Heavy Quark Limit Research Articles

QCD sum rules for positive and negative parity heavy baryons at next-to-leading order in αs -expansion

QCD sum rules for positive and negative parity heavy baryons in the heavy quark limit are formulated. We apply the method to Λ and Σ channels. We include the next-to-leading order corrections in αs-expansion to dimension 0 and 3 terms in the operator product expansion. The corrections lead to the considerable reduction of the predicted masses and significantly improves the stability with respect to the Borel parameter, especially for negative parity states. It is also found that, in the heavy quark limit, chiral odd condensates do not contribute to the negative parity states. Published by the American Physical Society 2024

Heavy-Quark Momentum Broadening in a Non-Abelian Plasma away from Thermal Equilibrium.

We perform classical-statistical real-time lattice simulations to compute real-time spectral functions and momentum broadening of quarks in the presence of strongly populated non-Abelian gauge fields. Based on a novel methodology to extract the momentum broadening for relativistic quarks, we find that the momentum distribution of quarks exhibit interesting nonperturbative features as a function of time due to correlated momentum kicks it receives from the medium, eventually going over to a diffusive regime. We extract the momentum diffusion coefficient for a mass range describing charm and bottom quarks and find sizable discrepancies from the heavy-quark limit.

Analysis of Tcc and Tbb based on the hadronic molecular model and their spin multiplets

Tcc(ccu¯d¯)+ has been reported by the LHCb experiment in 2022. The analysis using the Breit-Wigner parametrization found the small binding energy, 0.273 MeV, which is measured from the threshold of D*+D0. In this paper, we consider Tcc as a DD* hadronic molecule as a deuteronlike state. The one-boson exchange model is employed as for the heavy meson interactions, where we determine the cutoff parameter Λ to reproduce the reported binding energy of Tcc with I(JP)=0(1+). We discuss the properties of the bound state and also search for Tcc with quantum numbers other than 0(1+). Furthermore, we analyze Tbb as a bottom counterpart of Tcc, which involves two bottom quarks, and obtain several bound states. Finally, we consider the light-cloud basis for wave functions of the doubly heavy tetraquarks in the heavy quark limit. Using the basis, we find the spin multiplets of their bound states, indicating the spin structures of diquarks in Tcc and Tbb with the finite quark masses. Published by the American Physical Society 2024

Heavy quark fragmentation function in two-dimensional QCD in Nc→∞\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$N_c\\rightarrow \\infty $$\\end{document} limit

We carry out a comprehensive study of the quark-to-meson fragmentation function in the ’t Hooft model, i.e., the two-dimensional quantum chromodynamics (QCD) in Nc→∞\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$N_c\\rightarrow \\infty $$\\end{document} limit, following the operator definition pioneered by Collins and Soper. We apply the Hamiltonian approach as well as the diagrammatic approach to construct the functional form of the quark-to-meson fragmentation function in terms of the meson’s light-cone wave function. For the sake of comparison, we also investigate the heavy quark fragmentation into quarkonium in two-dimensional QCD within the framework of the nonrelativistic QCD (NRQCD) factorization, at the lowest order in quark velocity. In the heavy quark limit, the quark fragmentation function obtained from the ab initio method agrees well, both analytically and numerically, with that obtained from the NRQCD approach. This agreement might be regarded as a nontrivial justification for the validity of both field-theoretical approaches to compute the heavy quark fragmentation function.

Masses and magnetic moments of exotic fully heavy pentaquarks

Inspired by the observation of a resonant state X(6600) of fully charm tetraquark by the CMS experiment of LHCb Collaboration in double J/psi decay channel, we perform a systematical study of all configurations of fully heavy pentaquarks P_{Q_{1}Q_{2}Q_{3}Q_{{4}}bar{Q_{5}}} (Q_{i}=c,b, i=1,2,3,4,5) in their ground states in unified framework of MIT bag model. The color-spin wavefunctions of pentaquarks, classified via Young tableau and presented in terms of the Young–Yamanouchi bases, are used to compute masses and magnetic moments of fully heavy pentaquarks via numerical variational method, predicting a set of masses ranging from 8.229 GeV for the P_{ccccbar{c}} to 24.770 GeV for the P_{bbbbbar{b}}. Combining with computed masses of fully heavy mesons and baryons, we find that masses of fully heavy hadrons(mesons, baryons, tetraquarks and pentaquarks) with identical flavor rise almost linearly with the number of valence quarks in hadrons, being consistent with the heavy quark symmetry in the heavy-quark limit.

