Measuring V_ub and probing SUSY with double ratios of purely leptonic decays of B and D mesons

TL;DR

This paper proposes using double ratios of leptonic B and D meson decays to precisely measure the CKM element V_ub and to effectively probe supersymmetric models, reducing theoretical uncertainties.

Contribution

It introduces a method using double ratios of leptonic decays to measure V_ub with minimal theoretical error and enhances SUSY parameter space exploration.

Findings

Double ratios can eliminate decay constant dependence.

The method offers competitive precision for |V_ub| measurement.

Double ratios are more effective than individual decays for SUSY probing.

Abstract

The experimental prospects for precise measurements of the leptonic decays B_u -> tau nu / mu nu, B_s -> mu+ mu-, D -> mu nu and D_s -> mu nu / tau nu are very promising. Double ratios involving four of these decays can be defined in which the dependence on the values of the decay constants is essentially eliminated, thus enabling complementary measurements of the CKM matrix element V_ub with a small theoretical error. We quantify the experimental error in a possible future measurement of |V_ub| using this approach, and show that it is competitive with the anticipated precision from the conventional approaches. Moreover, it is shown that such double ratios can be more effective than the individual leptonic decays as a probe of the parameter space of supersymmetric models. We emphasize that the double ratios have the advantage of using |V_ub| as an input parameter (for which there is experimental information), while the individual decays have an uncertainty from the decay constants (e.g. f_B_s), and hence a reliance on theoretical techniques such as lattice QCD.