2,959 research outputs found

    ATLAS data quality operations and performance for 2015-2018 data-taking

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    Art铆culo escrito por un elevado n煤mero de autores, solo se referencian el que aparece en primer lugar, los autores pertenecientes a la UAM y el nombre del grupo de colaboraci贸n, si lo hubiereThe ATLAS detector at the Large Hadron Collider reads out particle collision data from over 100 million electronic channels at a rate of approximately 100 kHz, with a recording rate for physics events of approximately 1 kHz. Before being certified for physics analysis at computer centres worldwide, the data must be scrutinised to ensure they are clean from any hardware or software related issues that may compromise their integrity. Prompt identification of these issues permits fast action to investigate, correct and potentially prevent future such problems that could render the data unusable. This is achieved through the monitoring of detector-level quantities and reconstructed collision event characteristics at key stages of the data processing chain. This paper presents the monitoring and assessment procedures in place at ATLAS during 2015-2018 data-taking. Through the continuous improvement of operational procedures, ATLAS achieved a high data quality efficiency, with 95.6% of the recorded proton-proton collision data collected at s=13 TeV certified for physics analysi

    Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb鈭1 of pp collisions at s=13TeV with the ATLAS experiment

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    A search for flavour-changing neutral current (FCNC) events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81 fb鈭1 of proton鈥損roton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a b-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the tq纬 coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC t纬 production via a left-handed (right-handed) tu纬 coupling of 36 fb (78 fb) and on the branching ratio for t鈫捨硊 of 2.8脳10鈭5 (6.1脳10鈭5). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC t纬 production via a left-handed (right-handed) tc纬 coupling of 40 fb (33 fb) and on the branching ratio for t鈫捨砪 of 22脳10鈭5 (18脳10鈭5)