Estimates on the isospin-violating Λb→Σ0ϕ,Σ0J/ψ\Lambda_b\rightarrow \Sigma^0 \phi, \Sigma^0 J/\psi decays and the Σ−Λ\Sigma-\Lambda mixing

We analyse the two purely isospin-violating decays $\Lambda_b\rightarrow \Sigma^0 \phi$ and $\Lambda_b\rightarrow \Sigma^0 J/\psi$, proceed merely via the exchange topologies, in the framework of perturbative QCD approach. Assuming $\Sigma^0$ baryon belongs to the idealized isospin triplet with quark components of $usd$, the branching ratios of the two decay modes are predicted to be tiny, of the order $10^{-8}-10^{-9}$, leading to a difficulty in observing them. We then extend our study to include the $\Sigma-\Lambda$ mixing.It is found that the mixing has significant effect on the $\Lambda_b\rightarrow \Sigma$ decays, especially it can greatly increase the rate of the $J/\psi$ process, by as much as two orders of magnitude, yield $10^{-7}$, which should be searchable in the future. We also estimate a set of asymmetry observables with and without the mixing effect, which will be tested in coming experiments.Comment: 23 pages, 1 figure, 10 tables; to appear in PR

Mixing effects of η−η′\eta-\eta' in Λb→Λη(′)\Lambda_b\rightarrow \Lambda \eta^{(')} decays

We perform a thorough analysis of the $\eta-\eta'$ mixing effects on the $\Lambda_b\rightarrow \Lambda \eta^{(')}$ decays based on the perturbative QCD (PQCD) factorization approach. Branching ratios, up-down and direct $CP$ asymmetries are computed by considering four popular mixing schemes, such as $\eta-\eta'$, $\eta-\eta'-\eta_c$, $\eta-\eta'-G$, and $\eta-\eta'-G-\eta_c$ mixing formalism, where $G$ represents the physical pseudoscalar gluball. The PQCD predictions with the four mixing schemes does not change much for the $\eta$ channel but changes significantly for the $\eta'$ one. In particular, the value of $\mathcal{B}(\Lambda_b\rightarrow \Lambda \eta^{'})$ in the $\eta-\eta'-G-\eta_c$ mixing scheme exceeds the present experimental bound by a factor of 2, indicates the related mixing angles may be overestimated. Because of the distinctive patterns of interference between $S$-wave and $P$-wave amplitudes, the predicted up-down asymmetries for the two modes differ significantly. The obvious discrepancies among different theoretical analyses should be clarified in the future. The direct $CP$ violations are predicted to be at the level of a few percent mainly due to the tree contributions of the strange and nonstrange amplitudes suffer from the color suppression and CKM suppression. Finally, as a byproduct, we investigate the $\Lambda_b\rightarrow \Lambda \eta_c$ process, which has a large branching ratio of order $10^{-4}$, promising to be measured by the LHCb experiment. Our findings are useful for constraining the mixing parameters, comprehending the $\eta^{(')}$ configurations, and instructing experimental measurements.Comment: 19 pages,1 figure,7 tables, updated to match published versio

Estimates of exchange topological contributions and CPCP-violating observables in Λb→Λϕ\Lambda_b\rightarrow \Lambda \phi decay

The penguin-dominated two-body weak decay of $\Lambda_b\rightarrow \Lambda \phi$ is studied based on the perturbative QCD approach. In addition to the penguin emission diagrams, the penguin exchange and $W$ exchange ones are also accounted for. It is found that the penguin exchange contribution is in fact important and comparable to the penguin emission one, while the $W$ exchange contribution is highly Cabibbo-Kobayashi-Maskawa (CKM) suppressed. The predicted branching ratio, $\mathcal{B}(\Lambda_b\rightarrow \Lambda \phi)=7.1^{+3.6+1.9}_{-4.1-3.0}\times10^{-6}$, is larger than the previous theoretical estimates but in comparison with the data from Particle Data Group at the level of 1 standard deviation. We also explore some pertinent decay asymmetry parameters that characterize the angular decay distributions. The inclusion of the $W$ exchange contribution provides the nonzero weak phase difference, consequently, allowing us to estimate the direct $CP$ violation and true triple product asymmetries in the concerned process. The numerical results demonstrate that the direct $CP$ violation is at the level of a few percent, and the true triple product asymmetries are also predicted to be tiny, of order $10^{-3}-10^{-4}$. The observed small $CP$-violating observables have shown no significant deviations from zero. Our predictions will be subject to stringent tests with precise data from LHCb in the future.Comment: 22 pages, 4 figures, 12 table

Laparoscopic versus open distal pancreatectomy: A meta-analysis

SummaryObjectiveLaparoscopic distal pancreatectomy (LDP) is a minimally invasive surgical technique. The aim of the present study was to evaluate the currently available literature and compare the short-term clinical outcomes of patients who underwent LDP for left-sided pancreatic pathology with patients who underwent traditional open surgery.MethodsA literature search was performed to identify and compare studies that reported the clinical outcomes of both LDP and open distal pancreatectomy (ODP). Pooled odds ratios (OR) and weighted mean differences (WMD) with 95% confidence intervals (95% CI) were calculated using either fixed-effects or random-effects models.ResultsNineteen nonrandomized controlled studies were identified that matched the selection criteria and reported the clinical outcomes of 1935 patients, of whom 805 underwent LDP and 1130 underwent ODP. Compared with open surgery, reports on laparoscopic resection indicate potentially favorable outcomes in terms of operative blood loss (WMD: -273.11; 95% CI: -404.61 to -141.61), the requirement of a blood transfusion (OR: 0.28; 95% CI: 0.11–0.71), postoperative time until oral intake (WMD: -1.19; 95% CI: -1.87 to -0.50), time to first flatus (WMD: -1.03, 95% CI: -1.93 to -0.12), length of hospital stay (WMD: -3.87, 95% CI: -5.06 to -2.68), and overall morbidity (OR: 0.70, 95% CI: 0.56–0.87). There were no differences in terms of the extent of oncologic clearance and postoperative mortality.ConclusionLDP results in a faster postoperative recovery and a comparable oncologic clearance in comparison with open surgery. Additional large trials are required to delineate the long-term clinical outcomes of patients diagnosed with malignant neoplasms who undergo either of these two surgeries

On the exponents of primitive, ministrong digraphs with shortest elementary circuit length s

AbstractLet MDs(n) = {D | D is a primitive ministrong digraph with n vertices, and the shortest cycle length of D is s}, and bs(n) = max{γ(D) | D ∈ MDs(n)}, where γ(D) is the primitive exponent of D. Our main results are: (1) we give explicit expressions for bs(n); (2) for s ≠ 2, 6, we give a necessary and sufficient condition for a digraph D ∈ MDs(n) with γ(D) = bs(n)