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

1 online resource (viii, 43 p.) : ill. (chiefly col.)Includes abstract and appendices.Includes bibliographical references (p. 38-39).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

Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider

International audienceParticles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton–proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments—as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER—to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the high-luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity ‘dark showers’, highlighting opportunities for expanding the LHC reach for these signals