Leading Isgur-Wise form factor of ${\Lambda }_b\to {\Lambda }_{c1}$ transition using QCD sum rules

Abstract

The leading Isgur-Wise form factor $\xi (y)$ parametrizing the semileptonic transitions ${\Lambda }_b\to {\Lambda }_{c1}^{1/2}\ell \bar{\nu }$ and ${\Lambda }_b\to {\Lambda }_{c1}^{3/2}\ell \bar{\nu }$ is calculated by using the QCD sum rules in the framework of heavy quark effective theory, where ${\Lambda }_{c1}^{1/2}$ and ${\Lambda }_{c1}^{3/2}$ is the orbitally excited charmed baryon doublet with $J^P=(1^{-}/2,3^{-}/2)$. The interpolating currents with transverse covariant derivative are adopted for ${\Lambda }_{c1}^{1/2}$ and ${\Lambda }_{c1}^{3/2}$ 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.

Comments: 16 pages, 3 figures, to appear in PLB