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A bstract 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.

A bstract The dynamical studies on the non-leptonic weak decays of charmed baryons are always challenging, due to the large non-perturbative contributions at the charm scale. In this work, we develop the final-state rescattering mechanism to study the two-body non-leptonic decays of charmed baryons. The final-state interaction is a physical picture of long-distance effects. Instead of using the Cutkosky rule to calculate the hadronic triangle diagrams which can only provide the imaginary part of decay amplitudes, we point out that the loop integral is more appropriate, as both the real parts and the imaginary parts of amplitudes can be calculated completely. In this way, it can be obtained for the non-trivial strong phases which are essential to calculate CP violations. With the physical picture of long-distance effects and the reasonable method of calculations, it is amazingly achieved that all the nine existing experimental data of branching fractions for the Λ c + decays into an octet light baryon and a vector meson can be explained by only one parameter of the model. Besides, the decay asymmetries and CP violations are not sensitive to the model parameter, since the dependence on the parameter is mainly cancelled in the ratios, so that the theoretical uncertainties on these observables are lowered down.

Seroprevalence data suggest that a third of the world's population has been infected with the hepatitis E virus. Our aim was to assess efficacy and safety of a recombinant hepatitis E vaccine, HEV 239 (Hecolin; Xiamen Innovax Biotech, Xiamen, China) in a randomised, double-blind, placebo-controlled, phase 3 trial. Healthy adults aged 16–65 years in, Jiangsu Province, China were randomly assigned in a 1:1 ratio to receive three doses of HEV 239 (30 μg of purified recombinant hepatitis E antigen adsorbed to 0·8 mg aluminium hydroxide suspended in 0·5 mL buffered saline) or placebo (hepatitis B vaccine) given intramuscularly at 0, 1, and 6 months. Randomisation was done by computer-generated permuted blocks and stratified by age and sex. Participants were followed up for 19 months. The primary endpoint was prevention of hepatitis E during 12 months from the 31st day after the third dose. Analysis was based on participants who received all three doses per protocol. Study participants, care givers, and investigators were all masked to group and vaccine assignments. This trial is registered with ClinicalTrials.gov, number NCT01014845. 11 165 of the trial participants were tested for hepatitis E virus IgG, of which 5285 (47%) were seropositive for hepatitis E virus. Participants were randomly assigned to vaccine (n=56 302) or placebo (n=56 302). 48 693 (86%) participants in the vaccine group and 48 663 participants (86%) in the placebo group received three vaccine doses and were included in the primary efficacy analysis. During the 12 months after 30 days from receipt of the third dose 15 per-protocol participants in the placebo group developed hepatitis E compared with none in the vaccine group. Vaccine efficacy after three doses was 100·0% (95% CI 72·1–100·0). Adverse effects attributable to the vaccine were few and mild. No vaccination-related serious adverse event was noted. HEV 239 is well tolerated and effective in the prevention of hepatitis E in the general population in China, including both men and women age 16–65 years. Chinese National High-tech R&D Programme (863 programme), Chinese National Key Technologies R&D Programme, Chinese National Science Fund for Distinguished Young Scholars, Fujian Provincial Department of Sciences and Technology, Xiamen Science and Technology Bureau, and Fujian Provincial Science Fund for Distinguished Young Scholars.

Hepatitis E is caused by two viral genotype groups: human types and zoonotic types. Current understanding of the epidemiology of the zoonotic hepatitis E disease is founded largely on hospital-based studies. The epidemiology of hepatitis E was investigated in a community-based surveillance study conducted over one year in a rural city in eastern China with a registered population of 400,162. The seroprevalence of hepatitis E in the cohort was 38%. The incidence of hepatitis E was 2.8/10,000 person-years. Totally 93.5% of the infections were attributed to genotype 4 and the rest, to genotype 1. Hepatitis E accounted for 28.4% (102/359) of the acute hepatitis cases and 68.9% (102/148) of the acute viral hepatitis cases in this area of China. The disease occurred sporadically with a higher prevalence during the cold season and in men, with the male-to-female ratio of 3∶1. Additionally, the incidence of hepatitis E increased with age. Hepatitis B virus carriers have an increased risk of contracting hepatitis E than the general population (OR = 2.5, 95%CI 1.5-4.2). Pre-existing immunity to hepatitis E lowered the risk (relative risk  = 0.34, 95% CI 0.21-0.55) and reduced the severity of the disease. Hepatitis E in the rural population of China is essentially that of a zoonosis due to the genotype 4 virus, the epidemiology of which is similar to that due to the other zoonotic genotype 3 virus.

