双中微子模与半轻子稀有$\boldsymbol{B}$衰变的相互作用
Interplay of dineutrino modes with semileptonic rare $\boldsymbol{B}$-decays
摘要：
本文对双中微子模$b \to q \,ν\bar ν$、$q=d,s$和带电双轻子$b \to q \,\ell^+ \ell^-$跃迁进行了系统的整体分析。我们得到改进的，甚至是全新的限制双中微子分支比，包括衰变$B^0 \to (K^0 , X_s)\, ν\bar ν$，$B_s \to ϕ\,ν\bar ν$和$B^0 \to (π^0, ρ^0)\, ν\bar ν$从双中微子模式，目前是最好的约束：$B^+ \to (K^+,π^+, ρ^+) \,ν\bar ν$和$B^0 \to K^{*0} \,ν\bar ν$。使用SMEFT，我们得到新的味约束的双中微子模式，这是强于相应的带电双轻子罕见$b$衰变或Drell-Yan数据，$e τ$和$ττ$的最终状态，以及$b \to s$过程中的$μτ$的。该方法还允许把新的限制与顶夸克半轻子四费米子运营商。给出了双声道模式$b \to s \, τ^+ τ^-$和$b \to d \, τ^+ τ^-$的意义。此外，双中微子和带电双轻子之间的相互作用，使得在罕见的$B$ -衰变中，轻子的普适性可以得到具体而新颖的检验。对$b \to s \,μ^+ μ^-, \,s γ$跃迁进行全局拟合，我们发现轻子普适性预测了$1\,σ$处的$B^0 \to K^{*0} \,ν\bar ν$与$B^0 \to K^0 \,ν\bar ν$（$B^+ \to K^+ \,ν\bar ν$）分支分数之比在1.7到2.6（1.6到2.4）之间，该区域包括标准模型，并且可以用改进的带电双轻子数据缩小。在这个区域之外有相当大的空间，那里的普遍性被打破，可以用Belle II实验来探测。利用$B^0 \to μ^+ μ^-$、$B^0_s\to \bar{K}^{\ast 0}\,μ^+μ^-$和$ B^+ \to π^+\, μ^+ μ^-$数据的拟合结果，我们得到了$|Δb|=|Δd|=1$跃迁的类似关系。
英文摘要：
We present a systematic global analysis of dineutrino modes $b \to q \,ν\bar ν$, $q=d,s$, and charged dilepton $b \to q \,\ell^+ \ell^-$ transitions. We derive improved or even entirely new limits on dineutrino branching ratios including decays $B^0 \to (K^0 , X_s)\, ν\bar ν$, $B_s \to ϕ\,ν\bar ν$ and $B^0 \to (π^0, ρ^0)\, ν\bar ν$ from dineutrino modes which presently are best constrained: $B^+ \to (K^+,π^+, ρ^+) \,ν\bar ν$ and $B^0 \to K^{*0} \,ν\bar ν$. Using SMEFT we obtain new flavor constraints from the dineutrino modes, which are stronger than the corresponding ones from charged dilepton rare $b$-decay or Drell-Yan data, for $e τ$ and $ττ$ final states, as well as for $μτ$ ones in $b \to s$ processes. The method also allows to put novel constraints on semileptonic four-fermion operators with top quarks. Implications for ditau modes $b \to s \, τ^+ τ^-$ and $b \to d \, τ^+ τ^-$ are worked out. Furthermore, the interplay between dineutrinos and charged dileptons allows for concrete, novel tests of lepton universality in rare $B$-decays. Performing a global fit to $b \to s \,μ^+ μ^-, \,s γ$ transitions we find that lepton universality predicts the ratio of the $B^0 \to K^{*0} \,ν\bar ν$ to $B^0 \to K^0 \,ν\bar ν$ ($B^+ \to K^+ \,ν\bar ν$) branching fractions to be within 1.7 to 2.6 (1.6 to 2.4) at $1\,σ$, a region that includes the standard model, and that can be narrowed with improved charged dilepton data. There is sizable room outside this region where universality is broken and that can be probed with the Belle II experiment. Using results of a fit to $B^0 \to μ^+ μ^-$, $B^0_s\to \bar{K}^{\ast 0}\,μ^+μ^-$ and $ B^+ \to π^+\, μ^+ μ^-$ data we obtain an analogous relation for $|Δb|=|Δd|=1$ transitions.
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