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

We investigate the inverse moment of the B<inf>s</inf>-meson light-cone distribution amplitude (LCDA), denoted as λB<inf>s</inf> and defined within the heavy quark effective theory, through the calculation of B<inf>s</inf> → η<inf>s</inf> form factors. The presence of the s-quark inside the B<inf>s</inf>-meson dictates a notable departure of approximately 20% in the λB<inf>s</inf> value compared to the non-strange case λB<inf>q</inf>, as computed within the QCD sum rule approach, albeit with significant uncertainty. First, we compute the decay constant of the η<inf>s</inf>-meson utilizing two-point sum rules while retaining finite s-quark mass contributions. Next, we constrain the parameter λB<inf>s</inf> by calculating B<inf>s</inf> → η<inf>s</inf> form factors within the light-cone sum rule approach, using B<inf>s</inf>-meson LCDAs, and leveraging Lattice QCD estimates at zero momentum transfer from the HPQCD collaboration. Our findings yield λB<inf>s</inf> = 480 ± 92 MeV when expressing the B<inf>s</inf>-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 λB<inf>s</inf> value, with earlier analyses for other channels such as B<inf>s</inf> → D<inf>s</inf> and B<inf>s</inf> → K.