[en] We study the $K_S^0-<!--\; ???\; -->K_L^0$ asymmetries and $CP$ violations in charm-baryon decays with neutral kaons in the final state. The $K_S^0-<!--\; ???\; -->K_L^0$ asymmetry can be used to search for two-body doubly Cabibbo-suppressed amplitudes of charm-baryon decays, with the one in ${\mathrm{\Lambda <!--\; ??\; -->}}_c^{+}\to <!--\; ???\; -->p{K}_{S,L}^0$ as a promising observable. Besides, it is studied for a new $CP$-violation effect in these processes, induced by the interference between the Cabibbo-favored and doubly Cabibbo-suppressed amplitudes with the neutral kaon mixing. Once the new CP-violation effect is determined by experiments, the direct $CP$ asymmetry in neutral kaon modes can then be extracted and used to search for new physics. The numerical results based on $SU(3)$ symmetry will be tested by the experiments in the future.

[en] The SU(3) quark model encounters a great challenge in describing even-parity mesons. Specifically, the q anti q quark model has difficulties in understanding the light scalar mesons below 1 GeV, scalar and axial-vector charmed mesons and 1⁺ charmonium-like state X(3872). A common wisdom for the resolution of these difficulties lies on the coupled channel effects which will distort the quark model calculations. In this work, we focus on the near mass degeneracy of scalar charmed mesons, D_s0^* and D₀^*0, and its implications. Within the framework of heavy meson chiral perturbation theory, we show that near degeneracy can be qualitatively understood as a consequence of self-energy effects due to strong coupled channels. Quantitatively, the closeness of D_s0^* and D₀^*0 masses can be implemented by adjusting two relevant strong couplings and the renormalization scale appearing in the loop diagram. Then this in turn implies the mass similarity of B_s0^* and B₀^*0 mesons. The P₀^*P₁^' interaction with the Goldstone boson is crucial for understanding the phenomenon of near degeneracy. Based on heavy quark symmetry in conjunction with corrections from QCD and 1/m_Q effects, we obtain the masses of B^*_(s)0 and B^'_(s)1 mesons, for example, M_Bs0^* = (5715 ± 1) MeV + δΔ_S, M_B^'s1 = (5763 ± 1) MeV + δΔ_S with δΔ_S being 1/m_Q corrections. We find that the predicted mass difference of 48 MeV between B^'_s1 and B_s0^* is larger than that of 20-30 MeV inferred from the relativistic quark models, whereas the difference of 15 MeV between the central values of M_B^'s1 and M_B^'1 is much smaller than the quark model expectation of 60-100 MeV. Experimentally, it is important to have a precise mass measurement of D₀^* mesons, especially the neutral one, to see if the non-strange scalar charmed meson is heavier than the strange partner as suggested by the recent LHCb measurement of the D₀^*±. (orig.)

[en] Very recently, the LHCb collaboration has observed in the final state Λ_c⁺K^-π⁺π⁺ a resonant structure that is identified as the doubly charmed baryon Ξ_cc⁺⁺. Inspired by this observation, we investigate the weak decays of doubly heavy baryons Ξ_cc⁺⁺, Ξ_cc⁺, Ω_cc⁺, Ξ_bc^(')+, Ξ_bc^(')0, Ω_bc^(')0, Ξ_bb⁰, Ξ_bb^- and Ω_bb^- and focus on the decays into spin 1/2 baryons in this paper. At the quark level these decay processes are induced by the c → d/s or b → u/c transitions, and the two spectator quarks can be viewed as a scalar or axial vector diquark. We first derive the hadronic form factors for these transitions in the light-front approach and then apply them to predict the partial widths for the semileptonic and nonleptonic decays of doubly heavy baryons. We find that the number of decay channels is sizable and can be examined in future measurements at experimental facilities like LHC, Belle II and CEPC. (orig.)