One-loop analysis of the interactions between doubly charmed baryons and Nambu-Goldstone bosons

The interactions between the spin-1/2 doubly charmed baryons and Nambu-Goldstone bosons are analyzed within a manifestly relativistic baryon chiral perturbation theory up to next-to-next-to leading order, by using the so-called extended-on-mass-shell scheme. We utilize heavy diquark-antiquark symmetry to estimate the low-energy constants in the chiral effective Lagrangians. The S- and P-wave scattering lengths are predicted. We find that those diagrams, vanishing exactly in the heavy-quark limit, do contribute slightly to the S-wave scattering lengths in reality. The influence of the spin-3/2 doubly charmed baryons, as heavy-quark spin partners of the spin-1/2 ones, on the scattering lengths is discussed as well. Finally, S-wave phase shifts for elastic scattering processes are presented in the energy region near threshold. Our results in this work will not only be very useful for performing chiral extrapolations of future lattice QCD data, but also provide us chiral inputs for the investigation of the spectroscopy of doubly heavy baryons.

Study of singly heavy baryon lifetimes

We study the inclusive decay widths of singly heavy baryons with the improved bag model in which the unwanted center-of-mass motion is removed. Additional insight is gained by comparing the charmed and bottom baryons. We discuss the running of the baryon matrix elements and compare the results with the non-relativistic quark model (NRQM). While the calculated two-quark operator elements are compatible with the literature, those of the four-quark ones deviate largely. In particular, the heavy quark limit holds reasonably well in the bag model for four-quark operator matrix elements but is badly broken in the NRQM. We predict 1 − τ (Ωb)/τ( {Lambda}_b^0 ) = (8.34 ± 2.22)% in accordance with the current experimental value of left({11.5}_{-11.6}^{+12.2}right)% and compatible with (13.2 ± 4.7)% obtained in the NRQM. We find an excellent agreement between theory and experiment for the lifetimes of bottom baryons. We confirm that {Omega}_c^0 could live longer than {Lambda}_c^{+} after the dimension-7 four-quark operators are taken into account. We recommend to measure some semileptonic inclusive branching fractions in the forthcoming experiments to discern different approaches. For example, we obtain mathcal{BF}left({Xi}_c^{+}to X{e}^{+}{nu}_eright) = (8.57±0.49)% and mathcal{BF}left({Omega}_c^0to X{e}^{+}{nu}_eright) = (1.88 ± 1.69)% in sharp contrast to mathcal{BF}left({Xi}_c^{+}to X{e}^{+}{nu}_eright) = left({12.74}_{-2.45}^{+2.54}right)% and mathcal{BF}left({Omega}_c^0to X{e}^{+}{nu}_eright) = left({7.59}_{-2.24}^{+2.49}right)% found in the NRQM.

Strong decays of {P}_{psi}^N{(4312)}^{+} to J/ψ(ηc)p and {overline{D}}^{left(ast right)}{Lambda}_c within the Bethe-Salpeter framework

Based on the effective Lagrangian in the heavy quark limit, we calculate the one-boson-exchange interaction kernel of {P}_{psi}^N{(4312)}^{+} as the overline{D}{Sigma}_c molecular state in isospin- frac{1}{2} . We present the Bethe-Salpeter equation and wave function for the constituent particles to be a (pseudo)scalar meson and a frac{1}{2} baryon. By solving the Bethe-Salpeter equation, we obtain {P}_{psi}^N{(4312)}^{+} as the overline{D}{Sigma}_c molecular state with JP = {left(frac{1}{2}right)}^{-} . Combining the effective Lagrangian and the obtained BS wave function, the partial decay widths of {P}_{psi}^N{(4312)}^{+} to J/ψp, ηcp, {overline{D}}^{ast 0}{Lambda}_c^{+} and {overline{D}}^0{Lambda}_c^{+} are calculated to be 0.17, 0.085, 8.8, and 0.026 MeV, respectively, which are roughly consistent with the LHCb experimental measurements and some other theoretical researches. The obtain results indicate the fraction of {overline{D}}^{ast 0}{Lambda}_c^{+} channel amounts to ~ 90% of {P}_{psi}^N{(4312)}^{+} , and is a highly promising channel to be discovered in the near future experiments. Our results favor the interpretation of {P}_{psi}^N{(4312)}^{+} as the overline{D}{Sigma}_c molecular state with JP = {left(frac{1}{2}right)}^{-} and isospin I = frac{1}{2} .

