What is Nuclear Physics?
More than 99% of the mass of visible matter in the universe is nuclear matter. Protons and neutrons are the building blocks of atomic nuclei. Exotic forms of nuclear matter were present in the early universe and continue to exist today in neutron stars. Nuclear fusion processes at the core of our Sun are the source of the vast energy flow that sustains life on Earth. Nuclear fusion in stars and nuclear processes at the end of stellar life have formed the rich spectrum of elements we observe in nature.
Nuclear physics is the study of the structure of nuclei—their formation, stability, and decay. It aims to understand the fundamental nuclear forces in nature, their symmetries, and the resulting complex interactions between protons and neutrons in nuclei and among quarks inside hadrons, including the proton.
Experimental nuclear physics drives innovation in scientific instrumentation and has a far-reaching impact on research in other fields of science and engineering. From medicine—x-ray and magnetic resonance imaging, radiation therapies for cancer treatment—to materials science—x-ray lithography and neutron scattering—to propulsion and energy production—nuclear physicists have changed our world. Today's research in nuclear physics is not only unraveling fundamental questions about matter and energy but also enabling a host of new technologies in materials science, biology, chemistry, medicine, and national security.
Theoretical nuclear physics draws from a wide variety of fields such as statistical mechanics, fluid dynamics, statistics, particle physics, astrophysics, and gravity to understand fundamental properties of the universe on the smallest scales. Theorists use these tools to study the interior of neutron stars, simulate tiny versions of the Big Bang created in the laboratory, study fluid dynamic properties in relativistic systems, and calculate the microscopic interactions of quarks and gluons.
We have both experimental and theoretical groups covering a broad range of nuclear physics and related fields. We have joint speakers, seminars, journal clubs and other more informal interactions which provide unique learning opportunities for everyone in these groups.
What are we doing in Experimental Nuclear Physics at Illinois?
The Nuclear Physics Laboratory (NPL) at the University of Illinois at Urbana-Champaign carries out research in two broad areas. We are making precision measurements of neutron decay and searching for the neutron electric dipole moment and the axion. We also study both hot and cold QCD in relativistic heavy-ion experiments and in spin-dependent nucleon structure measurements .
We have significant state-of-the-art infrastructure to design and build scientific instrumentation in our laboratory. We focus on the development of instruments for novel experimental approaches to solving open questions in nuclear physics. Past and current examples include the large volume superconducting spectrometer magnet for the G0 experiment at Jefferson Laboratory, the cryogenic 4He target for the neutron EDM experiment at Oakridge National Laboratory, the W-trigger and the MPC, a forward EMC for the PHENIX experiment at Brookhaven National Laboratory, a large planar drift chamber for the COMPASS experiment at CERN, 6000 detector towers for the electromagnetic calorimeter for sPHENIX at Brookhaven National Lab and novel ultra-radiation-hard forward detectors for Pb-Pb and p-Pb physics in ATLAS at CERN.
We participate in several large-scale experiments at accelerator and reactor facilities in the United States and abroad. A careful balance between experiments in different stages—R&D, construction, data taking, data analysis—results in a broad spectrum of research opportunities. Our large group—nearly 50 graduate students, postdocs, and undergraduate student researchers—focuses on discovery in fundamental nuclear physics, modern data analysis techniques, and advanced instrumentation.
Experiments, status, and major goals
ARIADNE (Axion Resonant InterAction DetectioN Experiment) is an NMR-type experiment which searches for induced magnetization in a small sample of cryogenic, polarized helium-3 atoms as a dense, non-magnetic source mass is modulated in close proximity. This would be a signal of an exotic, spin-dependent interaction which could be mediated by the axion, a hypothesized, light, weakly-interacting particle that has emerged as a leading candidate for dark matter.
ATLAS Study of the quark-gluon plasma (QGP) produced in the collisions of large nuclei using the modification of jets from their vacuum fragmentation configurations as they propagate through the QGP. The Illinois group also is contributing to the two stage upgrade of the ATLAS Zero-Degree Calorimeter for the high luminosity LHC runs 3 (2022-2025) and 4 (2029-2032) and leads the development of a novel Reaction Plane Detector using AI reconstruction algorithms.
