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The study of $$ \overline{B}\to {D}^{\ast}\tau {\overline{\nu}}_{\tau } $$angular distribution can be used to obtain information about new physics (or beyond the Standard Model) couplings, which are motivated by various B anomalies. However, the inability to measure precisely the three-momentum of the lepton hinders such measurements, as the tau decay contains one or more undetected neutrinos. Here, we present a measurable angular distribution of $$ \overline{B}\to {D}^{\ast}\tau {\overline{\nu}}_{\tau } $$ by considering the additional decay $$ \tau \to \ell {\nu}_{\tau }{\overline{\nu}}_{\ell } $$, wℓ. The full process used is$$ \overline{B}\to {D}^{\ast}\left(\to D\pi \right)\tau \left(\to \ell {\nu}_{\tau }{\overline{\nu}}_{\ell}\right){\overline{\nu}}_{\tau } $$ $\overline{B}\to D^{\ast }\left(\to \mathrm{D\pi }\right)\tau \left(\to \ell {\nu }_{\tau }{\overline{\nu }}_{\ell }\right){\overline{\nu }}_{\tau }$, in which only theℓandD^*are reconstructed. A fit to the experimental angular distribution of this process can be used to extract information on new physics parameters. To demonstrate the feasibility of this approach, we generate simulated data for this process and perform a sensitivity study to obtain the expected statistical errors on new physics parameters from experiments in the near future. We obtain a sensitivity of the order of 5% for the right-handed current and around 6% for the tensor current. In addition, we use the recent lattice QCD data onB→D^*form factors and obtain correlations between form factors and new physics parameters. 

In this work, we explore the effect of neutrino nonstandard interactions (NSI) involving the charm quark at SND@LHC. Using an effective description of new physics in terms of four-fermion operators involving a charm quark, we constrain the Wilson coefficients of the effective interaction from two and three-body charmed meson decays. In our fit, we include charmed meson decays not only to pseudoscalar final states but also to vector final states and include decays to the η and η′ final states. We also consider constraints from charmed baryon decays. We then study the effect of new physics in neutrino scattering processes, involving charm production at SND@LHC, for various benchmark new physics couplings obtained from the low energy fits. Finally, we also study the effects of lepton universality violation (LUV) assuming that the new physics coupling is not lepton universal. 

Belle II has reported the first evidence for B+→K+νν¯ with a branching ratio 2.7σ higher than the standard model expectation. We explain this, and the MiniBooNE and muon anomalous magnetic moment anomalies in a model with a dark scalar that couples to a slightly heavier sterile Dirac neutrino and that communicates with the visible sector via a Higgs portal. We make predictions for rare kaon and other B meson decays. 

A<sc>bstract</sc> We study flavor changing neutral current decays ofBandKmesons in the dark U(1)_Dmodel, with the dark photon/darkZmass between 10 MeV and 2 GeV. Although the model provides an improved fit (compared to the standard model) to the differential decay distributions ofB → K^(∗)ℓ⁺ℓ⁻, withℓ=μ,e, andB_s→ ϕμ⁺μ⁻, the allowed parameter space is ruled out by measurements of atomic parity violation,K⁺→ μ⁺+invisibledecay, and$$ {B}_s-{\overline{B}}_s $$ $B_s-{\overline{B}}_s$mixing, among others. To evade constraints from low energy data, we extend the model to allow for (1) additional invisibleZ_Ddecay, (2) a direct vector coupling ofZ_Dto muons, and (3) a direct coupling ofZ_Dto both muons and electrons, with the electron coupling fine-tuned to cancel theZ_Dcoupling to electrons via mixing. We find that only the latter case survives all constraints.