A collaboration of particle physicists who have used CLEO subatomic particle detectors at Cornell to probe the limits of matter are celebrating the 500th scientific paper submitted to a peer-reviewed journal in the collaboration's three-decade history. This number of papers is larger than that of any other elementary particle physics collaboration.

The 500th paper, titled "Improved Measurements of Semileptonic Decays of D Mesons to pi and K Mesons," was submitted to Physical Review D and describes precise measurements that are key to understanding fundamental parameters in elementary particle theory.

Scientists in the CLEO collaboration, comprising 100 physicists from 21 institutions in the United States, Puerto Rico, Canada and the United Kingdom, study high-energy collisions of electrons and positrons -- the electron's antiparticle -- produced in the Cornell Electron Storage Ring (CESR).

The CLEO detectors, which went through several iterations through the years, obtained their first results in late 1979, and continued detecting the spray of particles from collisions in CESR through 2008, when CLEO data collection was completed.

Among the particles still being studied using the data already collected are the bottom and charm quarks, and their interactions via the strong and weak forces. Now, most CLEO scientists at Cornell are also performing work at the Large Hadron Collider particle accelerator in Switzerland.

The 500th CLEO Collaboration paper deals with the impact of the strong force on the decay of D mesons, particles composed of the charm quark. The measurements test theoretical calculations of the strong force, which have recently become more precise due to novel computing techniques called Lattice Quantum Chromodynamics -- a major focus of the CLEO collaboration.

The strong force measurements show that the theorists are on the right track, and sets the bar high for future calculations. These results, like many others in the past five years, take advantage of CESR in an energy region known as the "charm threshold," which is favorable for precise studies of D mesons.

The CESR program is supported by the National Science Foundation. CLEO collaborating institutions are supported by the National Science Foundation, the U.S. Department of Energy, the Natural Sciences and Engineering Research Council of Canada and the U.K. Science and Technology Facilities Council.