Young-Kee Kim in the Library for Symmetry
8/1/2005

Young-Kee Kim: Research

As an experimental scientist, I am working on particle physics whose goal is to understand how the universe works at the most fundamental level by discovering and understanding the fundamental constituents (called elementary particles) and the forces acting among them. My main physics interest is understanding the orgin of mass for elementary particles.

CDF at the Tevatron (1990 - 2013): At CDF experiment, my research group measured the masses of the W boson and the top quark very precisely (numerous measurements were made using different decade modes, different datasets and different analysis techniques). These measurements predicted the mass of the Higgs boson (the "core" of the very successful theory of particle physics, the Standard Model, and thought to be key to understanding why elementary particles have mass) to be less than 145 GeV.

My research group has also involved other topics measuring the diboson production process whose final states are similar to those of the Higgs boson process (this is an important step for designing Higgs searches), the Bs oscillation, the lifetime of the top quark (by measuring its width), the mass difference between the top and anti-top quarks, properties of the Z and W boson (their production cross section and forward-backward asymmetry), and decay rates of bottom and charm mesons.

ATLAS at the LHC (2010 - ): A new particle, which behaves like the predicted Higgs, was discovered at mass of 125 GeV by the ATLAS and CMS experiments at the LHC at CERN in 2012 via processes in which this particle decayed into a pair of photos, Z bosons and W bosons (H → γγ, ZZ, WW). Francois Englert and Peter Higgs received the Nobel prize in 2013 for their theoretical discovery of the Higgs mechanism.

The most critical goal at the LHC over the coming years is to develop a deeper understanding of the nature of this new particle. One key process yet to be observed is where the Higgs decays into a pair of bottom quarks (H → bb), the most frequent decay mode for the 125 GeV Higgs. This mode allows to study the Higgs boson's coupling to fermions (such as electrons and quarks) and to probe directly the mechanism for fermion mass generation via the Higgs. Many well-motivated new physics models predict significant deviations to the H → bb Standard Model rate. Thus this decay channel will be a good tool to explore new physics models.

Observing and studying H → bb is my main interest at the ATLAS experiment. This task will require significant improvements of b-jet triggers using the new tracking trigger (FTK) combined with the LHC accelerator and detector upgrades. In the past few years, my research group (my students and postdocs) has been heavily involved in the FTK (hardware and simulation) that has more capability and flexibility than the current trigger system. In addition, my group is working on the H → bb decay channel in the "vector-boson fusion" production mode using existing (Run I) data. In the next few years, my group activities will be

  1. Continue the FTK hardware work and simulation study; participate in testing, commissioning and initial operations of the FTK in 2015 (Run II)
  2. Produce physics results of the H → bb mode with Run I data. Through this analysis, we will gain experience on the current trigger limitation, which will help developing a trigger strategy with the FTK
  3. Development and commissioning of a b-jet trigger strategy with the FTK for H → bb events.

In addition, my ATLAS group studies new physics beyond the current understanding. Examples include searches for dark matter produced with top and bottom quarks and searches for a new vector boson W' → top + bottom.

Accelerator Physics (2009 - ): Although accelerator physics is an active research field, and accelerators are critical for particle physics research and other research areas in science, the U.S. has not been educating and training enough accelerator students. Thus, I have been giving some of my time to educating and training students in accelerator physics. The following is the list of topics and Ph.D. students:

  • Satomi Shiraishi: "Laser driven wakefield accelerator - Staging experiment"
  • Tim Zolkin: "Studies of beam dynamics at Fermilab Booster accelerator" and "Studies of non-linear lattice"
  • Alexander Vostrikov: "Achieving ultra high Q in superconducting niobium cavities"
  • Sergey Antipov: "Demonstration of beam properties requred for Project X superconducting RF linac"
  • Alexey Kochemirovsky: "Design and simulation of the vacuum muon cooling channel and experimental studies"
Physics 335 Projects for any 1st year grad. students - see here

Happy to have more graduate and undergraduate students for any of these subjects. Go to Young-Kee Kim's Homepage for contact information.