Using Muons and Protons to Probe the Structure of the Universe

Intellectual Merit: This proposal requests support for the PI and her group to participate in two separate experimental programs, each aimed at exploring the structure of our universe at the most fundamental level. The first program will map out how quarks and gluons fragment and hadronize into the particles that make up our visible universe. The PI, a graduate and an undergraduate student will utilize high energy proton-proton collisions at the Relativistic Heavy Ion Collider (RHIC) to extract longitudinal and transverse momentum dependent (TMD) jet fragmentation functions from distributions of identified pions, kaons and protons inside of fully reconstructed jets. These measurements will provide significant constraints on the gluon fragmentation functions, particularly in the case when the pion, kaon or proton assume a large fraction of the parent gluon’s momentum. They will also provide new insights into the transverse momentum distributions of these same particles relative to the jet axis. Information about unpolarized TMD fragmentation functions is sparse, largely because the interpretation of the existing data is complicated by the limited energy of the lepton-proton collisions used to make the measurements. Investigation of TMD fragmentation functions are an essential piece of a worldwide effort to advance our current picture of Quantum Chromodynamics, the formal theory of strong interactions within the Standard Model of particle physics. The second program aims to measure Beyond-the-Standard-Model signals which may contribute to the muon anomalous magnetic moment. Dirac predicted that all charged, point-like fermions, such as the muon, would have a g-factor of precisely 2. However, due to interactions with virtual particle fluctuations in the vacuum, the muon magnetic moment deviates from this expectation and acquires a non-zero anomalous magnetic moment aì. This term, often written as alpha(mu) = (g-2)/2 , encapsulates the contributions to the muon magnetic dipole moment from interactions with all fundamental particles that exist in our universe. A significant discrepancy between the Standard Model prediction and the measurement of aì would imply the existence of new particles and/or forces of nature. The previous measurement of aì by the E821 collaboration at Brookhaven National Laboratory points to a tantalizing +3s deviation from the Standard Model prediction, motivating the g-2 collaboration at Fermilab to make a new, 140 ppb measurement. This proposal requests support for the PI and two graduate students to expand their current efforts in the muon g-2 experiment at Fermilab. Contributions will include the development and support of the g-2 GEANT based simulation software package and simulation production as well as the development of the Q-method wa analysis in the 2019 and 2020 datasets. Broader impacts: The broader impacts resulting from past and future funding are the exposure and education of students from the high school through the post-graduate level to fundamental nuclear physics. The studies described here will provide graduate students with the necessary tools and knowledge to obtain postdoctoral work at other large colliders, such as the Large Hadron Collider, electron scattering facilities like Jefferson Lab and smaller non-accelerator based collaborations, such as FERMI or KATRIN. Undergraduate students funded by this proposal will continue to have the rare opportunity to experience the scientific culture and participate in experiments at National Laboratories. Finally, this proposal will support a variety of outreach activities by the P.I., such as participating in Youth Science Summits, judging science fairs and speaking to Kentucky undergraduate students about recent events in nuclear and particle physics.