Hadronic Shower Development in Tile Iron-Scintillator Calorimetry

The lateral and longitudinal profiles of hadronic showers detected by a prototype of the ATLAS Iron-Scintillator Tile Hadron Calorimeter have been investigated. This calorimeter uses a unique longitudinal configuration of scintillator tiles. Using a fine-grained pion beam scan at 100 GeV, a detailed picture of transverse shower behavior is obtained. The underlying radial energy densities for four depth segments and for the entire calorimeter have been reconstructed. A three-dimensional hadronic shower parametrization has been developed. The results presented here are useful for understanding the performance of iron-scintillator calorimeters, for developing fast simulations of hadronic showers, for many calorimetry problems requiring the integration of a shower energy deposition in a volume and for future calorimeter design

Probe of soft-QCD in minimum bias events of pp collisions with the ATLAS at the LHC

The study of the minimum-bias charged-particle distributions is reviewed. The data are obtained using the ATLAS detector at the LHC in proton-proton collisions at the centre-of-mass energies from 0.9 to13 TeV. The particles are required to have an absolute pseudorapidity less than 2.5. For charged-particle distributions study two transverse momentum thresholds cases, greater than 100 MeV and 500 MeV were taken. The charged-particle multiplicity, its dependence on the transverse momentum and pseudorapidity, dependence of the average transverse momentum on the charged-particle multiplicity and the KNO-scaling study are presented. The measured distributions are compared with the predictions of various tunings of Monte Carlo generator, which implement different minimum-bias models.The Monte Carlo model predictions qualitatively describe the data well, but with some significant discrepancies. Measurements of minimum-bias events by the ALICE and CMS Collaborations are presented.Comment: 73 pages, 51 figures, 7 table

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