CERN scientists measure spin-parity of charm baryons

At CERN, researchers from the LHCb collaboration have made a significant breakthrough by determining the spin-parity of singly heavy charm baryons for the first time. This discovery helps solve a long-standing question in the study of baryons, which are particles made of three quarks. Singly heavy baryons consist of one heavy quark, known as a charm quark, and two lighter quarks. Although these particles have been known for a while, their specific properties and behavior have been unclear. The study, published in Physical Review Letters, focuses on understanding the spin-parity, which indicates how these particles behave under different symmetry transformations. Co-author Guanyue Wan, a Ph.D. candidate at Peking University, explained that this work is important for testing theoretical models of quantum chromodynamics, the theory describing strong interactions. Understanding the spin-parity helps scientists grasp how quarks within baryons are arranged and how they interact. To find the spin-parity, researchers analyzed data from proton-proton collisions recorded between 2016 and 2018. They studied the decay process of bottom baryons to charm baryons, allowing them to examine the properties of the more stable charm baryons. The analysis revealed that the spin-parity is 3/2+, confirming a specific model of baryon structure. This finding also relied on examining how the orientation of the baryon’s spin impacted its decay, providing further evidence for the theory. The new measurements also rule out several competing theories about these particles' nature. In the future, researchers hope to apply similar methods to study other poorly understood baryons, advancing the field of particle physics and expanding our understanding of the matter that makes up the universe.