Abstract
Measurements of the single top-quark production cross-sections with the AT- LAS detector in ppcollisions at the Large Hadron Collider (LHC) are presented. Results of measurements of single top-quark production in the t- and Wt-channel, as well as the determination of the CKM matrix element |Vtb| are shown. Further, the separate mea- surement of the top- and antitop-quark t-channel production cross-section and the ratio of the two are presented, and several searches for exotic processes in single top-quark production are discussed. The latter include results from searches for flavour changing neutral currents, extra heavy charged gauge bosons (W � ), excited quarks, and searches for anomalous CP-violating couplings in the Wtb vertex.
Highlights
At hadron colliders top-quarks are produced predominantly in the form of top- / antitop-quark pairs in strong interactions
To extract the signal cross-section a profile likelihood fit is applied to the boosted decision trees (BDTs) output resulting in an estimated cross-section of σWt = 16.8 ± 2.9 ± 4.9 pb, which provides the first evidence of single top-quark Wt-channel production at the Large Hadron Collider (LHC) with a significance of 3.3σ and 3.4σ
Single-top quark production has been observed with high significance in the t-channel in different analyses using the full 2011 and parts of the 2012 dataset, with measured cross-sections compatible to the theory predictions
Summary
At hadron colliders top-quarks are produced predominantly in the form of top- / antitop-quark (tt) pairs in strong interactions. In contrast to single top-quark production at the Tevatron, where the t- and s-channel productions occurred at similar rates and the Wt-channel had an expected cross-section too small to be observed, the LHC energy provides sensitivity to investigate all three production processes. Any deviation of the observed top-quark properties, the production cross-sections or of the unitarity of the CKM matrix from the SM prediction provides a strong indicator for new physics, such as the existence of fourth generation fermions or the production of extra heavy gauge boson. ATLAS is a multi-purpose detector composed of an inner tracking system close to the interaction point, surrounded by a superconducting solenoid which provides a 2 T axial magnetic field, electromagnetic (EM) and hadronic calorimeters, and a muon spectrometer within a 0.5 T magnetic field from three superconducting toroids [4]
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