Search

Abstract In this work, we calculate the transition form factors of $$\Lambda _b$$ Λ b decaying into proton and $$N^*(1535)$$ N ∗ ( 1535 ) ( $$J^P={1/2}^+$$ J P = 1 / 2 + and $${1/2}^-$$ 1 / 2 - respectively) within the framework of light-cone sum rules with the distribution amplitudes (DAs) of $$\Lambda _b$$ Λ b -baryon. In the hadronic representation of the correlation function, we have isolated both the proton and the $$N^*(1535)$$ N ∗ ( 1535 ) states so that the $$\Lambda _b \rightarrow p, N^*(1535)$$ Λ b → p , N ∗ ( 1535 ) form factors can be evaluated simultaneously. Due to the less known properties of the baryons, we investigate three interpolating currents of the light baryons and five parametrization models for DAs of $$\Lambda _b $$ Λ b . Numerically, our predictions on the $$\Lambda _b \rightarrow p$$ Λ b → p form factors and the branching fractions of $$\Lambda _b\rightarrow p\ell \nu $$ Λ b → p ℓ ν from the Ioffe or the tensor currents are consistent with the Lattice simulation and the results from the light-baryon sum rules, as well as the experimental data of $$Br(\Lambda _b^0\rightarrow p\mu ^-{{\bar{\nu }}})$$ B r ( Λ b 0 → p μ - ν ¯ ) . The predictions on the form factors of $$\Lambda _b \rightarrow N^*(1535)$$ Λ b → N ∗ ( 1535 ) are very sensitive to the choice of the interpolating currents so that the relevant measurement could be helpful to clarify the properties of baryons.

Abstract 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.

Abstract The decay width of the $$D_s^{*}$$ D s ∗ meson is dominated by the electromagnetic mode $$D_s^*\rightarrow D_s \gamma $$ D s ∗ → 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 $$D_s^{*}\rightarrow \phi $$ D s ∗ → ϕ helicity form factors and discuss the experiment potential of discovering exclusive $$D_s^{*}$$ D s ∗ weak decays. The main result is the partial decay widths, which read as $$\varGamma _{D_s^*\rightarrow l \nu } = 2.44 \times 10^{-12} \, \textrm{GeV}$$ Γ D s ∗ → l ν = 2.44 × 10 - 12 GeV , $$\varGamma _{D_s^*\rightarrow \phi l \nu } = (3.28^{+0.82}_{-0.71}) \times 10^{-14} \, \textrm{GeV}$$ Γ D s ∗ → ϕ l ν = ( 3 . 28 - 0.71 + 0.82 ) × 10 - 14 GeV , $$\varGamma _{D_s^{*} \rightarrow \phi \pi } = ( 3.81^{+1.52}_{-1.33} ) \times 10^{-14} \, \textrm{GeV}$$ Γ D s ∗ → ϕ π = ( 3 . 81 - 1.33 + 1.52 ) × 10 - 14 GeV and $$\varGamma _{D_s^{*}\rightarrow \phi \rho } = ( 1.16^{+0.42}_{-0.39} ) \times 10^{-13} \, \textrm{GeV}$$ Γ D s ∗ → ϕ ρ = ( 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.

Abstract We reanalyze the $$\Lambda _b\rightarrow p$$ Λ b → p transition form factors in the perturbative QCD (PQCD) approach by including higher-twist light-cone distribution amplitudes (LCDAs) of a $$\Lambda _b$$ Λ b baryon and a proton. The previous PQCD evaluation performed decades ago with only the leading-twist $$\Lambda _b$$ Λ b baryon and proton LCDAs gave the form factors, which are two orders of magnitude smaller than indicated by experimental data. We find that the twist-4 $$\Lambda _b$$ Λ b baryon LCDAs and the twist-4 and -5 proton LCDAs contribute dominantly, and the enhanced form factors become consistent with those from lattice QCD and other nonperturbative methods. The estimated branching ratios of the semileptonic decays $$\Lambda _b\rightarrow p\ell {\bar{\nu }}_\ell $$ Λ b → p ℓ ν ¯ ℓ and the hadronic decay $$\Lambda _b\rightarrow p\pi $$ Λ b → p π are also close to the data. It implies that the b quark mass is not really heavy enough, and higher-power contributions play a crucial role, similar to the observation made in analyses of B meson transition form factors. With the formalism established in this work, we are ready to study various exclusive heavy baryon decays systematically in the PQCD approach.

Abstract We propose to search for the open heavy-flavor exotic states with the quark components of $$Qs{\bar{u}}{\bar{d}}$$ Q s u ¯ d ¯ with $$Q=b,c$$ 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 $$B_s\pi $$ B s π or $$D_s\pi $$ D s π thresholds of the configurations of $$Qu{\bar{s}}{\bar{d}}$$ Q u s ¯ d ¯ or $$Qd{\bar{s}}{\bar{u}}$$ Q d s ¯ 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.

