LDMX - A Light Dark Matter eXperiment

• Applicant: Dr. Felix Klitzner
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 499367463

The LDMX project is an accelerator based fixed-target experiment. It is designed to potentially discover light dark matter in the lower mass range between 1MeV and 1GeV. Currently it is in its research and development phase, which will end mid of 2023, followed by the roughly three year construction phase. Being involved in the project for two years via the fellowship program thus gives me the possibility to significantly contribute in the R&D phase and as well as bringing them one step close to the successful completion of the construction phase. Hidden sector dark matter theories provide an elegant solution to generate low dark matter masses below 1GeV. In the simplest scenarios the dark matter particle couples to normal matter via a new force, mediated by a new exchange particle, the so called dark photon. This dark photon can then decay into dark matter particles. To discover this light dark matter particles, LDMX will fire a 4 to 8GeV electron beam from the SLAC DASEL beamline into a 10% radiation length thin tungsten target. The electron interacts with the tungsten foil and radiates off a dark photon via dark bremsstrahlung. Since the kinematics of this process is distinctive, the electron will receive an appreciable transverse kick with respect to the prior trajectory. As neither the dark photon nor the dark matter particles are interacting via standard model processes, only the soft, wide-angle scattered outgoing electron will be visible in the detector. Thus, to only trigger on these events, LDMX has to reconstruct every single electron individually, measuring precisely its trajectory and energy. To achieve this, LDMX is composed out of three main sub-components: a silicon strip tracker, an electromagnetic calorimeter and a hadronic calorimeter. My project at Caltech mainly foresees studies on the hadronic calorimeter, which is made out of 25mm thick iron absorbers for energy loss and 20mm thick polystyrene scintillator bars for readout. The bar geometry for the construction phase is not yet final, which is why still lots of tests have to be performed in the Caltech laboratories. Tests foresee measurements with a radioactive Strontium-90 source for single bar characterization. For efficiency studies, multiple scintillator bars will be measured with cosmic muons. End of this year, a test beam with a smaller, prototype of the calorimeter is conducted at the T9 beamline at CERN. I will be responsible for the analysis of the collected data, as soon as I arrive at Caltech. Furthermore, I will be involved in developing a replacement for the tungsten target: an active LYSO target. LYSO, short for Lutetium–yttrium oxyorthosilicate, is an inorganic chemical compound scintillator. Reading out the target directly enables to veto events where a substantial amount of energy is deposited inside the target, which could fake the characteristic missing energy signal of the dark matter production process.

• DFG Programme: WBP Fellowship
• International Connection: USA
• Host: Professor Dr. David G. Hitlin