In the present paper, we suggest a convenient model for the vector $\rho$-meson longitudinal leading-twist distribution amplitude $\phi_{ 2;\rho}^\|$, whose distribution is controlled by a single parameter $B^\|_{ 2;\rho}$. By choosing proper chiral current in the correlator, we obtain new light-cone sum rules (LCSR) for the $B\to\rho$ TFFs $A_1$, $A_2$ and $V$, in which the $\delta^1$-order $\phi_{ 2;\rho}^\|$ provides dominant contributions. Then we make a detailed discussion on the $\phi_{ 2;\rho}^\|$ properties via those $B\to\rho$ TFFs. A proper choice of $B^\|_{ 2;\rho}$ can make all the TFFs agree with the lattice QCD predictions. A prediction of $|V_{ \rm ub}|$ has also been presented by using the extrapolated TFFs, which indicates that a larger $B^{ \|}_{ 2;\rho}$ leads to a larger $|V_{ \rm ub}|$. To compare with the BABAR data on $|V_{ \rm ub}|$, the longitudinal leading-twist DA $\phi_{ 2;\rho}^\|$ prefers a doubly-humped behavior.
Categories: hep-ph