Abstract We propose a systematic theoretical framework for the topological amplitudes of the heavy meson decays and their SU(N) decomposition. In the framework, the topologies are expressed in invariant tensors and classified into tree- and penguin-operator-induced diagrams according to which four-quark operators, tree or penguin, being inserted into their effective weak vertexes. The number of possible topologies contributing to one type of decay can be counted by permutations and combinations. The Wigner-Eckhart theorem ensures the topological amplitudes under flavor symmetry are the same for different decay channels. By decomposing the four-quark operators into irreducible representations of SU(N) group, one can get the SU(N) irreducible amplitudes. Taking the D → PP decay (P denoting a pseudoscalar meson) with SU(3) F symmetry as an example, we present our framework in detail. The linear correlation of topologies in the SU(3) F limit is clarified in group theory. It is found there are only nine independent topologies in all tree- and penguin-operator-induced diagrams contributing to the D → PP decays in the Standard Model. If a large quark-loop diagram, named T LP , is assumed, the large ∆A CP and the very different D 0 → K + K − and D 0 → π + π − branching fractions can be explained with a normal U-spin breaking. Moreover, our framework provides a simple way to analyze the SU(N) breaking effects. The linear SU(3) F breaking and the high order U-spin breaking in charm decays are re-investigated in our framework, which are consistent with literature. Analogous to the degeneracy and splitting of energy levels, we propose the concepts of degeneracy and splitting of topologies to describe the flavor symmetry breaking effects in decay. As applications, we analyze the strange-less D decays in SU(3) F symmetry breaking into Isospin symmetry and the charm-less B decays in SU(4) F symmetry breaking into SU(3) F symmetry.

Abstract After the discovery of the double-charm baryon $$\Xi _{cc}^{++}$$ Ξ cc + + by LHCb, one of the most important topics is to search for the bottom-charm baryons which contain a b quark, a c quark and a light quark. In this work, we study the two-body non-leptonic weak decays of a bottom-charm baryon into a spin-1/2 bottomed baryon and a light pseudoscalar meson with the short-distance contributions calculated under the factorization hypothesis and the long-distance contributions considering the final-state-interaction effects. The branching fractions of all fifty-seven decay channels are estimated. The results indicate that $$\Xi _{bc}^+\rightarrow \Xi _b^0\pi ^+$$ Ξ bc + → Ξ b 0 π + , $$\Xi _{bc}^{0}\rightarrow \Xi _{b}^{-}\pi ^+$$ Ξ bc 0 → Ξ b - π + and $$\Omega _{bc}^0\rightarrow \Omega _b^-\pi ^+$$ Ω bc 0 → Ω b - π + decay modes have relatively large decay rates and thus could be used to experimentally search for the bottom-charm baryons. The topological diagrams and the SU(3) symmetry of bottom-charm baryon decays are discussed.

Abstract The exotic states $$X_{0,1}(2900)$$ X 0 , 1 ( 2900 ) with the quark flavor of $$cs\bar{u}\bar{d}$$ c s u ¯ d ¯ are recently observed in the mass spectrum of $$D^+K^-$$ D + K - in $$B^-\rightarrow D^-D^+K^-$$ B - → D - D + K - by the LHCb collaboration. To explore the nature of $$X_{0,1}(2900)$$ 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 $$B^-\rightarrow D^- X_{0,1}$$ 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 $$B^-\rightarrow D^- X_{0,1}$$ B - → D - X 0 , 1 are revealed. It is manifested by $${B}^-\rightarrow \Lambda _c^-\Xi _c^{(\prime )0}$$ B - → Λ c - Ξ c ( ′ ) 0 and $$\Lambda _b^0\rightarrow P_c^+K^-$$ Λ b 0 → P c + K - that the rescattering mechanism can result in the relatively large branching fractions. The similar processes of $$B^-\rightarrow \pi ^-X_{0,1}$$ B - → π - X 0 , 1 are also analyzed. The isospins of $$X_{0,1}$$ X 0 , 1 can be investigated by $$B\rightarrow DX_{0,1}^{\pm ,0}$$ B → D X 0 , 1 ± , 0 decays.

Abstract 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 $$e^+e^-\rightarrow Z\rightarrow \nu N$$ 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 $$\sigma (e^+e^-\rightarrow \nu N\rightarrow \nu \ell jj)$$ σ(e+e-→νN→νℓjj) given by the Z-factories with integrated luminosities of 0.1, 1 and 10 $$\hbox {ab}^{-1}$$ 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.

Abstract 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 $${\bar{3}}$$ 3¯ , 6 and $${\overline{15}}$$ 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 $$X_{b6}$$ Xb6 states at the branching fraction up to be $$10^{-5}$$ 10-5 .

