Measurement of the integrated luminosity of the Phase 2 data of the Belle II experiment

From April to July 2018, a data sample at the peak energy of the γ(4S) resonance was collected with the Belle II detector at the SuperKEKB electron-positron collider. This is the first data sample of the Belle II experiment. Using Bhabha and digamma events, we measure the integrated luminosity of the data sample to be (496.3 ± 0.3 ± 3.0) pb-1, where the first uncertainty is statistical and the second is systematic. This work provides a basis for future luminosity measurements at Belle II

Search for pair-produced resonances decaying to quark pairs in proton-proton collisions at root s=13 TeV

A general search for the pair production of resonances, each decaying to two quarks, is reported. The search is conducted separately for heavier resonances (masses above 400 GeV), where each of the four final-state quarks generates a hadronic jet resulting in a four-jet signature, and for lighter resonances (masses between 80 and 400 GeV), where the pair of quarks from each resonance is collimated and reconstructed as a single jet resulting in a two-jet signature. In addition, a b-tagged selection is applied to target resonances with a bottom quark in the final state. The analysis uses data collected with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 35.9 fb(-1), from proton-proton collisions at a center-of-mass energy of 13 TeV. The mass spectra are analyzed for the presence of new resonances, and are found to be consistent with standard model expectations. The results are interpreted in the framework of R-parity-violating supersymmetry assuming the pair production of scalar top quarks decaying via the hadronic coupling lambda ''(312) or lambda ''(323) and upper limits on the cross section as a function of the top squark mass are set. These results probe a wider range of masses than previously explored at the LHC, and extend the top squark mass limits in the (t) over tilde -> qq' scenario.Peer reviewe

Automatic Numerical Analysis Based on Infinite-Precision Arithmetic

Abstract—Numerical analysis is an important process for cre-ating reliable numerical software. However, traditional analysis methods rely on manual estimation by numerical analysts, which is restricted by the problem size. Although some state-of-art software packages can check whether a program is numerical unstable, they cannot tell whether it is caused by ill-posed problem itself or by some improper implementation practices, while these packages work on the floating point values in the program. In this paper, we introduce an automatic framework that utilizes infinite-precision arithmetic to analyze large-scale numerical problems by computer. To eliminate rounding errors, the computing process iterates itself to increase intermediate precision until the calculation reaches the desired final precision. Then the framework perturbs the inputs and intermediate values of a certain numerical problem. By checking the gaps among different program outputs, the framework helps us understand whether the problem is well-conditioned or ill-conditioned. The framework also compares the infinite-precision arithmetic with fixed-precision arithmetic. The evaluation of a bunch of classical problems shows that our framework is able to detect the ill-conditioning in large-scale problems effectively

Room-Temperature Synthesis, Hydrothermal Recrystallization, and Properties of Metastable Stoichiometric FeSe

Room-temperature precipitation from aqueous solutions yields the hitherto unknown metastable stoichiometric iron selenide (ms-FeSe) with tetragonal anti-PbO type structure. Samples with improved crystallinity are obtained by diffusion-controlled precipitation or hydrothermal recrystallization. The relations of ms-FeSe to superconducting β-FeSe_1–<i>x</i> and other neighbor phases of the iron–selenium system are established by high-temperature X-ray diffraction, DSC/TG/MS (differential scanning calorimetry/thermogravimetry/mass spectroscopy), ⁵⁷Fe Mössbauer spectroscopy, magnetization measurements, and transmission electron microscopy. Above 300 °C, ms-FeSe decomposes irreversibly to β-FeSe_1–<i>x</i> and Fe₇Se₈. The structural parameters of ms-FeSe (<i>P</i>4/<i>nmm</i>, <i>a</i> = 377.90(1) pm, <i>c</i> = 551.11(3) pm, <i>Z</i> = 2), obtained by Rietveld refinement, differ significantly from literature data for β-FeSe_1–<i>x</i>. The Mössbauer spectrum rules out interstitial iron atoms or additional phases. Magnetization data suggest canted antiferromagnetism below <i>T</i>_N = 50 K. Stoichiometric non-superconducting ms-FeSe can be regarded as the true “parent” compound for the “11” iron-chalcogenide superconductors and may serve as starting point for new chemical modifications

Distinct formation history for deep-mantle domains reflected in geochemical differences

info:eu-repo/semantics/publishe