[en] We study the ratio of fragmentation fractions, f_Ξb/f_Λb, from the measurement of Ξ_b⁰ → Ξ_c⁺π^- and Λ_b⁰ → Λ_c⁺π^- with Ξ_c⁺/Λ_c⁺ → pK^-π⁺. With the branching fraction B(Ξ_c⁺ → pK^-π⁺) = (2.2±0.8)% obtained under the U-spin symmetry, the fragmentation ratio is determined as f_Ξb/f_Λb = 0.054±0.020. To reduce the above uncertainties, we suggest to measure the branching fractions of Ξ_c⁺ → p anti K^*0 and Λ_c⁺ → Σ⁺K^*0 at BESIII, Belle II and LHCb. (orig.)

[en] The exotic states X${}_{0,1}$(2900) with the quark flavor of $cs\stackrel{¯<!--\; ??\; -->}{u}\stackrel{¯<!--\; ??\; -->}{d}$ are recently observed in the mass spectrum of D${}^{+}$K${}^{-<!--\; ???\; -->}$ in B${}^{-<!--\; ???\; -->}$ → D${}^{-<!--\; ???\; -->}$D${}^{+}$K${}^{-<!--\; ???\; -->}$ by the LHCb collaboration. To explore the nature of X${}_{0,1}$(2900), except for analyzing their masses and decay widths as usually did in literatures, the study of their production mechanism in B-meson weak decays would provide another important information. The amplitude of B${}^{-<!--\; ???\; -->}$ → D${}^{-<!--\; ???\; -->}$X${}_{0,1}$ is non-factorizable. We consider the final-state-interaction effects and calculate them via the rescattering mechanism. The measured branching fractions of B${}^{-<!--\; ???\; -->}$ → D${}^{-<!--\; ???\; -->}$X${}_{0,1}$ are revealed. It is manifested by B${}^{-<!--\; ???\; -->}$ → Λ${}_c^{-<!--\; ???\; -->}$Ξ${}_c^{(\mathrm{\prime <!--\; ???\; -->})0}$ and Λ${}_b^0$ → P${}_c^{+}$K${}^{-<!--\; ???\; -->}$ that the rescattering mechanism can result in the relatively large branching fractions. The similar processes of B${}^{-<!--\; ???\; -->}$ → π${}^{-<!--\; ???\; -->}$X${}_{0,1}$ are also analyzed. The isospins of X${}_{0,1}$ can be investigated by B → DX${}_{0,1}^{\pm <!--\; ??\; -->,0}$ decays.

[en] We propose to search for the open heavy-flavor exotic states with the quark components of $Qs\stackrel{¯<!--\; ??\; -->}{u}\stackrel{¯<!--\; ??\; -->}{d}$ with Q=b,c via their weak decays. If there exist such exotic states below the BK or DK thresholds, they can only decay weakly. The advantages include: (i) the experimental backgrounds from the secondary decay vertex are much lower due to the long lifetimes, (ii) the productions are large enough for only one heavy quark in such states, (iii) the thresholds of BK or DK are about 260 MeV higher compared to the B${}_s$π or D${}_s$π thresholds of the configurations of $Qu\stackrel{¯<!--\; ??\; -->}{s}\stackrel{¯<!--\; ??\; -->}{d}$ or $Qd\stackrel{¯<!--\; ??\; -->}{s}\stackrel{¯<!--\; ??\; -->}{u}$, with a higher possibility to exist such weakly-decay particles, and (iv) if observed, their inner structures are easier understood since they can not be induced by the kinematic effects.

