Fundamental Neutron Physics: Probing TeV Physics with neV Neutrons

S@INT Seminar

Ultra Cold Neutrons (UCN) are free neutrons with kinetic energies up to several hundred nano-eV. Storage of UCN allows for the long observation times needed for precision measurement of many neutron observables. High-precision measurements, confronted with theoretical predictions, probe high-energy physics through loop effects. To illustrate the power of precision measurements in the fundamental neutron physics program, I will discuss two recent measurements: the lifetime and the electric dipole moment of the neutron. 

The UCNtau experiment recently reported the most precise measurement of the neutron lifetime, 877.75 +/- 0.28 (stat) +0.22/-0.16 (sys) s [PRL 127, 162501 (2021)]. This result, together with improved measurements of the axial coupling constant, will provide a determination of the CKM matrix element Vud, independent of nuclear decays, and address the recent tension in the CKM unitarity test. The search for the CP-violating electric dipole moment (EDM) of the neutron has reached, with the latest result from PSI, a sensitivity of (0.0±1.1(stat)±0.2(sys))e-26 e-cm [Phys. Rev. Lett. 124, 081803 (2020)]. In many scenarios, successful baryogenesis leads to strict lower bounds on the neutron and electron EDMs, only a factor of 2–3 below the current experimental limits. The new generation of nEDM searches will be sufficiently sensitive to provide a conclusive test of the origin of matter in the minimal supersymmetric model. In the US, two efforts are underway: the nEDM@LANL plans to reach 3e-27 e-cm with the upgraded UCN source, and the nEDM@SNS aims for < 5e-28 e-cm using an innovative superfluid helium technique. I will discuss the designs and report on the status of these experiments.

This event will take place in the INT seminar room (C-421). All interested graduate students and faculty are invited to attend.

Participants are also welcome to join via Zoom. Zoom link will be available via announcement email, or by contacting: amccoy10[at] or gsj6[at]

Chen-Yu Liu
Indiana University Bloomington
INT Seminar Room (C421)
Talk Slides
PDF12.81 MB