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arXiv 1709.09571hep-ph
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微扰QCD方法研究$B \to a_1(1260) b_1(1235)$的强子衰变

Hadronic decays of $B \to a_1(1260) b_1(1235)$ in the perturbative QCD approach

Hao-Yang Jing, Xin Liu, Zhen-Jun Xiao

备注：
13 pages, 1 figure, 5 tables, revtex file
发表信息：
Phys. Rev. D 96, 113002 (2017)
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摘要：

用微扰QCD（pQCD）方法计算了首阶$B \to a_1 b_1$衰变的分支比和极化分数，其中$a_1$（$b_1$）代表轴矢量$a_1(1260)[b_1(1235)]$态.将唯象分析与微扰计算相结合，得到以下结果：（a）预测了以纵向极化为主的$B \to a_1 b_1$衰变（除$B^+ \to b_1^+ a_1^0$模外）在$10^{-5}$到$10^{-6}$附近的大衰变率，并与QCD因子分解（QCDF）的结果在误差范围内基本一致，这一结果有望在大型强子对撞机和Belle-II实验中得到检验。大的$B^0 \to a_1^0 b_1^0$分支比可以为探索颜色抑制衰变的机制提供线索。(b)$a_1$和$b_1$介子的QCD行为的不同导致了$a_1$和$b_1$介子在不可因式分解的旁观者图中的相消（相长）贡献。因此，一个有趣的模式的分支比出现的颜色抑制的$B^0 \to a_1^0 a_1^0, a_1^0 b_1^0,$和$b_1^0 b_1^0$模式的pQCD方法，$Br(B^0 \to b_1^0 b_1^0) > Br(B^0 \to a_1^0 b_1^0) \gtrsim Br(B^0 \to a_1^0 a_1^0)$，这是不同的$Br(B^0 \to b_1^0 b_1^0) \sim Br(B^0 \to a_1^0 b_1^0) \gtrsim Br(B^0 \to a_1^0 a_1^0)$在QCDF和将在未来的实验验证。(c)在这些$B \to a_1 b_1$衰变中观察到大的朴素因子分解破坏效应。具体地说，大的不可因式分解的旁观者（弱湮灭）振幅有助于$B^0 \to b_1^+ a_1^-(B^+ \to a_1^+ b_1^0\; {\rm and}\; B^+ \to b_1^+ a_1^0)$模式，这需要通过精确测量来确认。

英文摘要：

We calculate the branching ratios and polarization fractions of the $B \to a_1 b_1$ decays in the perturbative QCD(pQCD) approach at leading order, where $a_1$($b_1$) stands for the axial-vector $a_1(1260)[b_1(1235)]$ state. By combining the phenomenological analyses with the perturbative calculations, we find the following results: (a) the large decay rates around $10^{-5}$ to $10^{-6}$ of the $B \to a_1 b_1$ decays dominated by the longitudinal polarization(except for the $B^+ \to b_1^+ a_1^0$ mode) are predicted and basically consistent with those in the QCD factorization(QCDF) within errors, which are expected to be tested by the Large Hadron Collider and Belle-II experiments. The large $B^0 \to a_1^0 b_1^0$ branching ratio could provide hints to help explore the mechanism of the color-suppressed decays. (b) the rather different QCD behaviors between the $a_1$ and $b_1$ mesons result in the destructive(constructive) contributions in the nonfactorizable spectator diagrams with $a_1(b_1)$ emission. Therefore, an interesting pattern of the branching ratios appears for the color-suppressed $B^0 \to a_1^0 a_1^0, a_1^0 b_1^0,$ and $b_1^0 b_1^0$ modes in the pQCD approach, $Br(B^0 \to b_1^0 b_1^0) > Br(B^0 \to a_1^0 b_1^0) \gtrsim Br(B^0 \to a_1^0 a_1^0)$, which is different from $Br(B^0 \to b_1^0 b_1^0) \sim Br(B^0 \to a_1^0 b_1^0) \gtrsim Br(B^0 \to a_1^0 a_1^0)$ in the QCDF and would be verified at future experiments. (c) the large naive factorization breaking effects are observed in these $B \to a_1 b_1$ decays. Specifically, the large nonfactorizable spectator(weak annihilation) amplitudes contribute to the $B^0 \to b_1^+ a_1^-(B^+ \to a_1^+ b_1^0\; {\rm and}\; B^+ \to b_1^+ a_1^0)$ mode(s), which demand confirmations via the precise measurements.

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