Experimental High-Energy Particle Physics
Professor, Physics and Astronomy
1989 B.A. Physics, Princeton University
1996 Ph.D. Physics, Stanford University
As a high-energy physics experimentalist, I study the fundamental constituents of matter and their interactions. The theoretical framework of the Standard Model of particle physics is astoundingly successful in describing the spectrum of known particles and their electroweak and strong interactions. As an experimentalist, my primary goal is to test the Standard Model and search for new phenomena that would indicate physics beyond the Standard Model. Searches for new physics can be carried out at low-energy colliders through precision tests or at the high-energy frontier where direct searches are possible. In the past I have exploited low-energy experiments to make precise measurements in flavor physics to search for and constrain new physics. The advent of the Large Hadron Collider (LHC), with its 14 TeV center of mass energy, brings an unparalleled opportunity to shift my focus to the energy frontier. My research spans three broad research agendas of high-energy physics, the first in my past of precision physics, and the others in my future at the energy frontier. Phrased as questions they are: What is the origin of CP violation? What is the origin of electroweak-symmetry breaking? What new physics lies beyond the Standard Model? The first research question is important since the amount of CP violation expected in the Standard Model is insufficient to explain the matter-antimatter asymmetry of the universe. In the Standard Model, CP violation arises through the weak interaction. Studying weak interactions of quarks allows us to unravel the structure of the couplings between the quarks and the W boson, the carrier of the weak charged current. These couplings are of great interest since they determine the amount of CP violation in the Standard Model. If the Standard Model is a complete description of the weak interaction, a unitary matrix (the CKM matrix) should govern the weak coupling of the quarks. Four parameters are sufficient to determine the CKM matrix, and one of the parameters leads to CP violation. Measurements of weak decay processes constrain the CKM matrix; by making many measurements we can over-constrain this matrix and test the consistency of the Standard Model. We might expect this test to fail, because we know there must be another source of CP violation to explain the baryon asymmetry of the universe. The study of quark flavor couplings is of further interest because the patterns of couplings in the CKM matrix is not predicted in the Standard Model, yet the pattern of large diagonal and increasingly smaller off-diagonal elements in the CKM matrix is suggestive of an as-yet-unknown physical origin, potentially at a very high mass scale. The second research question investigates electroweak symmetry breaking and tests a definitive prediction of the Standard Model that there is a scalar field permeating all of space-time. The coupling of this scalar field to other particles gives them mass. For the weak gauge bosons it is this coupling that breaks the symmetry of the unified electroweak theory, giving the W and Z bosons masses of about 100 GeV and leaving the photon massless. This symmetry-breaking mechanism also predicts that there should be a CKM quark-mixing matrix, but tells us nothing about the four parameters of that matrix. Without the Higgs mechanism, the Standard Model cannot explain electroweak symmetry breaking or the origin of mass. At sufficiently high energies, the Higgs field should be observable as a scalar particle, the Higgs boson. Direct observation of the Higgs in 2012 was crucially important to our understanding of particle physics and measurement of its properties now forms our view of electroweak symmetry breaking. The third research question also takes advantage of high-energy colliders to search for new particles and interactions beyond the Standard Model. When the LHC begins collecting data at the highest energies yet achieved, we will open a new window into particle physics. The discovery potential at the LHC is great. Supersymmetric theories hint at a unification of the strong and electroweak interactions and have viable dark matter candidates, although as yet none of the predicted superpartners to the known particles have been observed. The LHC has the potential to discover supersymmetry (SUSY) and study its rich spectrum. At high energies we can also probe for extra dimensions, which would lead to a replication of known particles in discernable patterns, and for quark compositeness, akin to Rutherford’s discovery of the tiny nucleus in the atom or the discovery that nucleons are composite particles made of quarks. Perhaps new gauge bosons, e.g. heavier copies of the W or Z, will be produced and give evidence of a new interaction or symmetry of nature. It remains an experimental question whether any of these extensions to the Standard Model are correct. It is important to carry out this research program because the Standard Model by itself is incomplete. Even if the Higgs boson is discovered and a unitary CKM matrix consistently explains CP violation, the Standard Model leaves unanswered questions. Why are there three generations of quarks and leptons? How does the structure of the quark and lepton mixing matrices arise, and how is it related to the pattern of particle masses? What is dark matter, and what is dark energy? How do we unify gravity with the other interactions? Investigating these and other perplexing questions may point the way to new fundamental physics at higher mass scales. Experiments at the LHC’s energy frontier are a prime opportunity to address these questions in the coming years.
Dr. Ecklund grew up in the San Francisco Bay Area and was an undergraduate at Princeton University where he studied Physics. He continued in graduate study in Physics, obtaining a Ph.D. in particle physics from Stanford University. He lived in Central New York and worked as a Research Associate at Cornell University for ten years before moving to a faculty position at the State University of New York at Buffalo. In 2008, he moved to Houston and Rice University where he currently is an Assistant Professor of Physics.