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

Abstract

The experimental prospects for precise measurements of the leptonic decays B u → τ ν/µν, B s → µ + µ − , D → µν and D s → µν/τ ν 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 Bs ), and hence a reliance on theoretical techniques such as lattice QCD.

Implications of LHC searches on SUSY particle spectra

“…We use the following 95% C.L. intervals, which include theoretical and experimental uncertainties [15,47,48]:…”

The decay B s → μ + μ −: updated SUSY constraints and prospects

“…A comparison of the constraints on specific SUSY models from the double ratio and from BR(B s → µ + µ − ) alone is of much interest because the theoretical input parameters |V ub | and f Bs for these two observables are independent. Such a comparative study was performed for the first time in [21], and it was shown that the double ratio can provide stronger constraints. In particular, the constraints from the double ratio are maximised (minimised) for smaller (larger) |V ub |, while the constraints from BR(B s → µ + µ − ) are maximised (minimised) for larger (smaller) f Bs .…”

“…Moreover, we consider an alternative observable which includes BR(B s → µ + µ − ), namely, a double ratio of leptonic decays [19,20]. The double ratio has no dependence on the absolute value of the decay constant f Bs , which is the main source of uncertainty in the SM prediction for BR(B s → µ + µ − ), and it was shown in [21] that this observable can provide competitive (or even superior) constraints on the SUSY parameter space. The main uncertainty in the SM prediction for the double ratio arises from the CKM matrix element |V ub |, for which the prospects of precise measurements at high-luminosity B factories are very promising.…”

Supersymmetry confrontsBs→μ+μ−: Present and future status

“…and D s ! =, it could be possible to enhance the sensitivity of the individual decays, through the cancellation of hadronic uncertainties, and stronger constraints can be obtained [13,16].…”