On the hunt for dark photons : improving the tracking of vertical drift chambers

Abstract

The current standard model (SM) of particle physics does not account for the dark matter (DM) presence within the universe. A theoretically proposed new force, governed by a U(1) Boson, has been an ongoing subject of experimental searches as a bridge between SM particles and DM models. An experimental search for the Dark Photon/A[prime] Boson will commence in experimental Hall A at Jefferson Lab some time in 2016-17. The Hall A High Resolution Spectrometer (HRS) will be used in attempt to detect the A[prime] Boson with masses O(50MeV - 500MeV ) as it decays into e[superscript -]e[superscript +] pairs. The high luminosity required for the experiment creates HRS trigger rates of 5 Mhz, which presents a problem for the tracking efficiency of the resultant e[superscript -]e[superscript +] pairs. The HRS uses four vertical drift chambers (VDC) to detect particle tracks by means of gas ionization. Previously, VDC signal data has been analyzed using an older "brute force" algorithm which was appropriate at much lower particle rates (lower Background). This presentation reports on a new VDC algorithm created to better handle higher particle traversal rates, and tested using previously obtained high-rate test data. This new analysis identifies a set of 'miss match' parameters [delta]S, which enable local cuts on background tracks. The new method identifies a final good track by constructing global tracks from multiple VDCs and minimizing their x[superscript 2]. Global tracking efficiencies are increased by the addition of these new local track constraints/cuts, which will meet the needs of the Dark Photon/ A[prime] Boson experimental search.