Light-cone Distribution Amplitudes of the Nucleon and Negative Parity Nucleon Resonances from Lattice QCD
Light-cone Distribution Amplitudes of the Nucleon and Negative Parity Nucleon Resonances from Lattice QCD
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DOI：
10.1103/physrevd.89.094511
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发表时间：
2014-03
影响因子：
5
通讯作者：
V. Braun;Sean P. Collins;B. Gläßle;M. Göckeler;A. Schäfer;R. Schiel;W. Söldner;A. Sternbeck;P. Wein
中科院分区：
文献类型：
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作者：
V. Braun;Sean P. Collins;B. Gläßle;M. Göckeler;A. Schäfer;R. Schiel;W. Söldner;A. Sternbeck;P. Wein
我们在不同体积和介子质量（m_pi = 150 MeV）的晶格上使用两种动态费米子（三叶草）对核子和负宇称核子共振的光锥分布振幅（DAs）进行了晶格研究。我们发现质子中的三个价夸克共享动量的比例为37%:31%:31%，其中较大的比例对应于携带质子螺旋度的u夸克，并确定了原点波函数在位置空间中的值，与现有的基于QCD求和规则的估计相比，该值较小。高阶矩受数据约束，在不确定度范围内都与零相容。我们还计算了与夸克角动量分布有关的高扭转DAs的归一化常数。此外，我们利用变分方法和自定义宇称投影算子研究了具有负宇称的状态。通过这种方法，我们能够分离出两个最低态的贡献，正如我们所认为的，它们可能分别对应于N*(1535)和N*(1650)和介子-核子连续体的混合物。结果表明，与第二次观测到的负宇称态和核子相比，我们鉴定的N*(1535)态具有非常不同的DA，这可能解释了实验中观察到的N*(1535)和N*(1650)衰变模式的差异。
We present the results of a lattice study of light-cone distribution amplitudes (DAs) of the nucleon and negative parity nucleon resonances using two flavors of dynamical (clover) fermions on lattices of different volumes and pion masses down to m_pi = 150 MeV. We find that the three valence quarks in the proton share their momentum in the proportion 37% : 31% : 31%, where the larger fraction corresponds to the u-quark that carries proton helicity, and determine the value of the wave function at the origin in position space, which turns out to be small compared to the existing estimates based on QCD sum rules. Higher-order moments are constrained by our data and are all compatible with zero within our uncertainties. We also calculate the normalization constants of the higher-twist DAs that are related to the distribution of quark angular momentum. Furthermore, we use the variational method and customized parity projection operators to study the states with negative parity. In this way we are able to separate the contributions of the two lowest states that, as we argue, possibly correspond to N*(1535) and a mixture of N*(1650) and the pion-nucleon continuum, respectively. It turns out that the state that we identify with N*(1535) has a very different DA as compared to both the second observed negative parity state and the nucleon, which may explain the difference in the decay patterns of N*(1535) and N*(1650) observed in experiment.