Searching for Dark Sectors with Proton Bremsstrahlung




Foroughi-Abari, Saeid

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This dissertation explores the sensitivity of high-luminosity colliders and fixed target facilities to low mass new physics in so-called dark sectors that are coupled to the Standard Model of particle physics. These new physics scenarios are motivated by the need to explain empirical puzzles, including the nature of the dark matter in the universe and the origin of neutrino mass. Avoiding over-production and reproducing the observed relic abundance of thermal dark matter candidates requires that low mass (sub-GeV) dark sector degrees of freedom are coupled to the Standard Model via new light force mediators. In this context, we revisit the minimal case of a scalar singlet S coupled to the Standard Model through the Higgs portal and impose new constraints by interpreting the dataset from the LSND experiment. Motivated by proposals for new searches at Fermilab and the Large Hadron Collider (LHC), the rate of proton bremsstrahlung of light dark vectors and scalars is revisited. The proton bremsstrahlung, which involves mixing with meson resonances, is a primary production mode in the forward direction near the resonance region. We derive an approximate method of evaluating the proton bremsstrahlung and compare the resulting distributions and rates with those obtained via variants of the Fermi- Weizsacker-Williams approximation. Additionally, the newly proposed LHC Forward Physics Facility (FPF) emerged as a highly promising site for searching for long-lived particles, millicharged particles, and especially for studying high-energy colliding neutrinos. Within this context, the FORMOSA experiment, located in the LHC forward region, is proposed to provide exceptional sensitivity in the search for millicharged particles by exploiting their scintillation signature. Furthermore, the thesis explores the FPF’s potential to probe the neutrino electromagnetic properties, including neutrino millicharge, magnetic moment, and charge radius, as well as the weak mixing angle, using an intense beam of highly energetic neutrinos of all three flavors. The study of new interactions within the neutrino sector can enhance our understanding of neutrinos and establish the connection between the dark sector and neutrino physics on a broader scale.



millicharged Particles, Dark Matter, Dark Sector, Proton Bremsstrahlung, Neutrino Magnetic Moment