Grant: Subatomic Physics Envelope - Project

There are still many unanswered questions today in particle physics and cosmology. Although we now have a highly successful Standard Model (SM) of particle physics that links 3 of the 4 known forces it is very clear that the SM is incomplete. It does not contain any Dark Matter (DM) particles and it cannot explain Dark Energy (DE) which is the largest component of the energy budget and is responsible for the accelerating expansion of the universe. Moreover, our visible universe makes up only about 5% of the total mass of the universe while DM contributes about 23%. The search for an understanding of the elusive DM is one of the greatest scientific quests of our age. In our current understanding, the known, uncharged particles, the three neutrinos, cannot be a major component of the inferred dark matter mass, and so we posit at least one as-yet unobserved new particle. Recently, there has been a focus on a mediator of a new fifth force with mass e- Ta A' --> e- Ta (e+e-). The use of the ARIEL e-linac has the benefit of allowing a relatively low beam energy, thus reducing the boost of the produced boson and opening up the small angles of these forward-going decay leptons. We propose a two spectrometer setup optimized for the anomaly region and a thin foil target to achieve sufficient luminosity. The magnets will be designed and constructed by the MIT group. Each spectrometer will be instrumented with a focal plane detector consisting of 3 GEM detector planes, read out via standard APV electronics. They will be provided by the Hampton University group. The GEMs will be followed by a layer of scintillating paddles as the fast trigger detectors. A consortium of Canadian institutions (UBC, Manitoba, Saint Mary's, TRIUMF, & Winnipeg) will design & construct the scintillators. They will also provide the readout electronics for the trigger system and handle the integration with the ARIEL accelerator. Stony Brook University will take care of the data acquisition and slow control system. In a 2nd stage experiment TRIUMF would install a beamline chicane to allow re-circulation of the electron beam through the accelerating cavity to increase the beam energy to 50 MeV and extend the reach of the experiment. If our CFI proposal is successful TRIUMF would also install a 2nd cryomodule to increase the beam energy up to 75 MeV in single user mode and allow simultaneous operation of DL and ARIEL at 50 MeV to significantly increase the reach of our experiment.