BL3 The Beam Lifetime (BL) experiment at the National Institute of Standards and Technology (NIST) measures the neutron lifetime using a different technique by observing neutron decay in flight. The neutron lifetime is determined by comparing the rate of beta-decay protons captured in a Penning trap to the rate of beam neutrons passing through the trap. The neutron lifetime measured using the beam method differs from that measured using the bottle method (UCNtau) by ~10 seconds. The continued disagreement hints at new physics, including neutron oscillations and low-energy physics in the dark sectors.
COMPASS (COmmon Muon Proton Apparatus for Structure and Spectroscopy) is a fixed-target experiment at CERN. It has been using the muon or hadron beams of the Super Proton Synchrotron (SPS) to scatter off a target of unpolarized or spin-polarized protons or deuterons, and unpolarized heavier nuclear targets. The SPS is also used to inject beams into the Large Hadron Collider (LHC).
neutron EDM The possible existence of a non-zero electric dipole moment of the neutron is of great fundamental interest and directly impacts our understanding of the nature of electro-weak and strong interactions. The experimental search for this moment has the potential to reveal new sources of T and CP violation. Such new sources would help us to understand the matter-antimatter asymmetry in the universe and challenge proposed extensions to the Standard Model.
Project 8 The energy of the beta emitted from tritium atoms near its endpoint energy, through simple kinematics, reveals the absolute mass of the electron neutrinos. The Project 8 experiment aims to measure the mass of neutrinos using a novel technique of Cyclotron Radiation Emission Spectroscopy (CRES) to reach an unparalleled sensitivity of 40 meV. This mass sensitivity covers the range of inverted neutrino mass hierarchy and reaches into the prediction for the normal hierarchy. To achieve this goal, we need to trap atomic tritiums. A magneto-gravitational trap using a Halbach array of permanent magnets, similar to the UCN trapping in the UCNτ experiment, could be readily applied to trap cold tritium atoms.
SeaQuest The Fermilab E-906/SeaQuest experiment is part of a series of fixed target Drell-Yan experiments designed to measure the antiquark structure of the nucleon and the modifications to that structure when the nucleon is embedded in a nucleus. Its principal goal is to extend the landmark measurement of the sea flavor asymmetry d(x)i u(x) in the proton made by its predecessor, E866, to the high-x regime.
sPHENIX The main physics motivation for the sPHENIX detector is the study of the quark-gluon plasma (QGP) produced in the collisions of large nuclei using the modification of jets from their vacuum fragmentation configurations as the propagate through the QGP. Together with the ATLAS program, the detectors at RHIC (sPHENIX) and the LHC (ATLAS) will allow us to constrain the temperature dependence of the properties of the QGP. The sPHENIX experiment also allows for the measurement of proton transverse-spin and transverse-momentum dependent effects.
UCNtau The UCNtau experiment measures the neutron lifetime using magnetically trapped ultracold neutrons (UCN) at the Los Alamos National Laboratory. In the UCNtau apparatus, UCN are magnetically levitated by an array of permanent magnets and confined by earth gravitational fields. The large volume of UCNtau, its asymmetrical construction, and the use of active neutron counting in-situ make it possible to reach a precise lifetime determination on the level of 1e-4, which is needed to test the unitarity of the CKM matrix and probe physics beyond the standard model.
Theory, collaborations, and major goals
MUSES is an interdisciplinary team of physics experts in lattice QCD, nuclear physics, gravitational wave astrophysics, relativistic hydrodynamics, and computer science experts in programming and front-end development. The goal of the collaboration is to help find answers to questions that bridge nuclear physics, heavy-ion physics, and gravitational phenomena such as: what exists within the core of a neutron star? What temperatures are reached when two neutron stars collide? What can nuclear experiments with heavy-ion collisions teach us about the strongest force in nature and neutron stars? https://muses.physics.illinois.edu/
ICASU is an interdisciplinary arena for research, education, and outreach. Members of the center seek answers to problems in fundamental physics at the intersections of cosmology, gravity, high energy, and nuclear physics. ICASU researchers ask questions such as: What is the universe made of at the most fundamental level? What are the principles, symmetries, and forces that govern the interactions of the fundamental particles and fields? and How does the universe work at all scales of energy, curvature, and size? These questions are explored in nuclear physics through the study of all forms of nuclear matter; in high energy physics through study of particle interactions at all energy scales; in cosmology through the study of the evolution of the universe; and in gravitational physics through the study of black holes, neutron stars and gravitational waves. ICASU focuses on the many connections among these fields and enables interdisciplinary research that deepens our understanding of the universe.
More information about other projects can be found on the Nuclear Theory Research Page!