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arXiv 1602.09112hep-phhep-ex
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寻找Majorana中微子的有利$B_c$衰变模式

Favoured $B_c$ Decay modes to search for a Majorana neutrino

Sanjoy Mandal, Nita Sinha

备注：
29 pages, 12 figures; Plots for Bc->Bsllpi mode redone to account for Bs reconstruction, more sections added to include additional Bc decay modes which provide tighter exclusion curves for the mixing angles. References and acknowledgements added. Text modified to widen scope of the paper
发表信息：
Phys. Rev. D 94, 033001 (2016)
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摘要：

最近，LHCb合作报告了观测到的衰变模式$B_{c}^{-}\rightarrow\overline{B}_{s}^{0}π^{-}$与最大的排他性分支分数之间的所有$B$介子的已知衰变模式。在这里，我们提出了一个搜索的几个轻子数违反$B_c$的衰变模式，只能由马约拉纳中微子诱导。区分中微子的狄拉克和马约拉纳性质是一个突出的问题，因此，所有可能的搜索马约拉纳中微子需要进行。由于轻子数违反模式预计是罕见的，当使用介子衰变模式进行这些搜索时，人们预计CKM青睐的模式是首选的; $B_{c}\rightarrow B_{s}$是这样一个过渡。随着共振增强的马约拉纳中微子介导的$B_{c}^{-}\rightarrow\overline{B}_{s}^{0}\ell_{1}{-}\ell_{2}^{-}π^{+}$模式，人们可以希望观察到这些罕见的模式，或者，甚至他们的非观察可以用来获得限制的混合角的重马约拉纳单线与轻味中微子的分支分数的上限，这是更紧密或兼容的结果从早期的研究。此外，我们发现，相对抑制模式$B_{c}^{-}\rightarrow J/ψ\ell_{1}^{-}\ell_{2}^{-}π^{+}$可以提供更严格的约束$\mid V_{e N}\mid^2$，$\mid V_{μN}\mid^2$，$\mid V_{e N} V_{μN}\mid$，并在更大的范围内的重中微子质量。此外，对于大于tau衰变中可获得的质量的质量，也可以获得$\mid V_{e N} V_{τN}\mid$、$\mid V_{μN} V_{τN}\mid$的排除区域。$\mathscr{B}\left(B_{c}^{-}\rightarrowπ^{+}\ell_{1}^{-}\ell_{2}^{-}\right)$的上限也会导致所有混合元素的严格排除曲线，包括迄今为止不受约束的质量范围内的$\mid V_{τN}\mid^2$。

英文摘要：

Recently, the LHCb collaboration reported the observation of the decay mode $B_{c}^{-}\rightarrow\overline{B}_{s}^{0}π^{-}$ with the largest exclusive branching fraction amongst the known decay modes of all the $B$ mesons. Here we propose a search for a few lepton-number violating decay modes of $B_c$ which can only be induced by Majorana neutrinos. Distinguishing between Dirac and Majorana nature of neutrinos is an outstanding problem and hence, all possible searches for Majorana neutrinos need to be carried out. Since the lepton number violating modes are expected to be rare, when using meson decay modes for these searches one expects CKM favoured modes to be the preferred ones; $B_{c}\rightarrow B_{s}$ is one such transition. With a resonance enhancement of the Majorana neutrino mediating the $B_{c}^{-}\rightarrow\overline{B}_{s}^{0}\ell_{1}{-}\ell_{2}^{-}π^{+}$ modes one can hope to observe these rare modes, or, even their non-observation can be used to obtain constraints on the mixing angles of the heavy Majorana singlet with the light flavour neutrinos from upper limits of the branching fractions which are tighter or compatible with results from earlier studies. Also, we find that the relatively suppressed mode $B_{c}^{-}\rightarrow J/ψ\ell_{1}^{-}\ell_{2}^{-}π^{+}$ can provide even tighter constraints on $\mid V_{e N}\mid^2$, $\mid V_{μN}\mid^2$, $\mid V_{e N} V_{μN}\mid$, and in a larger range of the heavy neutrino mass. Further, exclusion regions for $\mid V_{e N} V_{τN}\mid$, $\mid V_{μN} V_{τN}\mid$ can also be obtained for masses larger than those accessible in tau decays. Upper limits on $\mathscr{B}\left(B_{c}^{-}\rightarrowπ^{+}\ell_{1}^{-}\ell_{2}^{-}\right)$ can also result in stringent exclusion curves for all the mixing elements, including that for $\mid V_{τN}\mid^2$ in a mass range where it is unconstrained thus far.

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