Department of Physics Calendar
Physics Colloquium: Chen-Yu Liu (Indiana University)
Title: Measuring the Neutron Lifetime: Much Ado About Nothing?
Abstract: Neutrons are stable inside atomic nuclei. Outside the nucleus, they decay into a proton, electron, and antineutrino, with a lifetime of about 880 s. The rate of decay can be calculated precisely, using the theory of electroweak interactions, with an uncertainty on the order of 1E-4. The neutron decay rate sets the time scale of Big Bang Nucleosynthesis and determines the cosmic abundance of light elements. High-precision measurements of the neutron lifetime and decay asymmetries continue to test the Standard Model of particle physics and to probe for new physics beyond. Recent measurements using bottled neutrons have achieved lifetime uncertainties below 1 s (0.1%), but measurements using beam neutrons decaying in flight disagree by 10 s. This discrepancy has motivated much experimental effort as well as exotic theoretical conjectures, thus far without definite conclusions. In this colloquium, I will describe the challenges of precision neutron lifetime measurements, and illustrate with details from the UCNtau experiment which has yielded the most precise such measurement to date.
Host: Albert Young