Studies of deep inelastic scattering at ep collider HERA

点击翻译按钮获取中文摘要

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.