Revisiting $\bar B^0 \rightarrow Λ_c^+ \bar p$ decay with higher twist corrections

Abstract: We investigate the single-charmed baryonic decays $\bar B⁰ \to Λ_c⁺ \bar p$ and $\bar B⁰ \to \barΛ_c^- p$, which receive contributions from both $W$-emission and $W$-exchange topologies, within the framework of perturbative QCD (PQCD). Higher-power corrections associated with the hadronic light-cone distribution amplitudes (LCDAs) of both the initial- and final-state hadrons are systematically taken into account. We find that these higher-twist contributions play an important role in baryonic $B$ decays and cannot be neglected. A sizable destructive interference between the $W$-emission and $W$-exchange amplitudes is observed, which significantly reduces the predicted branching fraction of $\bar B⁰ \to Λ_c⁺ \bar p$ and leads to improved agreement with experimental measurements. The doubly Cabibbo-suppressed decay $\bar B⁰ \to \barΛ_c^- p$ is studied for the first time. Its branching fraction is predicted to be of order $10<sup>{-8}$, placing it within the reach of future high-luminosity experiments. We further present the first theoretical predictions for the decay asymmetry parameters of both channels, which provide additional observables for testing the underlying decay dynamics and can be confronted with future experimental data.

• The paper demonstrates that including higher twist LCDAs in the PQCD framework yields branching fractions in line with experiment and exposes significant destructive interference between W-emission and W-exchange amplitudes.
• The analysis incorporates Λ_c baryon LCDAs up to twist-4 and proton LCDAs up to twist-6, with higher twist contributions enhancing decay amplitudes by up to 30% due to endpoint effects.
• The study predicts large angular asymmetries and provides the first PQCD estimates for the suppressed B0 → 𝚃Λ_c⁻ p decay, highlighting new opportunities for experimental validation.

Revisiting $\bar B^0 \rightarrow Λ_c^+ \bar p$ Decay with Higher Twist Corrections

Motivation and Theoretical Framework

The study addresses the longstanding problem of accurately describing two-body charmful baryonic $B$ decays within QCD. These decays exhibit complex dynamics, with significant suppression compared to multibody channels. The particular focus is on $\bar B^0\to \Lambda_c^+ \bar p$ and its doubly Cabibbo-suppressed counterpart $\bar B^0\to \bar\Lambda_c^- p$, both receiving contributions from $W$-emission and $W$-exchange topologies.

The calculation is performed in the perturbative QCD (PQCD) framework, systematically incorporating higher-power contributions stemming from hadron light-cone distribution amplitudes (LCDAs). The formalism includes: leading and subleading $B$-meson LCDAs, $\Lambda_c$ baryon LCDAs up to twist-4, and proton LCDAs up to twist-6, with three phenomenological models for the $\Lambda_c$ LCDAs to probe nonperturbative uncertainties. The PQCD formalism exploits factorization, Sudakov resummation, and transverse-momentum dependence to maintain theoretical control over endpoint singularities and power corrections.

Branching Fractions and Topological Interference

Strong numerical results are obtained for the branching fraction:

$$\mathcal{B}(\bar {B}^0\rightarrow\Lambda_c^+\bar p) \approx (1.64 - 2.08) \times 10^{-5}$$

across Exponential, QCD sum rule, and Gegenbauer models for $B$0 LCDAs. These results agree with the latest world average $B$1 [ParticleDataGroup:2026aaa].

A central claim is the identification of destructive interference between $B$2-emission and $B$3-exchange amplitudes. The $B$4-exchange topology, previously neglected or assumed helicity-suppressed, contributes with roughly half the magnitude of the $B$5-emission amplitude and an opposite phase. This interference significantly reduces the predicted branching fraction. The analysis establishes that conventional assumptions about color or helicity suppression for baryonic $B$6 modes are not valid for charmful final states, where the presence of the heavy charm quark alleviates helicity suppression [Hsiao:2019wyd].

