Tau longitudinal and transverse polarizations from visible kinematics in (anti-)neutrino nucleus scattering
E. Hernández, J. Nieves, F. Sánchez, J. E. Sobczyk
备注：
11 pages, 5 figures. We have corrected a numerical error in our calculation. Figures have changed but the discussion and conclusions remain the same. An erratum will be published
发表信息：
Phys. Lett. B 829 (2022) 137046; Erratum Phys. Lett. B 836 (2023) 137612
Since the $ν_τ(\barν_τ) A_Z \to τ^\mp X$ reaction is notoriously difficult to be directly measured, the information on the dynamics of this nuclear process should be extracted from the analysis of the energy and angular distributions of the tau decay visible products. These distributions depend on the components of the tau-polarization vector. We give, for the first time, the general expression for the outgoing hadron (pion or rho meson) energy and angular differential cross section for the sequential $ν_τA_Z \to τ^-(π^- ν_τ, ρ^-ν_τ) X$ and $\barν_τA_Z \to τ^+(π^+ \barν_τ, ρ^+ \barν_τ) X$ reactions. Though all possible nuclear reaction mechanisms contribute to the distribution, it may be possible to isolate/enhance one of them by implementing appropriate selection criteria. For the case of the quasi-elastic reaction off oxygen and neutrino energies below 6 GeV, we show that the pion distributions are sensitive to the details of the tau-polarization components. We find significant differences between the full calculation, where the longitudinal and transverse components of the tau polarization vector vary with the energy and the scattering angle of the produced tau, and the simplified scheme in which the polarizations are set to one and zero (respective asymptotic values in the high energy regime). In addition to its potential impact on neutrino oscillation analyses, this result can be used to further test different nuclear models, since these observables provide complementary information to that obtained by means of the inclusive nuclear weak charged-current differential cross section. We also study the effects on the cross section of the $W_4$, $W_5$ nuclear structure functions, which contributions are proportional to the charged lepton mass, and therefore difficult to constrain in muon and electron neutrino experiments.
Tau properties in $B\to Dτν$ from visible final-state kinematics
在含有τ轻子的半轻子$B$衰变中，产生过程的特征会印在τ螺旋度态上。由于无法通过实验完全重建tau动量，因此关于tau性质的可用信息被编码在其可见衰变产物中。专注于过程$B\to Dτν$，我们发现明确的τ属性和运动学的带电粒子的衰变$τ\toπν$，$τ\toρν$，和$τ\to\ellν\barν$之间的关系。特别是，我们表明，垂直极化，$P_\perp$，和向前向后的不对称性，$A_τ$，τ轻子可以同时提取的带电粒子对$D$介子的角不对称性。对于最敏感的衰变通道$τ\toπν$，我们预计在BELLE II基于$50\,$ ab $^{-1}$数据的测量中，$P_\perp$和$A_τ$的相对统计精度约为$10\%$。
Revealing the Two-Fold Ambiguity: Tau Momentum Reconstruction and Its Impact on Entanglement Observables
Shaanxi Normal University（陕西师范大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；University of Chinese Academy of Science（中国科学院大学）