The dynamical studies on the non-leptonic weak decays of charmed baryons are always challenging, due to the large non-perturbative contributions at the charm scale. In this work, we develop the final-state rescattering mechanism to study the two-body non-leptonic decays of charmed baryons. The final-state interaction is a physical picture of long-distance effects. Instead of using the Cutkosky rule to calculate the hadronic triangle diagrams which can only provide the imaginary part of decay amplitudes, we point out that the loop integral is more appropriate, as both the real parts and the imaginary parts of amplitudes can be calculated completely. In this way, it can be obtained for the non-trivial strong phases which are essential to calculate CP violations. With the physical picture of long-distance effects and the reasonable method of calculations, it is amazingly achieved that all the nine existing experimental data of branching fractions for the \\(\\Lambda_c^+\\) decays into an octet light baryon and a vector meson can be explained by only one parameter of the model. Besides, the decay asymmetries and CP violations are not sensitive to the model parameter, since the dependence on the parameter is mainly cancelled in the ratios, so that the theoretical uncertainties on these observables are lowered down.

In this work we investigate the exclusive production of a pair of light neutral mesons in \\(e^+e^-\\) annihilation, where the final state bears an even \\(C\\)-parity. The production processes can be initiated via the photon fragmentation or the non-fragmentation mechanism. While the fragmentation contribution can be rigorously accounted, the non-fragmentation contributions are calculated within the framework of collinear factorization, where only the leading-twist light-cone distribution amplitudes (LCDAs) of mesons are considered. Mediately solely by the non-fragmentation mechanism, the production rates of double light neutral pseudoscalar mesons are too small to be observed at the commissioning \\(e^+e^-\\) facilities. In contrast, the production rates of a pair of light neutral vector mesons are greatly amplified owing to the significant kinematic enhancement brought by the fragmentation mechanism. It is found that, at \\(\\sqrt{s}=3.77\\) GeV, after including the destructive interference between the non-fragmentation and fragmentation contributions, the production rates for \\(e^+e^-\\to \\rho^{0}\\rho^{0}\\) and \\(\\rho^0\\omega\\) can be lowered by about 10\\% and 30\\% relative to the fragmentation predictions. Future precise measurement of these exclusive double neutral vector meson production channels at {\\tt BESIII} experiment may provide useful constraints on the LCDAs of light vector mesons.

The doubly charmed baryon \\(\\Xi_{cc}^{++}\\) has been observed by LHCb through the non-leptonic decay modes of \\(\\Xi_{cc}^{++}\\to\\Lambda_{c}^{+}K^{-}\\pi^{+}\\pi^{+}\\) and \\(\\Xi_{c}^{+}\\pi^{+}\\) in 2017. After that, the experimentalists turn their attention to finding other doubly charmed baryons \\(\\Xi_{cc}^{+}\\) and \\(\\Omega_{cc}^{+}\\). In this work, we investigate the nonleptonic weak decays of doubly charmed baryons \\({\\cal B}_{cc}\\to{\\cal B}_{c}P\\), where \\({\\cal B}_{cc}\\) denotes the doubly charmed baryons \\((\\Xi_{cc}^{++},\\Xi_{cc}^{+},\\Omega_{cc}^{+})\\), \\({\\cal B}_{c}\\) represents the singly charmed baryons \\(({\\cal B}_{\\bar{3}},{\\cal B}_{6})\\) and \\(P\\) is the light pseudoscalar. For these non-leptonic decay modes, their short-distance contributions can be accurately estimated in theoretical calculations. However, dealing with the long-distance contributions for final-state-interaction effects is challenging. To address this, we use the rescattering mechanism to calculate the long-distance contributions and first derive the whole hadronic loop contributions for these two-body nonleptonic decays of doubly charmed baryons. Then the decay widths and branching ratios of the 45 nonleptonic decays of doubly charmed baryon are predicted. Among that, the ratio of the branching ratios \\({\\cal RB}=\\frac{{\\cal B}(\\Xi_{cc}^{++}\\to\\Xi_{c}^{\\prime+}\\pi^{+})}{{\\cal B}(\\Xi_{cc}^{++}\\to\\Xi_{c}^{+}\\pi^{+})}=1.15\\pm0.45\\) is consistent with the experimental results within statistical errors.

