Exclusive Rare Decays of Heavy Baryons to Light Baryons: $Λ_b \ri ghtarrow Λγ$ and ${\Lambda }_b\to \Lambda l^{+}{l}^{-}$

Abstract

Rare decays ${\Lambda }_b\to \Lambda \gamma$ and ${\Lambda }_b\to \Lambda l^{+}{l}^{-}$ (l= e, $\mu$) are examined. We use QCD sum rules to calculate the hadronic matrix elements governing the decays. The $\Lambda$ polarization in the decays is analyzed and it is shown that the polarization parameter in ${\Lambda }_b\to \Lambda \gamma$ does not depends on the values of hadronic form factors. And the energy spectrum of $\Lambda$ in ${\Lambda }_b\to \Lambda l^{+}{l}^{-}$ is given.

10 pages, 4 figures, with minor modifications to Eq.(26), Appendix and Fig.4