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ATLAS Experiment at LHC: the Higgs Boson, Still Unique

Physicists from IRFU have announced that no "big brother" of the Higgs boson has been detected at the ATLAS experiment at CERN's LHC. Their results rely on new analyzes with higher sensitivity.
Published on 29 August 2017

Exploitation of the data provided by the LHC at 13 teraelectronvolts (1012 eV) between 2015 and 2016 shows the absence of a more massive particle similar to the Higgs boson.

A team of scientists from IRFU has focused on the search for an additional Higgs boson from its hypothetical decay into two Z bosons, which also disappear, generating either four leptons or two leptons and two neutrinos. These events are selected among all recorded collisions. For each of them, the mass of the initial particle is reconstructed from those of the particles in the final state. If the mass is random, the final state cannot be the result of a single particle. In this case, the result is interpreted as an upper limit of absence of the particle sought.

In particular, physicists from IRFU have developed a heavy Higgs boson model with a mass distribution that is "wide" instead of "narrow". This mass can reach from 1 to 10% of the mass of the particles, which is typically hundreds of gigaelectronvolts. In this case, the analysis must take into account various quantum interferences, especially between the standard Higgs boson and its big brother. For the first time, they were able to refine the analysis of experimental data using this model.

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