Grant: Subatomic Physics Envelope - Research Tools and Instruments

DarkLight is a small experiment, roughly 1 m by 1.5 m, which is about to begin construction at the TRIUMF electron linear accelerator (e-linac). DarkLight is designed to search for new particles beyond the known Standard Model called dark bosons. These dark bosons could be produced as radiation from electrons scattering through a dense target and would then decay into electron-positron pairs that can be measured by particle detectors. For DarkLight, the mass of dark photons to which the experiment will be sensitive is directly related to the energy of the electron beam striking the dense target. By increasing the e-linac beam energy from 30 mega electron-volts to 50 mega electron-volts, DarkLight will gain access to an extremely interesting dark photon mass range. This mass range aligns with possible hints of new physics from several experimental anomalies, including the muon g-2 result and the ATOMKI excess. Exploring this region is therefore of high priority for the international physics community.  The equipment to be funded by this NSERC RTI grant will be used to build a new beamline at the e-linac. The new beamline will be a semicircle of around 10 m length which, combined with a similar semicircle supported by other funding sources, forms a full "recirculating ring". Currently, the majority of the electron acceleration in the e-linac is achieved by a single accelerating "cryomodule" partway along the accelerator beamline. The new recirculating ring will enable the linear accelerator to pass the electron beam back through the accelerating cryomodule a second time, increasing its energy to 50 mega electron-volts. This will provide DarkLight with the beam energy it needs to make groundbreaking particle physics measurements. The construction of this recirculating ring is necessary to let DarkLight and TRIUMF take the exciting opportunity to contribute to the global search for dark bosons.