Formula omitted] mixing from lattice QCD

In heavy quark limit, the lowest-lying charmed baryons with two light quarks can form an SU(3) triplet and sextet. The Ξc in the SU(3) triplet and Ξc′ in the sextet have the same JPC quantum number and can mix due to the finite charm quark mass and the fact the strange quark is heavier than the up/down quark. We explore the Ξc–Ξc′ mixing by calculating the two-point correlation functions of the Ξc and Ξc′ baryons from lattice QCD. Based on the lattice data, we adopt two independent methods to determine the mixing angle between Ξc and Ξc′. After making the chiral and continuum extrapolation, it is found that the mixing angle θ is 1.2∘±0.1∘, which seems insufficient to account for the large SU(3) symmetry breaking effects found in weak decays of charmed baryons.

QQqqq¯ quark system, compact pentaquark, and gauge/string duality

For the case of two light flavors we propose the stringy description of the system consisting of two heavy and three light quarks, with the aim of exploring the quark organization inside the system and its low-lying Born-Oppenheimer potentials as a function of the heavy quark separation. Our analysis reveals several critical separations related to the processes of string reconnection, breaking and junction annihilation. We find that a compact pentaquark configuration makes the dominant contribution to the potential of the first excited state at small separations, and for separations larger than $0.1\,\text{fm}$, the antiquark-diquark-diquark structure emerges. Moreover, it turns out that the length scale of string junction annihilation is the same as that for the $QQ\bar q\bar q$ system. We also discuss the relation to the potential of the $QQq$ system and some relations among the masses of hadrons in the heavy quark limit.

New sum rules for the Bc→ J/ψ form factors

We derive new sum rules for the form factors of the {B}_cto J/psi ell {overline{nu}}_{ell } semileptonic transitions, employing the vacuum-to-Bc correlation function of the J/ψ-interpolating and b → c weak currents. In the heavy quark limit and at a space-like momentum transfer to the weak current, a local operator-product expansion is valid for this correlation function. As a result, in the leading power, the non-perturbative input is reduced to the decay constant of Bc meson. Furthermore, applying hadronic dispersion relation in the J/ψ channel, we find that a non-vanishing OPE spectral density in the duality interval of J/ψ emerges only at mathcal{O} (αs). We calculate this density in the relevant kinematic regime. The Bc → J/ψ form factors at space-like momentum transfer are then calculated from the new sum rules.

Is the Λc(2625)+ the heavy quark spin symmetry partner of the Λc(2595)+ ?

