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The DZero collaboration has found evidence for a new way in which elementary particles break the matter-antimatter symmetry of nature. This new type of CP violation is in disagreement with the predictions of the theoretical framework known as the Standard Model of particles and their interactions. The effect ultimately may help to explain why the universe is filled with matter while antimatter disappeared shortly after the big bang. Credit: DZero collaboration
The DZero result is based on the comparison of the distributions of positively and negatively charged muons (μ+ and μ-) emerging from high-energy proton-antiproton collisions produced by the Tevatron particle collider. A strong magnetic field inside the DZero particle detector forces the muons that emerge from those collisions to travel along a curved path. Two muons with opposite charge follow paths that curve in opposite direction (see graphic). Scientists first compared the muon distributions when the the magnetic field inside the DZero detector pointed in one direction (configuration 1) and then compared their distributions when the magnetic field had been reversed (configuration 2). If the matter-antimatter symmetry were perfect, the comparison of the muon distributions in the two configurations would yield the same result. Instead, the DZero experiment observed a one-percent deviation, evidence for a matter-antimatter asymmetry. Credit: Fermilab
The DZero collaboration comprises about 500 scientists from 19 countries who designed and built the 5,500-ton DZero detector and now collect and reconstruct collision data. They research a wide range of Standard Model topics and search for new subatomic phenomena. Credit: DZero collaboration
The Fermilab accelerator complex accelerates protons and antiprotons close to the speed of light. The Tevatron collider, four miles in circumference, produces millions of proton-antiproton collisions per second, maximizing the chance for discovery. Two experiments, CDF and DZero, record the collisions to look for signs of new particles and subatomic processes. Credit: Fermilab
The DZero detector records particles emerging from high-energy proton-antiproton collisions produced by the Tevatron. For this measurement of CP violation, scientists analyzed 10 trillion collisions collected over the last eight years. Credit: Fermilab