Particle Physics is the science of discovery of the fundamental constituents of matter and energy and is involved in the exploration of the Universe from the smallest to the largest scales. A remarkable achievement of Twentieth Century Particle Physics was the development of the Standard Model that describes impressively well a broad spectrum of fundamental particles such as quarks and leptons and the interactions (the forces) among them. But the Standard Model is incomplete and we know there is important physics that lies beyond it. What is the evidence? As an example, astronomical observations indicate that the known particles of the Standard Model make up only 1/6 of the total matter in the Universe. The remainder is called "Dark Matter" because we don't see it directly. A number of experiments are underway or in the planning stage to look for the Dark Matter, which might be one type of particle or possibly many or perhaps something else entirely. One hypothesized Dark Matter particle is called the Dark Photon (labeled the A') and it is expected to interact with the photon of the Standard Model (known to most of us as a gamma ray).
Intellectual Merit: This EArly concept Grant for Exploratory Research (EAGER) supports preliminary studies by a Cornell group led by Professor Peter Wittich to assess the technical feasibility, optimal design, physics reach, and approximate cost of a "high risk-high payoff" dark photon (A') search experiment at the Cornell Wilson Synchrotron Laboratory. The intended goal is to produce the A' in the reaction: (e+) + (e-) -> photon + A'. A positron (e+) beam is to be extracted from the synchrotron and directed onto a liquid hydrogen target that will provide the source of target electrons (which are constituents within the hydrogen atoms). The outgoing photon is detected in a crystal electromagnetic calorimeter and the A' itself is not detected directly, but rather is "observed" via its potential signature in the measured missing mass distribution.
The strategy of this dark photon search will differ from existing and planned experiments in several respects: (a) the dark photon is identified by a missing-mass technique, so the search does not depend on a specific decay mode, as most competing experiments do; (b) there is no assumption about dark photon lifetime, as is built into many experiments that use long beam dumps or electron-positron vertexing; and (c) there is no requirement that the dark photon decay at all. The only critical assumption needed for this search is that the dark photon should interact with ordinary photons.
This proposal addresses two of the science drivers of the recently released Report of the Particle Physics Project Prioritization Panel (called P5): Dark Matter and the Search for New Particles and Interactions. The unique facility provided by the Cornell storage ring's positron beam would allow this group to probe a new regime in Dark Matter physics, and also to possibly help explain the so-called "g-2 anomaly", a potentially related and highly interesting topic of current experimental research. Searching for this kind of physics beyond the Standard Model confronts fundamental symmetries, the nature of mass, the dimensionality of space, and the cosmological origins of our universe.
Broader Impacts: The proposal includes training of undergraduate and graduate students in cutting-edge research techniques associated with this EAGER project. Additionally the principal investigators on the proposal all contribute to an extensive program of outreach at Cornell: to local K-12 schools, including both in-school programs and out-of-school workshops for teachers, educators, and high school students; to the general public; and to undergraduates.