We use a $\mathcal{O}(\Lambda_\text{QCD}/m_c)$ heavy quark effective theory scheme, where only $\mathcal{O}(\Lambda_\text{QCD}/m_b)$ and perturbative QCD short distance corrections are neglected, to study the matrix elements of the scalar, pseudoscalar, vector, axial-vector and tensor currents between the $\Lambda_b$ ground state and the odd parity charm $\Lambda_c(2595)^+$ and $\Lambda_c(2625)^+$ resonances. We show that in the near-zero recoil regime, the scheme describes reasonably well, taking into account uncertainties, the results for the 24 form-factors obtained in lattice QCD (LQCD) just in terms of only 4 Isgur-Wise (IW) functions. We also find some support for the possibility that the $\Lambda_c(2595)^+$ and $\Lambda_c(2625)^+$ resonances might form a heavy-quark spin symmetry (HQSS) doublet. However, we argue that the available LQCD description of these two resonances is not accurate enough to disentangle the possible effects of the $\Sigma_c \pi$ and $\Sigma_c^*\pi$ thresholds, located only a few MeV above their position, and that it cannot be ruled out that these states are not HQSS partners. Finally, we study the ratio $\frac{d\Gamma[\Lambda_b\to \Lambda_{c,1/2^-}^* \ell \bar\nu_\ell]/dq^2}{d\Gamma[\Lambda_b\to \Lambda_{c,3/2^-}^*\ell \bar\nu_\ell]/dq^2}$ of the Standard Model differential semileptonic decay widths, with $q^\mu$ the momentum transferred between the initial and final hadrons. We provide a natural explanation for the existence of large deviations, near the zero recoil, of this ratio from 1/2 (value predicted in the infinite heavy quark mass limit, assuming that the $\Lambda_{c,1/2^-}^*$ and $\Lambda_{c,3/2^-}^*$ are the two members of a HQSS doublet) based on S-wave contributions to the $\Lambda_b\to \Lambda_{c,1/2^-}^*$ decay amplitude driven by a sub-leading IW function.

Static properties and semileptonic transitions of lowest-lying double heavy baryons* *Supported by Kosar University of Bojnord (Grant No. 0011191444)

The static properties and semileptonic decays of ground-state doubly heavy baryons are studied in the framework of a non-relativistic quark model. Using a phenomenological potential model, we calculate the ground-state masses and magnetic moments of doubly heavy Ω and Ξ baryons. In the heavy quark limit, we introduce a simple form of the universal Isgur-Wise function used as the transition form factor and then investigate the exclusive semileptonic decay widths and branching fractions for baryon transitions. Our obtained results are in agreement with other theoretical predictions.

Axial-Vector D_{1} Hadrons in D^{*}π Scattering from QCD.

We present I=1/2 D^{*}π scattering amplitudes from lattice QCD and determine two low-lying J^{P}=1^{+} axial-vector D_{1} states and a J^{P}=2^{+} tensor D_{2}^{*}. Computing finite-volume spectra at a light-quark mass corresponding to m_{π}≈391 MeV, for the first time, we are able to constrain coupled J^{P}=1^{+} D^{*}π amplitudes with ^{2S+1}ℓ_{J}=^{3}S_{1} and ^{3}D_{1} as well as coupled J^{P}=2^{+} Dπ(^{1}D_{2}} and D^{*}π(^{3}D_{2}} amplitudes via Lüscher's quantization condition. Analyzing the scattering amplitudes for poles we find a near-threshold bound state, producing a broad feature in D^{*}π{^{3}S_{1}}. A narrow bump occurs in D^{*}π{^{3}D_{1}} due to a D_{1} resonance. A single resonance is found in J^{P}=2^{+} coupled to Dπ and D^{*}π. A relatively low mass and large coupling are found for the lightest D_{1}, suggestive of a state that will evolve into a broad resonance as the light-quark mass is reduced. An earlier calculation of the scalar D_{0}^{*} using the same light-quark mass enables comparisons to the heavy-quark limit.

Heavy + heavy and heavy + light pseudoscalar to vector semileptonic transitions

Using a symmetry-preserving regularisation of a vector times vector contact interaction (SCI), we complete a systematic treatment of twelve semileptonic transitions with vector meson final states: Drightarrow rho , D_{(s)}rightarrow K^*, D_srightarrow phi , Brightarrow rho , B_srightarrow K^*, B_{(s)}rightarrow D_{(s)}^*, B_c rightarrow B_{(s)}^*, J/psi , D^*; and thereby finalise a unified analysis of semileptonic decays of heavy + heavy and heavy + light pseudoscalar mesons to both pseudoscalar and vector meson final states. The analysis is marked by algebraic simplicity, few parameters, and the ability to consistently describe systems from Nambu-Goldstone modes to heavy + heavy mesons. Regarding the behaviour of the transition form factors, the SCI results compare well wherever sound experimental or independent theory analyses are available; hence, the SCI branching fraction predictions should be a reasonable guide. Considering the ratios R(D_{(s)}^{(*)}), R(J/psi ), R(eta _c), whose values are key tests of lepton universality in weak interactions, the SCI values agree with Standard Model predictions. The B_{(s)}rightarrow D_{(s)}^* transitions are used to predict the precursor functions that evolve into the universal Isgur–Wise function in the heavy-quark limit, with results that conform with those from other sources where such are available. The study also exposes effects on the transition form factors that flow from interference between emergent hadron mass from the strong interaction and Higgs boson couplings via current-quark masses, including flavour symmetry violation.

