Top Physics

Top quark physics forms a core part of the ATLAS physics program at the LHC. Its large mass implies a large coupling to the Higgs boson, which has led to think that it may play a special role in the mechanism of electroweak symmetry breaking. For the same reason, many models for new physics predict the existence of new particles that would preferentially couple to top quarks. It is therefore essential to measure with the highest possible precision the top quark properties and confront them with the Standard Model predictions, as well as perform direct searches for new physics in the production and decay of top quarks.

The Top Physics group at IFIC has taken important coordination responsibilities at both ATLAS and LHC levels, as: Convening the ATLAS Top Physics group (2011-2013), ATLAS Single Top subgroup (2014) and the LHC Top Working group (2013-2015).

Using Run-1 data, the group has led and pioneered various top quark precision measurements sensitive to new physics effects. It had a significant contribution to the measurement of the top quark mass, a fundamental parameter to test the consistency of the Standard Model and its extensions, as well as in the measurement of the top quark pair production cross section with tau leptons in the final state, especially sensitive to the presence of new particles such as a charged Higgs boson. The group has also led in ATLAS measurements of the top quark and W boson polarisation observables, sensitive to possible anomalous couplings in the Wtb vertex, using t-channel single top quark produced events. Such measurements are sensitive to CP violation effects in the top sector and have led to first limits on the complex phases of the coupling.

With the new data from Run-2 at a higher center-of-mass energy, in addition to pursuing high precision measurements, the group is now also focused on direct searches for new physics (as the search for dark matter candidates produced in association with top quarks).