The electroweak standard model describes two of the four fundamental forces present in the universe. By conducting experiments that probe with increasing sensitivity phenomena that can be described with this model, it is hoped discrepancies will appear that will lead to a more complete understanding of the weak interaction. This interaction is responsible for the decay, or transformation, of the neutron into a proton, electron and antineutrino. By studying the correlations between the properties of the neutron and its decay products, more precise tests of the electroweak standard model can be performed. One of these correlations, known as little "a," involves the direction of emission of the electron and antineutrino from the decay region. Other neutron decay correlations are known to within 1%, but little "a" is only known to 4%. After several years of planning and construction, the aCORN ("a" CORrelation in Neutron decay) collaboration is in the process of installing an apparatus on the fundamental physics beamline at the NIST (National Institute of Standards and Technology) Center for Neutron Research (NCNR). Production data will be collected the rest of this year (2010) and into the next that will result in a 2% measurement of little "a." The NCNR will then shutdown for a series of upgrades resulting in a higher neutron flux. During this period, improvements and modifications will be made to the aCORN apparatus based on performance for the 2% measurement to make a sub-1% measurement once the NCNR upgrades are complete.
This grant will provide the support needed for DePauw University undergraduate students and the Principal Investigator to participate in the experiment during the 2% measurement, to determine the necessary modifications for a sub-1% measurement and to perform this measurement. The Principal Investigator has involved 20 undergraduates extensively in this experiment over the past several years. Of these 20, 12 first encountered this experiment during their freshman year and 9 became or already were physics majors. Of these 9, 3 have participated in other research programs via the NSF's REU (Research Experience for Undergraduates) program at major research universities and facilities such as Fermilab. Five of the 9 have also had further experiences working with the PI on experiments at Los Alamos National Laboratory and the Paul Scherrer Institut in Switzerland. By working on aCORN these students have been prepared to take on a wide variety of challenges ranging from other physics experiments to activities in other diverse fields such as biology, computer science and teaching.
