Studying Quantum Chromodynamics at LHCb

The protons and neutrons in the atomic nuclei of everyday matter are made of subnuclear particles called quarks and gluons. The project supported by this award will study how quarks and gluons scattered out of a proton or produced in high-energy particle collisions subsequently form new bound states. Additional measurements will investigate how strong nuclear charge, called color, flows through proton-proton scattering processes, searching for a theoretically predicted novel state of quarks and gluons that exhibit quantum correlations across colliding protons. Data from the Large Hadron Collider at the European Organization for Nuclear Research (CERN) will be used to perform the research, as part of the Large Hadron Collider Beauty (LHCb) experiment. The research performed will advance our understanding of how strong force bound states such as protons can be created, and the dynamics of their possible interactions. The project supported by this award will furthermore train young scientists from diverse backgrounds in nuclear physics. Training the next generation of nuclear physicists is critical to maintain expertise relevant to the nation's energy and defense needs and to continue advancing both applied and non-applied research in nuclear physics and technology. Specifically, this award will enable mentored research in nuclear physics on the LHCb experiment by a postdoctoral scholar and five Ph.D. students, including one who is Latina American and another who is African American. In the second year, a student from Mount Holyoke College, an undergraduate institution for women, will perform summer research in nuclear physics at the University of Michigan. The PI’s group will study how high-energy color-charged quarks hadronize into sprays of observable color-neutral bound states by performing a suite of complementary measurements at LHCb. Specifically, the measurements will compare charged hadron distributions in jets initiated predominantly by light versus heavy quarks, including investigation of the predicted suppression of hadron production with the mass of the quark; examine evidence for contributions from string breaking versus quark coalescence models of hadronization via measurements of baryon versus meson production as a function of event multiplicity; and study spin-momentum correlations in hadronization by measurement of spontaneous polarization of produced hyperons. The proposed hadronization program will contribute toward the ultimate, long-term goal of being able to predict statistically the fully correlated distributions of particles from different flavor high-energy fragmenting quarks. Separate measurements will explore the role of color flow in hadronic scattering processes by searching for experimental evidence of transverse-momentum-dependent factorization breaking and color entanglement. The specific observables include correlated production of nearly back-to-back Z boson-hadron and Z boson-jet pairs. The activities furthermore include contributions to the commissioning and optimization of the U.S.-led Upstream Tracker silicon detector upgrade for LHCb as well as its integration into the LHCb real-time-analysis framework. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.