STUDY ON THE SPIN STRUCTURE OF NUCLEONS

SMC（Spin Muon Collaboration）目前正在利用高能极化μ子和极化质子/氘靶进行实验。本实验的目的是弄清核子自旋的起源，并检验QCD用于预测强子内部夸克-胶子行为的有效性。SMC在CERN进行了两个实验，1993年测量了质子的自旋相关结构函数。1994年，测量了氘核的相同参数。前一个实验将数据点扩展到具有较高统计量的最低x区域。后者的数据正在分析中。质子自旋相关结构函数的测量已在下列条件下实现。(1)偏振μ介子束的强度为4 * 10^7ppp，偏振度为80%。(2)极化质子靶的尺寸为50 mm phi * 650 mm长。将一对这样的靶封壳以相反的极化方向安装在稀释低温恒温器中。偏振值约为45%。数据将x区域扩展到0.003，具有相当好的统计和系统误差。数据总数为4.4 * 10^6次事件，从质子数据中得出以下结果。(1)用朴素夸克模型假设计算的Eliis-Jaffe求和规则没有得到实验的验证。预测值和测量值之间大约有两个标准差。(2)质子内部的夸克自旋之和只能带来22%的贡献，奇异夸克自旋的贡献为-12%。这就需要寻找核子自旋的起源。(3)对检验QCD的关键关系Bjorken求和规则进行了检验，并保证其在误差范围内是正确的。

SMC (Spin Muon Collaboration) is now going on the experiment using the high energy polarized muon and polarized proton/deutron targets. This experiment aims at making clear the origin of the nucleon spin and cheking the validity of the QCD which is used for the prediction of the quark-gluon behavior inside hadrons. SMC has performed two experiments in this term (2 years) at CERN.In 1993, the spin dependent structure function of the proton has been measured. In 1994, the same parameter of the deuteron was measured. The former experiment extended the data points to the lowest x region with higher statistics. The latter data are now under analysis.The measurement of the spin-dependent structure function of proton has been achieved under the following conditions. (1) The polarized muon beam had an intensity of 4*10^7ppp with a polarization of 80%. (2) The polarized proton target has a dimension of 50mmphi* 650mmlong. A pair of this target capsuls are installed in a dilution cryostat with opposite direction of the polarization. The value of the polarization was about 45%. The data extended the x-region to 0.003 with fairly better statistical and systematic errors. Whole number of data was 4.4*10^6 events.From the proton data, the following results are derived. (1) The Eliis-Jaffe sum rule which is calculated by the assumption of naive quark model is not valified by the experiment. There is about two standard deviation between the prediction and measurement. (2) The sum of the quark spins inside proton can bring only 22% and the strange quark spin has a contribution of -12%. This requires to look for the origin of nucleon spin. (3) The Bjorken sum rule which is a key relation to check the QCD was tested and guaranteed to be correct within errors.