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Background Rejection in Atmospheric Cherenkov Telescopes using Recurrent Convolutional Neural Networks
No full textIn this work, we present a new, high performance algorithm for background rejection in imaging atmospheric Cherenkov telescopes. We build on the already popular machine-learning techniques used in gamma-ray astronomy by the application of the latest techniques in machine learning, namely recurrent and convolutional neural networks, to the background rejection problem. Use of these machine-learning techniques addresses some of the key challenges encountered in the currently implemented algorithms and helps to significantly increase the background rejection performance between 100 GeV and 100 TeV energies. We apply these machine learning techniques to the H.E.S.S. telescope array, first testing their performance on simulated data and then applying the analysis to two well known gamma-ray sources. With real observational data we find significantly improved performance over the current standard methods, with a 20–25% reduction in the background rate when applying the recurrent neural network analysis. Importantly, we also find that the convolutional neural network results are strongly dependent on the sky brightness in the source region which has important implications for the future implementation of this method in Cherenkov telescope analyses
Beam Halo and Bunch Purity Monitoring
No full textBeam halo measurements imply measurements of beam profiles with a very high dynamic range; in transverse and also longitudinal planes. This lesson gives an overview of high dynamic range instruments for beam halo measurements. In addition halo definitions and quantifications in view of beam instrumentation are discussed
Megahertz single-particle imaging at the European XFEL
No full textThe emergence of high repetition-rate X-ray free-electron lasers (XFELs) powered by superconducting accelerator technology enables the measurement of significantly more experimental data per day than was previously possible. The European XFEL is expected to provide 27,000 pulses per second, over two orders of magnitude more than any other XFEL. The increased pulse rate is a key enabling factor for single-particle X-ray diffractive imaging, which relies on averaging the weak diffraction signal from single biological particles. Taking full advantage of this new capability requires that all experimental steps, from sample preparation and delivery to the acquisition of diffraction patterns, are compatible with the increased pulse repetition rate. Here, we show that single-particle imaging can be performed using X-ray pulses at megahertz repetition rates. The results obtained pave the way towards exploiting high repetition-rate X-ray free-electron lasers for single-particle imaging at their full repetition rate
Measurement of differential cross sections and charge ratios for -channel single top quark production in proton-proton collisions at 13 TeV
No full textA measurement is presented of differential cross sections for t-channel single top quark and antiquark production in proton–proton collisions at a centre-of-mass energy of 13 by the CMS experiment at the LHC. From a data set corresponding to an integrated luminosity of 35.9, events containing one muon or electron and two or three jets are analysed. The cross section is measured as a function of the top quark transverse momentum (), rapidity, and polarisation angle, the charged lepton and rapidity, and the of the boson from the top quark decay. In addition, the charge ratio is measured differentially as a function of the top quark, charged lepton, and boson kinematic observables. The results are found to be in agreement with standard model predictions using various next-to-leading-order event generators and sets of parton distribution functions. Additionally, the spin asymmetry, sensitive to the top quark polarisation, is determined from the differential distribution of the polarisation angle at parton level to be , in agreement with the standard model prediction
Search for Higgs bosons in the final state with b-quarks in the semi-leptonic channel with the CMS 2017 data
No full textThe existence of several neutral Higgs states is predicted in many models comprising an enlargement of the Standard Model (SM) scalar sector, notably the general Two-Higgs-Doublet Model (2HDM) and the Minimal Supersymmetric Extension of the Standard Model (MSSM). Many of these scenarios predict an enhancement of the coupling of the neutral Higgs bosons to bottom quarks. A search for neutral Higgs bosons decaying into a -quark pair in the semi-leptonic channel and produced in association with at least an additional bottom quark at the LHC is presented. The corresponding data sample was collected at CMS during proton-proton collisions in 2017 at a centre-of-mass energy of TeV corresponding to an integrated luminosity of 36.5 . In the final state, a muon must lie within the cone of any of the two most energetic b-jets in the event. The latter are initiated from the partons stemming from the Higgs boson decay. The soft muon requirement drives down considerably the trigger rates, allowing to probe Higgs bosons with masses as low as 125 GeV. The observed di-jet invariant mass distribution is compatible with the background-only prediction of the Standard Model. Therefore, stringent exclusion limits are extracted on the production cross-section times branching fraction of the signal process for Higgs boson masses ranging up to 700 GeV. The exclusion limits are further translated into the parameter space of several MSSM and 2HDM benchmark scenarios
Photoionization of low-charged silicon ions
No full textSingle and multiple photoionization of Si1+, Si2+, and Si3+ ions have been investigated near thesilicon K-edge using the PIPE setup at beamline P04 of the synchrotron light source PETRA III operated byDESY in Hamburg, Germany. Pronounced resonance structures are observed for all ions which are associatedwith excitation or ionization of a K-shell electron. The experimental cross sections are compared with resultsfrom theoretical calculations
Role of V-V dimerization in the insulator-metal transition and optical transmittance of pure and doped thin films
No full textTheoretical uncertainties in the MSSM Higgs boson mass calculation
No full textThe remaining theoretical uncertainties from unknown higher-order corrections in the prediction for the light Higgs-boson mass of the MSSM are estimated. The uncertainties associated with three different approaches that are implemented in the publicly available code FeynHiggs are compared: the fixed-order diagrammatic approach, suitable for low SUSY scales, the effective field theory (EFT) approach, suitable for high SUSY scales, and the hybrid approach which combines the fixed-order and the EFT approaches. It is demonstrated for a simple single-scale scenario that the result based on the hybrid approach yields a precise prediction for low, intermediate and high SUSY scales with a theoretical uncertainty of up to for large stop mixing and for small stop mixing. The uncertainty estimate of the hybrid calculation approaches the uncertainty estimate of the fixed-order result for low SUSY scales and the uncertainty estimate of the EFT approach for high SUSY scales, while for intermediate scales it is reduced compared to both of the individual results. The estimate of the theoretical uncertainty is also investigated in scenarios with more than one mass scale. A significantly enhanced uncertainty is found in scenarios where the gluino is substantially heavier than the scalar top quarks. The uncertainty estimate presented in this paper will be part of the public code FeynHiggs