Analysis of $\Lambda_b \rar \Lambda \ell^+ \ell^-$ transition in SM4 using form factors from Full QCD

TL;DR

This paper investigates the impact of a hypothetical fourth-generation quark on the decay process of Lambda_b baryons into Lambda baryons and lepton pairs, using full QCD form factors to analyze observable deviations from the Standard Model.

Contribution

It provides a detailed analysis of the Lambda_b to Lambda transition in SM4 using full QCD form factors, highlighting significant deviations from SM predictions for heavy fourth-generation quark masses.

Findings

Branching ratio is higher in full QCD than in heavy quark effective theory.

Observables deviate significantly from SM when the fourth-generation quark mass exceeds 400 GeV.

Results suggest potential experimental signatures of SM4 effects.

Abstract

Using the responsible form factors calculated via full QCD, we analyze the $\Lambda_{b}\rightarrow \Lambda \ell^{+}\ell^{-}$ transition in the standard model containing fourth generation quarks (SM4). We discuss effects of the presence of $t'$ fourth family quark on related observables like branching ratio, forward-backward asymmetry, baryon polarization as well as double lepton polarization asymmetries. We also compare our results with those obtained in the SM as well as with predictions of the SM4 but using form factors calculated within heavy quark effective theory. The obtained results on branching ratio indicate that the $\Lambda_{b}\rightarrow \Lambda \ell^{+}\ell^{-}$ transition is more probable in full QCD comparing to the heavy quark effective theory. It is also shown that the results on all considered observables in SM4 deviate considerably from the SM predictions when $m_{t'}\geq 400 GeV$.