Beaujean Frederik, Bobeth Christoph, Jahn Stephan
C2PAP, Excellence Cluster Universe, Ludwig-Maximilians-Universität München, Garching, Germany.
Institute for Advanced Study, Technische Universität München, Garching, Germany.
Eur Phys J C Part Fields. 2015;75(9):456. doi: 10.1140/epjc/s10052-015-3676-2. Epub 2015 Sep 28.
The angular distribution of [Formula: see text] ([Formula: see text]) depends on two parameters, the lepton forward-backward asymmetry, [Formula: see text], and the flat term, [Formula: see text]. Both are strongly suppressed in the standard model and constitute sensitive probes of tensor and scalar contributions. We use the latest experimental results for [Formula: see text] in combination with the branching ratio of [Formula: see text] to derive the strongest model-independent bounds on tensor and scalar effective couplings to date. The measurement of [Formula: see text] provides a complementary constraint to that of the branching ratio of [Formula: see text] and allows us - for the first time - to constrain all complex-valued (pseudo-)scalar couplings and their chirality-flipped counterparts in one fit. Based on Bayesian fits of various scenarios, we find that our bounds even become tighter when vector couplings are allowed to deviate from the standard model and that specific combinations of angular observables in [Formula: see text] are still allowed to be up to two orders of magnitude larger than in the standard model, which would place them in the region of LHCb's sensitivity.
[公式：见正文]（[公式：见正文]）的角分布取决于两个参数，即轻子前后不对称性[公式：见正文]和平项[公式：见正文]。在标准模型中，这两者都受到强烈抑制，并构成了张量和标量贡献的灵敏探针。我们将[公式：见正文]的最新实验结果与[公式：见正文]的分支比相结合，得出了迄今为止关于张量和标量有效耦合的最强的与模型无关的界限。对[公式：见正文]的测量为[公式：见正文]的分支比测量提供了补充约束，并首次使我们能够在一次拟合中约束所有复值（伪）标量耦合及其手征翻转对应项。基于各种情形的贝叶斯拟合，我们发现，当允许矢量耦合偏离标准模型时，我们的界限甚至会变得更严格，并且[公式：见正文]中角可观测量的特定组合仍可能比标准模型中的值大两个数量级，这将使其处于LHCb的灵敏度范围内。
