ATLAS

Abstract:

The ASICs for the Phase 2 upgrade of the ATLAS and CMS pixel detectors have been jointly designed by the RD53 collaboration in 65 nm CMOS technology. One of the main design requirements of the ASICs was their ability to withstand an environment with unprecedented radiation doses, up to total ionzing doses (TID) of 1 Grad, delivered at a dose rate of around 20 krad/h. From simulation of the ASIC, the main limiting factor of the ASIC design is expected to be the small transistors used in the digital logic. As part of the ASIC characterization program, many dedicated irradiation measurements have been performed on ring oscillator circuits included in the chip for testing. This paper aims to summarize the main findings of these irradiation measurements, performed at the expected operational temperatures of the ASIC around −10 °C. First, the dose rate dependence of the damage to the digital logic is characterized in X-ray irradiations to low TID with varying dose rates. Then, results from X-ray irradiations and a long-term low dose rate irradiation using a Kr-85 source are compared, to estimate the expected damage at high TID delivered at a low dose rate. Finally, the combination of these measurements is used to predict the expected failure of the ASIC in terms of integrated luminosity collected by the ATLAS experiment, assuming the expected total ionizing doses for both the innermost layers in Barrel and Endcap of the upgraded ATLAS Inner Tracker (ITk).

Abstract:

Abstract A parametric simulation tool for pixel sensors is presented. A realistic pixel response is simulated purely based on measurement input, without requiring detailed knowledge of the underlying manufacturing process. As such, it provides an efficient alternative to the use of Technology Computer-Aided Design simulations, which typically depend on proprietary process information. Due to its parametric approach, the package is fast and thus particularly useful for larger detector systems and high hit rate environments. This work presents measurements, simulation and its validation for the MALTA2 sensor. It is a small collection electrode monolithic active pixel sensor produced in the Tower 180 nm complementary metal-oxide-semiconductor imaging process. Modifications to the sensor’s periphery, mainly in the hit merger, are studied in order to optimize the performance for tracking and calorimetry. This optimization is of special interest as part of the MALTA3 sensor redesign in the 65 nm Tower Partners Semiconductor Co. process.

Abstract:

A search is presented for emerging jets using 140fb-1$$140~\textrm{fb}^{-1}$$ of proton–proton collision data at s=13TeV$$\sqrt{s} = 13~\textrm{TeV}$$, collected by the ATLAS experiment between 2015 and 2018. The search looks for the existence of a dark sector with symmetries similar to those in quantum chromodynamics. This dark sector is populated with dark quarks, which undergo showering similar to quarks in the Standard Model, leading to a high multiplicity of long-lived dark hadrons within a dark jet. These dark hadrons subsequently decay to Standard Model particles via a new heavy scalar mediating particle ϕ$$\phi $$. This results in jets which contain multiple displaced vertices, known as emerging jets. This analysis targets four-jet topologies, with two emerging jets and two Standard Model jets, resulting from the decay of pair-produced scalar mediators. No significant excess above the Standard Model background is observed. For dark pion proper decay lengths of 20mm$$20~\textrm{mm}$$, mediator masses are excluded between 1 and 2TeV$$2~\textrm{TeV}$$ assuming a dark pion mass of 20GeV$$20~\textrm{GeV}$$.

Abstract:

Events with t-channel single top quarks are used to probe effective field theory operators in s=13$$ \sqrt{s}=13 $$ TeV proton–proton collision data corresponding to 140 fb−1 recorded by the ATLAS detector at the Large Hadron Collider. To extract a maximum amount of information from these events, the joint fourfold probability distribution for four kinematic angles is simultaneously analysed. A method leveraging Fourier techniques to handle the challenges arising from this approach is employed. The relevant effective field theory operators are those sensitive to top-quark decay and t-channel production vertices. Their Wilson coefficients are tightly constrained, with results compatible with Standard Model predictions.

Abstract:

A combination of measurements of the $CP$ properties of Higgs boson interactions with electroweak gauge bosons is presented, using $140{\mathrm{fb}}^{-1}$ of proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ recorded by the ATLAS detector. Results from vector boson fusion $H\to \tau \tau /W{W}^{*}/\gamma \gamma$ , inclusive $H\to Z{Z}^{*}$ , and $WH,H\to b\overline{b}$ channels are combined. No evidence of $CP$ violation is observed, and constrains on the $CP$ -violating operators in the Standard Model effective field theory framework (SMEFT) are set in the Warsaw basis. The results from the combination improve by over 40% on previous individual limits on $c_{H\tilde{W}}$ and, for the first time, simultaneous constraints on three coefficients $c_{H\tilde{W}}$ , $c_{H\tilde{B}}$ , and $c_{H\tilde{W}B}$ are set. These limits are the most stringent constraints to date on the relevant Wilson coefficients in the SMEFT framework with minimum model dependence.