Spin relaxation rate for heavy quarks in weakly coupled QCD plasma

We compute the relaxation rate of the spin density of heavy quarks in a perturbative QCD plasma to leading-log order in the coupling constant g. The spin relaxation rate Γs in spin hydrodynamics is shown to be Γs ~ g4 log(1/g)T(T/M)2 in the heavy-quark limit T/M ≪ 1, which is smaller than the relaxation rate of other non- hydrodynamic modes by additional powers of T/M. We demonstrate three different methods to evaluate the spin relaxation rate: 1) the Green-Kubo formula in the spin hydrodynamic regime, 2) the spin density correlation function in the strict hydrodynamic limit, and 3) quantum kinetic theory of the spin distribution function in momentum space. We highlight the interesting differences between these methods, while they are ultimately connected to each other by the underlying Ward-Takahashi identity for the non-conserved spin density.

2D energy-momentum tensor distributions of nucleon in a large- Nc quark model from ultrarelativistic to nonrelativistic limit

Form factors of the energy-momentum tensor (EMT) can be interpreted in certain frames in terms of spatial distributions of energy, stress, linear and angular momentum, based on 2D or 3D Fourier transforms. This interpretation is in general subject to ``relativistic recoil corrections,'' except when the nucleon moves at the speed of light like e.g. in the infinite-momentum frame. We show that it is possible to formulate a large-${N}_{c}$ limit in which the probabilistic interpretation of the nucleon EMT distributions holds also in other frames. We use the bag model formulated in the large-${N}_{c}$ limit as an internally consistent quark model framework to visualize the information content associated with the 2D EMT distributions. In order to provide more intuition, we present results in the physical situation and in three different limits: by considering a heavy-quark limit, a large system-size limit and a constituent-quark limit. The visualizations of the distributions in these extreme limits will help to interpret the results from experiments, lattice QCD, and other models or effective theories.

Next-to-leading order QCD calculation of Bc to charmonium tensor form factors

We present a next-to-leading order (NLO) QCD corrections to $B_c\to \eta_c$ and $B_c\to J/\psi$ tensor form factors within nonrelativistic QCD (NRQCD) framework. The full analytical results for $B_c$ to S-wave charmonium tensor form factors are obtained. We also studied the asymptotic behaviours of tensor form factors in hierarchy heavy quark limit, i.e. $m_b\to\infty,~ m_c\to\infty, ~\mathrm{and }~m_c/m_b\to0$. A compact expression for tensor form factors are given analytically in the hierarchy heavy quark limit. The relation among different form factors is also analyzed especially at large momentum recoil point. The numerical results for the $B_c$ to charmonium tensor form factors in all the physical region are given in the end.

