The measurable angular distribution of Λb0→Λc+→Λ0π+τ-→π-vτvτ decay

In Lambda b0-> Lambda c+-> Lambda 0 pi+tau -vtau decay, the solid angle of the final-state particle tau (-) cannot be determined precisely since the decay products of the tau (-) include an undetected nu (tau). Therefore, the angular distribution of this decay cannot be measured. In this work, we construct a measurable angular distribution by considering the subsequent decay tau (-)-> pi (-)nu (tau). The full cascade decay is Lambda b0-> Lambda c+-> Lambda 0 pi+tau--> pi -v tauvtau. The three-momenta of the final-state particles Lambda (0), pi (+), and pi (-) can be measured. Considering all Lorentz structures of the new physics (NP) effective operators and an unpolarized initial Lambda (b) state, the five-fold differential angular distribution can be expressed in terms of ten angular observables Kiq2E pi. By integrating over some of the five kinematic parameters, we define a number of observables, such as the Lambda (c) spin polarization P Lambda cq2 and the forward-backward asymmetry of pi (-) meson A(FB)(q(2)), both of which can be represented by the angular observables Kiq2. We provide numerical results for the entire set of the angular observables Kiq2 and Ki both within the Standard Model and in some NP scenarios, which are a variety of best-fit solutions in seven different NP hypotheses. We find that the NP which can resolve the anomalies in B-> Dtau -vtau decays has obvious effects on the angular observables Kiq2, except K1ssq2 and K1ccq2.

Automated summary

This paper investigates the Lambda b0 decay and constructs a measurable angular distribution to address issues that cannot be precisely determined in measurements. The study finds that different NP hypotheses have effects on angular observables, except for two specific observables.