Detailed Study of the Decay Lambda_b --> Lambda_c tau {\bar \nu}_{\tau}

TL;DR

This paper investigates the semi-leptonic decay Lambda_b to Lambda_c tau nu, exploring potential new physics beyond the standard model by analyzing decay widths, constraints on new interactions, and proposing observables to distinguish different new physics scenarios.

Contribution

It provides a detailed analysis of Lambda_b decay, considering various new physics interactions, and introduces criteria and observables to differentiate among these scenarios.

Findings

Constraints on new physics couplings derived from decay analysis

Left-handed current and two-Higgs-doublet models are favored

Proposed differential observable to distinguish new physics types

Abstract

We examine in detail the semi-leptonic decay $\Lambda_b \to \Lambda_c \tau{\bar \nu}_{\tau}$, which may confirm previous hints, from the analogous $B$ decay, of a new physics beyond the standard model. First of all, starting from rather general assumptions, we predict the partial width of the decay. Then we analyze the effects of five possible new physics interactions, adopting in each case five different form factors. In particular, for each term beyond the standard model, we find some constraints on the strength and phase of the coupling, which we combine with those found by other authors in analyzing the analogous semi-leptonic decays of $B$. Our analysis involves some dimensionless quantities, substantially independent of the form factor, but which, owing to the constraints, turn out to be strongly sensitive to the kind of non-standard interaction. We also introduce a criterion thanks to which one can discriminate among the various new physics terms: the left-handed current and the two-higgs-doublet model appear privileged, with a neat preference for the former interaction. Lastly, we suggest a differential observable that could, in principle, help to distinguish between the two cases.