Precision Measurements in Intermediate Energy Physics

Trustees Of Boston University, Boston

Investigators

Abstract

This award will support our group's leadership of two major new experiments at the Fermi National Accelerator Laboratory (Fermilab): Mu2e, and muon g-2 (E989). The Mu2e experiment at Fermilab, co-led by J. Miller will search for the lepton flavor violating (LFV) muon to electron conversion reaction at the 10^{-16} level, a factor of 10,000 times more sensitive than the present limit. B.L. Roberts is co-leading the muon g-2 experiment. Both experiments involve a dipole operator, and in the context of supersymmetry probe complementary aspects of that particular beyond-the-SM (BSM) theory. Mu2e is sensitive to a wider range of physics than the LFV decay of the positive muon to a photon and positron, which must go through the dipole interaction. The muon anomalous magnetic moment (g-2) is also sensitive to a wide range of BSM physics. It is a chiral-changing, flavor-diagonal interaction, which could have contributions from the chargino and neutralino in SUSY, or the "dark photon" from a hidden U(1) sector, or from Randall-Sundrum models. At present the difference between the SM and the Brookhaven experiment is around 3.5 standard deviations. Fermilab E989 is designed to cross the five standard deviation threshold. Whatever the result from Fermilab E989, it will provide an important constraint on the interpretation of new phenomena found at the LHC. The MuSun experiment is measuring the weak matrix element for muon capture on deuterium, which is related to the weak pp fusion matrix element that powers the sun. This award will support our group's leadership of two major new experiments at the Fermi National Accelerator Laboratory (Fermilab): Mu2e and muon g-2. It will also support our participation in two other experiments: the MuSun experiment at the Paul Scherrer Institute in Switzerland and the neutron electric dipole moment (EDM) experiment being prepared for Oak Ridge National Laboratory. J. Miller is co-leading the Fermilab Mu2e experiment that will search for the conversion of a muon into an electron without the emission of neutrinos. B.L. Roberts is co-leading the Fermilab muon g-2 experiment which will measure the magnetism associated with the muon a factor of four times more precisely than the previous experiment at the Brookhaven National Laboratory. Both of these experiments are looking for evidence of New Physics that cannot be explained by the Standard Model, a theory that at present describes all measured quantities in particle physics, but is known to be incomplete. Results from the previous g-2 experiment show a hint of something new, which should be clarified by the Fermilab experiment. This program is complementary to the searches at the energy frontier at the Large Hadron Collider in Geneva Switzerland. R. Carey is working on the MuSun experiment, which measures the rate at which a negative muon captures on the deuterium nucleus (made up of a proton and neutron), and breaks it apart by changing the proton into a neutron. This process is interesting since it can be related to the fusion of two protons together to form deuterium, the "burning of hydrogen" that powers the sun.