For the EU-funded team, discovery of the Higgs boson by the ATLAS and compact muon solenoid experiments at the European Organization for Nuclear Research (CERN) was the beginning of a quest to find out what the new particle was. An important property that they tried to determine was how it decays. Theory predicts that the Higgs boson lives only for a short time and disintegrates into several types of elementary particles. So far, decays into different types of gauge bosons ─ elementary particles that carry forces ─ were well established. The other family of particles, the fermions, make up the matter. According to the standard model of particle physics, fermions (like taus, electrons and quarks) acquire mass in the same manner as bosons, the Brout-Englert-Higgs mechanism. The Higgs boson could, therefore, decay directly to either bosons or fermions. During the ATLASHIGGS2TAUS (ATLAS Higgs to taus) project, results from the ATLAS experiment showed that the Higgs boson does indeed decay into tau leptons. This important finding was made possible through careful analysis of data produced by the 2010-2012 running of the Large Hadron Collider. However, only with new data will it be possible to determine if the compatibility remains or if another theoretical model is needed. The next Large Hadron Collider run began in 2015 and is expected to produce several times more existing data than the first run. ATLASHIGGS2TAUS physicists have contributed to the maintenance of the tau lepton reconstruction software used for the analysis of ATLAS measurements that ensured a smooth resumption of efforts. All the work was carried out within the ATLAS collaboration, an international collaboration of physicists from 38 countries.
Higgs boson, Large Hadron Collider, tau leptons, fermions, ATLAS experiment