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arXiv 0706.3628hep-ph
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B-> QCD中的eta（'）形状因子

B->eta(') Form Factors in QCD

Patricia Ball, G. W. Jones

备注：
21 pages; version to appear in JHEP
发表信息：
JHEP 0708:025,2007
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摘要：

我们计算了半轻子形状因子$f_+^{B\to η}(q^2)$和$f_+^{B\to η'}(q^2)$，从光锥上的QCD求和规则（LCSR），到QCD中的NLO，以及对于小到中等的q ^2，$0\leq q^2\leq 16 {\rm GeV}^2$。我们特别包括所谓的单重态贡献，即由于U（1）$_{\rm A}$异常，B介子的弱湮灭伴随着两个胶子的发射，这两个胶子直接耦合到$\etap$。这种影响包括在前捻精度中。在先前对来自LCSR的形状因子的计算中忽略了该贡献。我们发现单重态对$f_+^{B\to η'}$的贡献可以高达20%，而对$f_+^{B\to η}$的贡献正如预期的那样小得多，低于3%。我们还建议测量比率${\cal B}(B\toη' e ν)/{\cal B}(B\to ηe ν)$以更好地限制单重态贡献的大小。

英文摘要：

We calculate the semileptonic form factors $f_+^{B\to η}(q^2)$ and $f_+^{B\to η'}(q^2)$ from QCD sum rules on the light-cone (LCSRs), to NLO in QCD, and for small to moderate q^2, $0\leq q^2\leq 16 {\rm GeV}^2$. We include in particular the so-called singlet contribution, i.e.\ weak annihilation of the B meson with the emission of two gluons which, thanks to the U(1)$_{\rm A}$ anomaly, couple directly to $\etap$. This effect is included to leading-twist accuracy. This contribution has been neglected in previous calculations of the form factors from LCSRs. We find that the singlet contribution to $f_+^{B\to η'}$ can be up to 20%, while that to $f_+^{B\to η}$ is, as expected, much smaller and below 3%. We also suggest to measure the ratio ${\cal B}(B\toη' e ν)/{\cal B}(B\to ηe ν)$ to better constrain the size of the singlet contribution.

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