TTP97-38 Probing the helicity structure of $b\to s\gamma$ in $\Lambda_b \to \Lambda \gamma$

We investigate the rare decay $\Lambda_b \to \Lambda \gamma$ which receives both short and long distance contributions. We estimate the long distance contributions and find them very small. The form factors are obtained from $\Lambda_c \to \Lambda \ell \bar{\nu}_\ell$ using heavy quark symmetry and a pole model. The short distance piece opens a window to new physics and we discuss the sensitivity of $\Lambda_b \to \Lambda \gamma$ to such effects.