The detectors, known as High-Luminosity Zero Degree Calorimeters, or HL-ZDCs, will be assembled at KU’s Mechanical Prototyping Lab before being tested with high-energy particle beams at the Fermi National Accelerator Laboratory in Illinois. Once they pass calibration and performance checks, the instruments will be shipped to CERN, where they will be integrated into CMS ahead of the first heavy-ion data-taking period of the High-Luminosity Large Hadron Collider, currently scheduled for the middle of the 2030s.

The project is led by Michael Murray, a KU professor of physics and astronomy who also serves as the CMS HL-ZDC upgrade project leader, alongside KU Distinguished Professor Christophe Royon. KU postdoctoral researcher Georgios Krintiras will lead important parts of the detector’s data-reconstruction software. Together, the team will work across hardware design, materials engineering, electronics, simulation and data analysis, linking a Kansas laboratory to one of the largest international scientific collaborations ever assembled.

Zero Degree Calorimeters are positioned close to the LHC’s opposing particle beams, far from the central collision point of CMS. Their purpose is to capture energetic neutrons and photons that continue forward along the beamline after heavy-ion collisions. Because these particles escape at extremely small angles, they carry information that cannot be obtained from the central detector alone. By measuring their energy and distribution, physicists can reconstruct key features of collisions between lead nuclei, including how directly the nuclei struck one another.

That information is especially important in the study of quark-gluon plasma, a state of matter in which quarks and gluons are no longer confined inside protons and neutrons. Scientists believe this ultra-hot, dense form of matter existed during the first few millionths of a second after the birth of the universe. In modern experiments, it is recreated for fleeting moments when heavy atomic nuclei collide at nearly the speed of light. The pattern of forward-moving neutrons can help researchers distinguish nearly head-on collisions from glancing encounters and improve measurements of the plasma’s properties.

The upgraded calorimeters will also help identify ultraperipheral collisions. In these events, two nuclei pass close to one another without directly touching, yet their powerful electromagnetic fields interact. Such encounters can generate photons and other particles while preserving much of the nuclei’s forward motion. Separating these events from direct nuclear collisions is essential for studying electromagnetic interactions at unprecedented energies and for interpreting the complex signals recorded by CMS.

KU researchers are replacing the ZDCs that have served CMS through the first three major operating periods of the Large Hadron Collider. The High-Luminosity LHC will produce far more collisions, higher radiation levels and a denser stream of particles than the existing instruments were designed to withstand. The new detectors must therefore be narrower to fit into the restricted space around the beamline, faster to process signals arriving in rapid succession and more resistant to radiation damage.

The development effort will also give Kansas students direct experience with technologies used in frontier physics. Students will participate in precision manufacturing at KU, detector simulations, radiation-hard instrumentation, electronic readout systems and scientific software development. At Fermilab, they will work with specialists at the Test Beam Facility, where the completed calorimeters can be exposed to controlled particle beams. Training through Fermilab’s LHC Physics Center will further prepare them to analyze data once the upgraded collider begins operations.

“This project connects the full chain of experimental science,” Murray said. “Detectors assembled in Lawrence will be tested in a high-energy beam at Fermilab, installed at CERN and then used by an international collaboration to answer fundamental questions about matter.” The project is expected to deepen KU’s partnership with Fermilab while preserving advanced detector expertise and research infrastructure in Kansas. After installation, the two HL-ZDCs will provide CMS with a sharper view of the particles that flee along the beamline—turning some of the most difficult-to-detect remnants of nuclear collisions into clues about the universe’s earliest and most extreme state of matter.

Subject of Research: High-Luminosity Zero Degree Calorimeters for the Compact Muon Solenoid experiment at CERN’s Large Hadron Collider, with applications in heavy-ion physics, quark-gluon plasma research and ultraperipheral collisions.

Article Title: University of Kansas Wins $1 Million to Build Next-Generation Detectors for CERN’s High-Luminosity LHC

Web References: Compact Muon Solenoid; Large Hadron Collider; High-Luminosity LHC; KU Mechanical Prototyping Lab; Fermi National Accelerator Laboratory; Fermilab Test Beam Facility; Fermilab LHC Physics Center

References: University of Kansas project information; CERN information on the Compact Muon Solenoid and Large Hadron Collider; Fermi National Accelerator Laboratory information on detector testing and LHC research.

Image Credits: CERN

Keywords

Particle physics, particle accelerators, Large Hadron Collider, CERN, Compact Muon Solenoid, CMS, University of Kansas, zero degree calorimeter, high-luminosity LHC, quark-gluon plasma, heavy-ion collisions, subatomic particles, hadrons, detector technology, Fermilab

The result, published in Science Bulletin, focuses on hafnium-153, a neutron-deficient isotope located near the proton drip line. The proton drip line marks the region where nuclei contain so few neutrons relative to their number of protons that additional proton emission becomes energetically possible. Nuclei approaching this boundary are especially valuable to nuclear physicists because their unusual proton-to-neutron ratios expose weaknesses in existing theories of nuclear structure and help define the limits of nuclear stability.

