What is a Quantum Loop Diagram?
SLAC's PEP-II accelerator produces B mesons and their anti-particle, B-bar mesons. Both decay into other particles through the weak force, but the matter and antimatter particles decay at different rates because of an asymmetry in the behavior of the weak force (it violates charge-parity symmetry). According to the Standard Model of known physics, this asymmetry in matter and antimatter decays should remain the same no matter how decays occur. The data to date, however, indicates that in some types of decays show less symmetry than others. If this holds up, it means some kind of new physics is showing up in these rare decaysthanks to quantum loops.
A quantum loop means particles of any mass can instantly materialize, and then disappear, during the decay process. The brief-lived virtual particles are usually W bosons, which mediate the weak force. But other particles with similar behavior could enter the loop, including a charged Higgs particle, which physicists still ardently seek, or a neutralino, one of the proposed supersymmetry particles. This makes decays involving loops very sensitive to new physics at high masses. If the new particles participate in certain types of decays, they would alter the expected asymmetry between matter and antimatter decays.