Rare decays of $\Lambda_b \to \Lambda \gamma$ and $\Lambda_b \to \Lambda l^{+} l^{-}$ in universal extra dimension model

TL;DR

This paper investigates how universal extra dimensions affect rare Lambda_b decays, showing potential deviations in decay rates and asymmetries that could help constrain the size of extra dimensions.

Contribution

It provides a detailed analysis of Lambda_b decay observables within the universal extra dimension model, highlighting measurable effects of Kaluza-Klein modes on decay characteristics.

Findings

Approximately 25% suppression in $ ext{BR}( extLambda_b o extLambda extgamma)$ due to extra dimensions.

Around 10% enhancement in $ extLambda_b o extLambda l^{+} l^{-}$ decay rate from Kaluza-Klein contributions.

Zero-position of forward-backward asymmetry is sensitive to the compactification radius R.

Abstract

The exclusive weak decay of $\Lambda_b \to \Lambda \gamma$ and $\Lambda_b \to \Lambda l^{+} l^{-}$ are investigated in the Applequist-Cheng-Dobrescu model, which is an extension of the standard model in presence of universal extra dimensions. Employing the transition form factors obtained in the light-cone sum rues, we analyze how the invariant mass distribution, forward-backward asymmetry and polarization asymmetry of $\Lambda$ baryon of these decay modes can be used to constrain the only one additional free parameter with respect to the standard model, namely, the radius $R$ of the extra dimension. Our results indicate that the Kaluza-Klein modes can lead to approximately 25% suppression of the branching ratio of $\Lambda_b \to \Lambda \gamma$, however, their contributions can bring about 10% enhancement to the decay rate of $\Lambda_b \to \Lambda l^{+} l^{-}$. It is shown that the zero-position of forward-backward asymmetry of $\Lambda_b \to \Lambda \mu^{+} \mu^{-}$ is sensitive to the compactification parameter $R$ in this scenario, while the measurement of polarizations of $\Lambda$ baryon in the $\Lambda_b$ decays is not suitable to provide some valuable information for the universal extra dimension model.