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The measured mass of the Higgs boson implies that the symmetry-breaking vacuum is metastable. Cosmologists are trying to understand the symmetry-breaking Higgs phase transition, which took place early in the history of the universe, and whether that event explains the excess of matter over antimatter. Now that the Higgs boson (or something much like it) has been found at the Large Hadron Collider (LHC see Physics Today, September 2012, page 12), particle experimentalists are searching for more kinds of Higgs bosons and working to find out if the Higgs boson interacts with the dark matter that holds the universe together. And just as a particular glucose orientation breaks an underlying rotation symmetry, a nonvanishing vacuum expectation value of the Higgs boson field, as we will describe, breaks symmetries that would otherwise forbid masses for elementary particles. But in quantum field theory, the ground state, or vacuum, behaves like a many-body system. The study, titled " Search for nonresonant pair production of highly energetic Higgs bosons decaying to bottom quarks," was funded by the Department of Energy's Office of Science, High Energy Physics.It may seem that the above discussion has no relevance to particle physics in general or to the Higgs boson in particular. "We are looking forward to further improvements and additional such analyses with the upcoming LHC run that is just starting." "As recently as a decade ago, this analysis would be considered impossible, and undertaking it was inconceivable," says Spiropulu. "These highly energetic events are golden," says Xie, "and a powerful way to search for the elusive Higgs boson pairs." This team includes Caltech researchers Irene Dutta (MS '20), a graduate student Nan Lu, a postdoctoral scholar currently transitioning to a professor position and Maria Spiropulu, the Shang-Yi Ch'en Professor of Physics. Xie and other Caltech researchers have now adapted this method and designed new algorithms that use these same kinds of jet events to find the extremely rare double Higgs bosons. The researchers, including former Caltech undergraduate Eric Moreno (BS '21), now at MIT, and former Caltech graduate student Javier Duarte (PhD '17), now at UC San Diego, developed the method to help find single Higgs bosons more efficiently. The method looks for "boosted" pairs of Higgs bosons, which are those that have so much momentum that their decay products merge into a single jet, or spray, of particles.Ĭaltech researchers originally developed machine-learning algorithms based on neural networks to help search for these telltale boosted Higgs boson signatures, a process called Higgs-boson tagging. The new results help establish an improved, more sensitive method for searching for the Higgs boson pairs in the future. "The strength and nature of this self-interaction will tell us about the history of our universe, and how it will evolve in the future," he says. These pairs of Higgs bosons will interact with each other, explains co-author Si Xie, a research assistant professor of physics at Caltech and a scientist at Fermilab near Chicago. Even more rare, scientists theorize, is the creation of two Higgs bosons from such a collision. Higgs bosons are created only very rarely at the LHC in highly energetic collisions between two protons. Now, the CMS team, led by Caltech researchers, is reporting new results in the journal Physical Review Letters on the hunt for not one but two Higgs bosons. The landmark discovery was made at CERN's Large Hadron Collider (LHC) in Geneva, Switzerland, using two instruments, including the Compact Muon Solenoid (CMS), of which Caltech is a partner. In 2012, particle physicists announced they had at last detected the slippery Higgs boson, a hard-to-pin-down particle that has the special property of endowing other fundamental particles with mass.