Speaker
Description
Positronium, as a purely leptonic bound state, provides a unique laboratory for precision tests of bound-state QED. Among its measurable observables, the ortho-positronium decay rate plays a central role. Second-order corrections have been calculated, leading to a theoretical prediction at the 1 ppm level [1]. In contrast, the most precise experimental results remain two orders of magnitude less accurate [2][3], limited by both systematic and statistical uncertainties. At ETH Zurich we are developing a new precision experiment to measure the ortho-positronium decay rate in vacuum, combining and refining established techniques. A key improvement is a novel method to determine and subtract the time-dependent pick-off contribution arising from interactions with the cavity walls, which induces two-photon decays prior to the intrinsic three-photon vacuum decay. This approach relies on a PET-like detector with high spatial granularity and excellent timing and energy resolution. In addition, a dedicated confinement cavity has been designed and tested to retain ortho-positronium within a region of uniform detection efficiency, which is expected to reduce systematic uncertainties related to extrapolation procedures by at least one order of magnitude. Together with our positron beam and a dedicated tagging system, the experiment is expected to achieve the statistics required for a measurement below 10 ppm. We will present the experimental concept, validation of the methodology, preliminary results, and the current status of the setup.
References
[1] G. S. Adkins et al, Annals of Physics 295, 136–193 (2002).
[2] R.S.Vallery et al, Phys. Rev. Lett. 90, 203402 (2003).
[3] Y. Kataoka et al, Physics Letters B, 219-223 (2009).