Hafnium-153 contains 72 protons and 81 neutrons, making it significantly more proton-rich than the stable hafnium isotopes found in nature. Its existence is important because nuclear models must account for whether such a highly unbalanced nucleus remains bound, becomes weakly bound, or rapidly disintegrates. By measuring the isotope’s mass and confirming its survival through the experimental system, researchers obtained new evidence for how nuclear forces operate in an extreme environment where conventional patterns of stability begin to break down.

The experiment began with a beam of bismuth-209 ions generated by HIAF’s Booster Ring, or BRing. These energetic ions were directed onto a graphite target, causing projectile-fragmentation reactions. In this process, the incoming bismuth nuclei collide with carbon atoms and break apart, producing a broad mixture of radioactive fragments. Among the debris were the rare hafnium-153 nuclei, whose production probability was so low that only a handful could be expected even under high-intensity operating conditions.

The resulting mixture, known as a cocktail beam, was then sent through the HIgh rigidity Radioactive Ion Beam Line, or HIRIBL. This beamline separates reaction products according to their magnetic rigidity, a quantity determined by the momentum and electric charge of each ion. Efficient separation was essential because the desired hafnium-153 nuclei were surrounded by far more abundant isotopes and reaction products. HIRIBL allowed the researchers to filter and transport the nuclei of interest toward the facility’s precision measurement system.

The purified radioactive ions were injected into HIAF’s Spectrometer Ring, known as SRing, where the team used isochronous mass spectrometry. This technique is designed to determine the mass-to-charge ratio of short-lived nuclei without requiring them to reach an equilibrium orbit in the storage ring. Ions with different masses circulate with carefully related revolution times, allowing their identities to be inferred from timing signals produced during repeated passes through the ring. Because the method can register individual ions, it is particularly powerful for studying isotopes that are created only a few times.

Despite hafnium-153’s extremely low production cross section—the probability that the isotope will be formed in a collision—the researchers detected ten individual ions. Each event carried significant scientific weight because the isotope’s identification depended on the combined analysis of its timing behavior, magnetic rigidity, and position within the mass spectrum. The measurements indicate that hafnium-153 is either bound or weakly bound, meaning it can exist as a nuclear system rather than immediately ejecting a proton. The finding agrees with predictions from several contemporary nuclear mass models, while also supplying an experimental benchmark for future refinements.

The result was independently supported by experiments at the Radioactive Isotope Beam Factory operated by RIKEN in Japan. The near-simultaneous observations by two separate facilities strengthen the case that hafnium-153 has been reliably identified and demonstrate the international importance of mapping the proton-rich frontier. Independent confirmation is especially valuable in rare-isotope research, where conclusions may initially rest on only a few detected events and where backgrounds from neighboring nuclei can be difficult to eliminate.

Researchers say the observation highlights the combined performance of HIAF’s major components rather than the capability of a single instrument. The high intensity of the heavy-ion beam increases the number of rare nuclear reactions, HIRIBL provides the separation power needed to isolate fragile radioactive products, and SRing supplies the single-ion sensitivity required for precision mass measurements. Together, these systems create a platform for investigating nuclei that cannot be produced in useful quantities with conventional stable-beam experiments.

HIAF’s first physics result also points toward a broader research program involving the discovery of new isotopes, measurements of nuclear masses and lifetimes, and studies of matter under extreme proton-neutron imbalance. As beam intensity and experimental efficiency improve, the facility is expected to reach still rarer regions of the nuclear landscape. Each newly observed isotope can alter the boundaries used in nuclear models, offering clues about the origin of the elements, the behavior of matter inside explosive stellar events, and the fundamental forces that hold atomic nuclei together.

Subject of Research: Rare isotope discovery and nuclear structure near the proton drip line

Article Title: Discovery of isotope hafnium-153 near the proton drip line via isochronous mass spectrometry: extending the nuclear landscape with HIAF

News Publication Date: 2-Jul-2026

Web References: https://doi.org/10.1016/j.scib.2026.06.056

References: Science Bulletin, DOI: 10.1016/j.scib.2026.06.056

Image Credits: Photo by Institute of Modern Physics of the Chinese Academy of Sciences

Keywords

Hafnium-153, rare isotopes, nuclear physics, proton drip line, HIAF, isochronous mass spectrometry, radioactive ion beams, nuclear structure, heavy-ion accelerator, nuclear landscape