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

Performance of the ATLAS hadronic Tile calorimeter

The Tile Calorimeter (TileCal) of the ATLAS experiment at the LHC is the central hadronic calorimeter designed for reconstruction of hadrons, jets, tau-particles and missing transverse energy. TileCal is a scintillator-steel sampling calorimeter and it covers the region of pseudorapidity < 1.7. The scintillation light produced in the scintillator tiles is transmitted by wavelength shifting fibers to photomultiplier tubes (PMTs). The analog signals from the PMTs are amplified, shaped and digitized by sampling the signal every 25 ns. The TileCal frontend electronics reads out the signals produced by about 10000 channels measuring energies ranging from ~30 MeV to ~2 TeV. Each stage of the signal production from scintillation light to the signal reconstruction is monitored and calibrated. The performance of the calorimeter has been studied in-situ employing cosmic ray muons and a large sample of proton-proton collisions acquired during the operations of the LHC. Prompt isolated muons of high momentum from electroweak bosons decays are employed to study the energy response of the calorimeter at the electromagnetic scale. The calorimeter response to hadronic particles is evaluated with a sample of isolated hadrons and the modelling of the response by the Monte Carlo simulation is discussed. The calorimeter timing calibration and resolutions are studied with jets. Results on the calorimeter operation and performance are presented, including the calibration, stability, absolute energy scale, uniformity and time resolution. These results show that the TileCal performance is within the design requirements and has given essential contribution to reconstructed objects and physics results

Study of the H→ττH \rightarrow \tau \tau decay channel with ATLAS

After the discovery of the Higgs boson, the precision measurements of its properties and comparison with the Standard Model (SM) predictions became the crucial part of the LHC physics programme. A potential observation of deviations may lead to the discovery of a new physics beyond the Standard Model (BSM). The direct observation of the coupling of the Higgs boson to leptons and its measurements is of particular importance. In this contribution, the results of analyses of the Higgs boson properties in H->tau tau decay channel are presented. The measurements of Higgs boson boson signal strength in the tau tau final state are shown

Higgs Physics at HL-LHC

The large dataset of about 3 ab-1 that will be collected at the High Luminosity LHC (HL-LHC) will be used to measure Higgs boson processes in detail. Studies based on current analyses have been carried out to understand the expected precision and limitations of these measurements. The large dataset will also allow for better sensitivity to di-Higgs processes and the Higgs boson self-coupling. This talk will present the prospects for Higgs and di-Higgs results at the HL-LHC

ATLAS Tile Calorimeter time calibration, monitoring and performance in Run 2

The Tile Calorimeter (TileCal) is the central section of the hadronic calorimeter of the ATLAS experiment at the LHC. This sampling device uses steel plates as an absorber and scintillating tiles as the active medium and its response is calibrated to the electromagnetic scale by means of several dedicated calibration systems. The accurate time calibration is important for energy reconstruction, non-collision background removal as well as for specific physics analyses. The initial time calibration using so-called splash events and subsequent fine-tuning with collision data are presented. The monitoring of the time calibration with laser system and physics collision data is discussed as well as the corrections for sudden changes performed still before the recorded data are processed for physics analyses. Finally, the time resolution as measured with jets in Run 2 is presented

Studies of the response of the ATLAS Tile Calorimeter to beams of particles at the CERN test beams facility

The Large Hadron Collider (LHC) Phase II upgrade aims to increase the accelerator instantaneous luminosity by a factor of 10. Due to the expected higher radiation levels, aging of the current electronics and to provide the capability of coping with longer latencies of up to 35 µs needed by the trigger system at such high pileup levels, a new readout system of the ATLAS Tile Calorimeter (TileCal) is needed. A prototype of the upgrade TileCal electronics has been tested using the beam from the Super Proton Synchrotron (SPS) accelerator at CERN. Data were collected in 2016-2018 with beams of muons, electrons aat various incident energies and impact angles. This presentation summarizes the setup for particle identification and study of the ATLAS Tile Calorimeter data taking in preparation for the production of main boards and digitizer/shaper boards for the photo-multiplier tubes and the results of the analysis of muons data, used to study the dependence of the response on the incident point and angle in the cell and of electron data, used to determine the linearity of the electromagnetic energy measurement