Professor of Physics
Head, Graduate Program
Nuclear and Particle Physics
High Energy Physics Experiment
Wean Hall 7307
Education & Professional Experience
PhD: University of Erlangen-Nürnberg (Germany), Physics (1993)
M.S.: University of Erlangen-Nürnberg (Germany), Physics (1989)
American Physical Society
Professor of Physics, Carnegie Mellon University, 2009–
Indefinite Tenure, Carnegie Mellon University, 2005
Associate Professor, Carnegie Mellon University, 2000–09
Staff Scientist, Lawrence Berkeley National Laboratory, 1998–2000
Post-doctoral Research: Lawrence Berkeley National Laboratory, 1996–98
Post-doctoral Research: UC Berkeley, 1993–96
My research interests touch the interface between particle physics and cosmology. As an experimental high energy physicist, I study questions connecting particle physics phenomena to the fate of the universe. One of those questions concerns the fact that our visible universe appears to exhibit a dominance of matter over antimatter. Assuming the universe started in the Big Bang with the same amount of particles and anti-particles, the disappearance of the antimatter in the universe is still an unsolved mystery. Another question concerns the nature of dark matter that makes up about one quarter of the content of the universe.
As a member of the CDF experiment located at Fermilab near Chicago, Illinois, I study particle-antiparticle oscillations and the violation of the symmetries of nature under the combined action of charge conjugation Cand space inversion or parity P. Although the violation of CP invariance was first discovered in the system of neutral K mesons in 1964, the origin of CP violation is still not completely understood. However, CP violation is of great interest as it is expected to play an important role in understanding the predominance of matter over antimatter in the universe.
Decays of neutral B mesons are an ideal system to study CP violating effects as well as transitions of particles into their anti-particles and back. Examples of my research include: I was involved in an initial study of the CP violation parameter sin(2β) in B0 meson decays using CDF data; my group made significant contributions to the discovery of particle-antiparticle oscillation in decays of Bs0 mesons at CDF and we worked on a measurement of the CP violating phase βs in Bs0 → J/ψ φ decays. The first measurement of bounds on the CP violation parameter sin(2βs) indicated an intriguing discrepancy with predictions of the Standard Model of particles physics indicating hints to new physics phenomena, while an update of the analysis with more statistics shows a better agreement with the Standard Model prediction.
As a member of the CMS experiment operating at the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland, I study the nature of dark matter. The products from the collision of protons at the LHC may include dark matter particles that compose about 25% of the mass-energy in the universe. There are actually compelling arguments that the energies reached, when the LHC starts up again in 2015 at almost its design center-of-mass energy, are in the regime of producing dark matter particles. A favoured candidate for these dark matter particles is the neutralino, the lightest and most stable of a whole set of new supersymmetric partners to each of the known particles of the standard model. My group is involved in the search for signatures of dark matter in the CMS data through the production of supersymmetric particles that decay into photons and leptons in the final state. My dark matter research is in association with the McWilliams Center for Cosmology at CMU.
V. Khachatryan et al., Search for supersymmetry in events with a photon, a lepton, and missing transverse momentum in pp collisions at √s = 8 TeV, Phys. Lett. B 757, 6 (2016)
V. Khachatryan et al., Observation of the rare Bs0 →µ+µ− decay from the combined analysis of CMS and LHCb data, Nature 522, 68 (2015)
V. Khachatryan et al., Observation of the diphoton decay of the Higgs boson and measurement of its properties, The European Physical Journal C 74, 1140 (2014)
S. Chatrchyan et al., Search for new physics in events with photons, jets, and missing transverse energy in pp collisions at √s=7 TeV, J. High Energ. Phys. 2013, 1007 (2013)
T. Aaltonen et al., Measurement of the CP-violating phase βsJ/ψϕ in Bs0→J/ψ ϕ decays with the CDF II detector, Physical Review D 85, 072002 (2012)
F. Azfar et al., Formulae for the analysis of the flavor-tagged decay Bs0 → J/ψ ϕ, Journal of High Energy Physics 11, 158 (2010)
T. Aaltonen et al., First flavor-tagged determination of bounds on mixing-induced CP violation in Bs0→J/ψϕ decays, Physical Review Letters 100, 161802 (2008)
T. Aaltonen et al., Measurement of ratios of fragmentation fractions for bottom hadrons in pp̅ collisions at √s̅=1.96 TeV, Physical Review D 77, 072003 (2008)
A. Abulencia et al., Measurement of the Bs0-B̅s0 oscillation frequency, Physical Review Letters 97, 062003 (2006)
T. Affolder et al., Measurement of sin 2β from B→J/ψ Ks0 with the CDF detector, Physical Review D 61, 072005 (2000)