# Rare $\Lambda_b\to\Lambda l^+l^-$ and $\Lambda_b\to\Lambda\gamma$ decays in the relativistic quark model

## TL;DR

This paper calculates decay form factors and branching ratios for rare $ ext{Lambda}_b$ baryon decays into $ ext{Lambda}$ and lepton pairs or photons using a relativistic quark model, aligning well with recent LHCb data.

## Contribution

It introduces a comprehensive relativistic quark model calculation of decay form factors, including all relativistic effects, for $ ext{Lambda}_b$ rare decays, providing new theoretical predictions.

## Key findings

- Decay branching fractions agree with LHCb measurements.
- Explicit form factor dependence on momentum transfer is determined.
- Predictions for $ ext{Lambda}_b o ext{Lambda} au^+ au^-$ observables are provided.

## Abstract

Rare $\Lambda_b\to\Lambda l^+l^-$ and $\Lambda_b\to\Lambda\gamma$ decays are investigated in the relativistic quark model based on the quark-diquark picture of baryons. The decay form factors are calculated with the account of all relativistic effects including relativistic transformations of baryon wave functions from rest to moving reference frame and the contribution of the intermediate negative energy states. The momentum transfer squared dependence of the form factors is explicitly determined in the whole accessible kinematical range. The calculated decay branching fractions, various forward-backward asymmetries for the rare decay $\Lambda_b\to\Lambda \mu^+\mu^-$ are found to be consistent with recent detailed measurements by the LHCb Collaboration. Predictions for the $\Lambda_b\to\Lambda \tau^+\tau^-$ decay observables are given.