Ryan Patterson
Professor of Physics
California Institute of Technology
rbpatter at caltech.edu
Lauritsen 339

MC 356-48 HEP
California Institute of Technology
Pasadena, CA 91125


The discovery that neutrinos have non-zero mass has brought with it new complexity in the neutrino sector as well as a host of possible new phenomena in particle physics, astrophysics, and cosmology. As we explore this new complexity, many questions arise. Why does neutrino mixing look so different than quark mixing? Are maximal mixings present, and if so, what underlying symmetries cause this? What mechanism drives the smallness of the neutrino masses, and what does it imply about physics at ultra-high energy scales? Do neutrinos violate the combined charge/parity (CP) symmetry, and is this violation large enough to produce the universe we observe today – a universe full of matter but not antimatter?

My current research focuses on the neutrino sector of particle physics, addressing questions of weak mixing, neutrino masses, CP violation, and physics beyond the Standard Model. One piece of this is the currently operating NOvA experiment, a long-baseline neutrino oscillation experiment situated along Fermilab's NuMI neutrino beam. The broad physics program we are carrying out with NOvA includes: determining the ordering of the neutrino masses; constraining the phase δ of the PMNS matrix in search of leptonic CP violation; elucidating the flavor structure of neutrinos, in particular providing a leap in precision on whether the ν3 state is maximally mixed and, if it is not, determining whether the μ or τ flavor dominates; and providing new precision on the dominant "atmospheric" oscillation parameters |Δm232| and θ23. This program is supplemented by a range of both bread-and-butter and exotic measurements: neutrino-nucleus scattering, dark matter searches, supernova neutrinos, monopole searches, and more.

Nature can choose to make leptonic CP violation or non-maximal ν3 mixing arbitrarily hard to discover through careful parameter tuning, and some degeneracies can remain after NOvA if the CP phase lies in an unfavorable range. In more favorable cases, definitive CPv observation and precision measurements of PMNS mixing parameters still require a new experiment. My group is actively involved in the development of the next-generation DUNE experiment through which we are pursuing an ambitious physics program including an improved neutrino mass hierarchy measurement regardless of other parameter values; observation of leptonic CP violation at >5σ for 50% of parameter space; world-leading supernova neutrino observation capabilities, particularly (and uniquely) in the νe channel; and a wide range of searches for physics beyond the Standard Model, including baryon number violation. We have built and operated a single-phase liquid argon prototype detector (ProtoDUNE-SP) at CERN, and Far Detector site preparation is underway.

I was previously involved in the the MINOS long-baseline experiment, which completed data taking in 2012. In MINOS, I focused on θ13-driven νe appearance and on searches for new physics through comparisons of neutrino and antineutrino oscillations. Further back in time I was involved in the MiniBooNE program, with the primary goal of testing the unexpected LSND evidence for νμνe transitions at high apparent Δm2.

Members of the group

Alejandro Diaz [ Postdoctoral Scholar ]
Leon Mualem [ Research Scientist ]
Ryan Patterson [ Faculty ]
Varun Raj [ Graduate Student ]
Scott Schwartz [ Graduate Student ]
Kathryn Sutton [ Postdoctoral Scholar ]
Jason Trevor [ Engineer ]
Zoya Vallari [ Postdoctoral Scholar ]
Recent group alums
Kirk Bays [ former Postdoctoral Scholar ]
Joe Lozier [ former Graduate Student ]
Dan Pershey [ former Graduate Student ]

Selected presentations and articles
NOTE: I've most likely not updated this list lately. For a more complete and up-to-date publications list or for arXiv links to items below, see here.

Recent work is supported by the Department of Energy, the Alfred P. Sloan Foundation, the Beatrice and Sai-Wai Fu Graduate Fellowship, and Caltech.

NuMI Horn 1

Electron antineutrino appearance


NOvA Far Detector Site

NOvA Far Detector

LEM Technique

Electron Neutrino Event

Muon Neutrino Disappearance in NOvA

MINOS Far Detector