Faculty Type: 
Active Faculty
Professor of Physics

Varian Physics Bldg., Rm. 146
382 Via Pueblo Mall
Stanford University
Stanford, California 94305-4060

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What are the properties of neutrinos and what is their role in the universe?    How does gravity work?

Our  group does research relevant to the understanding of fundamental particles and interactions. The tools we use are borrowed from AMO, nuclear, and particle physics.

The group is operating of the largest double-beta decay experiment in the world (EXO-200) that recently discovered the two neutrino double-beta decay in Xe-136.   This is the slowest known process in the universe, with a half life of 2.11x10^21 years or 200 billion times the age of the universe!    EXO-200 also produced the tightest limit of neutrino masses and is collecting more data that will be used to answer the question of whether or not neutrinos are described by a 4-component wave function like all other fermions (neutrinos may be “Majorana” particles, described by 2-component wave functions, instead of Dirac particles.)

Also within the EXO program our group is developing a new method to extend the sensitivity of a future experiment. This work involves the identification of the barium atom produced in the double-beta decay of Xe using AMO techniques.

In the field of experimental gravity we just started a new program to investigate the nature of gravity at a scale near 1 micron. To do this we use submicron size quartz beads trapped in laser fields in vacuum, with several novel techniques to apply the gravitational force and detect its influence.

We also have a program to develop imaging detectors for gamma-ray astronomy as well as novel radiation detectors for application in homeland security and medical physics.

Career History

  • Fellow Italian Institute for Nuclear Research, 1987-89 
  • Research Fellow, Caltech, 1989-92 
  • Senior Research Fellow, Caltech, 1992-95 
  • Associate Professor, Stanford, 1995-2004 
  • Professor, Stanford, 2005-present