Studies in Elementary Particle Physics

Johns Hopkins University, Baltimore MD

Investigators

Abstract

The Standard Model of particle physics describes many of the micro-physical phenomena that have been observed since it was proposed over 50 years ago. In particular, one of the most spectacular predictions was the prediction of the Higgs boson, which was observed in 2012 at the CERN Large Hadron Collider. For all of its success, the Standard Model is likely incomplete. It does not describe the dark matter, which is the dominant part of the mass density of the universe. It does not explain why ordinary matter dominates over antimatter. The theory with a single Higgs boson is mathematically unstable, which suggests that there are Higgs siblings or new physical processes occurring at larger mass scales. One of the goals of this project is to improve our knowledge of the Higgs couplings, which can deviate by small amounts from the predictions of the Standard Model when heavier siblings exist. There can also be non-standard couplings that violate the Charge Conjugation Parity symmetry, which could explain the matter domination of the universe. Other goals are to search directly for the heavier states that could be produced at the LHC and to search for their possible effects on high mass Standard Model processes. This project advances our understanding of one of the key directions in particle physics and of our understanding of the basic physical laws of the universe. It exposes undergraduate students, graduate students, and postdoctoral fellows to state of the art detector technologies, computing technologies, and data analysis techniques. Those highly trained students and postdocs pursue careers in both academic and non-academic fields. The project also hosts a very successful Quarknet center that provides professional development opportunities for a community of about 25 Maryland area high school STEM teachers. This project is a program of experimental particle physics research within the CMS experiment at the CERN Large Hadron Collider (LHC). The project builds upon an ongoing program of research that led to the discovery of the Higgs boson and the characterization of its properties. The focus of the Higgs program is on the golden four-lepton decay channel, but also incorporating other decay channels into production mechanism related measurements. Kinematic information in both on-shell and off-shell production is used to make precision measurements of the Higgs boson mass, width, quantum numbers, CP properties, and more generally, the tensor structure of Higgs interactions with vector bosons and fermions within the framework of effective field theory. The project includes searches for heavier siblings of the observed state and other look-alike states such as top quark resonances, W' and Z' bosons, exotic gravitons, leptoquarks, and excited quarks and gluons. These are predicted by many extensions of the Standard Model. The techniques needed to identify and reconstruct the decays of these states were developed by the proponents using previous NSF support. In particular, the searches would use tracking enhancements, jet substructure techniques, machine learning techniques, and sophisticated likelihood variables. Finally, this project supports technical contributions to the operation of the CMS detector and to the study of new detector technology for high luminosity upgrades of the LHC. The operational contributions are based on techniques that are currently in use or are derived from those currently in use. The contributions to the study of detector upgrades are based on tools that were developed to support the present operation. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.