Charge Symmetry Breaking in dd->4He{\pi}0 with WASA-at-COSY

Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are currently used to develop a consistent description of CSB within the framework of chiral perturbation theory. In this work the experimental studies on the reaction dd->4He{\pi}0 have been extended towards higher excess energies in order to provide information on the contribution of p-waves in the final state. For this, an exclusive measurement has been carried out at a beam momentum of p=1.2 GeV/c using the WASA-at-COSY facility. The total cross section amounts to sigma(tot) = (118 +- 18(stat) +- 13(sys) +- 8(ext)) pb and first data on the differential cross section are consistent with s-wave pion production.Comment: 14 pages, 5 figure

Cross section ratio and angular distributions of the reaction p + d -> 3He + eta at 48.8 MeV and 59.8 MeV excess energy

We present new data for angular distributions and on the cross section ratio of the p + d -> 3He + eta reaction at excess energies of Q = 48.8 MeV and Q = 59.8 MeV. The data have been obtained at the WASA-at-COSY experiment (Forschungszentrum J\"ulich) using a proton beam and a deuterium pellet target. While the shape of obtained angular distributions show only a slow variation with the energy, the new results indicate a distinct and unexpected total cross section fluctuation between Q = 20 MeV and Q = 60 MeV, which might indicate the variation of the production mechanism within this energy interval.Comment: 9 pages, 9 figure

Search for a dark photon in the π0→e+e−γ\pi^0 \to e^+e^-\gamma decay

The presently world largest data sample of pi0 --> gamma e+e- decays containing nearly 5E5 events was collected using the WASA detector at COSY. A search for a dark photon U produced in the pi0 --> gamma U --> gamma e+e- decay from the pp-->pp\pi^0 reaction was carried out. An upper limit on the square of the U-gamma mixing strength parameter epsilon^2 of 5e-6 at 90% CL was obtained for the mass range 20 MeV <M_U< 100 MeV. This result together with other recent experimental limits significantly reduces the M_U vs. \epsilon^2 parameter space preferred by the measured value of the muon anomalous magnetic moment.Comment: 16 pages, 8 figures; improved analysis extending the exclusion region to 20 MeV<M_U< 100 MeV; implemented changes requested by referee

ABC Effect in Basic Double-Pionic Fusion --- Observation of a new resonance?

We report on a high-statistics measurement of the basic double pionic fusion reaction $pn \to d\pi^0\pi^0$ over the energy region of the so-called ABC effect, a pronounced low-mass enhancement in the $\pi\pi$-invariant mass spectrum. The measurements were performed with the WASA detector setup at COSY. The data reveal the ABC effect to be associated with a Lorentzian shaped energy dependence in the integral cross section. The observables are consistent with a resonance with $I(J^P) =0(3^+)$ in both $pn$ and $\Delta\Delta$ systems. Necessary further tests of the resonance interpretation are discussed

Backward single-pion production in the pd→3He π0\boldsymbol{pd\rightarrow {}^3\textrm{He}\,\pi^0} reaction with WASA-at-COSY

New data on the production of single neutral pions in the $pd\rightarrow{}^3\textrm{He}\,\pi^0$ reaction are presented. For fifteen proton beam momenta between $p_p=1.60\;\textrm{GeV}/c$ and $p_p=1.74\;\textrm{GeV}/c$, differential cross sections are determined over a large fraction of the backward hemisphere. Since the only previous systematic measurements of single-pion production at these energies were made in collinear kinematics, the present work constitutes a significant extension of the current knowledge on this reaction. Even this far above the production threshold, significant changes are found in the behaviour of the angular distributions over small intervals in beam momentum.Comment: 9 pages, 5 figures, 3 tables submitted to EPJ

Alexander Baumgarten on the Principle of Sufficicent Reason

This paper defends the Principle of Sufficient Reason, taking Baumgarten as its guide. The primary aim is not to vindicate the principle, but rather to explore the kinds of resources Baumgarten originally thought sufficient to justify the PSR against its early opponents. The paper also considers Baumgarten’s possible responses to Kant’s pre-Critical objections to the proof of the PSR. The paper finds that Baumgarten possesses reasonable responses to all these objections. While the paper notes that in the absence of a response to Kant’s Critical discussion of the PSR (which is omitted here due to limitations of space), this result does not vindicate the principle, it shows how this discussion provides a deeper understanding of what, according to Baumgarten, the PSR really assumes and intends, and prepares the way for a more responsible discussion of Kant’s critical objections to Baumgarten’s supposed proof.info:eu-repo/semantics/publishedVersio

PRC1 drives Polycomb-mediated gene repression by controlling transcription initiation and burst frequency

The Polycomb repressive system plays a fundamental role in controlling gene expression during mammalian development. To achieve this, Polycomb repressive complexes 1 and 2 (PRC1 and PRC2) bind target genes and use histone modification-dependent feedback mechanisms to form Polycomb chromatin domains and repress transcription. The interrelatedness of PRC1 and PRC2 activity at these sites has made it difficult to discover the specific components of Polycomb chromatin domains that drive gene repression and to understand mechanistically how this is achieved. Here, by exploiting rapid degron-based approaches and time-resolved genomics we kinetically dissect Polycomb-mediated repression and discover that PRC1 functions independently of PRC2 to counteract RNA polymerase II binding and transcription initiation. Using single-cell gene expression analysis, we reveal that PRC1 acts uniformly within the cell population, and that repression is achieved by controlling transcriptional burst frequency. These important new discoveries provide a mechanistic and conceptual framework for Polycomb-dependent transcriptional control

Ramified Cauchy problem for a class of Fuchsian operators with tangent characteristics (Painleve systemes, hypergeometoric systems and asymptotic analysis)

The WASA-at-COSY experiment has collected 3×107 events with η mesons produced via the reaction pd→He3η at T=1.0GeV. Using this data set, we evaluate the branching ratios of the decays η→π+π-γ, η→e+e-γ, η→π+π-e+e-, and η→e+e-e+e-. The branching ratios are normalized to the η→π+π-π0 decay. In addition an upper limit on a CP-violating asymmetry in η→π+π-e+e- is extracted

Layer-by-layer bioassembly of cellularized polylactic acid porous membranes for bone tissue engineering

The conventional tissue engineering is based on seeding of macroporous scaffold on its surface ("top-down" approach). The main limitation is poor cell viability in the middle of the scaffold due to poor diffusion of oxygen and nutrients and insufficient vascularization. Layer-by-Layer (LBL) bioassembly is based on "bottom-up" approach, which considers assembly of small cellularized blocks. The aim of this work was to evaluate proliferation and differentiation of human bone marrow stromal cells (HBMSCs) and endothelial progenitor cells (EPCs) in two and three dimensions (2D, 3D) using a LBL assembly of polylactic acid (PLA) scaffolds fabricated by 3D printing. 2D experiments have shown maintain of cell viability on PLA, especially when a co-cuture system was used, as well as adequate morphology of seeded cells. Early osteoblastic and endothelial differentiations were observed and cell proliferation was increased after 7 days of culture. In 3D, cell migration was observed between layers of LBL constructs, as well as an osteoblastic differentiation. These results indicate that LBL assembly of PLA layers could be suitable for BTE, in order to promote homogenous cell distribution inside the scaffold and gene expression specific to the cells implanted in the case of co-culture system