Heavy-flavor-conserving hadronic weak decays of charmed and bottom baryons

Three decades ago, heavy-flavor-conserving (HFC) weak decays of heavy baryons such as ${\mathrm{\ensuremath{\Xi}}}_{Q}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{Q}\ensuremath{\pi}$ and ${\mathrm{\ensuremath{\Omega}}}_{Q}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}_{Q}\ensuremath{\pi}$ for $Q=c$, $b$ had been studied within the framework that incorporates both heavy quark and chiral symmetries. It was pointed out that if the heavy quark in the HFC process behaves as a spectator, then the $P$-wave amplitude of ${\mathcal{B}}_{\overline{3}}\ensuremath{\rightarrow}{\mathcal{B}}_{\overline{3}}+\ensuremath{\pi}$, with ${\mathcal{B}}_{\overline{3}}$ being an antitriplet heavy baryon, will vanish in the heavy quark limit. Indeed, this is the case for ${\mathrm{\ensuremath{\Xi}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\pi}$ decays. For ${\mathrm{\ensuremath{\Xi}}}_{c}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}\ensuremath{\pi}$ decays, they receive additional nonspectator contributions arising from the $W$-exchange diagrams through the $cs\ensuremath{\rightarrow}dc$ transition. Spectator and nonspectator $W$-exchange contributions to the $S$-wave amplitude of ${\mathrm{\ensuremath{\Xi}}}_{c}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}\ensuremath{\pi}$ are destructive, rendering the $S$-wave contribution even smaller. However, the nonspectator effect on the $P$-wave amplitude was overlooked in all the previous model calculations until a very recent investigation within the framework of a constituent quark model in which the parity-conserving pole terms were found to be dominant in ${\mathrm{\ensuremath{\Xi}}}_{c}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}\ensuremath{\pi}$ decays. Since the pion produced in the HFC process is soft, we apply current algebra to study both $S$- and $P$-wave amplitudes and employ the bag and diquark models to estimate the matrix elements of four-quark operators. We confirm that ${\mathrm{\ensuremath{\Xi}}}_{c}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}\ensuremath{\pi}$ decays are indeed dominated by the parity-conserving transition induced from nonspectator $W$-exchange and that they receive largest contributions from the intermediate ${\mathrm{\ensuremath{\Sigma}}}_{c}$ pole terms. We also show that the $S$-wave of ${\mathrm{\ensuremath{\Omega}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}_{b}\ensuremath{\pi}$ decays vanishes in the heavy quark limit, while ${\mathrm{\ensuremath{\Omega}}}_{c}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}_{c}\ensuremath{\pi}$ receive additional $W$-exchange contributions via $cs\ensuremath{\rightarrow}dc$ transition. The $P$-wave contribution to ${\mathrm{\ensuremath{\Omega}}}_{c}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}_{c}\ensuremath{\pi}$ is enhanced by the ${{\mathrm{\ensuremath{\Xi}}}^{\ensuremath{'}}}_{c}$ pole, though it is not so dramatic as in the case of ${\mathrm{\ensuremath{\Xi}}}_{c}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}\ensuremath{\pi}$. The asymmetry parameter $\ensuremath{\alpha}$ is found to be positive, of order 0.70 and 0.74 for ${\mathrm{\ensuremath{\Xi}}}_{c}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\mathrm{\ensuremath{\Xi}}}_{c}^{+}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{\ensuremath{\pi}}^{0}$, respectively. The predicted branching fraction is of order $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ for ${\mathrm{\ensuremath{\Omega}}}_{c}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}_{c}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ for ${\mathrm{\ensuremath{\Omega}}}_{c}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}_{c}^{0}{\ensuremath{\pi}}^{0}$ both with the asymmetry parameter close to $\ensuremath{-}1$.

Nonleptonic two-body decays of Λb→Λcπ , ΛcK in the perturbative QCD approach

We study the color-allowed $\Lambda_b\rightarrow \Lambda_c \pi, \Lambda_cK$ decays in the perturbative QCD approach (PQCD) to lowest order in strong coupling constant $\alpha_s$. Both the factorizable and nonfactorizable contributions are taken into account in our calculations. It is found that these processes are dominated by the factorizable contributions, while the important nonfactorizable contributions can enhance the branching ratios by about 30$\%$. The decay branching ratios are predicted to be $\mathcal{B}(\Lambda_b\rightarrow \Lambda_c \pi)=6.7^{+4.1}_{-3.8}\times 10^{-3}$ and $\mathcal{B}(\Lambda_b\rightarrow \Lambda_c K)=5.0^{+4.0}_{-3.0}\times 10^{-4}$, where the uncertainties arise from the baryon light-cone distribution amplitudes (LCDAs), the heavy charm quark and charmed baryon masses, and the hard scales. It is shown that the asymmetry parameters in the two decays are approximately equal to -1, which is expected as in the heavy quark limit and the soft meson limit. Our predictions are consistent with the recent experimental data within errors. The obtained numerical results are also compared to those in the other theoretical approaches when they are available.