The sensitivities to anomalous quartic photon couplings at the Large Hadron Collider are estimated using diphoton production via photon fusion. The tagging of the protons proves to be a very powerful ...tool to suppress the background and unprecedented sensitivities down to 7 x 10 super(-15) GeV-4 are obtained, providing a new window on extra dimensions and strongly interacting composite states in the multi-TeV range. Generic contributions to quartic photon couplings from charged and neutral particles with arbitrary spin are also presented.
For the high luminosity upgrade of the LHC at CERN, ATLAS is considering the addition of a High Granularity Timing Detector (HGTD) in front of the end cap and forward calorimeters at |z|=3.5 m and ...covering the region 2.4<|η|<4 to help reducing the effect of pile-up. The chosen sensors are arrays of 50μm thin Low Gain Avalanche Detectors (LGAD). This paper presents results on single LGAD sensors with a surface area of 1.3×1.3 mm2 and arrays with 2×2 pads with a surface area of 2×2 mm2 or 3×3 mm2 each and different implant doses of the p+ multiplication layer. They are obtained from data collected during a beam test campaign in autumn 2016 with a pion beam of 120 GeV energy at the CERN SPS. In addition to several quantities measured inclusively for each pad, the gain, efficiency and time resolution have been estimated as a function of the position of the incident particle inside the pad by using a beam telescope with a position resolution of few μm. Different methods to measure the time resolution are compared, yielding consistent results. The sensors with a surface area of 1.3×1.3 mm2 have a time resolution of about 40 ps for a gain of 20 and of about 27 ps for a gain of 50 and fulfil the HGTD requirements. Larger sensors have, as expected, a degraded time resolution. All sensors show very good efficiency and time resolution uniformity.
Muons in the ATLAS detector are reconstructed by combining the information from the two tracking devices: the Inner Detector and the Muon Spectrometer (MS), located in the outermost part of the ...experiment. Until they reach the MS, muons traverse typically 100 radiation lengths (X0) of material, most part instrumented by the electromagnetic and hadronic calorimeters. The proper account for multiple scattering and energy loss effects is essential for the reconstruction and the use of the calorimeter measurement can improve the transverse momentum resolution, specially in case of high energy deposits. On the other hand, the calorimeter activity around a muon, or conversely its isolation, is one of the most powerful features to distinguish W and Z decays from semi-leptonic decays of heavy flavour mesons (containing b and c quarks). The principle of the software package that performs these tasks, called TrackInCaloTools is presented together with the expected performance in physics analyses.
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