERA

我们用德国DESY建造的独特的e-p对撞机HERA研究了深度非弹性电子-质子散射。赫拉提供高能碰撞，其最大四个动量转移平方(Q^2)达到10^5GeV^2。实验使用由12个国家合作建造和操作的多用途探测器(Zeus)进行。在这两年的时间里，收集了27.5GeV电子(或正电子)和920GeV质子的数据。总积分光度达到67pb-1。为了确定质子结构函数，在0.04GeV^2到30000GeV^2的宽Q^2范围内精确测量了中性电流截面。在高于200GeV^2的Q^2范围内测量了带电电流截面，并与基于微扰量子色动力学(QCD)的模型进行了拟合。结果表明，这些模型描述了~1GeV^2以上的质子结构函数。提取了质子内部夸克和胶子的分布。结果表明，随着Bjorken-x的减小，胶子迅速增加。精确地测定了强相互作用的耦合常数(α，S)，并发现它与其他完全不同的测量结果是一致的，例如e+e-和Ep实验中的喷流多重数。事实证明了强相互作用的普适性和QCD的有效性。当Q^2低于1GeV^2时，测量的结构函数低于QCD的预测值。在这些区域中，提取的胶子分布趋于负值。这可能表明微扰方法中的极限，尽管人们需要等待高阶计算的进展。在高Q^2下测量的截面与从低Q^2测量得到的外推是一致的。与标准模型的预期没有显著偏差。对轻夸克等新粒子的约束被设置。

We have studied deep inelastic electron-proton scatterings with the unique e-p collider HERA built at DESY in Germany. HERA provides high-energy collisions, whose maximum four momentum transfer squared(Q^2) reaches 10^5 GeV^2. The experiment was performed with a multi purpose detector (ZEUS) which was constructed and operated by an international collaboration of 12 countries. In this two year period, the data were collected with 27.5GeV electrons (or positrons) and 920GeV protons. Total integrated luminosity reached 67pb-1.Precise measurements of the neutral-current cross sections were performed in a wide Q^2 range from 0.04GeV^2 to 30000GeV^2 in order to determine the proton structure functions. Charged current cross sections were also measured in the Q^2 range above 200GeV^2. The results were fitted with models based on the perturbative quantum chromodynamics (QCD). It is found that the models describe the measured proton structure functions above 〜1GeV^2. Distributions of quarks and gluons inside the proton were extracted. It is found that the gluons increase rapidly as Bjorken-x decreases. The coupling coupling constant of the strong interaction(αs) is precisely determined and found to be consistent to the other results from completely different measurements such as jet-multiplicities in e+ e- and ep experiments. The fact demonstrates the universality of the strong interaction and the validity of the QCD.As Q^2 goes lower below 〜1GeV^2 measured structure functions lay below the QCD prediction. The extracted gluon distribution tends to become negative in the regions. These might indicates the limit in the perturbative approach although one needs to wait for the progress in the higher order calculations.The measured cross sections at high Q^2 were consistent with the extrapolation from low Q^2 measurements. There is no significant deviation from the expectation of the standard model. The constraint on new particles such as leptoquarks was set.