Detector Seminar

Turning light into matter: Investigating the Linear Breit-Wheeler process

by Brendan Kettle (Imperial College London)


The two-photon (linear) Breit-Wheeler mechanism is the simplest process through which light can be converted into matter. It plays an important role in many astrophysical scenarios and is of interest to the HEP community for the potential to create a photo-photon collider. However, despite its simplicity only the multi-photon (non-linear) process has yet been measured definitively in the laboratory. The linear process remains elusive as the particle production threshold relies on the product of the two colliding photons being greater in energy than the square of the electron rest mass (>(0.511 MeV)^2). This requires the interaction of two bright sources of gamma or X-rays housed at the same facility. In addition, competing non-vacuum processes producing electron-positron pairs, such as Bethe-Heitler, make measuring the linear Breit-Wheeler process in isolation even more challenging. For these reasons single particle detectors and the mitigation of background photons and secondary particles are crucial for observing the process. In an experiment performed at the Gemini laser in 2018 we collided 100 MeV gamma rays produced using a laser wakefield accelerator with a thermal bath of keV X-rays with the aim of detecting positrons from the linear Breit-Wheeler process. A magnetic chicane in combination with appropriate shielding was used to relay high energy particles from the interaction to a pair of TimePix3 detectors. We report on the success of the single particle detection system and an update on the on-going data analysis.

Zoom connection details are given in the invitation email.

Organized by

Dominik Dannheim (EP-LCD)