James Olsen

Professor of Physics
Office Phone
310 Jadwin

One of the continuing mysteries of the universe is why the fundamental constituents of matter, the quarks and leptons, come in different “flavors” arranged in three separate generations of matter with large mass splittings. In the standard model of particle physics, this flavor structure is connected to several fundamental questions, including CP violation and the origin of mass, through the Yukawa couplings of the fermions to the Higgs field. In recent years, the success of the standard model in describing a wide variety of flavor-changing processes has led to stringent constraints on the structure of possible extensions of the standard model, and possible explanations for the masses of the fundamental particles. These constraints play an important role in elucidating the nature of previous and future discoveries at the Large Hadron Collider (LHC), located at CERN near Geneva, Switzerland.

Our group played a leading role in the search for, and eventual observation of, the Higgs boson in its decay to two bottom quarks using the CMS detector at the LHC.  This has been one of the most challenging Higgs decay modes to observe at the LHC, and was originally thought to be out of reach. We are currently engaged in measuring the properties of this process with increased precision, and searching for signs of new physics in the Higgs couplings to bottom quarks and the W and Z bosons.

Prior to joining CMS, for more than a decade our group was engaged in elucidating the flavor structure of the quark sector through the study of CP violation using the BaBar detector at SLAC. We were the lead team on the discovery of direct CP violation in the B-meson system, and measured the angles alpha and gamma of the CKM Unitarity Triangle.


Selected Publications
  1. C. Palmer, S. Cooperstein, J. Olsen, with the CMS Collaboration, "Observation of Higgs Boson Decay to Bottom Quarks," Phys. Rev. Lett. 121, 121801 (2018).
  2. D. Lopes Pegna, M. Mooney, J. Olsen, with the CMS Collaboration "Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC," Phys. Lett. B 716, 12 (2012).
  3. D. Lopes Pegna and J. Olsen, with the CMS Collaboration, "Measurement of the B+ Production Cross Section in pp Collisions at sqrt(s) = 7 TeV", Phys. Rev. Lett. 106, 112001 (2011).
  4. J. Olsen and A. Telnov, with the BaBar Collaboration, "Observation of CP Violation in B0 -> π+ π-, K+π-", Phys. Rev. Lett. 99, 021603 (2007).
  5. J. Biesiada and J. Olsen, with the BaBar Collaboration, "Observation of B+ -> K(bar)0K+ and B0 -> K0K(bar)0", Phys. Rev. Lett. 97, 171805 (2006). [J. Biesiada won the 2008 APS Tanaka Dissertation Award for this work.]
  6. Y. P. Lau and J. Olsen, with the BaBar Collaboration, "Measurement of γ in B+/- -> D(*)0K+/- Decays with a Dalitz Analysis of D0 -> K0sπ+π- ", Phys. Rev. Lett. 95, 121802 (2005).
  7. N. Danielson and J. Olsen, with the BaBar Collaboration, "Direct CP Violating Asymmetry in B0 -> K+π- Decays", Phys. Rev. Lett. 93, 131801 (2004).