单选题An experiment that some hoped would reveal a new class of subatomic particles, and perhaps even point to clues about why the universe exists at all, has instead produced a first round of results that are mysteriously inconclusive. Dr. Conrad and William C. Louis presented their initial findings in a talk yesterday at the Fermi National Accelerator Laboratory where the experiment is being performed. The goal was to confirm or refute observations made in the 1990s in a Los Alamos experiment that observed transformations in the evanescent but bountiful particles known as neutrinos(微中子). Neutrinos have no electrical charge and almost no mass, but there are so many of them that they could collectively outweigh all the stars in the universe. The new experiment has attracted wide interest. That reflected in part the hope of finding cracks in the Standard Model, which encapsulates physicists' current knowledge about fundamental particles and forces. The Standard Model has proved remarkably effective and accurate, but it cannot answer some fundamental questions, like why the universe did not completely annihilate(毁灭) itself an instant after the Big Bang. The birth of the universe 13.7 billion years ago created equal amounts of matter and antimatter. Since matter and antimatter annihilate each other when they come in contact, that would have left nothing to coalesce into stars and galaxies. There must be some imbalance in the laws of physics that led to a slight preponderance of matter over antimatter, and that extra bit of matter formed everything in the visible universe. The imbalance, some physicists believe, may be hiding in the dynamics of neutrinos. Neutrinos come in three known types, or flavors. And they can change flavor as they travel. But the neutrino transformations reported in the Los Alamos data do not fit the three-flavor model, suggesting four flavors of neutrinos, if not more. The new experiment sought to count the number of times one flavor of neutrino, called a muon(μ介子), turned into another flavor, an electron neutrino. For most of the neutrino energy range they looked at, the scientists did not see any more electron neutrinos than would be predicted by the Standard Model. That ruled out the simplest ways of interpreting the Los Alamos neutrino data, Dr. Conrad and Dr. Louis said. But at the lower energies, the scientists did see more electron neutrinos than predicted: 369, rather than the predicted 273. That may simply mean that some calculations are off. Or it could point to a subtler interplay of particles, known and unknown. Dr. Louis said he was surprised by the results." I was sort of expecting a clear excess or no excess," he said. "In a sense, we got both./

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