Abstract After the discovery of the Higgs boson, several future experiments have been proposed to study the Higgs boson properties, including two circular lepton colliders, the CEPC and the FCC-ee, and one linear lepton collider, the ILC. We evaluate the precision reach of these colliders in measuring the branching ratios of the charged lepton flavor violating Higgs decays $$H\rightarrow e^\pm \mu ^\mp $$ H→e±μ∓ , $$e^\pm \tau ^\mp $$ e±τ∓ and $$\mu ^\pm \tau ^\mp $$ μ±τ∓ . The expected upper bounds on the branching ratios given by the circular (linear) colliders are found to be $${\mathcal {B}}(H\rightarrow e^\pm \mu ^\mp ) < 1.2~(2.1) \times 10^{-5}$$ B(H→e±μ∓)

Abstract 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 Λ c + → pK 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.

Abstract We study the ratio of fragmentation fractions, $$f_{\Xi _b}/f_{\Lambda _b}$$ fΞb/fΛb , from the measurement of $$\Xi _b^0\rightarrow \Xi _c^+\pi ^-$$ Ξb0→Ξc+π- and $$\Lambda _b^0\rightarrow \Lambda _c^+\pi ^-$$ Λb0→Λc+π- with $$\Xi _{c}^{+}/\Lambda _{c}^{+}\rightarrow p K^-\pi ^+$$ Ξc+/Λc+→pK-π+ . With the branching fraction $$\mathcal {B}(\Xi _c^+\rightarrow pK^-\pi ^+)=(2.2\pm 0.8)\%$$ B(Ξc+→pK-π+)=(2.2±0.8)% obtained under the U-spin symmetry, the fragmentation ratio is determined as $$f_{\Xi _b}/f_{\Lambda _b}$$ fΞb/fΛb $$\,\, =0.054\pm 0.020$$ =0.054±0.020 . To reduce the above uncertainties, we suggest to measure the branching fractions of $$\Xi _c^+\rightarrow p \overline{K}^{*0}$$ Ξc+→pK¯∗0 and $$\Lambda _c^+\rightarrow \Sigma ^+ K^{*0}$$ Λc+→Σ+K∗0 at BESIII, Belle II and LHCb.

Abstract Very recently, the LHCb collaboration has observed in the final state $$\Lambda _c^+ K^-\pi ^+\pi ^+$$ Λ c + K - π + π + a resonant structure that is identified as the doubly charmed baryon $$\Xi _{cc}^{++}$$ Ξ cc + + . Inspired by this observation, we investigate the weak decays of doubly heavy baryons $$\Xi _{cc}^{++}$$ Ξ cc + + , $$\Xi _{cc}^{+}$$ Ξ cc + , $$\Omega _{cc}^{+}$$ Ω cc + , $$\Xi _{bc}^{(\prime )+}$$ Ξ bc ( ′ ) + , $$\Xi _{bc}^{(\prime )0}$$ Ξ bc ( ′ ) 0 , $$\Omega _{bc}^{(\prime )0}$$ Ω bc ( ′ ) 0 , $$\Xi _{bb}^{0}$$ Ξ bb 0 , $$\Xi _{bb}^{-}$$ Ξ bb - and $$\Omega _{bb}^{-}$$ 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 $$c\rightarrow d/s$$ c → d / s or $$b\rightarrow u/c$$ 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.

Abstract The SU(3) quark model encounters a great challenge in describing even-parity mesons. Specifically, the $$q\bar{q}$$ qq¯ quark model has difficulties in understanding the light scalar mesons below 1 GeV, scalar and axial-vector charmed mesons and $$1^+$$ 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, $$D_{s0}^*$$ Ds0∗ and $$D_0^{*0}$$ 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 $$D_{s0}^*$$ Ds0∗ and $$D_0^{*0}$$ 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 $$B_{s0}^*$$ Bs0∗ and $$B_0^{*0}$$ B0∗0 mesons. The $$P_0^* P'_1$$ 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 $$1/m_Q$$ 1/mQ effects, we obtain the masses of $$B^*_{(s)0}$$ B(s)0∗ and $$B'_{(s)1}$$ B(s)1′ mesons, for example, $$M_{B_{s0}^*}= (5715\pm 1)\,\mathrm{MeV}+\delta \Delta _S$$ MBs0∗=(5715±1)MeV+δΔS , $$M_{B'_{s1}}=(5763\pm 1)\,\mathrm{MeV}+\delta \Delta _S$$ MBs1′=(5763±1)MeV+δΔS with $$\delta \Delta _S$$ δΔS being $$1/m_Q$$ 1/mQ corrections. We find that the predicted mass difference of 48 MeV between $$B'_{s1}$$ Bs1′ and $$B_{s0}^*$$ Bs0∗ 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 $$M_{B'_{s1}}$$ MBs1′ and $$M_{B'_1}$$ MB1′ is much smaller than the quark model expectation of 60–100 MeV. Experimentally, it is important to have a precise mass measurement of $$D_0^*$$ 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 $$D_0^{*\pm }$$ D0∗± .