The conventional wisdom in dealing with electromagnetic transition between heavy quarkonia is the multipole expansion, when the emitted photon has a typical energy of order quarkonium binding energy. Nevertheless, in the case when the energy carried by the photon is of order typical heavy quark momentum, the multipole expansion doctrine is expected to break down. In this work, we apply the \"hard-scattering\" approach originally developed to tackle the strongly hindered magnetic dipole (\\(M1\\)) transition [Y.~Jia {\\it et al.}, Phys. \\ Rev. \\ D. 82, 014008 (2010)] to the strongly hindered electric dipole (\\(E1\\)) transition between heavy quarkonia. We derive the factorization formula for the strongly hindered \\(E1\\) transition rates at the lowest order in velocity and \\(\\alpha_s\\) in the context of the non-relativistic QCD (NRQCD), and conduct a detailed numerical comparison with the standard predictions for various bottomonia and charmonia \\(E1\\) transition processes.

We propose a systematic theoretical framework for the topological amplitudes of the heavy meson decays and their \\(SU(N)\\) decomposition. In the framework, the topological amplitudes 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. By decomposing the four-quark operators into irreducible representations of \\(SU(N)\\) group, one can derive the \\(SU(N)\\) irreducible amplitudes from the tensor form of the topology. Taking the \\(D\\to PP\\) decay (\\(P\\) denoting a pseudoscalar meson) with \\(SU(3)_F\\) symmetry as an example, we show our framework in detail. The fact that some topologies are not independent in the \\(SU(3)_F\\) limit is explained by group theory. It is found that there are only nine independent topologies in all tree- and penguin-operator-induced diagrams contributing to the \\(D\\to PP\\) decays in the Standard Model. If a large quark-loop diagram is assumed, the large \\(\\Delta A_{CP}\\) and the very different \\(D^0\\to K^+K^-\\) and \\(D^0\\to \\pi^+\\pi^-\\) branching fractions can be explained with a normal \\(U\\)-spin breaking. Moreover, our framework provides a simple and systematic way to analyze the \\(SU(N)\\) breaking effects. As examples, 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. We propose the concepts of splitting and degeneracy of topologies, and use them to describe the charm-less bottom decay. We find \\(SU(3)_F\\) analysis for the charm-less \\(B\\) decays is different from the \\(D\\) decays because the charm-quark loop is beyond the \\(SU(3)\\) symmetry and should be investigated in the symmetry breaking chain of \\(SU(4)\\to SU(3)\\).

In the recent years, fruitful results on charmed baryons are obtained by BESIII, Belle and LHCb. We investigate the two-body non-leptonic decays of charmed baryons in the flavor \\(SU(3)\\) symmetry. Hundreds of amplitude relations are clearly provided, and are classified according to the \\(I\\)-, \\(U\\)- and \\(V\\)-spin symmetries. Among them, some amplitude relations are tested by the experimental data, or used to predict the branching fractions based on the exact flavor symmetry without any other approximation. Some relations of \\(K^0_S-K^0_L\\) asymmetries and \\(CP\\) asymmetries are obtained under the \\(U\\)-spin symmetry in the modes of charmed baryon decaying into neutral kaons. Besides, the \\(U\\)-spin breaking effect is explored in the \\(\\Lambda_c^+\\to \\Sigma^+K^{*0}\\) and \\(\\Xi_c^+\\to p\\bar{K}^{*0}\\) modes.