Experimental Particle Physics Research at High Energies

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One of the major intellectual achievements of the 20th century was the development of the Standard Model (SM) of particle physics. This model succeeded in classifying all the elementary particles known at the time into a hierarchy of groups having similar quantum properties. The validity of this model to date was confirmed by the discovery of the Higgs boson at the Large Hadron Collider (LHC). However, the Standard Model as it currently exists leaves open many questions about the universe, including such fundamental questions as to why the Higgs mass has the value it has. One of the primary functions of the Compact Muon Solenoid (CMS) experiment at the LHC, which remains the premier Energy Frontier particle accelerator, operating at the CERN laboratory near Geneva Switzerland, is to discover new physics beyond the Standard Model. This project will analyze data from the CMS experiment looking for signals of beyond the Standard Model. The work that will be accomplished with this award will impact three broad areas: 1) Upgrading the highly technical components of the CMS detector 2) workforce development and outreach to the broader community and 3) furthering the analysis techniques that might well discover new physics at the LHC. With the strong cooperative education program at Northeastern University, the group will continue to routinely involve undergraduates in meaningful six-month projects at CERN. The PIs will also continue their involvement with the Boston Area QuarkNet group (now in its 14th year) where they are able to reach out to local high school teachers and their students. The group members also share the excitement and knowledge of the discoveries and results with the broader public through lectures and presentations to audiences outside of particle physics. The work funded through this award will search for a number of new particle physics sectors where there are theoretical models of beyond the SM physics. A discovery of leptoquarks would provide a link between the quark sector and the lepton sectors and help to explain why both sectors contain three generations of matter. Detection of substantial invisible decays of the Higgs boson would answer important questions about the nature of electroweak symmetry breaking. Invisible decays of the Higgs are a signature of various beyond the standard model physics theories. In these, the Higgs can interact with new heavy particles which decay into particles that are usually not detected by the experiment (like neutrinos). Limits on the invisible decay rate of the Higgs boson also provide constraints on models of Dark Matter. This project's studies also include measurements of the differential cross section measurements of Standard Model processes, such as ZZ production, and W+jets production, that have sensitivity to new physics. These studies are tightly coupled with the new physics searches because the processes they measure are important backgrounds to the specific searches targeted. The presence of a signal in any of these channels would have profound impact on our understanding of particle physics, while establishing its absence would provide important constraints on models of physics beyond the Standard Model of particle physics.