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arXiv 2201.05537hep-ph
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$b\to c τ\, (μ\bar ν_μν_τ,πν_τ,ρν_τ) \barν_τ$反应中$τ-$衰变带电粒子的可见能量和角分布

Visible energy and angular distributions of the charged particle from the $τ-$decay in $b\to c τ\, (μ\bar ν_μν_τ,πν_τ,ρν_τ) \barν_τ$ reactions

N. Penalva, E. Hernández, J. Nieves

摘要:

我们研究了$d^2 Γ_d /(dωd\cosθ_d) $,$dΓ_d /d\cosθ_d$和$ dΓ_d /dE_d $分布,这是定义在可见光能量和极角的带电粒子从$τ-$衰变$b\to c τ\, (μ\bar ν_μν_τ,πν_τ,ρν_τ) \barν_τ$反应。前两个包含信息的横向τ自旋,τ角和τ角自旋不对称性的$H_b\to H_cτ\barν_τ$父衰变,从动力学的角度来看,他们比常用的一个,$d^2 Γ_d /(dωdE_d) $,因为后者只依赖于τ的纵向极化。我们注意到这些新的观测量的标准模型(SM)的预测偏差,考虑到新的物理(NP)运营商构建使用右手和左手中微子领域,在一个有效的场论方法。我们目前的结果为$Λ_b\toΛ_cτ\, (μ\bar ν_μν_τ,πν_τ,ρν_τ)\barν_τ$和$\bar B \to D^{(*)}τ\, (μ\bar ν_μν_τ,πν_τ,ρν_τ) \barν_τ$连续衰变,并讨论其使用不同的NP模型之间的解开。在这方面,我们表明,$dΓ_d /d\cosθ_d$,这应该是测量有足够好的统计,变得非常有用,特别是在$τ\to πν_τ$模式。在这项工作中进行的研究可能是特别相关的,由于最近LHCb测量的轻子味普适性比${\cal R}_{Λ_c}$与SM一致。实验通过强子衰变为$π^-π^+π^-ν_τ$来识别$τ$,而${\cal R}_{Λ_c}$的这一结果与$b$ -介子扇区的现象学相冲突,需要从其他tau重建通道中得到确认。

英文摘要:

We study the $d^2 Γ_d /(dωd\cosθ_d) $, $dΓ_d /d\cosθ_d$ and $ dΓ_d /dE_d $ distributions, which are defined in terms of the visible energy and polar angle of the charged particle from the $τ-$decay in $b\to c τ\, (μ\bar ν_μν_τ,πν_τ,ρν_τ) \barν_τ$ reactions. The first two contain information on the transverse tau-spin, tau-angular and tau-angular-spin asymmetries of the $H_b\to H_cτ\barν_τ$ parent decay and, from a dynamical point of view, they are richer than the commonly used one, $d^2 Γ_d /(dωdE_d) $, since the latter only depends on the tau longitudinal polarization. We pay attention to the deviations with respect to the predictions of the standard model (SM) for these new observables, considering new physics (NP) operators constructed using both right- and left-handed neutrino fields, within an effective field-theory approach. We present results for $Λ_b\toΛ_cτ\, (μ\bar ν_μν_τ,πν_τ,ρν_τ)\barν_τ$ and $\bar B \to D^{(*)}τ\, (μ\bar ν_μν_τ,πν_τ,ρν_τ) \barν_τ$ sequential decays and discuss their use to disentangle between different NP models. In this respect, we show that $dΓ_d /d\cosθ_d$, which should be measured with sufficiently good statistics, becomes quite useful, especially in the $τ\to πν_τ$ mode. The study carried out in this work could be of special relevance due to the recent LHCb measurement of the lepton flavor universality ratio ${\cal R}_{Λ_c}$ in agreement with the SM. The experiment identified the $τ$ using its hadron decay into $π^-π^+π^-ν_τ$, and this result for ${\cal R}_{Λ_c}$, which is in conflict with the phenomenology from the $b$-meson sector, needs confirmation from other tau reconstruction channels.

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