In this work, we study the semileptonic decay modes B-s(0) -> pi(+)pi(-)l(+)l(-) and D-s(+) -> pi(+)pi(-)l(+)nu in the kinematics region where the pi(+)pi(-) system has a invariant mass in the range 0.5-1.3 GeV. These processes are valuable towards the determination of S-wave pi(+)pi(-)light-cone distribution amplitudes whose normalizations are scalar form factors. We compare the results for scalar form factors predicted in unitarized chiral perturbation theory and extracted from the data on the B-s -> J/psi pi(+)pi(-). Then the B-s -> pi(+)pi(-) and D-s -> pi(+)pi(-) form factors are calculated in light-cone sum rules, based on which predictions for differential decay widths are made. The results are in good agreement with the experimental data on the Bs and Ds decays into pi(+)pi(-). More accurate measurements at BEPC, LHC and KEKB in the future will be helpful to examine our formalism and constrain the input parameters more precisely.
Shanghai Natural Science Foundation [15DZ2272100, 15ZR1423100]
; Open Project Program of State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, China [Y5KF111CJ1]
; Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry
; National Natural Science Foundation of China