Engineering topics
Publications and source records attributed to Alonso, A..
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Silicon pixel detectors are at the core of the current and planned upgrade of the ATLAS experiment at the LHC. Given their close proximity to the interaction point, these detectors will be exposed to an unprecedented amount of radiation over their lifetime. The current pixel detector will receive damage from non-ionizing radiation in excess of 10 15 1 MeV n eq /cm 2 , while the pixel detector designed for the high-luminosity LHC must cope with an order of magnitude larger fluence. We present a digitization model incorporating effects of radiation damage to the pixel sensors. The model is described in detail and predictions for the charge collection efficiency and Lorentz angle are compared with collision data collected between 2015 and 2017 (≤ 10 15 1 MeV n eq /cm 2 ).
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The optimized superconducting stellarator device Wendelstein 7-X (with major radius R = 5.5 m, minor radius $a$ = 0.5 m, and 30 m 3 plasma volume) restarted operation after the assembly of a graphite heat shield and 10 inertially cooled island divertor modules. This paper reports on the results from the first high-performance plasma operation. Glow discharge conditioning and ECRH conditioning discharges in helium turned out to be important for density and edge radiation control. Plasma densities of 1–4.5 × 10 19 m –3 with central electron temperatures 5–10 keV were routinely achieved with hydrogen gas fueling, frequently terminated by a radiative collapse. In a first stage, plasma densities up to 1.4 × 10 20 m –3 were reached with hydrogen pellet injection and helium gas fueling. Here, the ions are indirectly heated, and at a central density of 8 · 10 19 m –3 a temperature of 3.4 keV with $T_e/T_i$ = 1 was transiently accomplished, which corresponds to $nT_i(0)τ_E =$ 6.4 × 10 19 keV s m –3 with a peak diamagnetic energy of 1.1 MJ and volume-averaged normalized plasma pressure $\langleβ\rangle$ = 1.2%. The routine access to high plasma densities was opened with boronization of the first wall. After boronization, the oxygen impurity content was reduced by a factor of 10, the carbon impurity content by a factor of 5. The reduced (edge) plasma radiation level gives routinely access to higher densities without radiation collapse, e.g. well above 1 × 10 20 m –2 line integrated density and $T_e = T_i =$ 2 keV central temperatures at moderate ECRH power. Both X2 and O2 mode ECRH schemes were successfully applied. Core turbulence was measured with a phase contrast imaging diagnostic and suppression of turbulence during pellet injection was observed.
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A search for singly produced vector-like quarks Q , where Q can be either a T quark with charge +2/3 or a Y quark with charge ₋4/3, is performed in proton–proton collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 36.1 fb ₋1 , recorded with the ATLAS detector at the LHC in 2015 and 2016. The analysis targets Q → Wb decays where the W boson decays leptonically. No crtical deviation from the expected Standard Model background is observed. Upper limits are set on the QWb coupling strength and the mixing between the Standard Model sector and a singlet T quark or a Y quark from a ( B, Y ) doublet or a ( T, B, Y ) triplet, taking into account the interference effects with the Standard Model background. The upper limits set on the mixing angle are as small as |sin θ L | = 0.18 for a singlet T quark of mass 800 GeV, |sin θ R | = 0.17 for a Y quark of mass 800 GeV in a ( B, Y ) doublet model and |sin θL| = 0.16 for a Y quark of mass 800 GeV in a ( T, B, Y ) triplet model. Within a ( B, Y ) doublet model, the limits set on the mixing parameter |sin θ R | are comparable with the exclusion limits from electroweak precision observables in the mass range between about 900 GeV and 1250 GeV.
Cross-sections of associated production of a Higgs boson decaying into bottomquark pairs and an electroweak gauge boson, W or Z , decaying into leptons are measured as a function of the gauge boson transverse momentum. The measurements are performed in kinematic fiducial volumes defined in the ‘simplified template cross-section’ framework. The results are found using 79.8 fb ₋1 of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. All measurements are found to be in agreement with the Standard Model predictions, and limits are set on the parameters of an effective Lagrangian sensitive to modifications of the Higgs boson couplings to the electroweak gauge bosons.
Constraints on selected mediator-based dark matter models and a scalar dark energy model using up to 37 fb ₋1 $\sqrt{s}$ = 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015-2016 are summarised in this paper. The conclusions of experimental searches in a variety of final states are interpreted in terms of a set of spin-1 and spin-0 single-mediator dark matter simplified models and a second set of models involving an extended Higgs sector plus an additional vector or pseudo-scalar mediator. The searches considered in this paper constrain spin-1 leptophobic and leptophilic mediators, spin-0 colour-neutral and colour-charged mediators and vector or pseudo-scalar mediators embedded in extended Higgs sector models. In this case, also $\sqrt{s}$ = 8 TeV pp collision data are used for the interpretation of the results. The results are also interpreted for the first time in terms of light scalar particles that could contribute to the accelerating expansion of the universe (dark energy).