First observation of top quarks in heavy ion collisions
"The analysis was motivated by a theoretical paper co-authored by LIP researchers that proposes a unique method to study the time evolution of the quark gluon plasma"
The CMS experiment announced the first observation of top quark in lead-ion collisions (PbPb) at the LHC. The paper has just been accepted for publication in Physical Review Letters. The analysis was motivated by a recent theoretical study showing how this channel may be unique for achieve differential measurements that allow to probe the evolution of the quark gluon plasma, in contrast with the current observables that are averaged over time. The researchers Guilherme Milhano and Liliana Apolinário, from the LIP Phenomenology group, sign this study, developed in collaboration with researchers from Santiago de Compostela and CERN.
"Faster-moving top quarks provide later-time snapshots. By assembling snapshots taken with top quarks at a range of different speeds, we hope that it will eventually be possible to create a movie of the quark–gluon plasma’s evolution,” explains CERN-based researcher Guilherme Milhano, who co-authored a theoretical study on probing the quark–gluon plasma with top quarks. “The new CMS result represents the very first step down that road.”
The CMS collaboration saw evidence of top quarks in a large data sample from lead–lead collisions at an energy of 5.02 TeV. The team searched for collisions producing a top quark and a top antiquark. These quarks decay very quickly into a W boson and a b quark, which in turn rapidly decay into other particles. In the CMS analysis events were selected in which the final decay products are electrons or muons and jets of particles originating from b quarks.