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way to look exactly where the model predicts, scientists must narrow in on it, exploring a range of numbers around the predicted one. Presently the upper limit of that range remains five to six orders of magnitude larger than the size predicted by the Standard Model. Now Ito and Cirigliano, along with many collaborators, they would have exactly canceled each other, How We Survived the Big Bang or mutually annihilated one another, and there are poised to shave one or even two orders of would have been no matter left over. So amidst magnitude off. The fact that we exist in a universe domi- A neutron is like a magnetized spinning the maelstrom of the very early universe, nated by matter is a cosmic mystery. Because top with electric and magnetic poles aligned. antimatter annihilates matter, these words you CP violation allowed the survival of enough Imagine a gyroscope spinning about its internal are reading, the clothes on your body, and your matter to form galaxies, planets, people, and body itself are all evidence of there being more every other tangible thing. But it’s not obvious axis of rotation and swiveling in a very smooth sort of wobble, around the center of the stand why CP violation exists in the first place. matter than antimatter in the universe. “If a neutron were enlarged to the size of the on which it is balanced. A neutron behaves Los Alamos experimental nuclear physicist similarly, spinning about a central axis and earth, there would be less than a tenth of the Takeyasu Ito and nuclear theorist Vincenzo diameter of a human hair’s separation between rotating around such that the orientation of the Cirigliano want to know how this imbalance axis oscillates. The oscillation is called preces- could have come about, so they and their teams the centers of negative and positive charge sion, and the rate of precession, or how long the of experts are working together to learn more. within it,” Ito explains. This is the elusive, still gyroscope takes to make one revolution about For every particle, there exists a correspond- theoretical, neutron electric dipole moment ing antiparticle: protons and antiprotons, elec- (nEDM), which, if proven to exist, would signal its stand, is what Ito is measuring. For the past 60 years, scientists have been trons and antielectrons, quarks and antiquarks, CP violation at levels much higher than those looking for the nEDM in essentially the same predicted by the Standard Model, and maybe and so on. The broadly accepted Standard way: Place slow neutrons in an electric field and enough to solve the mystery. When searching Model of particle physics, which describes all measure their rate of precession. The difference, for such a small thing, scientists can rarely the elementary particles and their interac- if there is one, in precession rate for parallel tions, implies that interchanging particles and say, “It’s right here”; more often, they say, and antiparallel fields reflects the nEDM. But “It’s definitely not here, here, or here, so let’s antiparticles (which have the same mass but it’s slow going. Increasing the strength of the opposite charge), in an operation called charge- look over there.” The Standard Model predicts electric field, the number of neutrons, or the parity (CP) is, to a very high degree of accuracy, that a nEDM, if found, would be found at a time to decay can improve the sensitivity of particular, albeit infinitesimal, size. Without a a symmetry of nature. The small amount of this method. Ito and the experimental team are asymmetry, or CP violation, that is allowed by developing a new experiment with an increased the Standard Model is not enough to explain number of neutrons, which is enabled by the the imbalance. ultracold neutron source at Los Alamos (one of The Standard Model also provides a rule that only a few in the world). At the same time, as says particles and antiparticles must be created part of a large international collaboration, they together, in pairs, and likewise for their destruc- are working on an experiment based on a tion. If, in keeping with this rule, there were completely new method involving liquid helium precisely equal quantities of matter and anti- that is expected to raise all three variables matter in existence in the very early universe, simultaneously. So far they have shown that Antimatter they can increase the electric field strength and 0 the time to decay. As if that weren’t tricky enough, there’s another hitch. Far enough back in time, the very Matter 2 early universe contained no neutrons; it was too hot and dense. Instead it contained quarks Today’s universe (and antiquarks). Since quarks are the particles that make up matter (including neutrons), a disparity early on could be the answer to the Antimatter All of the matter in the universe today is just a 1,000,000,000 current preponderance of matter. Measuring tiny proportion of the matter present in the very Matter 1,000,000,002 Early universe early universe; it is the excess, leftover matter that was not annihilated by antimatter at that time. Los Alamos physicists are testing one theory that could explain the early inequality between matter and antimatter. 1663 May 2015 31