Probing physics beyond the Standard Model with the ATLAS Experiment

Figure 1: The reconstructed mass of the selected candidate events decaying to WW or ZZ bosons, with the qqqq final state. The black markers represent the data. The blue and green curves represent the hypothesized signal for two different masses. The red curve represents the Standard Model processes. Credit: ATLAS Collaboration/CERN

Although the discovery of the Higgs boson by the ATLAS and CMS Collaborations in 2012 completed the Standard Model, many mysteries remain unexplained. For instance, why is the mass of the Higgs boson so much lighter than expected, and why is gravity so weak?

Numerous models beyond the Standard Model attempt to explain these mysteries. Some explain the apparent weakness of gravity by introducing additional dimensions of space in which gravity propagates. One goes beyond that, and considers the real world as a higher-dimensional universe described by warped geometry, which leads to strongly interacting massive graviton states. Other models propose, for example, additional types of Higgs bosons.

All these models predict the existence of new heavy that can decay into pairs of massive weak bosons (WW, WZ or ZZ). The search for such particles has benefited greatly from the increase in the proton–proton collision energy during Run 2 of the Large Hadron Collider (LHC).

The W and Z bosons are carrier particles that mediate the weak force. They decay into other Standard Model particles, like charged leptons (l), neutrinos (ν) and quarks (q). These particles are reconstructed differently in the detector. Quarks, for instance, are reconstructed as localized sprays of hadrons, denoted jets. The two bosons could yield several combinations of these particles in the final states. The ATLAS Collaboration has released results on searches…

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