Higher Twist Effects and LCDA Hierarchy

The systematic inclusion of higher-twist LCDAs is shown to be crucial. Subleading $B$7 in the $B$8 meson and higher-twist components of both $B$9 and proton LCDAs contribute comparably to leading terms, often interfering constructively and enhancing the amplitude magnitude by up to 30%. Twist-3 $\bar B^0\to \Lambda_c^+ \bar p$0 LCDAs dominate over twist-2, in contrast to expectations from naive power counting, due to endpoint enhancement effects. Proton twist-6 contributions are suppressed as expected, confirming the convergence of the baryonic twist expansion.

Numerical uncertainties are dominated by nonperturbative shape parameters in the $\bar B^0\to \Lambda_c^+ \bar p$1 meson and proton LCDAs, with up to 50% variation.

Angular Asymmetries and New Observables

For $\bar B^0\to \Lambda_c^+ \bar p$2, the predicted up-down asymmetry parameter is large and positive, $\bar B^0\to \Lambda_c^+ \bar p$3 for Exponential and QCDSR models, with suppressed polarization parameters $\bar B^0\to \Lambda_c^+ \bar p$4 and $\bar B^0\to \Lambda_c^+ \bar p$5. This pattern arises from cancellation between partial wave amplitudes and is robust across LCDA models. These angular observables represent new targets for future experimental measurements, providing probes of baryon structure and decay dynamics.

Prediction for $\bar B^0\to \Lambda_c^+ \bar p$6

The first PQCD analysis of $\bar B^0\to \Lambda_c^+ \bar p$7 yields

$\bar B^0\to \Lambda_c^+ \bar p$8

placing this channel within reach of high-luminosity experiments. The amplitude ratio relative to the favored mode is only a few percent, indicating limited sensitivity to CKM phase $\bar B^0\to \Lambda_c^+ \bar p$9. Angular observables are nontrivial, with $\bar B^0\to \bar\Lambda_c^- p$0 positive ($\bar B^0\to \bar\Lambda_c^- p$1--$\bar B^0\to \bar\Lambda_c^- p$2) and $\bar B^0\to \bar\Lambda_c^- p$3 negative.

Practical and Theoretical Implications

The work establishes that a coherent PQCD treatment, including both $\bar B^0\to \bar\Lambda_c^- p$4-emission and $\bar B^0\to \bar\Lambda_c^- p$5-exchange topologies and higher-twist effects, is required for quantitative agreement with experiment. The destructive interference and absence of strong helicity suppression in charmful baryonic modes is a significant theoretical refinement. The convergence of the twist expansion, with dominant twist-3 contributions, supports continued efforts toward improved nonperturbative inputs.

On the practical side, the prediction for $\bar B^0\to \bar\Lambda_c^- p$6 offers prospects for new measurements, and angular asymmetries serve as clean tests of hadronic structure in heavy flavor decays. As both modes lack penguin contributions, Standard Model $\bar B^0\to \bar\Lambda_c^- p$7 violation is absent; any observed direct $\bar B^0\to \bar\Lambda_c^- p$8 asymmetry would be clear evidence of new physics.

Future Directions

Improved nonperturbative determinations of baryonic LCDAs (especially proton higher-twist components) are necessary for precision phenomenology. PQCD next-to-leading-order calculations would further reduce theoretical uncertainties. Time-dependent studies of suppressed and favored channels could, in principle, give access to CKM phases if sufficient statistics are achieved. High-luminosity experiments (Belle II, LHCb) should be able to test the predicted branching fractions and asymmetry parameters.

Conclusion

The paper provides a rigorous PQCD-based description of $\bar B^0\to \bar\Lambda_c^- p$9, demonstrating the necessity of including both $W$0-emission and $W$1-exchange diagrams and systematically accounting for higher-twist corrections. The resulting predictions for branching fractions and angular observables match current data and extend the theoretical understanding of baryonic $W$2 decays. The first predictions for $W$3 and associated angular parameters open new avenues for experimental and theoretical exploration, with implications for the study of hadronic structure, CKM phenomenology, and potential new physics.

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For technical details and complete formulae, see "Revisiting $W$4 decay with higher twist corrections" (2607.02876).