Precision measurement of the neutron spin asymmetries and spin-dependent structure functions in the valence quark region
Precision measurement of the neutron spin asymmetries and spin-dependent structure functions in the valence quark region
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DOI：
10.1103/physrevc.70.065207
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发表时间：
2004-05
影响因子：
3.1
通讯作者：
X. Zheng;E. al.
中科院分区：
文献类型：
--
作者：
X. Zheng;E. al.
我们测量了深非弹区三种运动学下的中子自旋不对称性和极化结构函数，分别为x=0.33，0.47和0.60，Q^2=2.7，3.5和4.8(GeV/c)$2。这些测量是使用5.7GeV的纵向极化电子束和极化的$3$He靶进行的。在$x=0.33$时，$A_1^n$和$g_1^n$的结果与以前的世界数据一致，并且在较高的两个$x$点处，世界数据的精度提高了大约一个数量级。新的$A_1^n$数据显示，在$x=0.47$附近有一个零交叉，在$x=0.60$处的值是显著正的。这些结果与之前世界数据的次要顺序QCD分析相一致。高x的数据趋势与成分夸克模型的预测一致，但与假设强子螺旋度守恒的前序微扰QCD(PQCD)的结果不一致。在这个运动学区域，$A_2^N$和$G_2^N$的结果具有可与世界上最好的数据相媲美的精度。结合以前的世界数据，对时刻d2^n$进行了估计，新的结果使这个量的精度提高了大约两倍。结合世界质子数据，从基于夸克部分子模型的新的g1^n/F1^n$值中提取了极化夸克分布函数。当施加强子螺旋度守恒时，对u/u的计算结果与各种模型的预测吻合得很好，而对d/d的计算结果与前序pQCD的预测不一致。
We report on measurements of the neutron spin asymmetries $A_{1,2}^n$ and polarized structure functions $g_{1,2}^n$ at three kinematics in the deep inelastic region, with $x=0.33$, 0.47 and 0.60 and $Q^2=2.7$, 3.5 and 4.8 (GeV/c)$^2$, respectively. These measurements were performed using a 5.7 GeV longitudinally-polarized electron beam and a polarized $^3$He target. The results for $A_1^n$ and $g_1^n$ at $x=0.33$ are consistent with previous world data and, at the two higher $x$ points, have improved the precision of the world data by about an order of magnitude. The new $A_1^n$ data show a zero crossing around $x=0.47$ and the value at $x=0.60$ is significantly positive. These results agree with a next-to-leading order QCD analysis of previous world data. The trend of data at high $x$ agrees with constituent quark model predictions but disagrees with that from leading-order perturbative QCD (pQCD) assuming hadron helicity conservation. Results for $A_2^n$ and $g_2^n$ have a precision comparable to the best world data in this kinematic region. Combined with previous world data, the moment $d_2^n$ was evaluated and the new result has improved the precision of this quantity by about a factor of two. When combined with the world proton data, polarized quark distribution functions were extracted from the new $g_1^n/F_1^n$ values based on the quark parton model. While results for $\Delta u/u$ agree well with predictions from various models, results for $\Delta d/d$ disagree with the leading-order pQCD prediction when hadron helicity conservation is imposed.