is conserved: {| border=0 |- style="height: 2em;" | || → || + |- style="height: 2em;" | || → || + + |} Lee and Yang's research into existing experimental results convinced them that parity was conserved for electromagnetic interactions and for the strong interaction. For this reason, scientists had expected that it would also be true for the weak interaction, but it had not been tested, and Lee and Yang's theoretical studies showed that it might not hold true for the weak interaction. Lee and Yang worked out a pencil-and-paper design of an experiment for testing conservation of parity in the laboratory. Because of her expertise in choosing and then working out the hardware manufacture, set-up, and laboratory procedures, Wu then informed Lee that she could carry out the experiment. Wu chose to do this by taking a sample of radioactive cobalt-60 and cooling it to cryogenic temperatures with liquid gases. Cobalt-60 is an isotope that decays by beta particle emission, and Wu was also an expert on beta decay. The extremely low temperatures were needed to reduce the amount of thermal vibration of the cobalt atoms to almost zero. Also, Wu needed to apply a constant and uniform magnetic field across the sample of cobalt-60 in order to cause the spin axes of the atomic nuclei to line up in the same direction. For this cryogenic work, she needed the facilities of the National Bureau of Standards and its expertise in working with liquid gases, and traveled to its headquarters in Maryland with her equipment to carry out the experiments. Lee and Yang's theoretical calculations predicted that the beta particles from the cobalt-60 atoms would be emitted asymmetrically and the hypothetical "law of conservation of parity" was invalid. Wu's experiment showed that this is indeed the case: parity is not conserved under the weak nuclear interactions. and are indeed the same particle, which is today known as a kaon, . This result was soon confirmed by her colleagues at Columbia University in different experiments, and as soon as all of these results were published—in two different research papers in the same issue of the same physics journal—the results were also confirmed at many other laboratories and in many different experiments. The discovery of parity violation was a major contribution to particle physics and the development of the Standard Model. The discovery actually set the stage for the development of