Direct CP violation in $\Lambda_b$ decays

TL;DR

This paper investigates direct CP violation in specific Lambda_b decays, providing theoretical predictions and comparing them with experimental data, highlighting potential tests of the Standard Model at collider experiments.

Contribution

The study offers detailed predictions of CP asymmetries in Lambda_b decays using the generalized factorization method, aligning with observed branching ratios and proposing measurable CP violations as tests of the Standard Model.

Findings

Predicted CP asymmetries in Lambda_b decays range from a few percent to over 30%.

Branching ratios for certain decay modes are estimated with specific uncertainties.

Large CP asymmetry in Lambda_b→p K*− decay is promising for experimental verification.

Abstract

We study direct CP violating asymmetries (CPAs) in the two-body $\Lambda_b$ decays of $\Lambda_b\to pM(V)$ with $M(V)=K^-(K^{*-})$ and $\pi^-(\rho^-)$ based on the generalized factorization method. After simultaneously explaining the observed decay branching ratios of $\Lambda_b\to (p K^-\,,\; p \pi^-)$ with ${\cal R}_{\pi K}\equiv {\cal B}(\Lambda_b\to p \pi^-)/{\cal B}(\Lambda_b\to p K^-)$ being $0.84\pm 0.09$, we find that their corresponding direct CPAs are $(5.8\pm 0.2,\,-3.9\pm 0.2)\%$ in the standard model (SM), in comparison with $(-5^{+26}_{-~5},\, -31^{+43}_{-~1})\%$ and $(-10\pm8\pm4,\, 6\pm7\pm3)\%$ from the perturbative QCD calculation and the CDF experiment, respectively. For $\Lambda_b\to ( p K^{*-},\, p\rho^-)$, the decay branching ratios and CPVs in the SM are predicted to be $(2.5\pm0.5,\,11.4\pm2.1)\times 10^{-6}$ with ${\cal R}_{\rho K^*}=4.6\pm0.5$ and $(19.6\pm1.6,\, -3.7\pm0.3)\%$, respectively. The uncertainties for the CPAs in these decay modes as well as ${\cal R}_{\pi K,\,\rho K^{*-}}$ mainly arise from the quark mixing elements and non-factorizable effects, whereas those from the hadronic matrix elements are either totally eliminated or small. We point out that the large CPA for $\Lambda_b\to p K^{*-}$ is promising to be measured by the CDF and LHCb experiments, which is a clean test of the SM.