‘Little a’ Collaboration

A small group led by Tulane University is planning an experiment to measure the beta-neutrino angular correlation, often referred to as the little ‘a’ coefficient, in neutron decay. We are essentially measuring the average angle between two of the particles that come out of neutron decay: the neutrino, and the electron (beta particle). As with the emiT experiment, this angular correlation can be calculated in the Standard Electroweak Model. A measured value will test our knowledge of the weak interaction. Unpolarized neutrons will be allowed to decay in a uniform magnetic field, and the beta and proton decay products will be detected. It is nearly impossible to detect the actual neutrinos, but the directions of the beta and recoil proton can be used to infer the direction of the neutrino.

A collaboration led by Tulane University and including the University of Indiana and DePauw University has just recieved funding for this experiment. Professor Brian Collett and I will provide the magnetic and electric fields. This will be challenging since we need a very uniform 400 G magnetic field ( ) over a large volume (2 m long, 5 cm diameter). Hamilton is also responsible for robotic field mapping and field alignment, a complete Monte Carlo simulation of the experiment and electric field design for the decay region. The initial magnetic design work was performed by Tomasz Konopka, ’02, in the fall of 2000, and his design was the one chosen by the collaboration in the spring of 2001. A prototype electron detector was started at NIST by Rachael Anderman, ’01, in the summer of 2000.