Signal and Background Studies at 8 GeV for the Light Dark Matter eXperiment

Sammanfattning: Light dark matter is a hypothesized form of dark matter in the 1 MeV to 1 GeV mass range. The Light Dark Matter eXperiment (LDMX) is an upcoming experiment to test the existence of light dark matter, by colliding an electron beam with a tungsten target and assembling a set of events that potentially indicate the existence of light dark matter. The three main detector components of the LDMX are a set of trackers, an electromagnetic calorimeter, and a hadronic calorimeter, each of which gives a collection of variables that can be used to assemble criteria to select potential dark matter events. The optimal selection criteria for a 4 GeV beam have already been established by the LDMX collaboration, but a higher beam energy will be used at later stages of the LDMX project, since higher energies provide better sensitivity. This thesis is the first step in exploring the creation of a viable set of selection criteria for the LDMX at an upgraded beam energy of 8 GeV. This was done by first achieving an understanding of the existing 4 GeV selection criteria, and then exploring new possibilities for additional selection criteria. A sample of ~17 million of the most difficult background events and ~1 million signal events was assembled, and a procedure was devised for creating a set of selection criteria that can reject all background events while maintaining a high signal efficiency. The final selection criteria for this exploration are: an electromagnetic calorimeter energy under 6274 MeV, an hadronic calorimeter energy under 15 MeV, a number of readout hits in the electromagnetic calorimeter less than 106, and a single recoil electron track. The signal efficiencies are: 83.77% for 1 MeV, 81.88% for 10 MeV, 71.26% for 100 MeV, and 67.26% for 1000 MeV dark matter mediator masses.