Rare Decays of \Lambda_b->\Lambda + \gamma and \Lambda_b ->\Lambda + l^{+} l^{-} in the Light-cone Sum Rules

TL;DR

This paper uses light-cone sum rules to analyze rare Lambda_b decays, examining the effects of higher twist distribution amplitudes and different wave function models on decay form factors and asymmetries.

Contribution

It introduces a detailed LCSR analysis of Lambda_b decays including higher twist effects and compares phenomenological models, revealing their impact on form factors and decay observables.

Findings

Higher twist distribution amplitudes have minimal impact on form factors under heavy quark spin symmetry.

Phenomenological models can produce form factors about five times larger than conformal expansion.

Calculated decay rates and asymmetries provide insights into the decay mechanisms of Lambda_b.

Abstract

Within the Standard Model, we investigate the weak decays of $\Lambda_b \to \Lambda + \gamma$ and $\Lambda_b \to \Lambda + l^{+} l^{-}$ with the light-cone sum rules approach. The higher twist distribution amplitudes of $\Lambda$ baryon to the leading conformal spin are included in the sum rules for transition form factors. Our results indicate that the higher twist distribution amplitudes almost have no influences on the transition form factors retaining the heavy quark spin symmetry, while such corrections can result in significant impacts on the form factors breaking the heavy quark spin symmetry. Two phenomenological models (COZ and FZOZ) for the wave function of $\Lambda$ baryon are also employed in the sum rules for a comparison, which can give rise to the form factors approximately 5 times larger than that in terms of conformal expansion. Utilizing the form factors calculated in LCSR, we then perform a careful study on the decay rate, polarization asymmetry and forward-backward asymmetry, with respect to the decays of $\Lambda_b \to \Lambda \gamma$, $\Lambda l^{+}l^{-}$.