[en] The decay width of the D${}_s^{\ast <!--\; ???\; -->}$ meson is dominated by the electromagnetic mode D${}_s^{\ast <!--\; ???\; -->}$ → D${}_s$γ, and it is thus the longest-lived charged vector meson. In light of this point, we perform the first QCD LCSRs calculation of D${}_s^{\ast <!--\; ???\; -->}$ → ϕ helicity form factors and discuss the experiment potential of discovering exclusive D${}_s^{\ast <!--\; ???\; -->}$ weak decays. The main result is the partial decay widths, which read as Γ${}_{D_s^{\ast <!--\; ???\; -->}\to <!--\; ???\; -->l\mathrm{\nu <!--\; ??\; -->}}$ = 2.44 × 10${}^{-<!--\; ???\; -->12}$ GeV, Γ${}_{D_s^{\ast <!--\; ???\; -->}\to <!--\; ???\; -->\mathrm{\varphi <!--\; ??\; -->}l\mathrm{\nu <!--\; ??\; -->}}$ = (3.28^{+0.82}_{-0.71}) × 10${}^{-<!--\; ???\; -->14}$ GeV, Γ${}_{D_s^{\ast <!--\; ???\; -->}\to <!--\; ???\; -->\mathrm{\varphi <!--\; ??\; -->}\mathrm{\pi <!--\; ??\; -->}}$ = (3.81${}_{-<!--\; ???\; -->1.33}^{+1.52}$) × 10${}^{-<!--\; ???\; -->14}$ GeV and Γ${}_{D_s^{\ast <!--\; ???\; -->}\to <!--\; ???\; -->\mathrm{\varphi <!--\; ??\; -->}\mathrm{\rho <!--\; ??\; -->}}$ = (1.16${}_{-<!--\; ???\; -->0.39}^{+0.42}$) × 10${}^{-<!--\; ???\; -->13}$ GeV. We show that these channels are promising in the near future, serving as the first experimental observation of weak decays of a vector meson, and would open up a new playground for precision test of the standard model.

[en] We analyze the capacity of future Z-factories to search for heavy neutrinos with their mass from 10 to 85 GeV. The heavy neutrinos N are considered to be produced via the process e${}^{+}$e${}^{-<!--\; ???\; -->}$→Z→νN and to decay into an electron or muon and two jets. By means of Monte Carlo simulation of such signal events and the Standard Model background events, we obtain the upper bounds on the cross sections σ(e${}^{+}$e${}^{-<!--\; ???\; -->}$→νN→νℓjj) given by the Z-factories with integrated luminosities of 0.1, 1 and 10 ab${}^{-<!--\; ???\; -->1}$ if no signal events are observed. Under the assumption of a minimal extension of the Standard Model in the neutrino sector, we also present the corresponding constraints on the mixing parameters of the heavy neutrinos with the Standard Model leptons, and find they are improved by at least one order compared to current experimental constraints.

[en] The exotic state X(5568) which was observed by D0 Collaboration is very likely to be a tetraquark state with four different valence quark flavors, though the existence was not confirmed by other collaborations. The possibility of such state still generates lots of interests in theory. In the paper, we will study the properties of the state under the SU(3) flavor symmetry. The four quark states with a heavy bottom quark and three light quarks(anti-quark) can form $\stackrel{¯<!--\; ??\; -->}{3}$, 6 and $\stackrel{¯<!--\; ??\; -->}{15}$ representations. The weak decays can be dominant and should be discussed carefully while these states are stable against the strong and electromagnetic interactions. Therefor we will study the multi-body semileptonic and nonleptonic weak decays systematically. With the help of SU(3) flavor symmetry, we can give the Hamiltonian in the hadronic level, then obtain the parameterized irreducible amplitudes and the relations of different channels. At the end of the article, we collect some Cabibbo allowed two-body and three-body weak decay channels which can be used to reconstruct X${}_{b6}$ states at the branching fraction up to be 10${}^{-<!--\; ???\; -->\text{â<!-- ?? -->}\text{ˆ<!-- ?? -->}\text{’<!-- ??? -->}5}$.

[en] Discoveries of tetraquarks not only enrich the hadronic spectrum but also provide more platforms to understand quantum chromodynamics. We study the production processes of hidden-charm and open-charm tetraquarks in B decays by analyzing their topological amplitudes. Relations between different channels are found, which confront tests by experiments to probe the nature of the tetraquarks. Furthermore, promising channels to find more tetraquarks are proposed.