Performance of the ATLAS Liquid Argon Calorimeter after three years of LHC operation and plans for a future upgrade

The ATLAS experiment is designed to study the proton-proton collisions produced at the Large Hadron Collider (LHC) at CERN. Liquid argon sampling calorimeters are used for all electromagnetic calorimetry as well as hadronic calorimetry in the endcaps. After installation in 2004--2006, the calorimeters were extensively commissioned over the three--year period prior to first collisions in 2009, using cosmic rays and single LHC beams. Since then, approximately 27 fb$\mathbf{^{-1}}$ of data have been collected at an unprecedented center of mass energy. During all these stages, the calorimeter and its electronics have been operating almost optimally, with a performance very close to specifications. This paper covers all aspects of these first years of operation. The excellent performance achieved is especially presented in the context of the discovery of the elusive Higgs boson. The future plans to preserve this performance until the end of the LHC program are also presented.Comment: 12 pages, 25 figures, Proceedings of talk presented in "Advancements in Nuclear Instrumentation Measurement Methods and their Applications", Marseille, 201

Search for Non-Pointing Photons in the Diphoton and Missing Transverse Energy Final State in 7 TeV pp Collisions Using the ATLAS Detector

A search for photons originating in the decay of a neutral long-lived particle produced in proton-proton collisions at sqrt(s) = 7 TeV is presented. The search was performed in the diphoton plus missing transverse energy final state, using the full data sample of 4.8 fb-1 of 7 TeV proton-proton collisions collected in 2011 with the ATLAS detector at the CERN Large Hadron Collider. The analysis exploits the capabilities of the ATLAS electromagnetic calorimeter to make precise measurements of the flight direction of photons, and utilizes the excellent time resolution of the calorimeter as an independent cross-check of the results. The search was conducted in the context of Gauge Mediated Supersymmetry Breaking models, where the lightest neutralino is the next-to-lightest supersymmetric particle and has a finite lifetime. In the family of models investigated, supersymmetric particles are produced in pairs due to R-parity conservation, eventually decaying to a pair of neutralinos, each subsequently decaying to a photon and a gravitino. The gravitinos escape the detector, giving rise to missing energy, while the photons can appear not to originate from the primary vertex of the event, and are measured with a delay with respect to the collision time. No excess was observed above the background expected from Standard Model processes. The results were used to set exclusion limits at 95% CL in the two-dimensional parameter space defined by the supersymmetry breaking scale and the lifetime of the lightest neutralino

Novel interpretation strategy for searches of singly produced vectorlike quarks at the LHC

Vectorlike quarks (VLQs) are potential signatures of physics beyond the standard model at the TeV energy scale, and major effort has been put forward at both the ATLAS and CMS experiments to search for these particles. To make these search results more relatable in the context of most plausible theories of VLQs, it is deemed important to present the analysis results in a general fashion. We investigate the challenges associated with such interpretations of singly produced VLQ searches and propose a generalized, semianalytical framework that allows for a model-independent casting of the results in terms of unconstrained free parameters of the VLQ Lagrangian. We also propose a simple parametrization of the correction factor to the single VLQ production cross section at large decay widths. We illustrate how the proposed framework can be used to conveniently represent statistical limits by numerically reinterpreting results from benchmark ATLAS and CMS analyses.The work of A. R., N. N., and T. A. is supported by the U.S. Department of Energy, Office of High Energy Physics, under Grant No. DE-SC0007890. N. C. acknowledges the support by FCT-Portugal, through Project No. CERN/FISPAR/0024/2019.info:eu-repo/semantics/publishedVersio

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

The ECFA Early-Career Researchers Panel: Report for the year 2023

The European Committee for Future Accelerators (ECFA) Early-Career Researcher (ECR) panel, which represents the interests of the ECR community to ECFA, presents in this document its initiatives and activities in the year 2023. This report summarises the process of the first big turnover in the panel composition at the start of 2023 and reports on the activities of the active working groups - either pursued from before or newly established. The overarching goal of the ECFA-ECR panel is to better understand and support the diverse interests of early-career researchers in the ECFA community and beyond.Editors: Jan-Hendrik Arling, Cecilia Borca, Armin Ilg, Arnau Morancho Tarda, Holly Pacey, Marko Pesut, Elisabetta Spadaro Norella and Marta Urbaniak. arXiv admin note: substantial text overlap with arXiv:2212.1123

ATLAS Run 1 searches for direct pair production of third-generation squarks at the Large Hadron Collider

This paper reviews and extends searches for the direct pair production of the scalar supersymmetric partners of the top and bottom quarks in proton-proton collisions collected by the ATLAS collaboration during the LHC Run 1. Most of the analyses use 20 fb$^{-1}$ of collisions at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV, although in some case an additional 4.7 fb$^{-1}$ of collision data at $\sqrt{s}$ = 7 TeV are used. New analyses are introduced to improve the sensitivity to specific regions of the model parameter space. Since no evidence of third-generation squarks is found, exclusion limits are derived by combining several analyses and are presented in both a simplified model framework, assuming simple decay chains, as well as within the context of more elaborate phenomenological supersymmetric models

Searches for Vector-Like Quarks and Leptoquarks Decaying to Tops in ATLAS and CMS

This talk contains a summary of recent analyses performed by the ATLAS and CMS collaborations, searching for Vector-Like Quarks and Leptoquarks decaying to top quarks

The Phase-I Trigger Readout Electronics Upgrade of the ATLAS Liquid Argon Calorimeters

Electronics developments are pursued for the trigger readout of the ATLAS Liquid-Argon Calorimeter towards the Phase-I upgrade scheduled in the LHC shut-down period of 2019-2020. Trigger signals with higher spatial granularity and higher precision are needed in order to improve the identification efficiencies of electrons, photons, tau, jets and missing energy, at high background rejection rates, already at the Level-1 trigger. The LAr Trigger Digitizer system will digitize the 34,000 channels (SuperCells) at a 40 MHz sampling frequency with 12 bit precision after the bipolar shaping of the front-end system. The data will be transmitted to the LAr Digital Processing system in the back-end to extract the transverse energies and perform the bunch-crossing identification. A demonstrator has been installed during Run-2, and the results of the data-taking have helped to validate the chosen technology. Results of ASIC developments including QA/QC and radiation hardness evaluations, performances of the pre-production boards and results of the system integration tests, progress of QA/QC of final production boards will be presented along with the overall system design