210563 research outputs found
Sort by
A Goldilocks Higgs
No full textThe Higgs may couple to a topological 4-form sector which yields a complex vacuum structure. In many of the resulting Higgs vacua electroweak symmetry is unbroken. In just as many it breaks when the 4-form flux is large enough. For a fixed value of flux, the symmetry breaking vacua have a smaller vacuum energy than the symmetric ones, where the difference is quantized because it is set by the 4-form flux. This leads to the possibility that there is a value of the 4-form flux for any UV contributions to the Higgs vev that automatically cancels it down to the right value, ∼ TeV, if the 4-form charges are quantized in the units of the electroweak scale. This would still leave the cosmological constant which could be selected anthropically. In addition, the 4-form couplings could lead to direct CP violation in a non-minimal Higgs sector
How tropical are seven- and eight-particle amplitudes?
No full textWe study tropical Grassmanians Tr in relation to cluster algebras, and assess their applicability to -particle amplitudes for . In super Yang-Mills theory, we first show that while the totally positive part of Tr may encompass the iterated discontinuity structure of the seven-point Maximally Helicity Violating (MHV) amplitude, it is too small for the Next-to-MHV helicity configuration. Then, using Tr we propose a finite set of 356 cluster -coordinates expected to contain the rational symbol letters of the eight-particle MHV amplitude, and discuss how the remaining square-root letters may be obtained from limits of infinite mutation sequences. Finally, we use a triangulation of the totally positive part of Tr to obtain the associated generalised biadjoint scalar amplitude in a form containing a near-minimal amount of spurious poles
Ruthenium 4d-to-2p X-ray Emission Spectroscopy: A Simultaneous Probe of the Metal and the Bound Ligands
No full textRuthenium 4d-to-2p X-ray emission spectroscopy (XES) was systematically explored for a series of Ru and Ru species. Complementary density functional theory calculations were utilized to allow for a detailed assignment of the experimental spectra. The studied complexes have a range of different coordination spheres, which allows the influence of the ligand donor/acceptor properties on the spectra to be assessed. Similarly, the contributions of the site symmetry and the oxidation state of the metal were analyzed. Because the 4d-to-2p emission lines are dipole-allowed, the spectral features are intense. Furthermore, in contrast with K- or L-edge X-ray absorption of 4d transition metals, which probe the unoccupied levels, the observed 4p-to-2p XES arises from electrons in filled-ligand- and filled-metal-based orbitals, thus providing simultaneous access to the ligand and metal contributions to bonding. As such, 4d-to-2p XES should be a promising tool for the study of a wide range of 4d transition-metal compounds
Update of inclusive cross sections of single and pairs of identified light charged hadrons
No full textWe report new measurements of the production cross sections of pairs of charged pions and kaonsas a function of their fractional energies using various fractional-energy definitions. Two different fractional-energy definitions were used and compared to the conventional fractional-energy definitionreported previously. The new variables aim at either identifying dihadron cross sections in terms of single-hadron fragmentation functions, or to provide a means of characterizing the transverse momentum created in the fragmentation process. The results were obtained applying the updated initial-state radiation correction used in other recent Belle publications on light-hadron production cross sections. In addition, production cross sections of single charged pions, kaons, and protons were also updated using this initial-state radiation correction. The cross sections are obtained from a 558 fb data sample collected at the resonance with the Belle detector at the KEKB asymmetric-energy collide
Studies of the semileptonic and decay processes with 34.6 fb of Belle II data
No full textWe report measurements of the and processes using 34.6 fb of collision events recorded by the Belle II experiment at the SuperKEKB asymmetric-energy collider. For the channel, we present first studies that isolate this decay from other semileptonic processes and backgrounds. We report a measurement of the branching fraction and obtain , in agreement with the world average. Here, the uncertainties are statistical, systematic, and related to slow pion reconstruction, respectively. The systematic uncertainties are limited by the statistics of auxiliary measurements and will improve in the future. We also report differential branching fractions in five bins of the hadronic recoil parameter for , unfolded to account for resolution and efficiency effects
