Searching for heavy photons in the HPS Experiment

Thesis/Dissertation · Tue Nov 01 00:00:00 EDT 2016

DOI:https://doi.org/10.2172/1431175· OSTI ID:1431175

Uemura, Sho ^[1]

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1. SLAC National Accelerator Lab., Menlo Park, CA (United States)

The Heavy Photon Search (HPS) is a new experiment at Jefferson Lab that searches for a massive U(1) vector boson (known as a heavy photon or A') in the MeV-GeV mass range and coupling weakly to ordinary matter through a kinetic mixing interaction. The HPS experiment seeks to produce heavy photons by electron bremsstrahlung on a fixed target, is sensitive to heavy photon decays to e⁺e^-, and targets the range in heavy photon mass m_A' ~ 20 - 600 MeV, and kinetic mixing strength epsilon² ~ 10^-5 - 10^-10. HPS searches for heavy photons using two signatures: a narrow mass resonance and displaced vertices. This dissertation presents the theoretical and experimental motivations for a heavy photon, the design and operation of the HPS experiment, and the displaced vertex search. The data used in this dissertation is the unblinded fraction of the 2015 HPS run, for the period of operation where the HPS silicon vertex tracker (SVT) was operated at its nominal position. This data was recorded from May 13 to May 18, 2015, at a beam energy of 1.056 GeV and a nominal beam current of 50 nA. The integrated luminosity is 119 nb^-1, which is equivalent to 0.172 days of ideal running at the nominal beam current. This dissertation presents results (signal significance and upper limits) from the displaced vertex search in the mass range m_A' ~ 20 - 60 MeV, and kinetic mixing strength epsilon² ~ 2 × 10^-8 - 10^-10. This search does not have sufficient sensitivity to exclude a canonical heavy photon at any combination of m_A' and epsilon². The strictest limit achieved in this analysis on the production of a particle that decays like a heavy photon is 115 times the expected production cross-section for a heavy photon. Factors limiting the sensitivity of this analysis are discussed. Projections of HPS performance with the full 2015 data set, and with planned improvements to the analysis, are presented. Comparisons are also made to earlier reach estimates.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1431175
• Report Number(s): JLAB-PHY-16-2462; DOE/OR/23177-4392
• Country of Publication: United States
• Language: English