Christopher W. Walter, Associate Professor  

Office Location: 271 Physics
Office Phone: (919) 660-2535
Email Address: chris.walter@duke.edu
Web Page: http://www.phy.duke.edu/~cwalter/

Specialties:
Experimental high energy physics

Education:
PhD, California Institute of Technology, 1997
MS, California Institute of Technology, 1991
BA, University of California at Santa Cruz, 1989

Research Categories: Experimental Particle Physics, Neutrino Physics, Particle-Astrophysics, Observational Cosmology

Current projects: The Super-Kamiokande Experiment, The T2K Experiment, The Hyper-Kamiokande Experiment, The LSST Dark Energy Science Collaboration

Research Description:

My current research program involves studying the properties of the neutrino, a notoriously difficult-to-detect sub-atomic particle. Intriguingly, it is possible that the existence of tiny neutrino masses can be explained by physics of the highest energy scales. These energies cannot be directly approached with accelerators today but existed in the early universe. Neutrinos may hold the imprint of processes in the beginning of our universe that determined the properties of the world today. Studying the nature of the neutrino may help understand what happened during that period. Foremost among the questions I hope to address is ``Why does there seem to be more matter in our universe than anti-matter?'' Neutrino physics is deeply tied to both particle physics and cosmology.

In Japan, I am working on a series of ongoing and future experiments which utilize the Super-Kamiokande (Super-K) detector in the central Japanese Alps. I study both naturally-occurring sources of neutrinos, and neutrinos which we make artificially in accelerators on the other side of Japan. In Super-K, I and my colleagues have published results that proved neutrinos ``oscillate'' between their types and have non-zero mass, overturning a commonly-held belief that they were massless. I followed this work up with the world's first ``long-baseline'' experiment, (the KEK to Kamioka experiment known as K2K), which confirmed that neutrino oscillations were occurring with the same parameters measured in natural sources by using a man-made neutrino beam. Our latest experiment, the Tokai to Kamioka experiment T2K, utilizing Super-K as the long-baseline target, started data-taking in January of 2010 and, in 2011, was the first experiment to find indications of the appearance of “electron-type” neutrinos in a “muon-type” neutrino beam. In 2013 we proved conclusively this transformation was occurring for the first time, thus demonstrating that all three types of neutrinos could change into each other. Utilizing over ten years of data, we also use the Super-K detector to look for evidence of the decay of protons. This would be a monumental discovery and would tell us something about energy scales out of reach of any accelerator we could even think to build.

Looking towards the future I am working on the next generation of giant underground detectors in Japan, the Hyper-Kamiokande experiment. This enormous detector will contain one megaton of water viewed by approximately 100,000 large photo-sensors. Recently, I also have started an effort in observational cosmology, joining a science collaboration for the LSST project, a giant survey telescope that will be located in Chile designed to make a 10 year, three dimensional survey of the entire visible sky. The LSST Dark Energy Science Collaboration will examine billions of galaxies and try to determine the nature of the mysterious “Dark Energy” which is unaccountably causing the universe to pushed apart at a faster and faster rate.

Areas of Interest:
Experimental Particle Physics
Neutrino Physics
Particle-Astrophysics
Observational Cosmology

Teaching (Spring 2015):

  • Physics 305.01, Intro to astrophysics Synopsis
    Physics 154, MW 08:30 AM-09:45 AM

Recent Publications   (More Publications)

  1. Zhang, H. and others, Supernova Relic Neutrino Search with Neutron Tagging at Super-Kamiokande-IV, Astropart.Phys., vol. 60 (2015), pp. 41-46 [pdf], [doi]  [abs].
  2. Abe, K. and others, Measurement of the neutrino-oxygen neutral-current interaction cross section by observing nuclear deexcitation $\gamma$ rays, Phys.Rev., vol. D90 no. 7 (2014), pp. 072012 [pdf], [doi]  [abs].
  3. Abe, K. and others, Test of Lorentz Invariance with Atmospheric Neutrinos [Submitted for Publication] (2014) [pdf]  [abs].
  4. Olive, K.A. and others, Review of Particle Physics, Chin.Phys., vol. C38 (2014), pp. 090001 [doi] .
  5. Takhistov, V. and others, Search for Trilepton Nucleon Decay via $p \rightarrow e^+ \nu \nu$ and $p \rightarrow \mu^+ \nu \nu$ in the Super-Kamiokande Experiment, Phys.Rev.Lett., vol. 113 (2014), pp. 101801 [pdf], [doi]  [abs].

Postdocs Mentored

  • Erin O'Sullivan (2014/11-present)  
  • Alex Himmel (2011 - present)  
  • Tarek Akiri (2011 - 2013)  
  • Jennifer Prendki (2010 - 2011)  
  • Roger Wendel (May, 2008 - present)  
  • Maximilien Fechner (2006 - 2008)  
  • Naho Tanimoto (2005 - 2008)