Probing the inverse moment of Bs-meson distribution amplitude via Bs→ns form factors

Abstract

We investigate the inverse moment of the Bs-meson light-cone distribution amplitude (LCDA), denoted as λBs and defined within the heavy quark effective theory, through the calculation of Bs→ηs form factors. The presence of the s-quark inside the Bs-meson dictates a notable departure of approximately 20% in the λBs value compared to the non-strange case λBq, as computed within the QCD sum rule approach, albeit with significant uncertainty. First, we compute the decay constant of the ηs-meson utilizing two-point sum rules while retaining finite s-quark mass contributions. Next, we constrain the parameter λBs by calculating Bs→ηs form factors within the light-cone sum rule approach, using Bs-meson LCDAs, and leveraging Lattice QCD estimates at zero momentum transfer from the HPQCD collaboration. Our findings yield λBs = 480 ± 92 MeV when expressing the Bs-meson LCDAs in the Exponential model, consistent with previous QCD sum rule estimate yet exhibiting a 1.5-fold improvement in uncertainty. Furthermore, we compare the form factor predictions, based on the extracted λBs value, with earlier analyses for other channels such as Bs→Ds and Bs→K.