Fermilab Steering Group Report

Chapter 4
Physics at the
Intensity Frontier


At the intensity frontier, the fields of neutrino science and precision physics offer promising pathways to physics breakthroughs not accessible to the LHC, the proposed ILC or nonaccelerator physics. In neutrino science:

  • On the near horizon, NOνA will be the only experiment with sensitivity to the ordering of neutrino mass.
  • The joint power of the Japanese T2K experiment and NOνA will begin to explore CP violation in neutrinos.
  • In the post-NOνA era, a longer-baseline neutrino program with Project X and a very large detector would have unique capabilities to resolve neutrino-mass ordering. This program would remain unique even in the presence of the contemplated Japanese program with a very large detector in the Kamioka mine, fed by a multi-MW proton beam from J-PARC.
  • By making possible 2 MW proton beams at any energy between 50 and 120 GeV, Project X would create the flexibility to have excellent neutrino physics reach with either wide-band or off-axis beams.
  • Project X, with a very large detector in the proposed DUSEL, would greatly enhance neutrino science.
  • A post-T2K Japanese neutrino oscillation program would work at a different energy and a different baseline from its U.S. counterpart. Together, these two programs could make discoveries not accessible to either one alone.

In precision physics:

  • Lepton flavor violation in muon decays offers a new window on physics beyond the Terascale, including leptogenesis and unification.
  • A muon-to-electron conversion experiment at Fermilab would have unprecedented sensitivity and provide the ability to zero in on the origins of lepton flavor violation.
  • New sources of flavor and CP violation predicted by Terascale physics have yet to be detected. Rare kaon decays offer a theoretically clean method of searching for these phenomena.
  • Project X would provide the opportunity for an experiment to detect 1000 neutral and charged K→πνv decays, offering a unique level of clean sensitivity to flavor- or CP-violating effects from Terascale physics.

What are neutrinos telling us? How did the universe come to be? Are there undiscovered principles of nature? What happened to the antimatter? Do all the forces become one?

An intensity-frontier program that provides unique experiments to address these profound questions of 21st-century physics would serve many scientific users. It would prepare future generations of U.S. particle physicists to exploit the potential of accelerator-based scientific opportunities in the U.S. and worldwide. At the intensity frontier, Project X would help pave the way to the extremely powerful energy- and intensity-frontier facilities—a neutrino factory and a muon collider—of the long-term future beyond the ILC.