Leading Isgur-Wise form factor of Λ_btoΛ_(c1) transition using QCD sum rules

The leading Isgur-Wise form factor $\xi(y)$ parametrizing the semileptonic transitions $\Lambda_b\to\Lambda^{1/2}_{c1}\ell\bar\nu$ and $\Lambda_b\to\Lambda^{3/2}_{c1}\ell\bar\nu$ is calculated by using the QCD sum rules in the framework of heavy quark effective theory, where $\Lambda^{1/2}_{c1}$ and $\Lambda^{3/2}_{c1}$ is the orbitally excited charmed baryon doublet with $J^P=(1^-/2,3^-/2)$. The interpolating currents with transverse covariant derivative are adopted for $\Lambda^{1/2}_{c1}$ and $\Lambda^{3/2}_{c1}$ in the analysis. The slope parameter $\rho^2$ in linear approximation of the Isgur-Wise function is obtained to be $\rho^2=2.01$, and the interception to be $\xi(1)=0.29$. The decay branching ratios are estimated.