Using ultracold neutrons to constrain the neutron electric dipole moment Tamas Budner

Outline Motivation Experiment Future Considerations What is the neutron electric dipole moment (nEDM), and why study it? What can it tell us about the baryon-antibaryon asymmetry in the universe? Experiment What is the current experimental upper limit for the nEDM? What makes a neutron ultracold, and why is this useful for measurements? How do experimental results compare with theory? Future Considerations What is the future of fundamental symmetries research related to search for the nEDM? T. Budner, PHY 802 Final Presentation

CP-violation: Why is there something rather than nothing? CP-symmetry – particle dynamics are the same under spatial inversion (parity) and charge conjugation Baryon-antibaryon asymmetry, an example of CP-violation Standard Model (SM) prediction: ~10-20 Observation: ~10-10 Electroweak baryogenesis? EDM violates P- and T-symmetries [1]. Electric dipole changes direction under parity exchange, magnetic dipole under time-reversal. T. Budner, PHY 802 Final Presentation

Precision experiment using UCNs Institut Laue-Langevin (ILL), Grenoble, France Neutron spin polarization precesses along the axis aligned with the electromagnetic field with Larmor frequency [2] Ultracold neutrons [3]: Kinetic energy much less than eV Total reflection incident on surface Lifetime ~1000 s Can be trapped in magnetic or material bottle Ramsey interferometry to measure frequency Experimental apparatus. T. Budner, PHY 802 Final Presentation

Limits on the nEDM ILL current experimental upper limit on nEDM: Lattice QCD calculations for the upper bound of the nEDM [4]: Data from the ILL experiment. Measured EDM as a function of relative frequency shift of neutrons and Hg atoms. (Top) Magnetic field pointing up relative to the ground. (Bottom) Magentic field pointing down. T. Budner, PHY 802 Final Presentation

The future of nEDM research using UCNs Precision increasing by order of magnitude about every ten years, approaching theoretical upper limit for supersymmetric theories TRIUMF in Canada to develop “Superthermal Spallation” UCN source, projected to be the highest density source of UCNs in the world [5]. (Below) Schematic of new UCN beam source at TRIUMF. Fast neutrons from the target are slowed to ultra-cold speeds (<8 m/s) and directed to the UCN experimental area. (Above) Chronology of experimental upper limits for nEDM. T. Budner, PHY 802 Final Presentation

In Summary The existence of a nEDM would be an example of CP-violation, which might help explain baryon-antibaryon asymmetry in our universe. Current experimental upper limits place the nEDM at no greater than on the order of 10-26 e·cm, while lattice QCD calculations suggest upper bound on the order of 10-28 e·cm. Most modern measurements utilize UCN sources, increasing the interest in this experimental technique. T. Budner, PHY 802 Final Presentation

References [1] A. P. Serebov, et al., Phys. Rev. C 92, 055501 (2015). [2] C. A. Baker, D. D. Doyle, P. Geltenbort, et al., Phys. Rev. Lett. 97, 131801 (2006). [3] R. Golub, J. M. Pendlebury, Rep. Prog. Phys., Vol. 42, 1979. [4] T. Bhattacharya, et al., Phys. Rev. Lett. 115, 212002 (2015). [5] "TRIUMF : Canada's National Laboratory for Particle and Nuclear Physics." UCN | TRIUMF : Canada's National Laboratory for Particle and Nuclear Physics. T. Budner, PHY 802 Final Presentation

Thank you! Questions? T. Budner, PHY 802