The unprecedented intensity of x-ray free-electron laser sources has enabled single-particle x-ray diffraction imaging (SPI) of various biological specimens in both two-dimensional projection and ...three dimensions (3D). The potential of studying protein dynamics in their native conditions, without crystallization or chemical staining, has encouraged researchers to aim for increasingly higher resolutions with this technique. The currently achievable resolution of SPI is limited to the sub-10 nanometer range, mainly due to background effects, such as instrumental noise and parasitic scattering from the carrier gas used for sample delivery. Recent theoretical studies have quantified the effects of x-ray pulse parameters, as well as the required number of diffraction patterns to achieve a certain resolution, in a 3D reconstruction, although the effects of detector noise and the random particle orientation in each diffraction snapshot were not taken into account. In this work, we show these shortcomings and address limitations on achievable image resolution imposed by the adaptive gain integrating pixel detector noise.
Measurement of the luminosity in the ZEUS experiment at HERA II Adamczyk, L.; Andruszkow, J.; Bold, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2014, Letnik:
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The luminosity in the ZEUS detector was measured using photons from electron bremsstrahlung off protons. In 2001 the HERA collider was upgraded for operation at higher luminosity. At the same time ...the luminosity-measuring system of the ZEUS experiment was modified to tackle the expected higher photon rate and synchrotron radiation. The existing lead-scintillator calorimeter was equipped with radiation hard scintillator tiles and shielded against synchrotron radiation. In addition, a magnetic spectrometer was installed to measure the luminosity independently using photons converted in the beam-pipe exit window. The redundancy provided a reliable and robust luminosity determination with a systematic uncertainty of 1.7%. The experimental setup, the techniques used for luminosity determination and the estimate of the systematic uncertainty are reported.
The European X-ray Free Electron Laser (European XFEL) is a cutting-edge user facility that generates per second up to 27,000 ultra-short, spatially coherent X-ray pulses within an energy range of ...0.26 to more than 20 keV. Specialized instrumentation, including various 2D X-ray detectors capable of handling the unique time structure of the beam, is required. The one-megapixel AGIPD (AGIPD1M) detectors, developed for the European XFEL by the AGIPD Consortium, are the primary detectors used for user experiments at the SPB/SFX and MID instruments. The first AGIPD1M detector was installed at SPB/SFX when the facility began operation in 2017, and the second one was installed at MID in November 2018. The AGIPD detector systems require a dedicated infrastructure, well-defined safety systems, and high-level control procedures to ensure stable and safe operation. As of now, the AGIPD1M detectors installed at the SPB/SFX and MID experimental end stations are fully integrated into the European XFEL environment, including mechanical integration, vacuum, power, control, data acquisition, and data processing systems. Specific high-level procedures allow facilitated detector control, and dedicated interlock systems based on Programmable Logic Controllers ensure detector safety in case of power, vacuum, or cooling failure. The first 6 years of operation have clearly demonstrated that the AGIPD1M detectors provide high-quality scientific results. The collected data, along with additional dedicated studies, have also enabled the identification and quantification of issues related to detector performance, ensuring stable operation. Characterization and calibration of detectors are among the most critical and challenging aspects of operation due to their complex nature. A methodology has been developed to enable detector characterization and data correction, both in near real-time (online) and offline mode. The calibration process optimizes detector performance and ensures the highest quality of experimental results. Overall, the experience gained from integrating and operating the AGIPD detectors at the European XFEL, along with the developed methodology for detector characterization and calibration, provides valuable insights for the development of next-generation detectors for Free Electron Laser X-ray sources.
High-precision HERA data corresponding to a luminosity of around 1 fb−1 have been used in the framework of eeqq contact interactions (CI) to set limits on possible high-energy contributions beyond ...the Standard Model to electron-quark scattering. Measurements of the inclusive deep inelastic cross sections in neutral and charged current ep scattering were considered. The analysis of the ep data has been based on simultaneous fits of parton distribution functions including contributions of CI couplings to ep scattering. Several general CI models and scenarios with heavy leptoquarks were considered. Improvements in the description of the inclusive HERA data were obtained for a few models. Since a statistically significant deviation from the Standard Model cannot be established, limits in the TeV range were set on all models considered.
At large values of x , the parton distribution functions (PDFs) of the proton are poorly constrained and there are considerable variations between different global fits. Data at such high x have ...already been published by the ZEUS Collaboration, but not yet used in PDF extractions. A technique for comparing predictions based on different PDF sets to the observed number of events in the ZEUS data is presented. It is applied to compare predictions from the most commonly used PDFs to published ZEUS data at high Bjorken x . A wide variation is found in the ability of the PDFs to predict the observed results. A scheme for including the ZEUS highx data in future PDF extractions is discussed.
The photoproduction of isolated photons has been measured in diffractive events recorded by the ZEUS detector at HERA. Cross sections are evaluated in the photon transverse-energy and pseudorapidity ...ranges 5<ETγ<15 GeV and −0.7<ηγ<0.9, inclusively, and also with a jet with transverse energy and pseudorapidity in the ranges 4<ETjet<35 GeV and −1.5<ηjet<1.8, using a total integrated electron-proton luminosity of 456 pb−1. A number of kinematic variables were studied and compared to predictions from the rapgap Monte Carlo model. An excess of data is observed above the rapgap predictions for zPmeas>0.9, where zPmeas is the fraction of the longitudinal momentum of the colorless “Pomeron” exchange that is transferred to the photon-jet final state, giving evidence for direct Pomeron interactions.
Events with two or more leptons (electrons or muons) with high transverse momentum are measured in electron-proton collisions at HERA using the data samples collected in the period 1994-2007. Yields ...of di-lepton and tri-lepton events are investigated and a general good agreement is found with the Standard Model (SM) prediction. Multi-lepton events at high transverse momenta, where the SM prediction is low, are of special interest as these signature might reveal new physics beyond the Standard Model. An example is the single production of a doubly-charged Higgs boson (H±±) decaying into a high mass pair of same charge leptons. This possibility has been investigated and H±± decays involving electrons, muons and taus are considered. No evidence for doubly-charged Higgs production is observed and mass-dependent upper limits are derived on the Yukawa couplings hij of the Higgs boson to leptons of flavour i and j.
Production of exclusive dijets in diffractive deep inelastic Formula omitted scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 372 pb Formula omitted. The ...measurement was performed for Formula omitted-p centre-of-mass energies in the range Formula omitted and for photon virtualities Formula omitted. Energy flows around the jet axis are presented. The cross section is presented as a function of Formula omitted and Formula omitted, where Formula omitted, x is the Bjorken variable and Formula omitted is the proton fractional longitudinal momentum loss. The angle Formula omitted is defined by the Formula omitted-dijet plane and the Formula omitted- Formula omitted plane in the rest frame of the diffractive final state. The Formula omitted cross section is measured in bins of Formula omitted. The results are compared to predictions from models based on different assumptions about the nature of the diffractive exchange.
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