粲海夸克对粲偶素光谱的影响有多大？
How much do charm sea quarks affect the charmonium spectrum?
摘要：
粲偶素态的性质正在或将被B工厂Belle II和BESIII，LHCb和PANDA实验以及未来的Super-c-Tau工厂深入研究。精确的晶格计算提供了有价值的输入，并通过模拟海洋中的上夸克、下夸克和奇异夸克获得了一些结果。研究了海洋中粲夸克对粲偶素谱、粲夸克质量的重整化群不变和粲夸克标量含量的影响。后者是通过直接计算粲偶素质量的质量导数得到的。我们在一个模型中做了这个研究，QCD有两个简并的粲夸克。由于没有轻夸克，我们可以达到非常小的晶格间距，低至0.023 fm。通过与纯规范理论的比较，我们发现海中的粲夸克对超精细分裂的影响在2%以下。最显著的影响是eta_c介子的夸克质量为5%，粲夸克含量为3%。考虑到我们模拟了两个粲夸克，这些估计是单个粲夸克贡献的上界。我们表明，使用O（a）改进的威尔逊夸克对粲偶素谱进行安全连续外推需要晶格间距<0.06 fm。一个有用的关系的投影到期望的宇称的运营商在两点函数计算扭曲质量费米子证明。
英文摘要：
The properties of charmonium states are or will be intensively studied by the B-factories Belle II and BESIII, the LHCb and PANDA experiments and at a future Super-c-tau Factory. Precise lattice calculations provide valuable input and several results have been obtained by simulating up, down and strange quarks in the sea. We investigate the impact of a charm quark in the sea on the charmonium spectrum, the renormalization group invariant charm-quark mass and the scalar charm-quark content of charmonium. The latter is obtained by the direct computation of the mass-derivatives of the charmonium masses. We do this investigation in a model, QCD with two degenerate charm quarks. The absence of light quarks allows us to reach very small lattice spacings down to 0.023 fm. By comparing to pure gauge theory we find that charm quarks in the sea affect the hyperfine splitting at a level below 2%. The most significant effects are 5% in the quark mass and 3% in the value of the charm quark content of the eta_c meson. Given that we simulate two charm quarks these estimates are upper bounds for the contribution of a single charm quark. We show that lattice spacings <0.06 fm are needed for safe continuum extrapolations of the charmonium spectrum with O(a) improved Wilson quarks. A useful relation for the projection to the desired parity of operators in two-point functions computed with twisted mass fermions is proven.
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