Direct CP violation in ${\Lambda }_b$ decays

Abstract

We study direct CP violating asymmetries (CPAs) in the two-body ${\Lambda }_b$ decays of ${\Lambda }_b\to pM(V)$ with $M(V)=K^{-}(K^{\ast -})$ 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 ${\mathcal{R}}_{\pi K}\equiv \mathcal{B}({\Lambda }_b\to p{\pi }^{-})/\mathcal{B}({\Lambda }_b\to p{K}^{-})$ 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 $(-5_{-5}^{+26},-31_{-1}^{+43})\%$ and $(-10\pm 8\pm 4,6\pm 7\pm 3)\%$ from the perturbative QCD calculation and the CDF experiment, respectively. For ${\Lambda }_b\to (p{K}^{\ast -},p{\rho }^{-})$, the decay branching ratios and CPVs in the SM are predicted to be $(2.5\pm 0.5,11.4\pm 2.1)\times 10^{-6}$ with ${\mathcal{R}}_{\rho K^{\ast }}=4.6\pm 0.5$ and $(19.6\pm 1.6,-3.7\pm 0.3)\%$, respectively. The uncertainties for the CPAs in these decay modes as well as ${\mathcal{R}}_{\pi K,\rho K^{\ast -}}$ 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 ${\Lambda }_b\to p{K}^{\ast -}$ is promising to be measured by the CDF and LHCb experiments, which is a clean test of the SM.

9 pages, 1 figure

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• Measurements of Direct CP Violating Asymmetries in Charmless Decays of Strange Bottom Mesons and Bottom Baryons
• Fourth Generation CP Violation Effect on B -> K pi, phi K and rho K in NLO PQCD
• Measurements of Direct CP-Violating Asymmetries in Charmless Decays of Bottom Baryons
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