First search for the (1D) in B decays at Belle
No full textThe first dedicated search for the η(1D) is carried out using the decays B→ η(1D)K, B → η(1D), B→ η(1D)πK, and B→ η(1D)π with η(1D) → hγ. No significant signal is found. For the η(1D) mass range between 3795 and 3845 MeV/c, the branching-fraction upper limits are determined to be ℬ(B→ η(1D)K) × ℬ(η(1D) → hγ) < 3.7 × 10, ℬ(B→ η(1D)K) × ℬ(η(1D) → hγ) < 3.5 × 10, ℬ(B→ η(1D)πK) × ℬ(η(1D) → hγ) < 1.0 × 10, and ℬ(B→ η(1D)π) × ℬ(η(1D) → hγ) < 1.1 × 10 at 90% C.L. The analysis is based on the 711 fb data sample collected on the ϒ(4S) resonance by the Belle detector, which operated at the KEKB asymmetric-energy ee collider.[graphic not available: see fulltext
Characterization of megahertz X-ray laser beams by multishot desorption imprints in PMMA
No full textProper diagnostics of intense free-electron laser (FEL) X-ray pulses is indisputably important for experimental data analysis as well as for the protection of beamline optical elements. New challenges for beam diagnostic methods are introduced by modern FEL facilities capable of delivering powerful pulses at megahertz (MHz) repetition rates. In this paper, we report the first characterization of a defocused MHz 13.5-nm beam generated by the free-electron laser in Hamburg (FLASH) using the method of multi-pulse desorption imprints in poly(methyl methacrylate)(PMMA). The beam fluence profile is reconstructed in a novel and highly accurate way that takes into account the nonlinear response of material removal to total dose delivered by multiple pulses. The algorithm is applied to experimental data of single-shot ablation imprints and multi-shot desorption imprints at both low (10 Hz) and high (1 MHz) repetition rates. Reconstructed response functions show a great agreement with the theoretical desorption response function model
Search for Dark Matter Produced in Association with Heavy Standard Model Particles at s√=13 TeV with the ATLAS Detector at the LHC
No full textDark Matter composes a significant part of the Universe, while its physical nature remains unknown. This thesis presents two searches for Dark Matter produced in association with heavy Standard Model particles using pp collision data at a center-of-mass energy of s√=13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Moreover, jet mass scale calibrations for variable-radius calorimeter jets are performed to improve the reconstruction performance of heavy particles in boosted event topologies. A data sample corresponding to an integrated luminosity of 36.1 fb−1 is analyzed in the EmissT+V (hadronic) search, which selects processes with hadronic decays of W and Z bosons in association with large missing transverse energy. The EmissT+tt¯ (fully-hadronic) search is performed using 126.7 fb−1 of collision data and targets events containing fully-hadronically decaying top quark pairs and medium missing transverse energy. No significant excess over the Standard Model prediction is observed in both analyses. The results of the EmissT+V (hadronic) search are interpreted in terms of constraints on the parameter space of spin-1 vector mediator simplified model and mediator masses of up to 650 GeV are excluded for Dark Matter masses of up to 250 GeV at 95% confidence level with a dark sector coupling of 1.0 and a coupling to Standard Model particles of 0.25. The results of the EmissT+tt¯ (fully-hadronic) search are interpreted in the framework of spin-0 mediator simplified models with unitary couplings. For scalar and pseudo-scalar mediators, masses below 190 GeV and 240 GeV are excluded assuming a Dark Matter mass of 1 GeV, respectively. The implications of these results are discussed and compared to results from current direct detection experiments
Nonresonant Raman spectra of the methyl radical CH simulated in variational calculations
No full textWe report first-principles variational simulation of the non-resonant Raman spectrum for the methyl radical (CH) in the electronic ground state. Calculations are based on a high level ab initio potential energy and dipole moment surfaces of CH and employ the accurate variational treatment of the ro-vibrational dynamics implemented in the general code TROVE [S. N. Yurchenko, W. Thiel, and P. Jensen, J. Mol. Spectrosc. 245, 126–140 (2007); A. Yachmenev and S. N. Yurchenko, J. Chem. Phys. 143, 014105 (2015)]. TROVE can be applied to arbitrary molecules of moderate size and we extend here its capabilities towards simulations of Raman spectra. The simulations for CH are found to be in a good agreement with the available experimental data