Inclusive rare ${\mathrm{\Lambda }}_b$ decays to photon

Inclusive $H_b\to X_s\gamma$ decays, with $H_b$ a beauty baryon, are treated exploiting an expansion up to the third order in the inverse of the $b$ quark mass $m_b$ and to LO in ${\alpha }_s$, keeping the dependence on the hadron spin. Double distribution $\frac{d^2\mathrm{\Gamma }}{dyd\cos {\theta }_P}$ is computed for polarized baryons, with $y=2E_{\gamma }\mathrm{/}{m}_b$, $E_{\gamma }$ the photon energy and ${\theta }_P$ the angle between the baryon spin vector and the photon momentum in the $H_b$ rest-frame. Modifications to the photon polarization asymmetry can probe effects of physics beyond the Standard Model. A systematic method to treat the singular terms in the photon energy spectrum obtained by the OPE is proposed.