This project supported particle physics research that was part of the Compact Muon Solenoid experiment at the CERN Large Hadron Collider.  Our group played a key role in CMS' discovery of the Higgs boson in the late spring of 2012 and showed that the properties of the new particle were consistent with those expected for the Higgs.  This project continued the study of the Higgs boson in the period from 2020-2023 when the sample of Higgs bosons had increased by an order of magnitude. Our group has updated and refined their original measurements and added a number of new measurements that are sensitive to possible deviations of the Higgs couplings to W/Z/photon, gluons, and fermions. The measurements of the Higgs width are sensitive to possible unseen Higgs decays to "dark matter" particles. We have been able to distinguish the dominant underlying production mechanisms and show that their relative sizes are also consistent with expectations. 
These measurements strongly suggest that the so-called Higgs mechanism is indeed responsible for generating the masses of all of the elementary particles in the Standard Model [the masses of the neutrinos may be more complicated].  They have not revealed any evidence that the Higgs field plays a role in the matter/antimatter asymmetry of the universe. These findings certainly have considerable intellectual merit.  

The Standard Model with a single Higgs boson has mathematical inconsistencies at large mass scales.  Many theories that address the mathematical problems contain families of Higgs bosons.  In those scenarios, the observed Higgs boson would be the lightest member of the family.  Our group has also searched for possible heavier siblings using the same four lepton final state that was key to the original discovery.  Many theories with Higgs families also contain new heavy particles.  Our group has searched for heavy Higgs siblings and other new heavy particles that decay into the much lighter top quarks, weak force gauge bosons W and Z, and "light" Higgs bosons.  Because the daughter particles are unstable and are much lighter than the heavy parent particle, they typically decay into collimated jets of the long-lived particles that are actually observed in the CMS detector.  Even though a top quark decays into three daughters of its own, it can appear as a single jet of nearby particles.  This makes it hard to distinguish from a jet of particles produced a less interesting strong interaction process.  Using techniques developed in part by the JHU theory group, it is possible to examine the substructure of jets to separate those from decaying W/Z bosons or top quarks and those from more common strong interaction processes.  Our group has been at the forefront of this field and has produced some of the world's most sensitive searches for new states that decay into top-antitop pairs, gauge boson pairs, Higgs boson pairs, and binary combinations of the three kinds of daughter particles like top+W, and W+Higgs.  Our group has pioneered the use of unsupervised machine learning techniques to search for new physical states that can be trained from data and do not require simulation or a priori knowledge of the new states.  Our group has also studied the production of the lepton pairs looking for interference effects from possible heavy new states that are too heavy to observe directly at the present LHC. Like the light Higgs studies, these measurements and technical developments are advancing our knowledge of how the universe works and have considerable intellectual merit.

The broader impacts of the project are primarily in education.  It has provided a wide range of training and career development for the undergraduate, graduate, and postdoctoral researchers. Students learn particle physics from working on their thesis topics, attending seminars at Fermilab, CERN and JHU, and interacting with their supervisors.  All of the students and postdocs have received substantial exposure to state of the art computing techniques needed to analyze very large data sets and to manipulate large databases. They have been deeply involved in various aspect of data processing, reconstruction, pattern reconstruction, simulation, and statistical analysis. All of them are qualified to work in many areas should they decide to leave academic research.

Our Quarknet center has provided training and professional development to an aggregate group of more than 25 Baltimore area high school science teachers. They have been exposed to a number of lectures on basic physics, particle physics, and classroom pedagogical tricks. They have also constructed useful demonstration and laboratory apparatus. Several have received college credit though the Quarknet program.
 The project has contributed significantly to scientific outreach through the annual JHU Physics Fair.

Last Modified: 09/08/2023
Modified by: Morris Swartz